Method and apparatus for signaling mapping function of chroma quantization parameter

Abstract

To provide a method for obtaining a chrominance quantization parameter (QP) for a chrominance component on the basis of a luminance QP for a luminance component.SOLUTION: This method is performed by a decoder, and the method includes parsing a received bitstream to obtain a luminance QP and information about a mapping function (f) that associates a QP index (QPi) with a chrominance QP (QPc), obtaining a QPi based at least in part on the luminance QP, obtaining a mapping function on the basis of the obtained information, and obtaining a QPc on the basis of the obtained mapping function and the obtained QPi.SELECTED DRAWING: Figure 13

Description

[Technical field]

[0001] This patent application claims priority to U.S. Provisional Patent Application No. 62 / 839,6076, filed April 26, 2019, International Patent Application No. PCT / RU2019 / 000444, filed June 21, 2019, U.S. Provisional Patent Application No. 62 / 871,197, filed July 7, 2019, and U.S. Provisional Patent Application No. 62 / 872,238, filed July 9, 2019.

[0002] FIELD OF THE DISCLOSURE Embodiments of the present application relate generally to the field of image and / or video decoding, and more specifically to an apparatus and method for chroma quantization parameter signaling. [Background technology]

[0003] Video coding (video encoding and decoding) is used in a wide range of digital video applications, such as broadcast digital TV, video transmission over the Internet and mobile networks, real-time conversation applications such as video chat, video conferencing, DVDs and Blu-ray Discs, video content collection and editing systems, and video cameras for security purposes.

[0004] The amount of video data required to render even a relatively short video can be substantial, which can pose challenges when streaming or otherwise communicating the data over communication networks with limited bandwidth capacity. Thus, video data is typically compressed before being communicated over today's telecommunications networks. The size of the video can also be an issue when the video is stored in a storage device, since memory resources may be limited. Video compression devices often use software and / or hardware to code the video data at the source prior to transmission or storage, thereby reducing the amount of data required to represent a digital video image. The compressed data is then received at the destination by a video decompressor, which decodes the video data. With limited network resources and ever-increasing demands for higher video quality, improved compression and decompression techniques that improve compression ratios with little or no sacrifice in picture quality are desirable. Summary of the Invention

[0005] Embodiments of the present application provide devices and methods for encoding and decoding according to the independent claims.

[0006] These and other objects are achieved by the subject matter of the independent claims. Further implementations are evident from the dependent claims, the description and the drawings.

[0007] The present disclosure discloses a method for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luma QP for a luma component, the method being performed by a decoder, the method comprising: Receive the bitstream, Parsing the bitstream to obtain the luma QP and information about a chroma QP mapping table that associates a QP index (QPi) with the chrominance QP (QPc); obtaining the QPi based at least in part on the luminance QP; Obtaining the chroma QP mapping table based on the obtained information; Obtaining a QPc based on the obtained chroma QP mapping table and the obtained QPi; Obtaining a chrominance quantization parameter based on the obtained QPc; It has the following.

[0008] Therefore, the chroma QP mapping table is obtained based on the information signaled in the bitstream.

[0009] In the above-mentioned method, qP Cb , qP Cr and qP CbCr but, qP Chroma =Clip3(-QpBdOffset,63,Qp Y ), qP Cb =ChromaQpTable[0][qP Chroma ], qP Cr =ChromaQpTable[1][qP Chroma ], qP CbCr =ChromaQpTable[2][qP Chroma ], It can be derived as Chroma quantization parameter Qp' for Cb and Cr components Cb and Qp' Cr , as well as joint Cb-Cr coding Qp' CbCr but, Qp' Cb =Clip3(-QpBdOffset,63,qP Cb +pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset Cb )+QpBdOffset, Qp' Cr =Clip3(-QpBdOffset,63,qP Cr+pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset Cr )+QpBdOffset, Qp' CbCr =Clip3(-QpBdOffset,63,qP CbCr +pps_joint_cbcr_qp_offset_value+slice_joint_cbcr_qp_offset+CuQpOffset CbCr )+QpBdOffset, It can be derived as ChromaQpTable is the chroma QP mapping table; QPi is qP Chroma Corresponding to, QPc is qP Cb , qP Cr and qP CbCr Corresponding to, QpBdOffset is the formula: QpBdOffset=6*bit_depth_minus8 where: bit_depth_minus8 is in the range 0 to 8 inclusive, pps_cb_qp_offset and pps_cr_qp_offset are respectively Qp' Cb and Qp' Cr The luma quantization parameter Qp' used to derive Y Specify an offset for pps_joint_cbcr_qp_offset_value is the Qp' CbCr The luma quantization parameter Qp' used to derive Y Specify an offset for slice_cr_qp_offset is Qp' Cr Specifying a difference to be added to the value of pps_cr_qp_offset when determining the value of the quantization parameter; slice_cb_qp_offset is Qp' CbSpecifying a difference to be added to the value of pps_cb_qp_offset when determining the value of the quantization parameter; slice_joint_cbcr_qp_offset is Qp' CbCr Specifies the difference to be added to the pps_joint_cbcr_qp_offset_value when determining the value of Variable CuQpOffset Cb , CuQpOffset Cr , and CuQpOffset CbCr Qp' for the decoder Cb , Qp' Cr , and Qp' CbCr Specifies the values ​​used when determining each value of the quantization parameter.

[0010] In the above method, the chroma QP mapping table may associate each element x of set X, which may correspond to a QPi within the allowed QPi range supported by the decoder, or any subset of set X, with one element y of set Y, which may correspond to a QPc within the allowed QPc range supported by the decoder.

[0011] In the above method, the values ​​of the chroma QP mapping table may satisfy a mapping function.

[0012] In the above method, the mapping function may be a piecewise mapping function, and the information of the piecewise mapping function may comprise breakpoints, change points, or pivot points of the piecewise mapping function.

[0013] In the above method, the number of breakpoints, change points, or pivot points and their respective x and y coordinates may be signaled in the bitstream either directly or based on a delta value between the coordinates of the current pivot point and the coordinates of the previous pivot point.

[0014] Therefore, to further reduce signaling overhead, the difference between the corresponding x and y coordinates of the current pivot point and the corresponding x and y coordinates of the previous pivot point may be signaled in the bitstream. In particular, at the first point, the difference from some starting_point may be signaled. The starting_point may either be some predefined point or may be signaled in the bitstream. In some implementations, the starting_point may be constrained to be one-to-one, in which case one coordinate is sufficient to define the starting_point.

[0015] In the above method, the mapping function is linear equation, exponential equation, Logarithmic equation, or Combining the above equations, It may be a piecewise function based on

[0016] In the above method, the parameter of the piece of the piece function is y=slope*x+b The linear equation given by slope and b are parameters of the linear equation, slope=(Ey-Dy) / (Ex-Dx), b=Dy-slope*Dx, where D and E are pivot points with coordinates Dx, Dy and Ex, Ey respectively.

[0017] In the above method, the information of the chroma QP mapping table may be signaled jointly for all chrominance components.

[0018] In the above method, the information in the chroma QP mapping table may comprise an indicator indicating whether the mapping functions are signaled separately or jointly for the chrominance components.

[0019] In the above method, the information in the chroma QP mapping table is At the sequence level in the sequence parameter set, or At the picture level in the picture parameter set, or At the tile group level, within a tile group parameter set, or Within the adaptation parameter set, or In the Supplemental Extension Information (SEI) message, It can be signaled.

[0020] In the above method, parsing of the chroma QP mapping information, which is information about the chroma QP mapping table, may depend on the specification of a chroma sampling format.

[0021] In the above method, the specification of the chroma sampling format is as follows: [Table 1] can be given according to chroma_format_idc indicates the index of the chroma sampling format, In monochrome sampling, there is only one sample array, nominally considered the luma array, In 4:2:0 sampling, each of the two chroma arrays has half the height and half the width of the luma array, In 4:2:2 sampling, each of the two chroma arrays has the same height and half the width of the luma array, For 4:4:4 sampling, depending on the value of the flag separate_colour_plane_flag the following can apply: If separate_colour_plane_flag is equal to 0, each of the two chroma arrays has the same height and width as the luma array; Otherwise, if separate_colour_plane_flag is equal to 1, the three colour planes are treated as a separately monochrome sampled picture; separate_colour_plane_flag equal to 1 specifies that the three colour components of the 4:4:4 chroma format are coded separately, separate_colour_plane_flag equal to 0 specifies that the colour components are not coded separately; when separate_colour_plane_flag is equal to 1, the coded picture consists of three separate components, each of which consists of coded samples of one colour plane (Y, Cb or Cr), and uses a monochrome coding syntax, where each colour plane is associated with a specific colour_plane_id value; Depending on the value of separate_colour_plane_flag, the value of the variable ChromaArrayType may be assigned as follows: - if separate_colour_plane_flag is equal to 0, ChromaArrayType is set equal to chroma_format_idc, - Otherwise (separate_colour_plane_flag is equal to 1), ChromaArrayType is set equal to 0.

[0022] Thus, the conditional signaling of chroma QP mapping information may depend on the chroma sampling format. For example, if the chroma format is monochrome (sampling format is 4:0:0), no mapping table is signaled. Having separately coded color components (separate_colour_plane_flag equals 1) is another example of when no chroma mapping table is signaled. This allows to save bits of signaling of the chroma QP mapping table when chroma components are not present or are coded separately.

[0023] In the above method, the presence of the flag chroma_qp_mapping_flag and / or the chroma Qp mapping information may depend on the chroma format sampling as specified in one of the following tables: [Table 2] or [Table 3] or [Table 4] or [Table 5] chroma_format_idc equal to 3 indicates that the chroma sampling format is 4:2:0, seq_parameter_set_rbsp() points to the sequence parameter set raw byte sequence payload, chroma_format_idc indicates the chroma sampling format index, chroma_qp_mapping_flag equal to 1 signals that the chroma Qp mapping function is C Qp as a function of qPi used to deriveC (Chroma Qp) default specifications are stipulated, chroma_qp_mapping_flag equal to 0 means that the Qp C Specifies that a default chroma Qp mapping table is used to derive chroma_qp_mapping_flag, and if chroma_qp_mapping_flag is not present, chroma_qp_mapping_flag is inferred to be equal to 0, sps_joint_cbcr_enabled_flag equal to 0 specifies that joint coding of chroma residual is disabled, sps_joint_cbcr_enabled_flag equal to 1 specifies that joint coding of chroma residual is enabled, same_qp_table_for_chroma equal to 1 specifies that only one chroma QP mapping table is signaled, which applies to the Cb residual and the Cr residual, and also to the joint Cb-Cr residual when sps_joint_cbcr_enabled_flag is equal to 1; same_qp_table_for_chroma equal to 0 specifies that two chroma QP mapping tables are signaled in the SPS: one for Cb and Cr, and an additional one for the joint Cb-Cr when sps_joint_cbcr_enabled_flag is equal to 1; chroma_qp_table_present_flag equal to 1 specifies that a user-defined chroma QP mapping table, ChromaQpTable, is signaled, chroma_qp_table_present_flag equal to 0 specifies that no user-defined chroma QP mapping table is signaled and a predefined chroma QP mapping table is used; cqp_mapping_data() points to the chroma Qp mapping information; 14. The method according to claim 12 or 13.

[0024] In the above method, the mapping function may be a monotonically increasing function.

[0025] This therefore constrains the mapping function to be a monotonically increasing (non-decreasing) function.

[0026] In the above method, the pivot points of the mapping function may be signaled in the bitstream based on delta values ​​using unsigned integer codes.

[0027] Therefore, a monotonically increasing function can be achieved by using an unsigned ue(v) code to code the pivot points dx and df(x).

[0028] In the above method, the unsigned integer code is an unsigned integer zeroth order Exp-Golomb code.

[0029] In the above method, the information of the mapping function is a first value a 0 and starting_point_value (delta_a 0 ), and the first value a0 of the subset A may have the difference (delta_a 0 ) based on a 0 =starting_point_value+delta_a 0 where starting_point_value is either signaled in the bitstream or is a predefined value.

[0030] Since the points of the mapping function are classified into two classes of defined behavior and the number of points where the mapping function does not increase is limited, the signaling overhead is reduced compared to direct signaling of each value of the mapping function.

[0031] In the above method, the starting point value starting_point_value may be one of: 0, 21, 30, maxQPi>>1, where maxQPi is the maximum QPi value supported by the decoder.

[0032] In the above method, the first pivot point is qpInVal[i][0]=qp_table_start_minus26[i]+26, qpOutVal[i][0]=qpInVal[i][0], can be given by qp_table_start_minus26[i]+26 specifies the starting luma and chroma QP used to describe the i-th chroma QP mapping table.

[0033] In the above-mentioned method, For i=0..numQpTables-1, the i-th chroma QP mapping table, ChromaQpTable[i], may be derived as follows: qpInVal[i][0]=qp_table_start_minus26[i]+26 qpOutVal[i][0]=qpInVal[i][0] for(j=0;j<=num_points_in_qp_table_minus1[i];j++){ qpInVal[i][j+1]=qpInVal[i][j]+delta_qp_in_val_minus1[i][j]+1 qpOutVal[i][j+1]=qpOutVal[i][j]+(delta_qp_in_val_minus1[i][j]^delta_qp_diff_val[i][j]) } ChromaQpTable[i][qpInVal[i][0]]=qpOutVal[i][0] for(k=qpInVal[i][0]-1;k>=-QpBdOffset;k--) ChromaQpTable[i][k]=Clip3(-QpBdOffset,63,ChromaQpTable[i][k+1]-1) for(j=0;j<=num_points_in_qp_table_minus1[i];j++){ sh=(delta_qp_in_val_minus1[i][j]+1)>>1 for(k=qpInVal[i][j]+1,m=1;k<=qpInval[i][j+1];k++,m++) ChromaQpTable[i][k]=ChromaQpTable[i][qpInVal[i][j]]+((qpOutVal[i][j+1]-qpOutVal[i][j])*m+sh) / (delta_qp_in_val_minus1[i][j]+1) } for(k=qpInVal[i][num_points_in_qp_table_minus1[i]+1]+1;k<=63;k++) ChromaQpTable[i][k]=Clip3(-QpBdOffset,63,ChromaQpTable[i][k--1]+1).

[0034] The above method may further include a predetermined chroma QP mapping table, and the bitstream may include an indicator indicating whether to use the predetermined chroma QP mapping table or a chroma QP mapping table signaled within the bitstream.

[0035] In the above method, the predetermined chroma QP mapping table comprises: [Table 6] It can be expressed as:

[0036] In the above method, the predetermined chroma QP mapping table comprises: [Table 7] It can be expressed as:

[0037] In the above method, the information of the chroma QP mapping table can be signaled directly or indirectly within the bitstream.

[0038] The present disclosure further provides a decoder having processing circuitry for carrying out the above-mentioned method.

[0039] The present disclosure further provides a computer program product having program code for performing the above-mentioned method.

[0040] The present disclosure further provides a decoder having one or more processors and a non-transitory computer-readable storage medium coupled to the processors and storing programming for execution by the processors, the programming, when executed by the processors, configuring the decoder to perform the above-mentioned method.

[0041] The present disclosure further provides a decoder for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component, the decoder comprising: a receiving unit configured to receive a bitstream; a parsing unit configured to parse the bitstream to obtain the luminance QP and information about a chroma QP mapping table that associates a QP index (QPi) with the chrominance QP (QPc); a first obtaining unit configured to obtain the QPi based at least in part on the luminance QP; a second obtaining unit configured to obtain the chrominance QP mapping table based on the obtained information; a third obtaining unit configured to obtain a QPc based on the obtained chroma QP mapping table and the obtained QPi; and a fourth obtaining unit configured to obtain a chrominance quantization parameter based on the obtained QPc.

[0042] Having information about the chroma QP mapping table in the bitstream allows adjusting to specific characteristics of the input video signal, e.g. SDR or HDR, or different intensities and distributions on the luminance and chrominance channels, thus improving compression efficiency as well as improving the balance between chroma and luma components in the reconstructed video signal.

[0043] In the above mentioned decoder, qP Cb , qP Cr and qP CbCr but, qP Chroma =Clip3(-QpBdOffset,63,Qp Y ), qP Cb =ChromaQpTable[0][qP Chroma ], qP Cr =ChromaQpTable[1][qP Chroma ], qP CbCr =ChromaQpTable[2][qP Chroma ], It can be derived as Chroma quantization parameter Qp' for Cb and Cr components Cb and Qp' Cr , as well as joint Cb-Cr coding Qp' CbCr but, Qp' Cb =Clip3(-QpBdOffset,63,qP Cb +pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset Cb )+QpBdOffset, Qp' Cr =Clip3(-QpBdOffset,63,qP Cr +pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset Cr )+QpBdOffset, Qp' CbCr=Clip3(-QpBdOffset,63,qP CbCr +pps_joint_cbcr_qp_offset_value+slice_joint_cbcr_qp_offset+CuQpOffset CbCr )+QpBdOffset, It is derived as ChromaQpTable is the chroma QP mapping table; QPi is qP Chroma Corresponding to, QPc is qP Cb , qP Cr and qP CbCr Corresponding to, QpBdOffset is the formula: QpBdOffset=6*bit_depth_minus8 where: bit_depth_minus8 is in the range 0 to 8 inclusive, pps_cb_qp_offset and pps_cr_qp_offset are respectively Qp' Cb and Qp' Cr The luma quantization parameter Qp' used to derive Y Specify an offset for pps_joint_cbcr_qp_offset_value is the Qp' CbCr The luma quantization parameter Qp' used to derive Y Specify an offset for slice_cr_qp_offset is Qp' Cr Specifying a difference to be added to the value of pps_cr_qp_offset when determining the value of the quantization parameter; slice_cb_qp_offset is Qp' Cb Specifying a difference to be added to the value of pps_cb_qp_offset when determining the value of the quantization parameter; slice_joint_cbcr_qp_offset is Qp' CbCrSpecifies the difference to be added to the pps_joint_cbcr_qp_offset_value when determining the value of Variable CuQpOffset Cb , CuQpOffset Cr , and CuQpOffset CbCr Qp' for the decoder Cb , Qp' Cr , and Qp' CbCr Specifies the values ​​used when determining each value of the quantization parameter.

[0044] In the above-mentioned decoder, the chroma QP mapping table may associate each element x of set X, which may correspond to a QPi within the allowed QPi range supported by the decoder, or any subset of set X, with one element y of set Y, which may correspond to a QPc within the allowed QPc range supported by the decoder.

[0045] In the above decoder, the values ​​of the chroma QP mapping table may satisfy a mapping function.

[0046] In the above mentioned decoder, the mapping function may be a piecewise mapping function and the information of the piecewise mapping function may comprise breakpoints, change points or pivot points of the piecewise mapping function.

[0047] This aspect allows the function behavior of the complete range of QPs supported by the decoder to be described with limited signaling overhead by signaling only the points where the function changes its behavior (e.g., the slope of a line), and allows the function to be described as a piecewise function between the change points or pivot points.

[0048] In the above-mentioned decoder, the number of breakpoints, change points, or pivot points and their respective x and y coordinates can be signaled in the bitstream either directly or based on a delta value between the coordinates of the current pivot point and the coordinates of the previous pivot point.

[0049] In the above mentioned decoder, the mapping function is linear equation, exponential equation, Logarithmic equation, or Combining the above equations, It may be a piecewise function based on

[0050] Using a predefined equation form (e.g., a linear equation) for the piecewise function allows function values ​​between pivot points to be obtained without explicit signaling, which beneficially reduces the signaling overhead of describing the mapping function.

[0051] In the above decoder, the parameters of the partitions of the partition function are: y=slope*x+b The linear equation given by slope and b are parameters of the linear equation, slope=(Ey-Dy) / (Ex-Dx), b=Dy-slope*Dx, where D and E are pivot points with coordinates Dx, Dy and Ex, Ey respectively.

[0052] In the above mentioned decoder, the information of the chroma QP mapping table can be signaled jointly for all chrominance components.

[0053] In the above mentioned decoder, the information of the chroma QP mapping table may comprise an indicator indicating whether the chroma QP mapping table is signaled separately or jointly for the chrominance components.

[0054] This aspect allows for further increased flexibility in controlling the quantization process by having different chroma QP mapping tables for different chroma channels when the different chroma channels (e.g., Cb and Cr channels) have different signal characteristics, which allows for further increased compression efficiency.

[0055] In the above decoder, the information in the chroma QP mapping table is: At the sequence level in the sequence parameter set, or At the picture level in the picture parameter set, or At the tile group level, within a tile group parameter set, or Within the adaptation parameter set, or In the Supplemental Extension Information (SEI) message, It can be signaled.

[0056] In the above decoder, parsing of the chroma QP mapping information, which is information about the chroma QP mapping table, may depend on the specification of the chroma sampling format.

[0057] In the above decoder, the specification of the chroma sampling format is as follows: [Table 8] can be given according to chroma_format_idc indicates the index of the chroma sampling format, In monochrome sampling, there is only one sample array, nominally considered the luma array, In 4:2:0 sampling, each of the two chroma arrays has half the height and half the width of the luma array, In 4:2:2 sampling, each of the two chroma arrays has the same height and half the width of the luma array, For 4:4:4 sampling, depending on the value of the flag separate_colour_plane_flag the following can apply: If separate_colour_plane_flag is equal to 0, each of the two chroma arrays has the same height and width as the luma array; Otherwise, if separate_colour_plane_flag is equal to 1, the three colour planes are treated as a separately monochrome sampled picture; separate_colour_plane_flag equal to 1 specifies that the three colour components of the 4:4:4 chroma format are coded separately, separate_colour_plane_flag equal to 0 specifies that the colour components are not coded separately; when separate_colour_plane_flag is equal to 1, the coded picture consists of three separate components, each of which consists of coded samples of one colour plane (Y, Cb or Cr), and uses a monochrome coding syntax, where each colour plane is associated with a specific colour_plane_id value; Depending on the value of separate_colour_plane_flag, the value of the variable ChromaArrayType is assigned as follows: - if separate_colour_plane_flag is equal to 0, ChromaArrayType is set equal to chroma_format_idc, - Otherwise (separate_colour_plane_flag is equal to 1), ChromaArrayType is set equal to 0.

[0058] Conditional signaling of chroma QP mapping information depending on the chroma sampling format further reduces the signaling overhead. For example, if the chroma format is monochrome (sampling format is 4:0:0), no mapping table is signaled. Having separately coded color components (separate_colour_plane_flag equals 1) is another example of when no chroma mapping table is signaled. This allows to save bits of signaling of the chroma QP mapping table when chroma components are not present or are coded separately.

[0059] In the above mentioned decoders, the presence of the flag chroma_qp_mapping_flag and / or the chroma Qp mapping information may depend on the chroma format sampling as specified in one of the following tables: [Table 9] or [Table 10] or [Table 11] or [Table 12] chroma_format_idc equal to 3 indicates that the chroma sampling format is 4:2:0, seq_parameter_set_rbsp() points to the sequence parameter set raw byte sequence payload, chroma_format_idc indicates the chroma sampling format index, chroma_qp_mapping_flag equal to 1 signals that the chroma Qp mapping function is CQp as a function of qPi used to derive C (Chroma Qp) default specifications are stipulated, chroma_qp_mapping_flag equal to 0 means that the Qp C Specifies that a default chroma Qp mapping table is used to derive chroma_qp_mapping_flag, and if chroma_qp_mapping_flag is not present, chroma_qp_mapping_flag is inferred to be equal to 0, sps_joint_cbcr_enabled_flag equal to 0 specifies that joint coding of chroma residual is disabled, sps_joint_cbcr_enabled_flag equal to 1 specifies that joint coding of chroma residual is enabled, same_qp_table_for_chroma equal to 1 specifies that only one chroma QP mapping table is signaled, which applies to the Cb residual and the Cr residual, and also to the joint Cb-Cr residual when sps_joint_cbcr_enabled_flag is equal to 1; same_qp_table_for_chroma equal to 0 specifies that two chroma QP mapping tables are signaled in the SPS: one for Cb and Cr, and an additional one for the joint Cb-Cr when sps_joint_cbcr_enabled_flag is equal to 1; chroma_qp_table_present_flag equal to 1 specifies that a user-defined chroma QP mapping table, ChromaQpTable, is signaled, chroma_qp_table_present_flag equal to 0 specifies that no user-defined chroma QP mapping table is signaled and a predefined chroma QP mapping table is used; cqp_mapping_data() points to the chroma Qp mapping information.

[0060] In the above mentioned decoder, the mapping function may be a monotonically increasing function.

[0061] Imposing this constraint on the mapping function makes it possible to avoid setting mapping functions that have, for example, unexpected, undesirable, "strange" behavior when the chroma QP decreases with increasing luma QP, in other words avoiding cases where the chroma quality increases with decreasing luma quality. Having a monotonically increasing constraint allows the luma and chroma quality to be synchronized. As an additional advantage, this constraint makes it possible to save bits of signaling of the mapping function information by eliminating the need to describe negative increments of the function.

[0062] In the above mentioned decoder, the pivot points of the mapping function may be signaled in the bitstream based on delta values ​​using unsigned integer codes.

[0063] Signaling the difference instead of the direct value allows further bit savings: the monotonically increasing constraint on the mapping function ensures that the delta values ​​are always non-negative, which further allows bits to be saved by eliminating the need to signal a sign bit for the pivot point delta by using an unsigned integer code.

[0064] In the above mentioned decoder, the unsigned integer code may be an unsigned integer zeroth order Exp-Golomb code.

[0065] In the above mentioned decoder, the information of the mapping function is a first value a 0 and starting_point_value (delta_a 0 ), and the first value a0 of the subset A can be calculated by subtracting the difference (delta_a 0 ) based on a 0 =starting_point_value+delta_a 0 where starting_point_value is either signaled in the bitstream or is a predefined value.

[0066] In the above mentioned decoder, the starting point value starting_point_value can be one of 0, 21, 30, maxQPi>>1, where maxQPi is the maximum QPi value supported by the decoder. Selecting an appropriate starting_point_value allows to save more bits of signaling of the initial value.

[0067] In the above mentioned decoder, the first pivot point is qpInVal[i][0]=qp_table_start_minus26[i]+26, qpOutVal[i][0]=qpInVal[i][0], can be given by qp_table_start_minus26[i]+26 specifies the starting luma and chroma QP used to describe the i-th chroma QP mapping table.

[0068] In the decoder described above, the i-th chroma QP mapping table ChromaQpTable[i], for i=0..numQpTables-1, may be derived as follows: qpInVal[i][0]=qp_table_start_minus26[i]+26 qpOutVal[i][0]=qpInVal[i][0] for(j=0;j<=num_points_in_qp_table_minus1[i];j++){ qpInVal[i][j+1]=qpInVal[i][j]+delta_qp_in_val_minus1[i][j]+1 qpOutVal[i][j+1]=qpOutVal[i][j]+(delta_qp_in_val_minus1[i][j]^delta_qp_diff_val[i][j]) } ChromaQpTable[i][qpInVal[i][0]]=qpOutVal[i][0] for(k=qpInVal[i][0]-1;k>=-QpBdOffset;k--) ChromaQpTable[i][k]=Clip3(-QpBdOffset,63,ChromaQpTable[i][k+1]-1) for(j=0;j<=num_points_in_qp_table_minus1[i];j++){ sh=(delta_qp_in_val_minus1[i][j]+1)>>1 for(k=qpInVal[i][j]+1,m=1;k<=qpInval[i][j+1];k++,m++) ChromaQpTable[i][k]=ChromaQpTable[i][qpInVal[i][j]]+((qpOutVal[i][j+1]-qpOutVal[i][j])*m+sh) / (delta_qp_in_val_minus1[i][j]+1) } for(k=qpInVal[i][num_points_in_qp_table_minus1[i]+1]+1;k<=63;k++) ChromaQpTable[i][k]=Clip3(-QpBdOffset,63,ChromaQpTable[i][k--1]+1).

[0069] The above-mentioned decoder may further include a predetermined chroma QP mapping table, and the bitstream may include an indicator indicating whether to use the predetermined chroma QP mapping table or a chroma QP mapping table signaled within the bitstream.

[0070] This allows to signal information about the mapping table only when it is useful, i.e. when the characteristics of the luma and chroma channels are significantly different from the general case, as in the case of HDR signals, and to use a predefined mapping table that is suitable for the general case, which allows to save signaling overhead in the most general case for which the predefined mapping table is optimized.

[0071] In the above decoder, the predetermined chroma QP mapping table comprises: [Table 13] It can be expressed as:

[0072] In the above decoder, the predetermined chroma QP mapping table comprises: [Table 14] It can be expressed as:

[0073] In the above mentioned decoder, the information of the chroma QP mapping table can be signaled directly or indirectly within the bitstream.

[0074] The method according to the first aspect of the invention can be performed by an apparatus according to the third aspect of the invention. Further features and implementations of the apparatus according to the third aspect of the invention correspond to the features and implementations of the method according to the first aspect of the invention.

[0075] The method according to the second aspect of the invention can be performed by an apparatus according to the fourth aspect of the invention. Further features and implementations of the apparatus according to the fourth aspect of the invention correspond to the features and implementations of the method according to the second aspect of the invention.

[0076] According to a fifth aspect, the invention relates to an apparatus for decoding a video stream, comprising a processor and a memory, the memory storing instructions for causing the processor to carry out the method according to the first aspect.

[0077] According to a sixth aspect, the invention relates to an apparatus for encoding a video stream, comprising a processor and a memory, the memory storing instructions for causing the processor to carry out the method according to the second aspect.

[0078] According to a seventh aspect, a computer readable storage medium is proposed having stored thereon instructions which, when executed, cause one or more processors to be configured to encode video data, the instructions causing the one or more processors to perform a method according to the first aspect or the second aspect or a method according to any possible embodiment of the first aspect or the second aspect.

[0079] According to an eighth aspect, the invention relates to a computer program having a program code for performing, when the computer program is run on a computer, the method according to the first aspect or the second aspect or the method according to any possible embodiment of the first aspect or the second aspect.

[0080] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects, and advantages will become apparent from the description, drawings, and claims. [Brief description of the drawings]

[0081] Hereinafter, embodiments of the application will be described in more detail with reference to the accompanying figures and drawings. [Figure 1A] 1 is a block diagram illustrating an example of a video coding system configured to implement embodiments of the invention. [Figure 1B] FIG. 2 is a block diagram illustrating another example of a video coding system configured to implement embodiments of the invention. [Diagram 2]FIG. 2 is a block diagram illustrating an example of a video encoder configured to implement embodiments of the invention. [Diagram 3] FIG. 2 is a block diagram illustrating an example of a video decoder configured to implement embodiments of the invention. [Figure 4] FIG. 1 is a block diagram showing an example of an encoding device or a decoding device. [Diagram 5] FIG. 13 is a block diagram showing another example of an encoding device or a decoding device. [Figure 6] Schematic representation of a mapping function of quantization parameter index QPi to chroma quantization parameters QPc for HEVC (black, 61) and H.264|AVC (gray, 62) according to [2]. [Figure 7] FIG. 7 is a schematic representation of the HEVC mapping function of quantization parameter index QPi to chroma quantization parameter QPc for the supported QP range, where 72 is the HEVC mapping function and 71 is the one-to-one mapping function. [Figure 8] FIG. 8 shows a tabular representation of the function of quantization parameter index QPi to chroma quantization parameter QPc for HEVC (82) and modified mapping function (83). Table 81 represents a monotonically increasing one-to-one function, while tables 84, 85, and 86 represent the difference between the current and previous values ​​of the corresponding one-to-one function (81), HEVC mapping function (82), and modified mapping function (83), with 87 representing an exemplary point where the difference is zero. [Figure 9] 1 is an example of a piecewise linear representation 93 of a mapping function 92 using two pivot points D (94) and E (95). [Figure 10] FIG. 1 is a schematic representation of an HEVC mapping function of quantization parameter index QPi to chroma quantization parameter QPc for supported QP ranges, where 102 is the HEVC mapping function with chroma Qp offset equal to 1 and 101 is the one-to-one mapping function. [Figure 11]This is an actual VVC chroma Qp mapping table as a function of qPi. [Figure 12] 1 illustrates an adjustment mapping function according to the present disclosure. [Figure 13] 1 illustrates a method for obtaining a chrominance quantization parameter according to the present disclosure. [Figure 14] 1 illustrates a decoder according to the present disclosure.

[0082] In the following, unless explicitly stated otherwise, the same reference signs refer to the same features or at least functionally equivalent features. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] In the following description, reference is made to the accompanying drawings, which form a part of the disclosure and which show by way of example certain aspects of embodiments of the invention or in which embodiments of the invention may be used. It is understood that the embodiments of the invention may be used in other ways and may include structural or logical changes not shown in the drawings. Therefore, the following detailed description should not be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

[0084] For example, it is understood that disclosure regarding a described method may also apply to a corresponding apparatus or system configured to perform the method, and vice versa. For example, when one or more particular method steps are described, a corresponding apparatus may include one or more units, e.g., functional units, for performing the described one or more method steps (e.g., one unit performing the one or more steps, or multiple units each performing one or more of the steps), even if such one or more units are not explicitly described or shown in the figures. On the other hand, for example, when a particular apparatus is described based on one or more units, e.g., functional units, a corresponding method may include steps for performing the functions of the one or more units (e.g., one step performing the functions of the one or more units, or multiple steps each performing the functions of one or more of the units), even if such one or more steps are not explicitly described or shown in the figures. Furthermore, it is understood that features of various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically stated otherwise.

[0085] Video coding typically refers to the processing of a sequence of pictures that form a video or a video sequence. Instead of the term "picture", the terms "frame" or "image" are sometimes used as synonyms in the field of video coding. Video coding (or, in general, coding) has two parts: video encoding and video decoding. Video encoding is performed at the source side and typically involves processing the original video picture (e.g., by compression) to reduce the amount of data needed to represent the video picture (for more efficient storage and / or transmission). Video decoding is performed at the destination side and typically involves the reverse processing to the encoder to reconstruct the video picture. Embodiments that refer to "coding" of a video picture (or, in general, a picture) shall be understood to relate to "encoding" or "decoding" of the video picture or the respective video sequence. The combination of the encoding and decoding parts is also called CODEC (Coding and Decoding).

[0086] In the case of lossless video coding, the original video picture can be reconstructed, i.e., the reconstructed video picture has the same quality as the original video picture (assuming there is no transmission or other data loss during storage or transmission). In the case of lossy video coding, further compression is performed, e.g., by quantization, to reduce the amount of data representing the video picture, and the video picture cannot be perfectly reconstructed at a decoder, i.e., the quality of the reconstructed video picture is low or poor compared to the quality of the original video picture.

[0087] Some video coding standards belong to the group of "lossy hybrid video codecs" (i.e., they combine spatial and temporal prediction in the sample domain with 2D transform coding that applies quantization in the transform domain). Each picture of a video sequence is typically divided into a set of non-overlapping blocks, and coding is typically performed at the block level. In other words, at the encoder, video is typically processed or encoded at the block (video block) level, e.g., by generating a predictive block using spatial (intra-picture) prediction and / or temporal (inter-picture) prediction, subtracting the predictive block from a current block (the block currently being processed / to be processed) to obtain a residual block, transforming the residual block, and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), while at the decoder, the inverse process to the encoder is applied to the encoded or compressed block in order to reconstruct the current block for representation. Furthermore, the encoder replicates the decoder processing loop so that both generate the same predictions (eg, intra-prediction and inter-prediction) and / or reconstructions for processing, ie, coding, subsequent blocks.

[0088] In the following embodiment of a video coding system 10, a video encoder 20 and a video decoder 30 are described with reference to FIGS. 1-3.

[0089] 1A is a schematic block diagram of an example coding system 10 that may utilize techniques of the present application, such as video coding system 10 (or coding system 10 for short). A video encoder 20 (or encoder 20 for short) and a video decoder 30 (or decoder 30 for short) of video coding system 10 represent examples of devices that may be configured to perform techniques according to various examples described herein.

[0090] As shown in FIG. 1A, coding system 10 includes a source device 12 configured to provide encoded picture data 21, for example to a destination device 14 that decodes encoded picture data 13.

[0091] The source device 12 comprises an encoder 20 and may additionally, that is to say optionally, comprise a picture source 16 , a pre-processor (or pre-processing unit) 18 , for example a picture pre-processor 18 , and a communication interface or unit 22 .

[0092] Picture source 16 may comprise or be any kind of picture capture device, e.g. a camera for capturing real world pictures, and / or any kind of picture generation device, e.g. a computer graphics processor for generating computer animated pictures, or any kind of other device for obtaining and / or providing real world pictures, computer generated pictures (e.g. screen content, virtual reality (VR) pictures) and / or any combination thereof (e.g. augmented reality (AR) pictures). Picture source may be any kind of memory or storage for storing any of the above mentioned pictures.

[0093] As distinguished from the pre-processor 18 and the processing performed by the pre-processing unit 18 , the pictures or picture data 17 may also be referred to as raw pictures or raw picture data 17 .

[0094] The pre-processor 18 is configured to receive the (raw) picture data 17 and perform pre-processing on the picture data 17 to obtain a pre-processed picture 19 or pre-processed picture data 19. The pre-processing performed by the pre-processor 18 may comprise, for example, cropping, color format conversion (e.g., from RGB to YCbCr), color correction, or noise removal. It may be appreciated that the pre-processing unit 18 may be an optional component.

[0095] Video encoder 20 is configured to receive preprocessed picture data 19 and to provide encoded picture data 21 (as will be described in further detail, e.g., with reference to FIG. 2 below). Communications interface 22 of source device 12 may be configured to receive encoded picture data 21 and to transmit encoded picture data 21 (or any further processed version thereof) over communications channel 13 to another device, e.g. destination device 14 or any other device, for storage or direct reconstruction.

[0096] The destination device 14 comprises a decoder 30 (eg, a video decoder 30) and may additionally, i.e. optionally, comprise a communications interface or unit 28, a post-processor 32 (or post-processing unit 32), and a display device 34.

[0097] The communications interface 28 of the destination device 14 is configured to receive the encoded picture data 21 (or any further processed version thereof), for example directly from the source device 12 or from any other source, for example a storage device such as a coded picture data storage device, and to provide the encoded picture data 21 to a decoder 30.

[0098] The communications interface 22 and the communications interface 28 may be configured to transmit or receive the encoded picture data 21 or the encoded data 13 via a direct communications link between the source device 12 and the destination device 14, such as a direct wired or wireless connection, or via any type of network, such as a wired or wireless network or any combination thereof, or any type of private and public network, or any type of combination thereof.

[0099] The communications interface 22 may be configured, for example, to package the encoded picture data 21 into a suitable format, such as packets, and / or process the encoded picture data using any type of transmission coding or processing for transmission over a communications link or network.

[0100] The communications interface 28 forms a counterpart to the communications interface 22 and may be configured, for example, to receive transmitted data and process the transmitted data using any type of corresponding transmission decoding or processing and / or depackaging to obtain encoded picture data 21.

[0101] Both communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces, as indicated by the arrow of communication channel 13 in FIG. 1A pointing from source device 12 to destination device 14, or may be configured as bidirectional communication interfaces and may be configured to send and receive messages, such as to set up a communication link and / or connection to acknowledge and exchange other information related to a data transmission, such as a coded picture data transmission.

[0102] The decoder 30 is arranged to receive the encoded picture data 21 and to provide decoded picture data 31 or decoded pictures 31 (as will be described in further detail below, for example with reference to FIG. 3 or FIG. 5).

[0103] The post-processor 32 of the destination device 14 is configured to post-process the decoded picture data 31 (also called reconstructed video data), e.g. the decoded picture 31, to obtain post-processed picture data 33, e.g. a post-processed picture 33. The post-processing performed by the post-processing unit 32 may comprise, e.g., color format conversion (e.g., from YCbCr to RGB), color correction, cropping, or resampling, or any other processing, e.g. to prepare the decoded picture data 31 for display by a display device 34.

[0104] A display device 34 of the destination device 14 is configured to receive the post-processed picture data 33 for displaying the picture, e.g., to a user or viewer. The display device 34 may be or include any type of display for presenting the reconstructed picture, e.g., an integrated or external display or monitor. The display may include, for example, a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a plasma display, a projector, a micro LED display, a liquid crystal on silicon (LCoS), a digital light processor (DLP), or any other type of display.

[0105] 1A depicts source device 12 and destination device 14 as separate devices, an embodiment of the devices may also include both or both the functionality of source device 12 or corresponding functionality and destination device 14 or corresponding functionality. In such an embodiment, source device 12 or corresponding functionality and destination device 14 or corresponding functionality may be implemented using the same hardware and / or software, or by separate hardware and / or software, or any combination thereof.

[0106] As will be clear to a person skilled in the art based on the description, the presence and (exact) functional division of different units or functions within source device 12 and / or destination device 14 as shown in FIG. 1A may vary depending on the actual device and application.

[0107] Encoder 20 (e.g., video encoder 20) or decoder 30 (e.g., video decoder 30), or both encoder 20 and decoder 30, may be implemented by processing circuitry as shown in FIG. 1B, such as, for example, one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, hardware, dedicated to video coding, or any combination thereof. Encoder 20 may be implemented by processing circuitry 46 to embody various modules as described with respect to encoder 20 of FIG. 2 and / or any other encoder system or subsystem described herein. Decoder 30 may be implemented by processing circuitry 46 to embody various modules as described with respect to decoder 30 of FIG. 3 and / or any other decoder system or subsystem described herein. The processing circuitry may be configured to perform various operations as described below. When the techniques are implemented partially in software, as shown in Figure 5, an apparatus may perform the techniques of this disclosure by storing software instructions on a suitable non-transitory computer-readable storage medium and executing those instructions in hardware using one or more processors. Either video encoder 20 or video decoder 30 may be integrated as part of a combined encoder / decoder (CODEC) in a single apparatus, as shown in Figure 1B, for example.

[0108] The source device 12 and the destination device 14 may comprise any of a wide range of devices, including any type of handheld or fixed device, such as, for example, a notebook or laptop computer, a mobile phone, a smart phone, a tablet or tablet computer, a camera, a desktop computer, a set-top box, a television, a display device, a digital media player, a video game console, a video streaming device (e.g., a content service server or a content delivery server), a broadcast receiver device, a broadcast transmitter device, or the like, and may use no operating system or any type of operating system. In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

[0109] In some cases, the video coding system 10 shown in FIG. 1A is merely an example, and the techniques of the present application may be applied to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between an encoder and a decoder. In other examples, data may be retrieved from local memory and streamed over a network, etc. A video encoder may encode data and store it in memory, and / or a video decoder may retrieve data from memory and decode it. In some examples, encoding and decoding are performed by devices that simply encode data to memory and / or retrieve data from memory and decode it without communicating with each other.

[0110] For ease of explanation, embodiments of the invention are described herein with reference to, for example, reference software for High Efficiency Video Coding (HEVC) or Versatile Video Coding (VVC), a next-generation video coding standard developed by the Joint Collaboration Team on Video Coding (JCT-VC) between the ITU-T Video Coding Experts Group (VCEG) and the ISO / IEC Motion Picture Experts Group (MPEG). Those skilled in the art will appreciate that embodiments of the invention are not limited to HEVC or VVC.

[0111] Encoder and encoding method FIG. 2 shows a schematic block diagram of an example of a video encoder 20 configured to implement the technology of the present application. In the example of FIG. 2, the video encoder 20 includes an input 201 (or an input interface 201), a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy coding unit 270, and an output 272 (or an output interface 272). The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254, and a division unit 262. The inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown). The video encoder 20 shown in FIG. 2 may also be referred to as a hybrid video encoder, or a video encoder according to a hybrid video codec.

[0112] The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, and the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, while the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244, and the intra prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20, which corresponds to the signal path of a decoder (see video decoder 30 of FIG. 3). The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244, and the intra prediction unit 254 may also be referred to as forming a “built-in decoder” of the video encoder 20.

[0113] Picture & Picture Split (Picture & Block) The encoder 20 may be configured to receive, for example via an input 201, a picture 17 (or picture data 17), for example a picture of a sequence of pictures forming a video or a video sequence. The received picture or picture data may also be a preprocessed picture 19 (or preprocessed picture data 19). For simplicity, the following description refers to the picture 17. The picture 17 may also be referred to as a current picture or a picture to be coded (particularly in video coding, to distinguish the current picture from other pictures, for example previously coded and / or decoded pictures of the same video sequence, i.e. a video sequence that also includes the current picture).

[0114] A (digital) picture is or can be considered as a two-dimensional array or matrix of samples with intensity values. The samples in the array may also be referred to as pixels (short for picture element) or pels. The number of samples in the horizontal and vertical directions (or axes) of the array or picture defines the size and / or resolution of the picture. For color representation, typically three color components are used, i.e. a picture is represented by or may contain three sample arrays. In an RGB format or color space, a picture has corresponding red, green and blue sample arrays. However, in video coding, each pixel is typically represented in a luminance and chrominance format or color space, e.g. YCbCr, which has a luminance component denoted by Y (sometimes L is used instead) and two chrominance components denoted by Cb and Cr. The luminance (or luma for short) component Y represents the brightness or gray level intensity (e.g., as in a grayscale picture), and the two chrominance (or chroma for short) components Cb and Cr represent the chromaticity or color information components. Thus, a picture in YCbCr format has a luminance sample array of luminance sample values ​​(Y) and two chrominance sample arrays of chrominance values ​​(Cb and Cr). A picture in RGB format can be converted or transformed into YCbCr format and vice versa, a process also known as color transformation or conversion. If a picture is monochrome, the picture may only have a luminance sample array. Thus, a picture may be, for example, an array of luma samples in a monochrome format, or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 color formats.

[0115] An embodiment of video encoder 20 may have a picture division unit (not shown in FIG. 2 ) configured to divide picture 17 into multiple (typically non-overlapping) picture blocks 203. These blocks may also be referred to as root blocks, macroblocks (H.264 / AVC), or coding tree blocks (CTBs) or coding tree units (CTUs) (H.265 / HEVC and VVC). The picture division unit may be configured to divide each picture into corresponding blocks using the same block size for all pictures of a video sequence and a corresponding grid that defines the block size, or to vary the block size between pictures, or between subsets or groups of pictures.

[0116] In a further embodiment, the video encoder may be configured to directly receive block 203 of picture 17, such as one, some, or all of the blocks forming picture 17. Picture block 203 may also be referred to as a current picture block or a picture block to be coded.

[0117] Similar to the picture 17, the picture block 203 is also considered or can be considered as a two-dimensional array or matrix of samples having intensity values ​​(sample values), but of smaller dimensions than the picture 17. In other words, the block 203 may have, for example, one sample array (e.g., a luma array in case of a monochrome picture 17, or a luma array or a chroma array in case of a color picture), or three sample arrays (e.g., a luma array and two chroma arrays in case of a color picture 17), or some other number and / or type of arrays depending on the color format applied. The number of samples in the horizontal and vertical directions (or axes) of the block 203 determines the size of the block 203. Thus, the block may be, for example, an M×N (M columns×N rows) array of samples, or an M×N array of transform coefficients.

[0118] The embodiment of video encoder 20 shown in FIG. 2 may be configured to encode picture 17 on a block-by-block basis, eg, encoding and prediction are performed for each block 203 .

[0119] The embodiment of video encoder 20 shown in FIG. 2 may further be configured to divide and / or encode pictures by using slices (also referred to as video slices), where a picture may be divided into or encoded using one or more slices (typically non-overlapping), and each slice may have one or more blocks (e.g., CTUs).

[0120] The embodiment of video encoder 20 shown in FIG. 2 may further be configured to divide and / or encode a picture by using tile groups (also referred to as video tile groups) and / or tiles (also referred to as video tiles), where a picture may be divided into or encoded using one or more tile groups (typically non-overlapping), and each tile group may have, for example, one or more blocks (e.g., CTUs) or one or more tiles, and each tile may be, for example, rectangular in shape and may have one or more blocks (e.g., CTUs), such as complete blocks or partial blocks.

[0121] Residual calculation The residual calculation unit 204 may be configured to calculate a residual block 205 (also referred to as residual 205) based on the picture block 203 and a prediction block 265 (further details regarding the prediction block 265 will be provided later), for example by subtracting sample values ​​of the prediction block 265 from sample values ​​of the picture block 203 on a sample-by-sample (pixel-by-pixel) basis to obtain a residual block 205 in the sample domain.

[0122] conversion The transform processing unit 206 may be configured to apply a transform, such as a discrete cosine transform (DCT) or a discrete sine transform (DST), to the sample values ​​of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and may represent the residual block 205 in the transform domain.

[0123] The transform processing unit 206 may be configured to apply an integer approximation of the DCT / DST, such as the transform specified for H.265 / HEVC. Compared to an orthogonal DCT transform, such an integer approximation is typically scaled by a certain factor. In order to preserve the norm of the residual block processed by the forward transform and the inverse transform, an additional scaling factor is applied as part of the transform process. The scaling factor is typically selected based on certain constraints, such as the scaling factor being a power of two due to shift operations, the bit depth of the transform coefficients, a trade-off between accuracy and implementation cost, etc. A certain scaling factor may be specified for the inverse transform, for example by the inverse transform processing unit 212 (and for the corresponding inverse transform, for example by the inverse transform processing unit 312 in the video decoder 30), and a corresponding scaling factor for the forward transform, for example by the transform processing unit 206 in the encoder 20, may be specified accordingly.

[0124] An embodiment of the video encoder 20 (respectively the transform processing unit 206) may be configured to output transform parameters, e.g., one or more types of transform, via the entropy coding unit 270, e.g., directly or in an encoded or compressed form, so that, for example, the video decoder 30 may receive and use the transform parameters for decoding.

[0125] quantization The quantization unit 208 may be configured to quantize the transform coefficients 207, for example by applying scalar quantization or vector quantization, to obtain quantized coefficients 209, which may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

[0126] The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded to an m-bit transform coefficient during quantization, where n is greater than m. The degree of quantization may be changed by adjusting a quantization parameter (QP). For example, in the case of scalar quantization, different scaling may be applied to achieve finer or coarser quantization. A smaller quantization step size corresponds to a finer quantization and a larger quantization step size corresponds to a coarser quantization. The applicable quantization step sizes may be indicated by the quantization parameter (QP). The quantization parameter may be, for example, an index to a predefined set of applicable quantization step sizes. For example, a small quantization parameter may correspond to a finer quantization (smaller quantization step size) and a large quantization parameter may correspond to a coarser quantization (larger quantization step size), and vice versa. Quantization may include division by the quantization step size, and corresponding and / or inverse dequantization, e.g., by the inverse quantization unit 210, may include multiplication by the quantization step size. Some standard embodiments, e.g., HEVC, may be configured to use the quantization parameter to determine the quantization step size. In general, the quantization step size may be calculated based on the quantization parameter using a fixed-point approximation of an equation that includes a division. An additional scaling factor may be introduced for quantization and dequantization to restore the norm of the residual block, and the norm of the residual block may be changed due to the scaling used for the fixed-point approximation of the equation for the quantization step size and the quantization parameter. In one implementation, the scaling of the inverse transform and dequantization may be combined. Alternatively, customized quantization tables may be used and signaled from the encoder to the decoder, e.g., in the bitstream. Quantization is a lossy operation, and the loss increases with increasing quantization step size.

[0127] The picture compression level is controlled by a quantization parameter that may be fixed for the whole picture (e.g., by using the same quantization parameter value) or may have different quantization parameter values ​​for different regions of the picture. In YCbCr 4:2:0 and 4:2:2 video, the signal characteristics of the luma and chroma components are quite different. In particular, chroma often exhibits a strong low-pass characteristic. If strong quantization is applied, it may happen that the chroma information is completely quantized to zero, which will lead to a complete loss of color. Therefore, to prevent this, the quantizer step size for chroma is adapted by reducing the chroma quantizer step size for high QP values ​​[2].

[0128] In the High Efficiency Video Coding (HEVC) standard defined in [1], the chroma quantization parameter QPc is derived according to Table 1, where qPi is equal to the associated luma quantization parameter plus a chroma QP offset value signaled in the picture parameter set (PPS) and / or slice header. The derivation of a chroma QP value from an associated luma QP value can be adjusted by signaling a different chroma QP offset value. A positive chroma QP offset value will result in a coarser quantizer for the associated chroma component. [Table 15]

[0129] Quantization parameter index QP for HEVC (black) and H.264|AVC (gray) according to [2] i Chroma quantization parameter QP c A schematic representation of the mapping to is presented in FIG.

[0130] In the HEVC standard, the QP value for a luminance (or luma) coding block (CB) is derived based on a predicted QP (qPY_PRED), which in turn depends on the CB position within a frame / slice / tile. Y The variables are derived according to Equation 1: Qp Y =((qPY PRED +CuQpDeltaVal+64+2*QpBdOffsetY)%(64+QpBdOffsetY))-QpBdOffsetY (Equation 1) where CuQpDeltaVal is the delta QP value signaled or derived for the coding unit (CU), and QpBdOffsetY is a constant offset that depends on the luma bit depth (from the HEVC standard, this term corresponds to the "bit depth of the samples of the luma array"). Finally, the quantization parameter Qp Y ' can be calculated by the following Equation 2: Qp Y '=Qp Y +QpBdOffsetY (Equation 2) The variables qPCb and qPCr are set equal to the value of QpC as specified in a mapping table (e.g., Table 1) based on index qPi being equal to qPiCb or qPiCr, respectively, where qPiCb and qPiCr are derived according to Equation 3 as follows: qPiCb=Clip3(-QpBdOffsetC,69,QpY+pps_cb_qp_offset+slice_cb_qp_offset) qPiCr=Clip3(-QpBdOffsetC,69,QpY+pps_cr_qp_offset+slice_cr_qp_offset) (Formula 3) where QpBdOffsetC is a constant offset depending on the chroma bit depth (from the HEVC standard, this term corresponds to “bit depth of samples of the chroma array”), pps_cb_qp_offset or pps_cr_qp_offset is a fixed offset for the Cb or Cr component signaled by the picture parameter set (PPS), and slice_cb_qp_offset or slice_cr_qp_offset is a fixed offset for the Cb or Cr component signaled in the slice header,

number

[0131] Chroma quantization parameters (Qp Cb ' and Qp Cr ') is derived as follows: Qp Cb '=qP Cb +QpBdOffsetC Qp Cr '=qP Cr +QpBdOffsetC (Formula 5) Variable qP Cb and qP Cr are qPi Cb and qPi Cr Based on the index qPi, which is equal to C The value is set equal to the value of

[0132] VVC is an emerging standard, and the draft 5th edition of the specification [] includes the following steps for deriving the chroma quantization parameters: - When treeType is equal to DUAL_TREE_CHROMA, the variable Qp Y is the luma quantization parameter Qp of the luma coding unit covering the luma position (xCb+cbWidth / 2, yCb+cbHeight / 2). Y is set equal to - variable qP Cb, qP Cr and qP CbCr is derived as follows: qPi Cb =Clip3(-QpBdOffset C ,69,Qp Y +pps_cb_qp_offset+slice_cb_qp_offset) (8-926) qPi Cr =Clip3(-QpBdOffset C ,69,Qp Y +pps_cr_qp_offset+slice_cr_qp_offset) (8-927) qPi CbCr =Clip3(-QpBdOffset C ,69,Qp Y +pps_joint_cbcr_qp_offset+slice_joint_cbcr_qp_offset) (8-928) - If ChromaArrayType is equal to 1, the variable qP Cb , qP Cr , and qP CbCr are qPi Cb , qPi Cr and qPi CbCr Based on the index qPi, which is equal to Qp' CbCr =qP CbCr +QpBdOffsetC (8-931) Qp as specified in Table 2 C The value is set equal to the value of - otherwise, the variable qP Cb , qP Cr and qP CbCr are qPi Cb , qPi Cr and qPi CbCr Based on the index qPi being equal to , it is set equal to Min(qPi, 63). - chroma quantization parameter Qp' for the Cb and Cr components Cb and Qp' Cr , as well as joint Cb-Cr coding Qp' CbCr is derived as follows: Qp'Cb =qP Cb +QpBdOffset C (8-929) Qp' Cr =qP Cr +QpBdOffset C (8-930) Qp' CbCr =qP CbCr +QpBdOffset C (8-931) [Table 16] where pps_cb_qp_offset and slice_cb_qp_offset are picture-level and slice-level chroma QP offset values ​​signaled in the picture parameter set (PPS) and / or slice header, respectively.

[0133] Since chroma compression efficiency has been significantly improved in VVC through the inclusion of chroma-specific coding tools such as chroma separation trees and CCLM, the chroma Qp mapping function may require adjustment.

[0134] It can be seen that the same chroma Qp mapping table (Table 2) is used as in the HEVC standard (Table 1). In contrast to HEVC, Qp' is used to derive the quantization parameters for the blocks. Cb and Qp' Cr In addition to Qp' CbCr is introduced and the Cb and Cr color components are jointly quantized. CbCr The parameters are also derived based on the chroma Qp mapping function defined in Table 2.

[0135] As mentioned above, the derivation of chroma QP values ​​from the associated luma QP values ​​can be adjusted by signaling different chroma QP offset values. A positive chroma QP offset value will result in a coarser quantizer for the associated chroma component. Figure 10 shows an example of an HEVC / VVC chroma Qp mapping function with a chroma Qp offset equal to 1.

[0136] An embodiment of video encoder 20 (respectively quantization unit 208) may be configured to output a quantization parameter (QP), e.g., directly or encoded, via entropy coding unit 270, so that, for example, video decoder 30 may receive and apply the quantization parameter for decoding.

[0137] inverse quantization Inverse quantization unit 210 is configured to apply the inverse quantization of quantization unit 208 to the quantized coefficients, e.g., by applying the inverse of the quantization scheme applied by quantization unit 208, based on or using the same quantization step size as quantization unit 208, to obtain dequantized coefficients 211. The dequantized coefficients 211, which are also sometimes referred to as dequantized residual coefficients 211, correspond to the transform coefficients 207, but are typically not the same as the transform coefficients due to losses due to quantization.

[0138] Reverse transformation The inverse transform processing unit 212 is configured to apply an inverse transform of the transform applied by the transform processing unit 206, such as an inverse discrete cosine transform (DCT), an inverse discrete sine transform (DST), or other inverse transform, to obtain a reconstructed residual block 213 (or corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as a transform block 213.

[0139] Reconstruction The reconstruction unit 214 (e.g., adder or summer 214) is configured to add the transform block 213 (i.e., the reconstructed residual block 213) to the prediction block 265, for example by adding the sample values ​​of the reconstructed residual block 213 and the sample values ​​of the prediction block 265 sample by sample, to obtain a reconstructed block 215 in the sample domain.

[0140] filtering The loop filter unit 220 (or "loop filter" 220 for short) is configured to filter the reconstruction block 215 to obtain a filtered block 221, or in general, to filter the reconstructed samples to obtain filtered samples. The loop filter unit is configured, for example, to smooth pixel transitions or to otherwise improve video quality. The loop filter unit 220 may include one or more loop filters, such as, for example, a deblocking filter, a sample-adaptive offset (SAO) filter, or one or more other filters, such as, for example, a bilateral filter, an adaptive loop filter (ALF), a sharpening filter, a smoothing filter, or a collaborative filter, or any combination thereof. Although the loop filter unit 220 is illustrated in FIG. 2 as an in-loop filter, in other configurations, the loop filter unit 220 may be implemented as a post-loop filter. The filtered block 221 may also be referred to as a filtered reconstruction block 221.

[0141] Embodiments of video encoder 20 (respectively loop filter unit 220) may be configured to output loop filter parameters (e.g., sample adaptive offset information, etc.), e.g., directly or in an encoded manner, via entropy coding unit 270, so that, for example, decoder 30 may receive and apply the same loop filter parameters or respective loop filters for decoding.

[0142] Decoded Picture Buffer The decoded picture buffer (DPB) 230 may be a memory that stores reference pictures or reference picture data in general for encoding video data by the video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as, for example, dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The decoded picture buffer (DPB) 230 may be configured to store one or more filtered blocks 221. The decoded picture buffer 230 may also be configured to store other previous filtered blocks, such as previously reconstructed and filtered blocks 221, of the same current picture or of a different picture, such as a previous reconstructed picture, and may provide a complete previous reconstructed or decoded picture (and corresponding reference blocks and samples) and / or a partially reconstructed current picture (and corresponding reference blocks and samples), for example for inter prediction. The decoded picture buffer (DPB) 230 may also be configured to store one or more unfiltered reconstruction blocks 215, or in general, unfiltered reconstructed samples, for example in the case where the reconstruction blocks 215 are not filtered by the loop filter unit 220, or may be configured to store any other further processed version of the reconstruction blocks or reconstructed samples.

[0143] Mode selection (splitting & predicting) The mode selection unit 260 comprises a partitioning unit 262, an inter prediction unit 244, and an intra prediction unit 254, and is configured to receive or obtain original picture data, e.g., original block 203 (current block 203 of current picture 17), and reconstructed picture data, e.g., filtered and / or unfiltered reconstructed samples or blocks of the same (current) picture and / or from one or more previous decoded pictures, e.g., from a decoded picture buffer 230 or another buffer (e.g., a line buffer, not shown). The reconstructed picture data is used as reference picture data for prediction, e.g., inter prediction or intra prediction, to obtain a prediction block 265 or a predictor 265.

[0144] The mode selection unit 260 may be configured to determine or select a partitioning (including no partitioning) and a prediction mode (e.g., intra or inter prediction mode) for the current block prediction mode and generate a corresponding prediction block 265, which is used for calculation of the residual block 205 and for reconstruction of the reconstruction block 215.

[0145] An embodiment of the mode selection unit 260 may be configured to select a partitioning and prediction mode (e.g., from those supported by or available to the mode selection unit 260) that provides the best match or, in other words, the smallest residual (smallest residual means better compression for transmission or storage) or the smallest signaling overhead (smallest signaling overhead means better compression for transmission or storage), or that considers or balances both. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate distortion optimization (RDO), i.e., to select the prediction mode that provides the smallest rate distortion. Terms such as "best," "minimum," and "optimum" in this context do not necessarily mean an overall "best," "minimum," "optimum," etc., but may also mean the achievement of a termination criterion or selection criterion, such as a value above or below a threshold or other constraint, which may lead to a "suboptimal selection," but reduced complexity and processing time.

[0146] In other words, the division unit 262 can be configured to divide the block 203 into smaller block partitions or sub-blocks (which also form blocks), e.g., using quadtree partitioning (QT), binary tree partitioning (BT) or ternary tree partitioning (TT), or any combination thereof repeatedly, and to perform prediction on each of the block partitions or sub-blocks, e.g., where the mode selection includes selecting a tree structure of the block 203 to be divided, and a prediction mode is applied to each of the block partitions or sub-blocks.

[0147] The partitioning (eg, by partitioning unit 260) and prediction processes (eg, by inter prediction unit 244 and intra prediction unit 254) performed by an example video encoder 20 are described in further detail below.

[0148] Split The partitioning unit 262 may partition (or split) the current block 203 into smaller partitions, e.g., blocks of smaller size, e.g., square or rectangular. These smaller blocks, which may also be referred to as sub-blocks, may be further partitioned into even smaller partitions. This is also called tree partitioning or hierarchical tree partitioning, and may recursively partition, e.g., a root block at root tree level 0 (hierarchical level 0, depth 0), into two or more blocks at the next lower tree level, e.g., a node at tree level 1 (hierarchical level 1, depth 1), which may again be partitioned into two or more blocks at the next lower level, e.g., tree level 2 (hierarchical level 2, depth 2), and so on, until the partitioning is terminated, e.g., by a termination criterion being met, e.g., a maximum tree depth or a minimum block size being reached. Blocks that are not further partitioned are also called leaf blocks or leaf nodes of the tree. A tree with a division into two partitions is called a binary tree (BT), a tree with a division into three partitions is called a ternary tree (TT), and a tree with a division into four partitions is called a quad tree (QT).

[0149] As mentioned above, the term "block" as used herein is a portion of a picture, particularly a square or rectangular portion. With reference to HEVC and VVC, for example, a block can be or correspond to a coding tree unit (CTU), a coding unit (CU), a prediction unit (PU), and a transform unit (TU), and / or correspond to a corresponding block, such as a coding tree block (CTB), a coding block (CB), a transform block (TB), or a prediction block (PB).

[0150] For example, a coding tree unit (CTU) can be or have a CTB of luma samples of a picture with three sample arrays, a CTB of two corresponding chroma samples, or a CTB of samples of a monochrome picture or a picture coded with three separate color planes, and a syntax structure used to code the samples. Correspondingly, a coding tree block (CTB) can be an N×N block of samples with some value N, and the division of a component into multiple CTBs is a partition. A coding unit (CU) can be or have a coding block of luma samples of a picture with three sample arrays, a coding block of two corresponding chroma samples, or a coding block of samples of a monochrome picture or a picture coded with three separate color planes, and a syntax structure used to code the samples. Correspondingly, a coding block (CB) can be an M×N block of samples with some values ​​M and N, and the division of a CTB into multiple coding blocks is a partition.

[0151] In an embodiment, for example, according to HEVC, a coding tree unit (CTU) can be split into CUs by using a quadtree structure denoted as coding tree. A decision is made at the CU level whether a picture region is coded using inter-picture (temporal) prediction or intra-picture (spatial) prediction. Each CU can be further split into one, two, or four PUs according to a PU split type. Within one PU, the same prediction process is applied, and related information is transmitted to the decoder on a PU basis. After obtaining a residual block by applying a prediction process based on the PU split type, the CU can be split into transform units (TUs) according to another quadtree structure similar to the coding tree for the CU.

[0152] In an embodiment, according to the latest video coding standard currently under development, for example called Versatile Video Coding (VVC), a combined quad-tree-binary tree (QTBT) partitioning is used to partition the coding block. In the QTBT block structure, the CUs can have either a square or rectangular shape. For example, a coding tree unit (CTU) is first partitioned by a quad-tree structure. The quad-tree leaf nodes are further partitioned by a binary tree structure or a ternary tree or triple tree structure. The partition tree leaf nodes are called coding units (CUs), and their segmentation is used for prediction and transformation processes without further partitioning. This means that CUs, PUs, and TUs have the same block size in the QTBT coding block structure. In parallel, multiple partitions, for example ternary tree partitioning, may be used with the QTBT block structure.

[0153] In one example, mode selection unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

[0154] As mentioned above, video encoder 20 may be configured to determine or select a best or optimal prediction mode from a (e.g., predetermined) set of prediction modes, which may include, for example, multiple intra-prediction modes and / or multiple inter-prediction modes.

[0155] Intra prediction The set of intra prediction modes may, for example, have 35 different intra prediction modes, e.g., non-directional modes such as DC (or average) mode and planar mode, or directional modes, as specified for HEVC, or may have 67 different intra prediction modes, e.g., non-directional modes such as DC (or average) mode and planar mode, or directional modes, as specified for VVC.

[0156] The intra prediction unit 254 is configured to generate an intra prediction block 265 according to an intra prediction mode from a set of intra prediction modes using reconstructed samples of neighboring blocks of the same current picture.

[0157] The intra prediction unit 254 (or, generally, the mode selection unit 260) is further configured to output intra prediction parameters (or, generally, information indicating the intra prediction mode selected for the block) to the entropy encoding unit 270 in the form of a syntax element 266 for inclusion in the encoded picture data 21 so that, for example, the video decoder 30 may receive and use the prediction parameters for decoding.

[0158] Inter Prediction The set of inter prediction modes (or possible inter prediction modes) depends on the available reference pictures (i.e., previous, at least partially decoded pictures, e.g., stored in DBP 230) and other inter prediction parameters, such as whether the entire reference picture or only a portion of it, e.g., a search window area around the area of ​​the current block, is used to search for the best matching reference block, and / or whether pixel interpolation, e.g., half-pel and / or quarter-pel interpolation, is applied.

[0159] In addition to the above prediction modes, skip mode and / or direct mode may also be applied.

[0160] The inter prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (neither shown in FIG. 2). The motion estimation unit may be configured to receive or obtain a picture block 203 (current picture block 203 of current picture 17) and a decoded picture 231 or at least one or more previous reconstructed blocks, such as reconstructed blocks of one or more other / different previous decoded pictures 231, for motion estimation. For example, a video sequence may have a current picture and a previous decoded picture 231, or in other words, the current picture and the previous decoded picture 231 may be part of or form a series of pictures that form a video sequence.

[0161] The encoder 20 may be configured to, for example, select a reference block from multiple reference blocks of the same picture or multiple different pictures among multiple other pictures, and provide the reference picture (or reference picture index) and / or an offset (spatial offset) between the position (x,y coordinates) of the reference block and the position of the current block as an inter-prediction parameter to the motion estimation unit, which offset is also called a motion vector (MV).

[0162] The motion compensation unit is configured to obtain, for example by receiving, inter prediction parameters and perform inter prediction based on or using the inter prediction parameters to obtain an inter prediction block 265. The motion compensation performed by the motion compensation unit may include fetching or generating a prediction block based on a motion / block vector determined by motion estimation, possibly performing interpolation to sub-pixel accuracy. Interpolation filtering may generate additional pixel samples from known pixel samples, thus potentially increasing the number of candidate prediction blocks that can be used to code the picture block. Upon receiving a motion vector for the PU of the current picture block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference picture lists.

[0163] The motion compensation unit may also generate syntax elements associated with blocks and video slices for use by video decoder 30 in decoding picture blocks of the video slices. In addition to, or as an alternative to, slices and their respective syntax elements, tile groups and / or tiles and their respective syntax elements may be generated or used.

[0164] Entropy Coding The entropy encoding unit 270 is configured to, for example, apply an entropy encoding algorithm or scheme (e.g., a variable length coding (VLC) scheme, a context adaptive VLC scheme (CAVLC), an arithmetic coding scheme, binarization, context adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or other entropy encoding method or technique) or bypass (without compression) to the quantized coefficients 209, the inter-prediction parameters, the intra-prediction parameters, the loop filter parameters, and / or other syntax elements to obtain encoded picture data 21, e.g. in the form of an encoded bitstream 21, which can be output using an output 272 so that, for example, the video decoder 30 may receive and use these parameters for decoding. Encoded bitstream 21 may be transmitted to video decoder 30 or may be stored in memory for later transmission or retrieval by video decoder 30 .

[0165] Other configuration variations of the video encoder 20 can be used to encode the video stream. For example, a non-transform-based encoder 20 can quantize the residual signal directly for a particular block or frame without using a transform processing unit 206. In another implementation, the encoder 20 can have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit.

[0166] Decoder and decoding method 3 shows an example of a video decoder 30 configured to implement the techniques of the present application. The video decoder 30 is configured to receive coded picture data 21 (e.g., coded bitstream 21), e.g., coded by encoder 20, to obtain a decoded picture 331. The coded picture data or bitstream comprises information for decoding the coded picture data, e.g., data representing picture blocks of coded video slices (and / or tile groups or tiles) and associated syntax elements.

[0167] In the example of Figure 3, the decoder 30 includes an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g., adder 314), a loop filter 320, a decoded picture buffer (DBP) 330, a mode application unit 360, an inter prediction unit 344, and an intra prediction unit 354. The inter prediction unit 344 may be or include a motion compensation unit. The video decoder 30 may, in some examples, perform a decoding pass that is generally inverse to the encoding pass described with respect to the video encoder 100 from Figure 2.

[0168] As described with respect to encoder 20, inverse quantization unit 210, inverse transform processing unit 212, reconstruction unit 214, loop filter 220, decoded picture buffer (DPB) 230, inter prediction unit 344, and intra prediction unit 354 are also referred to as forming a “built-in decoder” of video encoder 20. Accordingly, inverse quantization unit 310 may be identical in function to inverse quantization unit 110, inverse transform processing unit 312 may be identical in function to inverse transform processing unit 212, reconstruction unit 314 may be identical in function to reconstruction unit 214, loop filter 320 may be identical in function to loop filter 220, and decoded picture buffer 330 may be identical in function to decoded picture buffer 230. Accordingly, the descriptions of the respective units and functions of video encoder 20 apply correspondingly to the respective units and functions of video decoder 30.

[0169] Entropy Decoding The entropy decoding unit 304 is configured to parse the bitstream 21 (or, in general, the coded picture data 21) and, e.g., perform entropy decoding on the coded picture data 21 to obtain, e.g., quantized coefficients 309 and / or decoded coding parameters (not shown in FIG. 3), e.g., any or all of inter prediction parameters (e.g., reference picture indexes and motion vectors), intra prediction parameters (e.g., intra prediction modes or indices), transform parameters, quantization parameters, loop filter parameters, and / or other syntax elements. The entropy decoding unit 304 may be configured to apply a decoding algorithm or scheme corresponding to the encoding schemes described with respect to the entropy encoding unit 270 of the encoder 20. The entropy decoding unit 304 may be further configured to provide the inter prediction parameters, intra prediction parameters and / or other syntax elements to the mode application unit 360, and to provide other parameters to other units of the decoder 30. The video decoder 30 may receive syntax elements at a video slice level and / or a video block level. In addition to or as an alternative to slices and their respective syntax elements, tile groups and / or tiles and their respective syntax elements may be received and / or used.

[0170] inverse quantization Inverse quantization unit 310 may be configured to receive a quantization parameter (QP) (or, generally, information regarding inverse quantization) and quantized coefficients from coded picture data 21 (e.g., by parsing and / or decoding, e.g., by entropy decoding unit 304) and apply inverse quantization to the decoded quantized coefficients 309 based on the quantization parameter to obtain dequantized coefficients 311, which may also be referred to as transform coefficients 311. The inverse quantization process may include using the quantization parameter determined by video encoder 20 for each video block in a video slice (or tile or tile group) to determine the degree of quantization, and similarly, the degree of inverse quantization to be applied.

[0171] Inverse transformation The inverse transform processing unit 312 may be configured to receive the dequantized coefficients 311, also referred to as transform coefficients 311, and apply a transform to the dequantized coefficients 311 to obtain a reconstructed residual block 213 in the sample domain. The reconstructed residual block 213 may also be referred to as a transform block 313. The transform may be an inverse transform, for example an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may further be configured to receive transform parameters or corresponding information from the coded picture data 21 (e.g., by parsing and / or decoding, for example, by the entropy decoding unit 304) and determine the transform to apply to the dequantized coefficients 311.

[0172] Reconstruction The reconstruction unit 314 (e.g., adder or summer 314) may be configured to add the reconstructed residual block 313 to the prediction block 365, for example by adding together sample values ​​of the reconstructed residual block 313 and sample values ​​of the prediction block 365, to obtain a reconstructed block 315 in the sample domain.

[0173] filtering The loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstruction block 315 to obtain a filtered block 321, e.g., to smooth pixel transitions or otherwise improve video quality. The loop filter unit 320 may include one or more loop filters, such as, for example, a deblocking filter, a sample-adaptive offset (SAO) filter, or one or more other filters, such as, for example, a bilateral filter, an adaptive loop filter (ALF), a sharpening filter, a smoothing filter, or a collaborative filter, or any combination thereof. Although the loop filter unit 320 is shown in FIG. 3 as an in-loop filter, in other configurations, the loop filter unit 320 may be implemented as a post-loop filter.

[0174] Decoded Picture Buffer The decoded video blocks 321 of the picture are then stored in a decoded picture buffer 330, which may be used as a reference picture for subsequent motion compensation of other pictures and / or may store the decoded picture 331 for output for a respective display.

[0175] The decoder 30 is arranged to output the decoded pictures 311, for presentation or display to a user, eg via an output 312.

[0176] prediction In functionality, the inter prediction unit 344 may be the same as the inter prediction unit 244 (in particular, a motion compensation unit), and the intra prediction unit 354 may be the same as the intra prediction unit 254, performing split or partition decision and prediction based on the partition and / or prediction parameters or respective information received (e.g. by parsing and / or decoding by the entropy decoding unit 304) from the coded picture data 21. The mode application unit 360 may be configured to perform prediction (intra prediction or inter prediction) for each block based on the reconstructed picture, block or respective sample (filtered or unfiltered) to obtain a prediction block 365.

[0177] When a video slice is coded as an intra-coded (I) slice, the intra prediction unit 354 of the mode application unit 360 is configured to generate a prediction block 365 for a picture block of the current video slice based on the signaled intra prediction mode and data from a previously decoded block of the current picture. When a video picture is coded as an inter-coded (i.e., B or P) slice, the inter prediction unit 344 (e.g., a motion compensation unit) of the mode application unit 360 is configured to generate a prediction block 365 for a video block of the current video slice based on the motion vector and other syntax elements received from the entropy decoding unit 304. In inter prediction, the prediction block may be generated from one of the reference pictures in one of the reference picture lists. The video decoder 30 may construct the reference frame lists, List 0 and List 1, using a default construction technique based on the reference pictures stored in the DPB 330. The same or similar may apply to or with embodiments that use tile groups (e.g., video tile groups) and / or tiles (e.g., video tiles) in addition to or instead of slices (e.g., video slices), e.g., video may be coded using I, P or B tile groups and / or tiles.

[0178] Mode application unit 360 is configured to determine prediction information for the video blocks of the current video slice by parsing the motion vectors or related information and other syntax elements, and uses the prediction information to generate a prediction block for the current video block being decoded. For example, mode application unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra prediction or inter prediction) used to code the video blocks of the video slice, an inter prediction slice type (e.g., B slice, P slice, or GPB slice), construction information for one or more of the reference picture lists for the slice, a motion vector for each inter coded video block of the slice, an inter prediction status for each inter coded video block of the slice, and other information for decoding the video blocks in the current video slice. The same or similar may also apply to or with embodiments that use tile groups (e.g., video tile groups) and / or tiles (e.g., video tiles) in addition to or instead of slices (e.g., video slices), e.g., video may be coded using I, P, or B tile groups and / or tiles.

[0179] The embodiment of video decoder 30 shown in FIG. 3 may be configured to divide and / or decode pictures by using slices (also referred to as video slices), where a picture may be divided into or decoded using one or more slices (typically non-overlapping), and each slice may have one or more blocks (e.g., CTUs).

[0180] The embodiment of video decoder 30 shown in FIG. 3 may further be configured to divide and / or decode a picture by using tile groups (also referred to as video tile groups) and / or tiles (also referred to as video tiles), where a picture may be divided into or decoded using one or more tile groups (typically non-overlapping), and each tile group may have, for example, one or more blocks (e.g., CTUs) or one or more tiles, and each tile may be, for example, rectangular in shape and may have one or more blocks (e.g., CTUs), such as complete blocks or partial blocks.

[0181] Other variations of the video decoder 30 may be used to decode the encoded picture data 21. For example, the decoder 30 may generate an output video stream without using a loop filtering unit 320. For example, a non-transform-based decoder 30 may inverse quantize the residual signal directly for a particular block or frame without using an inverse transform processing unit 312. In another implementation, the video decoder 30 may have the inverse quantization unit 310 and the inverse transform processing unit 312 combined into a single unit.

[0182] It should be understood that in the encoder 20 and the decoder 30, the processing result of the current step may be further processed before being output to the next step, for example, after the interpolation filtering, the motion vector derivation, or the loop filtering, further operations such as clipping or shifting may be performed on the processing result of the interpolation filtering, the motion vector derivation, or the loop filtering.

[0183] It should be noted that further operations may be applied to the derived motion vector of the current block (including but not limited to control point motion vector in affine mode, sub-block motion vector in affine, planar, ATMVP modes, temporal motion vector, etc.). For example, the value of the motion vector is constrained to a predefined range according to its representation bit. If the representation bit of the motion vector is bitDepth, the range is -2^(bitDepth-1) to 2^(bitDepth-1)-1, where "^" means exponent. For example, if bitDepth is set equal to 16, the range is -32768 to 32767, and if bitDepth is set equal to 18, the range is -131072 to 131071. For example, the value of the derived motion vector (e.g., MV of four 4x4 sub-blocks in one 8x8 block) is constrained such that the maximum difference between the integer parts of the MV of those four 4x4 sub-blocks is less than or equal to N pixels, e.g., less than or equal to 1 pixel. Here we provide two methods to constrain the motion vectors according to bitDepth.

[0184] Method 1: Remove the overflow MSB (Most Significant Bit) using flow arithmetic ux=(mvx+2 bitDepth )%2 bitDepth (1) mvx=(ux>=2 bitDepth-1 )?(ux-2 bitDepth ):ux (2) uy=(mvy+2 bitDepth )%2 bitDepth (3) mvy=(uy>=2 bitDepth-1 )?(uy-2 bitDepth ):uy (4) where mvx is the horizontal component of the motion vector of the image block or sub-block, mvy is the vertical component of the motion vector of the image block or sub-block, ux and uy denote intermediate values, For example, if the value of mvx is -32769, then after applying equations (1) and (2), the resulting value is 32767. In computer systems, decimal numbers are stored as two's complement numbers. The two's complement of -32769 is 1, 0111, 1111, 1111 (17 bits), then the MSB is discarded and the resulting two's complement is 0111, 1111, 1111, 1111 (decimal number is 32767), which is the same as the output by applying equations (1) and (2).

[0185] ux=(mvpx+mvdx+2 bitDepth )%2 bitDepth (5) mvx=(ux>=2 bitDepth-1 )?(ux-2 bitDepth ):ux (6) uy=(mvpy+mvdy+2 bitDepth )%2 bitDepth (7) mvy=(uy>=2 bitDepth-1 )?(uy-2 bitDepth ):uy (8) These operations may be applied between the sum of mvp and mvd as shown in equations (5)-(8).

[0186] Method 2: Eliminate the overflow MSB by clipping the value vx=Clip3(-2 bitDepth-1 ,2 bitDepth-1 -1,vx) vy=Clip3(-2 bitDepth-1 ,2 bitDepth-1 -1,vy) where vx is the horizontal component of the motion vector of the image block or sub-block, vy is the vertical component of the motion vector of the image block or sub-block, x, y and z correspond to the three input values ​​of the MV clipping process, respectively, and the definition of the function Clip3 is as follows:

number

[0187] 4 is a schematic diagram of a video coding device 400 according to one embodiment of the disclosure. The video coding device 400 is suitable for implementing the disclosed embodiments described herein. In one embodiment, the video coding device 400 may be a decoder, such as the video decoder 30 of FIG. 1A, or an encoder, such as the video encoder 20 of FIG. 1A.

[0188] The video coding device 400 includes an ingress port 410 (or input port 410) and a receiver unit (Rx) 420 for receiving data, a processor, logic unit, or central processing unit (CPU) 430 for processing the data, a transmitter unit (Tx) 440 and an egress port 450 (or output port 450) for transmitting the data, and a memory 460 for storing the data. The video coding device 400 may also have optical-to-electrical (OE) and electrical-to-optical (EO) components coupled to the ingress port 410, the receiver unit 420, the transmitter unit 440, and the egress port 450 for the egress or ingress of optical or electrical signals.

[0189] The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more of a CPU chip, a core (e.g., as a multi-core processor), an FPGA, an ASIC, and a DSP. The processor 430 is in communication with the ingress port 410, the receiver unit 420, the transmitter unit 440, the egress port 450, and the memory 460. The processor 430 includes a coding module 470. The coding module 470 implements the above-disclosed embodiments. For example, the coding module 470 implements, processes, prepares, or provides various coding operations. The inclusion of the coding module 470 thus provides a substantial improvement to the functionality of the video coding device 400 and realizes the transformation of the video coding device 400 to a different state. Alternatively, the coding module 470 is implemented as instructions stored in the memory 460 and executed by the processor 430.

[0190] Memory 460 may include one or more disks, tape drives, and solid state drives, and may also be used as an overflow data storage device to store programs when such programs are selected for execution, as well as to store instructions and data retrieved during program execution. Memory 460 may be, for example, volatile and / or non-volatile, and may be read-only memory (ROM), random access memory (RAM), ternary content-addressable memory (TCAM), and / or static random access memory (SRAM).

[0191] FIG. 5 is a simplified block diagram of a device 500 that may be used as either or both of source device 12 and destination device 14 from FIG. 1 according to an example embodiment.

[0192] The processor 502 in the device 500 may be a central processing unit, or may be any other type of device or devices now existing or later developed capable of manipulating or processing information. Although the disclosed implementations may be implemented with a single processor as shown, such as processor 502, advantages in speed and efficiency may be achieved using two or more processors.

[0193] The memory 504 in the apparatus 500 may, in one implementation, be a read-only memory (ROM) device or a random access memory (RAM) device. Any other suitable type of storage device may be used as the memory 504. The memory 504 may include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 may further include an operating system 508 and application programs 510, which include at least one program that enables the processor 502 to perform the methods described herein. For example, the application programs 510 may include applications 1-N, which further include a video coding application that performs the methods described herein.

[0194] The device 500 may also include one or more output devices, such as a display 518. The display 518, in one example, may be a touch-sensitive display that combines a display with touch-sensitive elements operable to sense touch input. The display 518 may be coupled to the processor 502 via the bus 512.

[0195] Although depicted here as a single bus, bus 512 of device 500 may be comprised of multiple buses. Additionally, secondary storage 514 may be directly coupled to the other components of device 500 or may be accessed over a network, and may comprise a single integrated unit, such as a memory card, or multiple units, such as multiple memory cards. Device 500 may thus be implemented in a wide variety of configurations.

[0196] Versatile Video Coding (VVC)VVC is a new developing standard for coding both standard and high dynamic range video content. High Dynamic Range Video (HDR Video) describes video with a higher dynamic range than that of Standard Dynamic Range Video (SDR Video). Key features of HDR video are brighter whites, deeper blacks, and at least 10 bits of color depth (versus 8 bits in SDR video) to maintain accuracy across this expanded range. Although technically distinct, the term "HDR video" is commonly understood to also mean a wide color gamut.

[0197] Currently, SDR and HDR are commercially deployed and will coexist for a long time. SDR content is typically coded as Non-Constant Luminance (NCL) Y'CbCr Gamma in BT.709 or BT.2020 containers. HDR content is typically coded as NCL Y'CbCr PQ, Constant Luminance ICtCp PQ, or NCL Y'CbCr HLG in BT.2020 / BT.2100 containers. The current VVC specification specifies only one mapping table for mapping luma to chroma quantization parameters (Table 1). The table is inherited from HEVC and is only designed for SDR content. As reported in [3], using the default QpC table causes chroma artifacts at low bitrates, especially in achromatic regions. This document proposes to add a chroma mapping table (or tables) specific to HDR content.

[0198] Considering that the newly developed standard will be deployed over several years and the diversity of signal types to be processed may be increased, it may be desirable to have flexibility in the mapping table specification. Also, using content-specific chroma QP mapping tables may bring more options for encoder optimization. A simple solution is to specify the mapping table at the picture / slice / tile group level. However, considering that the QP range supported by the codec may be wide enough (e.g., in VVC, it is in the range of 0 to 63), a direct table specification may consume a significant amount of bits. We further describe a method for signaling the chroma QP mapping table that allows to reduce the bit consumption. It should be further understood that the relationship between the luma QP and the chroma QP may be expressed either as a function or as a table representation, and here and hereafter, the mapping table and the mapping function are used synonymously.

[0199] FIG. 7 is a schematic representation of the HEVC mapping function of quantization parameter index QPi to chroma quantization parameter QPc for the supported QP range, where 72 is the HEVC mapping function and 71 is the one-to-one mapping function.

[0200] It should be recalled at this point to better understand the present disclosure that a function is called monotonically increasing, i.e., also called increasing or non-decreasing, if f(x)<=f(y) for all x and y, where x<=y, and thus f preserves order. It should be understood that x and y are from the set over which the function is defined.

[0201] For linear functions, the slope is defined as df(x) / dx. See above, by definition of a non-decreasing function, dx and df(x) always have the same sign. Therefore, in turn, df(x) / dx and the slope are always non-negative. See below, this can be achieved by using an unsigned ue(v) code to encode the pivot points dx and df(x).

[0202] According to a first embodiment of the invention, the luma-to-chroma mapping function is a monotonically increasing (non-decreasing) function that is divided into two classes of regions. Class A is the flat region (732) where the function is not increasing (i.e. is flat), i.e. f(x)-f(x-1)=0, and class B region is the region (731) where the function is increasing, i.e. f(x)-f(x-1)=c, where c is a function of x and c(x)>=1, and in the more specific case, in the class B region, the function has an increment of 1 for each successive input argument, i.e. f(x)-f(x-1)=1. A set X of input argument values ​​x is divided into two non-overlapping sets. Set A corresponds to function values ​​from the non-increasing region (class A) and set B corresponds to function values ​​from the increasing region (class B), where X=A+B.

[0203] FIG. 8 depicts an exemplary mapping table that refers to an example of a function delta value (87) equal to zero, i.e., a flat region, and a corresponding argument value x (88). For example, in the HEVC mapping table 82, set A consists of the values 30, 35, 37, 39, 41, and 43. In another exemplary modified mapping table 83, set A consists of the values 30, 39, 43 (or 35, 39, 43). According to the first embodiment, set A is signaled within the bitstream, and the decoder constructs a mapping function, for example, in table form, according to the information about set A obtained from the bitstream. Assuming X is, for example, a set of QP ranges (e.g., 0 to 63) supported by the decoder, B can be derived as B = X - A, and since the mapping function behavior is defined for the input arguments of sets A and B, the mapping function can be constructed, for example, in table form using the following exemplary pseudo-code that uses the assumption that the first value of the mapping function corresponding to x = 0 is 0: chroma_qp_mapping_table[0]=0; / / Initialization for(i=1;i<=maxQP;i++) / / maxQP is the maximum QP supported by the decoder { int incStep=1; / / Function increment for set B for(j=0;j<cQpFlatSize;j++) / / cQpFlatSize is the size of set A { if(i==cQpFlat[j]) / / cQpFlat is an array having elements of set A { incStep=0; / / Zero function increment for set A (flat) break; } } chroma_qp_mapping_table[i]=chroma_qp_mapping_table[i-1]+incStep; }

[0204] The following is another example pseudocode illustrating how one QPc can be calculated based on a given QP index QPi: int getQPc(int QPi) { int QPi = i; int sum=0; for(int j=0;j <cQpFlatSize;j++) { sum=sum+(cQpFlat[j]<=QPi?1:0); } int QPc = QPi - sum; return QPc }

[0205] Note that in some implementation sets, the set X may be some subset of the QP ranges supported by the decoder, which may be predetermined or signaled in the bitstream.

[0206] It should be noted that the definition of the flat (non-increasing) region of the mapping function can also be given in the form using the current and next input argument values, i.e., using f(x+1)-f(x)=0. It will be understood that such a definition does not change the logic of signaling and obtaining the mapping function. For example, a similar effect can be achieved by putting the value x+1 into the set A.

[0207] Since the points of the mapping function are classified into two classes of defined behavior and the number of points where the mapping function does not increase is limited, the signaling overhead is reduced compared to direct signaling of each value of the mapping function.

[0208] To obtain set A at the decoder side, the bitstream contains information about the size of the set (number of elements) and the element values.

[0209] According to a first aspect of the embodiment, the size of set A (sizeA) is directly signaled in the bitstream using one of the appropriate codes, for example binary, unary, truncated unary, truncated binary, Golomb or Exp-Golomb codes. In some implementations with the constraint that set A has a non-zero size, the value sizeA-1 is signaled in the bitstream. This allows to save one bit of signaling.

[0210] According to a second aspect of the embodiment, the values ​​of the elements of set A (e.g. 30, 39, 43) are directly signaled in the bitstream using one of the appropriate codes, e.g. binary, unary, truncated unary, truncated binary, Golomb or Exp-Golomb codes. The corresponding mapping function can be represented as a table in the following exemplary form: [Table 17]

[0211] It should be understood that this above table can be used to define a default mapping function when signaling of the mapping table via the bitstream is not enabled or is not supported by the encoder / decoder.

[0212] In another exemplary embodiment according to the second aspect, the values ​​of the elements of set A are equal to (35, 39, 43). The corresponding mapping function can be represented as a table in the following exemplary form: [Table 18]

[0213] It should be understood that this above table can be used to define a default mapping function when signaling of the mapping table via the bitstream is not enabled or is not supported by the encoder / decoder.

[0214] According to the third aspect, the value of the current element (a i ) and the value of the preceding element (a i-1 ) between (delta_a i ) for each element except the first element (e.g., for i>0, delta_a i =a i -a i-1 ) is signaled. Having an ordered set A allows us to eliminate negative differences and save signaling a sign bit. Also, knowing that the element values ​​in set A are unique (non-repeating) allows us to signal delta_a i is always greater than zero, which means that delta_a i -1, providing a further reduction in signaling overhead.

[0215] The first value a of set A 0 is signaled as a difference from some starting_point_value, which is either signaled in the bitstream or is some predefined value, e.g., 0, 21, 30, maxQP>>1, where maxQP is the maximum QP value supported by the decoder, e.g., 63, and starting_point_value may also depend on the content type (e.g., SDR or HDR). 0 is signaled according to the method described above. Selecting an appropriate starting_point_value makes it possible to save a bit of signaling of the initial value.

[0216] Below is an example of a syntax table and corresponding semantics for the above mentioned signaling method.

[0217] Chroma QP mapping data syntax: [Table 19]

[0218] Chroma QP Mapping Data Semantics: cqp_flat_points_minus1 plus 1 specifies the number of points beyond which the mapping function does not increase; cqp_delta_fp0 specifies the delta value between the first element of the set of points where the mapping function does not increase and starting_point_value, where starting_point_value is equal to 21 (in alternative implementations starting_point_value can be 0, or 26, or 32, or can be determined based on the supported QP range, e.g. as maxQP / 2). cqp_delta_fp_minus1[i] plus 1 specifies the delta value between the i-th element and the (i-1)-th element of the set of points where the mapping function does not increase; The variable cQpFlatSize is derived as follows: cQpFlatSize=cqp_flat_points_minus1+1 The variable cQpFlat[] is derived as follows: cQpFlat[0]=cqp_delta_fp0+starting_point_value; for(i=1;i <cQpFlatSize;i++){ cQpFlat[i]=cqp_delta_fp_minus1[i]+1+cQpFlat[i-1] } The chroma QP mapping table cqpMappingTable[] is derived as follows: cqpMappingTable[0]=0; for(i=1;i<=maxQP;i++) incStep=1 for(j=0;j <cQpFlatSize;j++) { if(i==cQpFlat[j]) { incStep=0 } } cqpMappingTable[i]=cqpMappingTable[i-1]+incStep; } where maxQP is the maximum supported QP.

[0219] In one possible implementation when starting_point_value is 0, cqp_delta_fp0 specifies the value of the first element of the set of points above which the mapping function does not increase.

[0220] An alternative semantics to achieve the same result and make it possible to obtain a QPc based on a particular QP index QPi is as follows: sum=0 for(j=0;j <cQpFlatSize;j++){ sum = sum + (cQpFlat[j] <= QPi ? 1:0) } QPc=QPi-sum

[0221] A possible implementation when starting_point_value is 0 may have the following syntax and semantics: [Table 20] Or, as an alternative example: [Table 21]

[0222] chroma_qp_mapping_flag equal to 1 specifies that a chroma Qp mapping table is signaled and takes precedence over Table 2 used to derive QpC. chroma_qp_mapping_flag equal to 0 specifies that the default chroma Qp mapping table specified in Table 2 is used to derive QpC. When chroma_qp_mapping_flag is not present, it is inferred to be equal to 0; cqp_flat_points_minus1 plus 1 specifies the number of points beyond which the mapping function does not increase; cqp_fp0 specifies the first element of the set of points for which the mapping function is non-increasing; cqp_delta_fp_minus1[i] plus 1 specifies the delta value between the i-th and (i-1)-th elements of the set of points at which the mapping function does not increase.

[0223] The variable cQpFlatSize is derived as follows: cQpFlatSize=cqp_flat_points_minus1+1 The variable cQpFlat[] is derived as follows: cQpFlat[0] = cqp_fp0; for(i=1;i <cQpFlatSize;i++){ cQpFlat[i]=cqp_delta_fp_minus1[i]+1+cQpFlat[i-1] } The chroma QP mapping table cqpMappingTable[] is derived as follows: cqpMappingTable[0]=0; for(i=1;i<=maxQP;i++) incStep=1 for(j=0;j <cQpFlatSize;j++) { if(i==cQpFlat[j]) incStep=0 } cqpMappingTable[i]=cqpMappingTable[i-1]+incStep; } where maxQP is the maximum supported QP.

[0224] In one example, qP Cb , qP Cr and qP CbCr is derived as follows: qP Chroma =Clip3(-QpBdOffset,63,Qp Y ); qP Cb =ChromaQpTable[0][qP Chroma ]; qP Cr =ChromaQpTable[1][qP Chroma ]; qP CbCr =ChromaQpTable[2][qP Chroma ]; Chroma quantization parameter Qp' for Cb and Cr components Cb and Qp' Cr , as well as joint Cb-Cr coding Qp' CbCr is derived as follows: Qp' Cb =Clip3(-QpBdOffset,63,qP Cb +pps_cb_qp_offset+slice_cb_qp_offset+CuQpOffset Cb )+QpBdOffset; Qp' Cr =Clip3(-QpBdOffset,63,qP Cr +pps_cr_qp_offset+slice_cr_qp_offset+CuQpOffset Cr )+QpBdOffset; Qp' CbCr =Clip3(-QpBdOffset,63,qP CbCr +pps_joint_cbcr_qp_offset_value+slice_joint_cbcr_qp_offset+CuQpOffsetCbCr )+QpBdOffset; ChromaQpTable is the chroma QP mapping table; QPi is qP Chroma Corresponding to; QPc is qP Cb , qP Cr and qP CbCr Corresponding to; QpBdOffset is the formula: QpBdOffset=6*bit_depth_minus8 is a bit depth offset calculated based on the bit depth of the samples in the luma array and chroma array using bit_depth_minus8 must be in the range 0 to 8 inclusive; pps_cb_qp_offset and pps_cr_qp_offset are respectively Qp' Cb and Qp' Cr The luma quantization parameter Qp' used to derive Y Specify an offset for pps_joint_cbcr_qp_offset_value is the Qp' CbCr The luma quantization parameter Qp' used to derive Y Specify an offset for slice_cr_qp_offset is Qp' Cr Specifying a difference to be added to the value of pps_cr_qp_offset when determining the value of the quantization parameter; slice_cb_qp_offset is Qp' Cb Specifies a difference to be added to the value of pps_cb_qp_offset when determining the value of the quantization parameter; slice_joint_cbcr_qp_offset is Qp' CbCr Specifies the difference to be added to the pps_joint_cbcr_qp_offset_value when determining the value of Variable CuQpOffset Cb , CuQpOffset Cr , and CuQpOffsetCbCr Qp' for the decoder Cb , Qp' Cr , and Qp' CbCr Specifies the values ​​used when determining each value of the quantization parameter.

[0225] In some implementations, the derivation of the array of non-incrementing points cQpFlat can utilize picture-level and slice-level chroma QP offsets (pps_cr_qp_offset, slice_cr_qp_offset): The variable cQpFlat[] is derived as follows: cQpFlat[0] = cqp_fp0; for(i=1;i <cQpFlatSize;i++){ cQpFlat[i]=cqp_delta_fp_minus1[i]+1+cQpFlat[i-1]-pps_cr_qp_offset-pps_cr_qp_offset }

[0226] The following is an example that uses an array of non-increasing points, cQpFlat, obtained based on information parsed from the bitstream, that is integrated into the chrominance QP derivation process: When ChromaArrayType is not equal to 0 and treeType is equal to SINGLE_TREE or DUAL_TREE_CHROMA, the following applies: - When treeType is equal to DUAL_TREE_CHROMA, the variable Qp Y is the luma quantization parameter Qp of the luma coding unit covering the luma position (xCb+cbWidth / 2, yCb+cbHeight / 2). Y is set equal to - variable qP Cb , qP Cr and qP CbCr is derived as follows: qPi Cb =Clip3(-QpBdOffsetC,69,Qp Y+pps_cb_qp_offset+slice_cb_qp_offset) (8-928) qPi Cr =Clip3(-QpBdOffsetC,69,Qp Y +pps_cr_qp_offset+slice_cr_qp_offset) (8-929) qPi CbCr =Clip3(-QpBdOffsetC,69,Qp Y +pps_joint_cbcr_qp_offset+slice_joint_cbcr_qp_offset) (8-930) - If ChromaArrayType is equal to 1, the variable qP Cb , qP Cr and qP CbCr is expressed as follows: Qp C is set equal to the value of: Qp C =qPi-QpShift, where the variable QpShift is derived as follows: QpShift=0 for(j=0;j <cQpFlatSize;j++){ QpShift=QpShift+(cQpFlat[j]<=qPi?1:0) }

[0227] The variable cQpFlat in the example given above can be used to define and initialize a default mapping table. The following is an example of cQpFlat that can be used as a default: cQpFlat={30,35,37,39,41,43} cQpFlat={30,39,43} cQpFlat={35,39,43}cQpFlat={35,39,41,43} cQpFlat={22,23,25,27,29,31,33,35,39,40,41,43,47,49,51,53,55} cQpFlat={21,22,24,25,26,27,29,30,31,32,33,35,42,47,49,51,53,55}

[0228] To allow the value of cQpFlat[0] to be lower than starting_point_value, cqp_delta_fp0 can be negative and the signaling of this parameter can include a sign bit or can use a signed Exp-Golomb code, as specified in the following example: [Table 22]

[0229] Alternatively, in some example implementations, the size and value of set A are signaled in the following manner: 1. Read the indicator whether the following bitstream information contains elements of set A; 2. If the indicator is TRUE, read the element value, for example according to the methods described in aspect 2 or aspect 3. Repeat step 1; 3. If the indicator is negative (FALSE), stop reading information related to set A.

[0230] In this implementation, the size of the set A is the number of indicators with positive values.

[0231] Having the constraint that set A is not empty allows us to implement signaling of the size and values ​​of set A in the following way: 1. Reading the element value, for example according to the method described in embodiment 2 or embodiment 3; 2. Read an indicator whether the subsequent bitstream information contains another element of set A; 3. If the indicator is positive (TRUE), repeat step 1 and then step 2; 4. If the indicator is negative (FALSE), stop reading information related to set A.

[0232] In this implementation, the size of set A is the number of indicators with positive values ​​plus 1. Having the constraint that set A is not empty allows eliminating the signaling of one additional indicator, which further reduces the signaling overhead.

[0233] It should be mentioned that the signaling of the size of set A and the element values ​​above can be implemented using any suitable code, such as binary, unary, truncated unary, truncated binary, Golomb, or Exp-Golomb codes.

[0234] In some realizations of the mapping function, the number of elements in the flat region (set A) can be greater than the number of elements in the growing region (set B). In that case, it is beneficial to signal the elements of set B instead of using the method described above.

[0235] According to a second embodiment of the invention, the class B region of the luma-to-chroma mapping function is k Each subset B k But the mapping function there is the same increment c k Contains an element x with: f(x)-f(x-1)=c k If x∈B k , where c k is one of the natural numbers (e.g., 0, 1, 2, 3, 4, …).

[0236] In other words, if subset B is k are divided into a number of different subsets according to the amount of mapping function increment at point x.

[0237] In the example shown in FIG. 10, the area indicated by 1031 corresponds to a mapping function increment (c kThe area indicated by 1032 has a function increment (c k The area indicated by 1032 has a function increment (c k =0). The table below illustrates the division of the subset Bk corresponding to the example functions shown in FIG. [Table 23] where maxQP is the maximum QP value supported by the decoder (e.g., 0 to 63).

[0238] According to the third embodiment, the bitstream comprises information about the number of subsets Bk signalled in the bitstream, the function increment ck for each subset signalled in the bitstream, the size of each subset Bk signalled in the bitstream and the point of each subset Bk signalled in the bitstream.

[0239] Below are examples of if constructs and semantics: [Table 24] cqp_set_num is the number of sets of points for which the chroma Qp mapping table has a non-default behavior (it is understood that under the default behavior function the function increment is equal to 1, and in general the default behavior can be defined in other ways, e.g. as a previously signaled mapping function or a default mapping function); cqp_set_inc[k] specifies the function increment at the kth set of points; cqp_set_size[k] specifies the number of points in the kth set; cqp_fp0 specifies the first element of the set of points for which the mapping function is non-increasing; cqp_set_point[k][i] specifies the i-th element of the k-th set (here, as in the example above, we can use the coding of the delta between i-th and (i-1)-th for elements other than i=0); The variable cQpFlatSize is derived as follows: cQpFlatSize=cqp_flat_points_minus1+1 The variable cQpFlat[] is derived as follows: cQpFlat[0] = cqp_fp0; for(i=1;i <cQpFlatSize;i++){ cQpFlat[i]=cqp_delta_fp_minus1[i]+1+cQpFlat[i-1] } The chroma QP mapping table cqpMappingTable[] is derived as follows: cqpMappingTable[0]=0; for(i=1;i<=maxQP;i++) incStep=1 / / (sets the default behavior) for(k=0;k <cqp_set_num;k++){ for(j=0;j <cqp_set_size[k];j++){ if(i==cqp_set_point[k][i]) incStep=cqp_set_inc[k] } } cqpMappingTable[i]=cqpMappingTable[i-1]+incStep; } where maxQP is the maximum supported QP.

[0240] A specific Qp based on a specific QP index (qPi) C The derivation of the value can be described as follows: Qp C =qPi+QpShift, where the variable QpShift is derived as follows: QpShift=0 defInc=1 for(k=0;k <cqp_set_num;k++){ for(j=0;j <cqp_set_size[k];j++){ if(qPi<=cqp_set_point[k][i]) QpShift=QpShift+cqp_set_inc[k]-defInc } } Here, the variable defInc=1 defines the default function increment (eg, equal to 1 in the given example).

[0241] Or alternatively: Qp C =qPi+QpShift, where the variable QpShift is derived as follows: QpShift=0 defInc=1 for(k=0;k <cqp_set_num;k++){ for(j=0;j <cqp_set_size[k];j++){ QpShift=QpShift+(cqp_set_point[k][i]<=qPi?cqp_set_inc[k]-defInc:0) } }

[0242] Note that the value for the variable cqp_set_inc[k] is signaled (e.g., signaled using a signed Exp-Golomb code(se(v))), allowing further flexibility to have negative increments of the function, i.e., the mapping function decrease maintains the same semantics.

[0243] As a second aspect of the second embodiment, the chroma QP mapping table information can be used to modify the default mapping function or a previously signaled mapping function. This can be used to adapt the mapping function to a particular part of a video sequence to increase compression efficiency by better utilizing changing video signal characteristics. According to this aspect, the above mentioned default function behavior (or increment) is replaced by the existing mapping function increment. An example semantics may be as follows: The chroma QP mapping table cqpMappingTable[] is derived as follows: cqpMappingTable[0]=0; for(i=1;i<=maxQP;i++) incStep=cqpMappingTablePrev[i]-cqpMappingTablePrev[i-1] / / (previous mapping function increment) for(k=0;k <cqp_set_num;k++){ for(j=0;j <cqp_set_size[k];j++){ if(i==cqp_set_point[k][j]) incStep=cqp_set_inc[k] } } cqpMappingTable[i]=cqpMappingTable[i-1]+incStep; } where maxQP is the maximum QP supported and cqpMappingTablePrev is the previously signaled or default mapping table.

[0244] A specific Qp based on a specific QP index (qPi) C The derivation of the value can be described as follows: Qp C =qPi+QpShift, where the variable QpShift is derived as follows: QpShift=0 defInc=cqpMappingTablePrev[qPi]-cqpMappingTablePrev[qPi-1] for(k=0;k <cqp_set_num;k++){ for(j=0;j <cqp_set_size[k];j++){ if(qPi<=cqp_set_point[k][i]) QpShift=QpShift+cqp_set_inc[k]-defInc } } Here, the variable defInc defines the increment of the previous mapping function (cqpMappingTablePrev).

[0245] Or alternatively: Qp C =qPi+QpShift, where the variable QpShift is derived as follows: QpShift=0 defInc=cqpMappingTablePrev[qPi]-cqpMappingTablePrev[qPi-1] for(k=0;k <cqp_set_num;k++){ for(j=0;j <cqp_set_size[k];j++){ QpShift=QpShift+(cqp_set_point[k][i]<=qPi?cqp_set_inc[k]-defInc:0) } } Here, the variable defInc defines the increment of the previous mapping function (cqpMappingTablePrev).

[0246] The usage described in the second embodiment allows excluding the pps_cr_qp_offset and slice_cr_qp_offset parameters from the QP index (qPi) calculation and using the luma QP as an input argument of the mapping function, which simplifies the chroma QP parameter derivation formula and eliminates the need to signal the chroma QP offset parameters pps_cr_qp_offset and slice_cr_qp_offset in the bitstream.

[0247] The pps_cr_qp_offset and slice_cr_qp_offset parameters may be applied after applying the mapping function.

[0248] Below is the syntax and semantics of another example that has no restriction on how large the mapping function increases at each point, but still has the restriction that the mapping function is non-decreasing.

[0249] Sequence Parameter Set Syntax [Table 25]

[0250] Semantics: Option 2, table-based To derive the chroma Qp mapping table based on the signaled parameters, the following semantics are proposed: same_сqp_table equal to 1 specifies that only one chroma QP mapping table is signaled to apply to both Cb and Cr components as well as to joint Cb-Cr coding. same_сqp_table equal to 0 specifies that three chroma QP mapping tables are signaled within the SPS; cqp_set_num_m1[n] plus 1 specifies the number of sets of points for which the nth chroma Qp mapping function has a delta value other than 1; cqp_set_inc[n][k] specifies the chroma Qp mapping function increment at the kth set of points and is constrained to be different from 1; cqp_set_size_m1[n][k] plus 1 specifies the number of points in the set; cqp_set_delta_m1[n][k][i] plus 1 specifies the i-th element of the set if i is equal to 0, and specifies the delta value between the i-th and (i-1)-th elements otherwise; The array cqp_set_point[n][k][i] specifies the set of points for which the nth chroma Qp mapping table has a delta value other than 1, and is derived as follows: cqp_set_point[n][k][i]=cqp_set_delta_m1[n][k][i]+1+(i>0?:cqp_set_point[n][k][i-1]:0) The n-th chroma QP mapping table cqpMappingTable[i] for n=0..same_qp_table_for_chroma?0:2 is derived as follows: cqpMappingTable[n][0]=0 cqpMappingTable[n][i]=cqpMappingTable[n][i-1]+incStep,withi=1..63 Here, incStep is initialized to 1 and modified as follows: for k=0..cqp_set_num_m1[n], and j=0..cqp_set_size_m1[n][k]: - If(i==cqp_set_point[n][k][j]) incStep=cqp_set_inc[n][k]

[0251] In some implementations, it may be beneficial to avoid storing the entire mapping table to save memory. To achieve that, a derivation process for a particular chroma Qp value is provided, for which the syntax elements and semantics are the same as in Option 1, but no maintenance of the cqpMappingTable is required: same_сqp_table equal to 1 specifies that only one chroma QP mapping table is signaled to apply to both Cb and Cr components as well as to joint Cb-Cr coding. same_сqp_table equal to 0 specifies that three chroma QP mapping tables are signaled within the SPS; cqp_set_num_m1[n] plus 1 specifies the number of sets of points for which the nth chroma Qp mapping function has a delta value other than 1; cqp_set_inc[n][k] specifies the chroma Qp mapping function increment at the kth set of points and is constrained to be different from 1; cqp_set_size_m1[n][k] plus 1 specifies the number of points in the set; cqp_set_delta_m1[n][k][i] plus 1 specifies the i-th element of the set if i is equal to 0, and specifies the delta value between the i-th and (i-1)-th elements otherwise; The array cqp_set_point[n][k][i] specifies the set of points for which the nth chroma Qp mapping table has a delta value other than 1, and is derived as follows: cqp_set_point[n][k][i]=cqp_set_delta_m1[n][k][i]+1+(i>0?:cqp_set_point[n][k][i-1]:0)

[0252] Semantics: Option 2, tableless In some implementations, it may be beneficial to avoid storing the entire mapping table to save memory. To achieve that, a derivation process for a particular chroma Qp value is provided, for which the syntax elements and semantics are the same as in Option 1, but no maintenance of the cqpMappingTable is required: same_сqp_table equal to 1 specifies that only one chroma QP mapping table is signaled to apply to both Cb and Cr components as well as to joint Cb-Cr coding. same_сqp_table equal to 0 specifies that three chroma QP mapping tables are signaled within the SPS; cqp_set_num_m1[n] plus 1 specifies the number of sets of points for which the nth chroma Qp mapping function has a delta value other than 1; cqp_set_inc[n][k] specifies the chroma Qp mapping function increment at the kth set of points and is constrained to be different from 1; cqp_set_size_m1[n][k] plus 1 specifies the number of points in the set; cqp_set_delta_m1[n][k][i] plus 1 specifies the i-th element of the set if i is equal to 0, and specifies the delta value between the i-th and (i-1)-th elements otherwise; The array cqp_set_point[n][k][i] specifies the set of points for which the nth chroma Qp mapping table has a delta value other than 1, and is derived as follows: cqp_set_point[n][k][i]=cqp_set_delta_m1[n][k][i]+1+(i>0?:cqp_set_point[n][k][i-1]:0)

[0253] Derivation Process When treeType is equal to DUAL_TREE_CHROMA, the variable Qp Yis the luma quantization parameter Qp of the luma coding unit covering the luma position (xCb+cbWidth / 2, yCb+cbHeight / 2). Y is set equal to - For n=0..2, the array QpMapOffset[n] is initialized with 0. If ChromaArrayType is equal to 1, QpMapOffset is modified as follows: for k=0..cqp_set_num_m1[n] and i=0..cqp_set_size_m1[n][k]: - QpMapOffset[n]=QpMapOffset[n]+(cqp_set_point[n][k][i]<=Qp Y ?cqp_set_inc[n][k]-1:0). - Variable QpOffset Cb , QpOffset Cr , and QpOffset CbCr is derived as follows: QpOffset Cb =QpMapOffset[0]+pps_cb_qp_offset+slice_cb_qp_offset QpOffset Cr =QpMapOffset[1]+pps_cr_qp_offset+slice_cr_qp_offset QpOffset CbCr =QpMapOffset[2]+pps_cbcr_qp_offset+slice_cbcr_qp_offset - chroma quantization parameter Qp' for Cb and Cr components and joint Cb-Cr coding Cb and Qp' Cr and Qp' CbCr is derived as follows: Qp′ Cb =Clip3(-QpBdOffset C ,63,Qp Y +QpOffset Cb )+QpBdOffset C (8-931) Qp′ Cr=Clip3(-QpBdOffset C ,63,Qp Y +QpOffset Cr )+QpBdOffset C (8-932) Qp′ CbCr =Clip3(-QpBdOffset C ,63,Qp Y +QpOffset CbCr )+QpBdOffset C (8-933)

[0254] It should be noted that separate mapping tables can be used for Cb and Cr, i.e., mapping table information for Cb can be obtained based on the bitstream, and mapping table information for Cr can be obtained based on the bitstream.

[0255] According to a third embodiment, the mapping function is represented as a piecewise function and the information signalled in the bitstream are the breakpoints (or change points, or pivot points) of the piecewise function, for example 94, 95 as shown in FIG.

[0256] In the simplest scheme, the number of pivot points and their x and y coordinates are signaled in the bitstream as information for obtaining a mapping function. In a similar manner as described in aspect 1 of the first embodiment, the size of the set having pivot points can be constrained to have a size greater than zero, in which case a value size-1 is signaled in the bitstream. Note that "information for obtaining a mapping function" may be written as "information of a mapping function", and "information for obtaining..." may be written as "information of...".

[0257] In a first aspect of the third embodiment, a piecewise linear function is used to represent the mapping function.

[0258] In a further implementation, one can constrain that the first point in the set (point D94) belongs to the monotonic one-to-one function 91 and it is sufficient to signal one coordinate, e.g. Dx, where Dy is derived as Dy = Dx. Furthermore, if we assume that the last segment (or piece) of the piecewise linear function is parallel to the one-to-one function, then point F96 does not need to be signaled and the parameters of the last segment are derived based on point E95 and the knowledge that the last segment is parallel to the one-to-one function.

[0259] To further reduce signaling overhead, the difference between the corresponding x and y coordinates of the current pivot point (e.g., E95) and the previous pivot point (e.g., D94) is signaled in the bitstream. For the first point, the difference from some starting_point is signaled. The starting_point is either some predefined point or is signaled in the bitstream. In some implementations, the starting_point can be constrained to be on a one-to-one line, in which case one coordinate is sufficient to define the starting_point.

[0260] To achieve monotonically increasing mapping functions, the difference between the corresponding x and y coordinates of the current and previous pivot points is constrained to be non-negative, e.g., greater than or equal to 0. To signal the difference, an unsigned code, e.g., an unsigned integer zeroth order Exp-Golomb code, can be used.

[0261] It should be noted that the above-mentioned embodiment 1 and embodiment 2 can coexist in one implementation of the decoder. The most suitable method, for example, having fewer bits for signaling, is selected by the encoder and signaled in the bitstream by a corresponding indicator. In some implementations, the decoder can use a predefined mapping function and an option to use a mapping function derived from the bitstream. In that case, the option is signaled in the bitstream by a corresponding indicator. Since the appropriate mapping function may depend on the specific signal characteristics of the sequence or a part thereof, the encoder can decide whether to use the predefined mapping function or to spend some additional bits on signaling the mapping function in the bitstream to achieve better compression efficiency and balanced luma and chroma quality in the reconstructed image.

[0262] Different parts of a sequence may have different signal characteristics and correspondingly different optimal mapping functions. To provide the ability to change the mapping function for different parts of a sequence, the bitstream includes an indicator, e.g., at the picture, slice, or tile group level, or in the adaptation parameter set, that indicates whether to change the mapping function. This allows for increased compression efficiency by better tuning to the particular signal characteristics of parts of the sequence.

[0263] Below is an example syntax table corresponding to signaling mapping function information in a sequence parameter set: [Table 26] Example semantics for the above syntax table are as follows: chroma_qp_mapping_flag equal to 1 signals that the chroma Qp mapping function is CAs a function of qPi (derived based on luma Qp) used to derive C Specifies that this takes precedence over the default specification of (chroma Qp). chroma_qp_mapping_flag equal to 0 specifies that the C Specifies that a default chroma Qp mapping table is used to derive chroma_qp_mapping_flag. When chroma_qp_mapping_flag is not present, chroma_qp_mapping_flag is inferred to be equal to 0.

[0264] Note that in some implementations, chroma_qp_mapping_flag can be omitted and systematically set to 1. What this means is that the chroma Qp mapping information (cqp_mapping_data()) is always present in the bitstream.

[0265] A video signal transmitted in a bitstream may have different chroma format sampling structures. The following is an example of a chroma sampling format specification: [Table 27] In monochrome sampling, there is only one sample array, nominally considered the luma array; In 4:2:0 sampling, each of the two chroma arrays has half the height and half the width of the luma array; In 4:2:2 sampling, each of the two chroma arrays has the same height and half the width of the luma array; For 4:4:4 sampling, depending on the value of separate_colour_plane_flag the following applies: If separate_colour_plane_flag is equal to 0, each of the two chroma arrays has the same height and width as the luma array; Otherwise (separate_colour_plane_flag is equal to 1), the three colour planes are treated as a separately monochrome sampled picture.

[0266] In some implementations, the chroma_qp_mapping_flag and / or the chroma Qp mapping information (cqp_mapping_data()) can depend on the chroma sampling format as exemplarily specified in the table below, where chroma_format_idc equal to 3 indicates that the chroma sampling format is 4:2:0: [Table 28]

[0267] Another example is this: [Table 29]

[0268] It should be noted at this point that if a picture is monochrome, it may only have an array of luminance samples. Thus, a picture may be, for example, an array of luma samples in monochrome format, or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2, and 4:4:4 color formats.

[0269] The following is an example of a syntax table corresponding to signaling mapping function information within an adaptation parameter set: [Table 30] Here, CQP_APS is an identifier of the chroma QP mapping table information.

[0270] The suitable mapping function may depend on the codec efficiency in compressing the color components and the signal characteristics of the particular sequence. This may be even more of a consideration for HDR content, because color information is very important in this type of content. Also, the Cb and Cr components may have different characteristics and thus different optimal mapping functions. It may be beneficial to have different mapping functions for the Cb and Cr components to better match the type and characteristics of the content. To provide this capability, in some advantageous implementations, the bitstream has information to obtain mapping functions for both the Cb and Cr components.

[0271] In a further advantageous implementation that allows for flexibility, the bitstream has an indicator indicating whether mapping functions are signaled for both Cb and Cr components. If the indicator is TRUE, the decoder obtains two mapping functions corresponding to the Cb and Cr components from the bitstream and uses them in the reconstruction process. Otherwise, a single mapping function is used for the reconstruction of the Cb and Cr components.

[0272] Figure 11 shows the VVC chroma Qp mapping table as a function of qPi. As can be seen, the luma-to-chroma mapping function is a monotonically increasing (non-decreasing) function that can be divided into two class regions. In the class A region, the function is non-increasing (or flat), i.e., f(x)-f(x-1)=0, and in the class B region, the function is increasing, i.e., f(x)-f(x-1)=1.

[0273] In a signaling method, we propose to signal points of class A (flat region) in the bitstream using a differential representation (e.g., cqp_delta_fpi=A[i]-A[i-1]). According to the proposed method, the decoder constructs a mapping function using information about the points of set A. For the remaining points in the allowed Qp range, it is assumed that the mapping function is monotonically increasing with a step size of 1. For example, to reproduce the current VVC mapping function, the following points need to be signaled: 30, 35, 37, 39, 41, and 43.

[0274] A new syntax element chroma_qp_mapping_flag is added to the SPS. When the value of chroma_qp_mapping_flag is equal to 0, the default chroma Qp mapping table is used. When the value of chroma_qp_mapping_flag is equal to 1, the chroma Qp mapping table is signaled.

[0275] Example Sequence Parameter Set Syntax [Table 31] To derive the chroma Qp mapping table based on the signaled parameters, the following semantics are proposed: chroma_qp_mapping_flag equal to 1 signals that a chroma Qp mapping table is not specified. C This specification takes precedence over Table 8-15, which is the specification of QpC as a function of qPi used to derive chroma_qp_mapping_flag. A chroma_qp_mapping_flag equal to 0 specifies that Qp C Specifies that the default chroma Qp mapping table specified in Table 8-15, which is the specification of QpC as a function of qPi used to derive , shall be used. When chroma_qp_mapping_flag is not present, it is inferred to be equal to 0; cqp_flat_points_minus1 plus 1 specifies the number of points beyond which the mapping function does not increase; cqp_fp0 specifies the first element of the set of points for which the mapping function is non-increasing; cqp_delta_fp_minus1[i] plus 1 specifies the delta value between the i-th and (i-1)-th elements of the set of points at which the mapping function does not increase.

[0276] The variable cQpFlatSize is derived as follows: cQpFlatSize=cqp_flat_points_minus1+1 The variable cQpFlat[] is derived as follows: cQpFlat[0] = cqp_fp0; for(i=1;i <cQpFlatSize;i++){ cQpFlat[i]=cqp_delta_fp_minus1[i]+1+cQpFlat[i-1] } The chroma QP mapping table cqpMappingTable[] is derived as follows: cqpMappingTable[0]=0; for(i=1;i<=maxQP;i++) incStep=1 for(j=0;j <cQpFlatSize;j++) { if(i==cQpFlat[j]) incStep=0 } cqpMappingTable[i]=cqpMappingTable[i-1]+incStep; }

[0277] As a second aspect of the proposal, we evaluated an adjustment mapping function with non-increasing regions at points 35, 39, and 43. The adjustment mapping function is shown in FIG. Using an adjusted chroma Qp mapping function with flat regions at points 35, 39 and 43, we obtained the following results. The mapping table was adjusted using a test configuration file that uses the proposed signaling mechanism. In this experiment, we keep the chroma QP offset equal to 1 for the AI ​​configuration only. For configurations RA, LDB and LDP, the chroma QP offset is set to 0.

[0278] Table A. Coding performance of the adjusted mapping table for VTM5.0 [Table 32]

[0279] We noticed that the use of VTM5.0 as anchor leads to crossing of RD curves for some sequences. This may make the BD rate figures irrelevant. To get the correct figures, we estimate the performance against VTM5.0 by taking the difference between the performance of tests with VTM5.0 and the adjusted mapping table against HM. In Table B below, the left part represents the BD rate difference with VTM5.0, the middle part reports the coding performance of the adjusted table against HM16.20, and the right part gives the coding performance of VTM5.0 against HM for comparison.

[0280] Table B. Coding performance difference of the adjusted mapping table for VTM5.0 with HM as the anchor [Table 33]

[0281] Further, Fig. 13 illustrates a method for obtaining a chrominance quantization parameter according to the present disclosure. Fig. 13 illustrates a method for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component, the method being executed by a decoder. The method of Fig. 13 includes a step 1601 of receiving a bitstream, a step 1603 of parsing the bitstream to obtain a luminance QP and information about a chroma QP mapping table that associates a QP index (QPi) with a chrominance QP (QPc), a step 1605 of obtaining a QPi based at least in part on the luminance QP, a step 1607 of obtaining a chroma QP mapping table based on the obtained information, a step 1609 of obtaining a QPc based on the obtained chroma QP mapping table and the obtained QPi, and a step 1611 of obtaining a chrominance quantization parameter based on the obtained QPc.

[0282] Further, Fig. 14 illustrates a decoder 30 according to the present disclosure. Fig. 13 illustrates a decoder 30 for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component. The decoder of Fig. 13 includes a receiving unit 3001 configured to receive a bitstream, a parsing unit 3003 configured to parse the bitstream to obtain a luminance QP and information about a chroma QP mapping table that associates a QP index (QPi) with a chrominance QP (QPc), a first obtaining unit 3005 configured to obtain a QPi based at least in part on the luminance QP, a second obtaining unit 3007 configured to obtain a chroma QP mapping table based on the obtained information, a third obtaining unit 3009 configured to obtain a QPc based on the obtained chroma QP mapping table and the obtained QPi, and a fourth obtaining unit 3011 configured to obtain a chrominance quantization parameter based on the obtained QPc.

[0283] It should be understood that although the first, second, third and fourth acquisition units 3005, 3007, 3009, 3011 are shown as separate units, two or more or all of these units may effectively be realized by a common acquisition unit or common multiple acquisition units, respectively.

[0284] Mathematical Operators The mathematical operators used in this application are similar to those used in the C programming language, but more precisely define the results of integer division and arithmetic shift operations, and define further operations such as exponentiation and real division. Numbering and counting conventions generally start at 0, e.g., "the first" is number 0-th, "the second" is number 1-th, etc.

[0285] Arithmetic Operators The following arithmetic operators are defined as follows:

number

[0286] Logical Operators The following logical operators are defined as follows: x&&y The Boolean logic "and" of x and y x||y The Boolean "or" of x and y ! Boolean logic “not” x?y:zIf x is TRUE or not equal to 0, then evaluate the y value; otherwise, evaluate the z value.

[0287] Relational Operators The following relational operators are defined as follows: > Greater than >= Greater than or equal to < Less than <= Less than or equal == Equal != Not equal.

[0288] When a relational operator is applied to a syntactic element or variable to which the value "na" (not applicable) is assigned, the value "na" is treated as a unique value for that syntactic element or variable. The value "na" is considered not equal to other values.

[0289] Bitwise operators The following bitwise operators are defined as follows: & Bitwise "and". When operating on integer arguments, it operates on the two's complement representation of the integer values. When operating on binary arguments that contain fewer bits than the other argument, the shorter argument is extended by adding leading bits equal to 0. | Bitwise "or". When operating on integer arguments, it operates on the two's complement representation of the integer values. When operating on binary arguments that contain fewer bits than the other argument, the shorter argument is extended by adding leading bits equal to 0. ^ Bitwise "exclusive or". When operating on integer arguments, it operates on the two's complement representation of the integer values. When operating on binary arguments that contain fewer bits than the other argument, the shorter argument is extended by adding leading bits equal to 0. x>>y Arithmetic right shift of the two's complement integer representation of x by y binary digits. This function is defined only for non - negative integer values of y. The bit shifted into the most significant bit (MSB) as a result of the right shift has the same value as the MSB of x before the shift operation. x<<y Arithmetic left shift of the two's complement integer representation of x by y binary digits. This function is defined only for non - negative integer values of y. The bit shifted into the least significant bit (LSB) as a result of the left shift has a value equal to 0.

[0290] Assignment operators The following arithmetic operators are defined as follows: = Assignment operator ++ Increment, i.e., x++ is equivalent to x=x+1; when used in an array index, it evaluates to the value of the variable before the increment operation. -- Decrement, i.e., x--, is equivalent to x=x-1; when used in an array index, it evaluates to the value of the variable before the decrement operation. += increment by specified amount, i.e., x+=3 is equivalent to x=x+3 and x+=(-3) is equivalent to x=x+(-3). -= Decrement by specified amount, i.e. x-=3 is equivalent to x=x-3 and x-=(-3) is equivalent to x=x-(-3).

[0291] Range Notation The following notation is used to specify ranges of values: x=y..zx takes integer values ​​starting from y through z, inclusive, where x, y, and z are integers and z is greater than y.

[0292] Mathematical Functions The following mathematical functions are defined:

number

[0293] Order of precedence of operations If the precedence order is not explicitly stated using parentheses in an expression, the following rules apply: - Operations with higher precedence are evaluated before any operations with lower precedence. - Operations of equal precedence are evaluated in order from left to right.

[0294] The table below defines the precedence of operations from highest to lowest, with higher positions in the table indicating higher precedence.

[0295] For operators that are also used in the C programming language, the precedence order used in this specification is the same as that used in the C programming language. [Table 34]

[0296] Text description of logical operations In the text, a statement of logical operations written mathematically in the following form: if(condition 0) statement 0 else if(condition 1) statement 1 ... else / * Mention information about remaining conditions * / Statement n can be written as: ...as follows / ...the following applies: - If condition 0, statement 0 - Otherwise, if condition 1, statement 1 - ... - Otherwise (mention of information about the remaining conditions), statement n.

[0297] Each "If...otherwise, if...otherwise, ..." statement in the text is introduced with "...as follows" or "...the following applies" immediately followed by "If...". The last condition in an "If...otherwise, if...otherwise, ..." is always "Otherwise, ...". Interleaved "If...otherwise, if...otherwise, ..." statements can be identified by matching the "...as follows" or "...the following applies" with the closing "Otherwise, ...".

[0298] In the text, a statement of logical operations written mathematically in the following form: if(condition 0a && condition 0b) statement 0 else if(condition 1a || condition 1b) statement 1 ... else statement n can be written as: ...as follows / ...the following applies: - If all of the following conditions are true, statement 0: - condition 0a - condition 0b - Otherwise, if one or more of the following conditions are true, statement 1: - condition 1a - condition 1b - ... - Otherwise, statement n.

[0299] In the text, a statement of logical operations written mathematically in the following form: if(condition 0) statement 0 if(condition 1) statement 1 can be written as: If condition is 0, statement is 0 If condition 1, then statement 1.

[0300] Although embodiments of the invention have been described primarily in terms of video coding, it should be noted that embodiments of coding system 10, encoder 20 and decoder 30 (and corresponding system 10), as well as other embodiments described herein, may also be configured for still picture processing or coding, i.e., processing or coding of individual pictures independent of preceding or successive pictures, as in video coding. In general, when picture processing coding is limited to a single picture 17, only inter prediction units 244 (encoder) and 344 (decoder) may not be available. For example, all other functions (also referred to as tools or techniques) of the video encoder 20 and the video decoder 30, such as residual calculation 204 / 304, transform 206, quantization 208, inverse quantization 210 / 310, (inverse) transform 212 / 312, partitioning 262 / 362, intra prediction 254 / 354, and / or loop filtering 220, 320, as well as entropy coding 270 and entropy decoding 304, may be equally used for still picture processing.

[0301] The embodiments of, e.g., the encoder 20 and the decoder 30, and the functions described herein with reference to, e.g., the encoder 20 and the decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium or transmitted over a communication medium as one or more instructions or code and executed by a hardware-based processing unit. A computer-readable medium may include a computer-readable storage medium, which corresponds to a tangible medium, e.g., a data storage medium, or a communication medium, which includes any medium that facilitates the transfer of a computer program from one place to another, e.g., according to a communication protocol. Thus, a computer-readable medium may generally correspond to (1) a tangible computer-readable storage medium that is non-transitory, or (2) a communication medium, e.g., a signal or carrier wave. A data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to retrieve instructions, code, and / or data structures for implementing the techniques described in this disclosure. A computer program product may include a computer-readable medium.

[0302] By way of example, and without limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly referred to as a computer-readable medium. For example, if instructions are transmitted from a website, server, or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of the medium. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals, or other transitory media, but are instead directed to non-transitory, tangible storage media. Disk and disc, as used herein, include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and Blu-ray discs, where a disk typically reproduces data magnetically and a disc reproduces data optically using a laser. Combinations of the above should also be included within the scope of computer readable media.

[0303] The instructions may be executed by one or more processors, such as, for example, one or more digital signal processors (DSPs), general-purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry. Thus, the term "processor" as used herein may refer to any of the above structures, or any other structure suitable for implementing the techniques described herein. Furthermore, in some aspects, the functionality described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or may be incorporated into a combined codec. These techniques may also be implemented entirely in one or more circuit or logic elements.

[0304] The techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC), or a set of ICs (e.g., a chipset). Various components, modules, or units are described in this disclosure to highlight functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by multiple different hardware units. Rather, as described above, the various units may be combined into a codec hardware unit or may be provided by a collection of interoperating hardware units, including one or more processors as described above, together with suitable software and / or firmware.

[0305] 1. A method for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component, the method being performed by a decoder, the method comprising: Parsing the received bitstream to obtain luma QP and information of a mapping function (f) relating a QP index (QPi) to a chroma QP (QPc); Obtaining a QPi based at least in part on the luminance QP; Obtain a mapping function based on the obtained information; and Obtain QPc based on the obtained mapping function and the obtained QPi. It has the following.

[0306] Having information about the chroma QP mapping table in the bitstream allows adjusting to specific characteristics of the input video signal, e.g. SDR or HDR, or different intensities and distributions on the luminance and chrominance channels, thus improving compression efficiency as well as improving the balance between chroma and luma components in the reconstructed image.

[0307] In the above method, the mapping function associates each element x of set X corresponding to a QPi within the allowed QPi range supported by the decoder (e.g., 0 to 63, or other part of the supported range, such as, for example, 20 to 50), or some subset of set X, to one element y of set Y corresponding to a QPc within the allowed QPc range supported by the decoder (e.g., 0 to 63, or other part of the supported range, such as, for example, 0 to 59 or 18 to 46).

[0308] For example, the QPi range and the QPc range may be the same or different.

[0309] In the above method, the mapping function is a monotonically increasing (non-decreasing) function.

[0310] Imposing this constraint on the mapping function makes it possible to avoid setting mapping functions that have, for example, unexpected, undesirable, "strange" behavior when the chroma QP decreases with increasing luma QP, in other words avoiding cases where the chroma quality increases with decreasing luma quality. Having a monotonically increasing constraint allows the luma and chroma quality to be synchronized. As an additional advantage, this constraint makes it possible to save bits of signaling of the mapping function information by eliminating the need to describe negative increments of the function.

[0311] In the above method, a set X contains a subset A in which the mapping function f is non-increasing, e.g.: For any x in a subset A, f(x)-f(x-1)=0 It is.

[0312] For example, A = {30, 39, 43}, f(30)-f(29) = 0, f(39)-f(38) = 0, or f(43)-f(42) = 0; or A = {35, 39, 43}, f(35)-f(34) = 0, f(39)-f(38) = 0, or f(43)-f(42) = 0.

[0313] In the above method, a set X contains a subset B on which the mapping function f is augmented, i.e.: For any x in a subset B, f(x)-f(x-1)=c, A+B=X, and c is a natural number greater than or equal to 1.

[0314] For example, c=1 or 2, or c may be a function of x, where c(x)>=1.

[0315] In any one of the above methods, the set X includes a subset B on which the mapping function f is augmented, i.e.: For any x in a subset B, f(x)-f(x-1)=c, where c is a natural number greater than or equal to 1.

[0316] For example, c=1 or 2, or c may be a function of x, where c(x)>=1.

[0317] The present disclosure discloses the following 41 further aspects, which are listed as follows from the first aspect to the forty-first aspect.

[0318] A first aspect of a method for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component, the method being performed by a decoder, the method comprising: parsing a received bitstream to obtain a luminance QP and information on a mapping function (f) relating a QP index (QPi) to a chrominance QP (QPc); obtaining a QPi based at least in part on the luminance QP; obtaining a mapping function based on the obtained information; and obtaining a QPc based on the obtained mapping function and the obtained QPi.

[0319] In a second aspect of the method of the first aspect, the mapping function associates each element x of set X corresponding to a QPi within the allowed QPi range supported by the decoder, or any subset of set X, to one element y of set Y corresponding to a QPc within the allowed QPc range supported by the decoder.

[0320] A third aspect of the method according to the second aspect, wherein the mapping function is a monotonically increasing (non-decreasing) function.

[0321] A fourth aspect of the method according to the second or third aspect, wherein the set X comprises a subset A in which the mapping function f is not increasing, e.g. For any x in a subset A, f(x)-f(x-1)=0 It is.

[0322] A fifth aspect of the method according to the fourth aspect, wherein the set X includes a subset B on which the mapping function f is augmented, i.e. for any x in the subset B, f(x)-f(x-1)=c and A+B=X, where c is a natural number greater than or equal to 1.

[0323] A sixth aspect of the method according to any one of the second to fourth aspects, wherein the set X comprises a subset B on which the mapping function f is augmented, i.e. for any x in the subset B, f(x)-f(x-1)=c, where c is a natural number greater than or equal to 1.

[0324] A seventh aspect of the method, according to the fifth or sixth aspect, wherein the mapping function for the subset B is defined as follows: f(x)-f(x-1)=1 for any x in the subset B.

[0325] An eighth aspect of the method according to any one of the first to seventh aspects, wherein the information of the mapping function is a size of the subset A (sizeA) and an element a of the subset A. i has information on.

[0326] This advantageously makes it possible to save bits by signaling only those points (subset A) where the functional behavior differs from the normal predefined behavior (subset B).

[0327] A ninth aspect of the method according to any one of the first to eighth aspects, wherein the information of the mapping function comprises a size of the subset A.

[0328] A tenth aspect of the method according to any one of the first to ninth aspects, wherein the information of the mapping function is based on element a of the subset A. i has a direct value of

[0329] An eleventh aspect of the method according to any one of the eighth to tenth aspects, wherein the information of the mapping function is i The current value of and element a i-1 The difference between the preceding value of i ) with value a i is obtained as follows: for any i>0, a i =a i-1 +delta_a i .

[0330] Signaling the difference instead of the direct value allows further saving of bits.

[0331] A twelfth aspect of the method according to any one of the eighth to tenth aspects, wherein the information of the mapping function is a first value a 0and starting_point_value (delta_a 0 ) and the first value a of subset A 0 However, the difference (delta_a 0 ) based on a 0 =starting_point_value+delta_a 0 where starting_point_value is either signaled in the bitstream or is a pre-defined value, e.g. 0, 21, 30, maxQPi>>1, where maxQPi is the maximum QPi value supported by the decoder, e.g. 63.

[0332] A thirteenth aspect of a method according to any one of the first to twelfth aspects, wherein information of the mapping function is signaled in the bitstream using one of the following codes: binary, fixed length, unary, truncated unary, truncated binary, Golomb or Exp-Golomb codes.

[0333] A fourteenth aspect of the method according to any one of the first to thirteenth aspects, wherein the mapping function is obtained using a defined functional behavior of subsets A and B, i.e. for any input argument x from subset B, e.g. f(x)-f(x-1)=1, the function increases by e.g. 1, and for any input argument x from subset A, e.g. f(x)-f(x-1)=0, the function is flat, assuming that the first value of the mapping function corresponding to x=0 is 0, which can for example be implemented iteratively using the following pseudocode: chroma_qp_mapping_table[0]=0; / / initialization for(i=1;i<=maxQP;i++) / / maxQP is the maximum QP supported by the decoder { int incStep=1; / / Function increment for set B for(j = 0; j < cQpFlatSize; j++) / / cQpFlatSize is the size of set A { if(i == cQpFlat[j]) / / cQpFlat is an array having elements of set A { incStep = 0; / / zero function increment for set A (flat) break; } } chroma_qp_mapping_table[i] = chroma_qp_mapping_table[i - 1] + incStep; }

[0334] A 15th aspect of the method according to any one of the 4th to 14th aspects, wherein the information of the mapping function has the information of the value b of the subset B, and the subset A is obtained as A = X - B.

[0335] This enables obtaining the function behavior for the entire set X of supported QPi values with a minimized signaling overhead by signaling only the points where the function behavior differs from the predefined behavior.

[0336] A 16th aspect of the method according to any one of the 4th to 14th aspects, wherein the subset B includes the sub - subset B k and the sub - subset B k includes elements x where the mapping function has the same increment c k : x ∈ B k such that f(x) - f(x - 1) = c k where c k is a natural number, for example, c k is equal to 0, 1, 2, 3, 4,.... In other words, the subset B can be split into different sub - subsets according to the amount of the mapping function increment at the points x of the sub - subset Bk.

[0337] This is where the function has different acceleration increases (c kThis allows for increased flexibility in the mapping function definition by adding points that can have

[0338] A seventeenth aspect of the method according to the sixteenth aspect, wherein the information of the mapping function is k At least one size (size B k ) and sub-subset B k At least one element b of i It has information that:

[0339] Aspect 18 of the method according to aspect 16 or aspect 17, wherein the information of the mapping function is k The increment value of the mapping function at the point is known.

[0340] A 19th aspect of the method according to the 16th or 17th aspect, wherein the information of the mapping function is k The number of pieces of information is

[0341] A 20th aspect of the method according to any one of the 16th to 19th aspects, further comprising: k The information) is retrieved using the following syntax: [Table 35]

[0342] A twenty-first aspect of the method according to any one of the sixteenth to nineteenth aspects, comprising: k The information) is retrieved using the following syntax: [Table 36]

[0343] A 22nd aspect of the method according to the second or third aspect, wherein the mapping function is a piecewise function and the information of the mapping function comprises breakpoints, change points or pivot points of the piecewise function.

[0344] This aspect allows describing function behavior with limited signaling overhead by signaling only the points where the function changes its behavior (e.g., the slope of a line), and allows describing the function as a piecewise function between the change points or pivot points.

[0345] A twenty-third aspect of a method according to the twenty-second aspect, wherein the number of breakpoints, or change points, or pivot points, and their x and y coordinates are signaled in the bitstream in a direct form or by using the difference between the current point coordinates and the previous point coordinates.

[0346] Signalling the difference allows further saving of bits as opposed to signalling the direct values ​​of the pivot point coordinates.

[0347] A twenty-fourth aspect of the method according to the twenty-second or twenty-third aspect, wherein the mapping function is a piecewise function based on a linear equation, an exponential equation, a logarithmic equation, or a combination of the above equations.

[0348] Using a predefined equation form (e.g., a linear equation) for the piecewise function allows function values ​​between pivot points to be obtained without explicit signaling, which beneficially reduces the signaling overhead of describing the mapping function.

[0349] A twenty-fifth aspect of the method according to the twenty-fourth aspect, wherein parameters of the piecewise function are obtained based on the pivot points, e.g. as an example in the case of a linear equation: slope=(Ey-Dy) / (Ex-Dx), b=Dy+slope*Dx, where D(94) and E(95) are exemplary change points with coordinates Dx, Dy, and Ex, Ey respectively, and slope and b are parameters of the linear equation, e.g. y=slope*x+b.

[0350] To achieve monotonically increasing mapping functions, the slope should be non-negative, which can be achieved by applying the constraint that the deltas (Ey-Dy) and (Ex-Dx) have the same sign, specifically non-negative, e.g., greater than or equal to 0. To achieve this, an unsigned code, e.g., an unsigned integer zeroth order Exp-Golomb code, can be used to signal the difference. As a further technical benefit, having the monotonically increasing constraint allows the delta to be signaled using an unsigned code, which allows saving bits of the sign of the delta.

[0351] A 26th aspect of the method according to the second or third aspect, wherein the set X includes a subset C, and the information of the mapping function comprises information of a start index (x_start) of the subset C and an end index (x_end) of the subset C.

[0352] A 27th aspect of the method according to the 25th or 26th aspect, wherein the information of the mapping function comprises information of a delta value of the mapping function f(x)-f(x-1) for any x in the subset C.

[0353] A twenty-eighth aspect of the method according to the twenty-seventh aspect, wherein the delta value is obtained using the following syntax: [Table 37] Here, sps_qpc_cb_delta[i] represents the delta value.

[0354] A twenty-ninth aspect of the method, according to the twenty-seventh aspect, wherein the delta value is in the range of 0 to 1.

[0355] A 30th aspect of the method according to the 29th aspect, wherein the delta value is obtained using the following syntax: [Table 38] Here, sps_qpc_cb_delta[i] represents the delta value.

[0356] A thirty-first aspect of a method according to any one of the twenty-sixth to thirty-first aspects, wherein the mapping function information is signaled using one of the following codes: binary, fixed length, unary, truncated unary, truncated binary, Golomb, or Exp-Golomb codes.

[0357] A 32nd aspect of the method according to any one of the 1st to 31st aspects, wherein the decoder further comprises a predetermined mapping function, and the bitstream comprises an indicator indicating whether to use the predetermined mapping function or to signal the mapping function within the bitstream.

[0358] This aspect allows to signal information about the mapping function only when it is useful, i.e. when the characteristics of the luma and chroma channels are significantly different from the general case, as in the case of HDR signals, and allows to use a predefined mapping function that is suitable for the general case, which allows to save signaling overhead in most general cases.

[0359] A thirty-third aspect of the method according to any one of the first to thirty-second aspects, wherein the mapping function information is signaled for both Cb and Cr components (chrominance components).

[0360] A thirty-fourth aspect of the method according to any one of the first to thirty-third aspects, wherein the mapping function information comprises an indicator indicating whether the mapping functions are signaled separately for the Cb and Cr components or jointly.

[0361] This aspect allows for more flexibility in controlling the quantization process when different chroma channels (Cb and Cr) have different signal characteristics, and thus allows for more efficient compression.

[0362] A 35th aspect of a method according to any one of the 1st to 34th aspects, wherein information of the mapping function is signaled at a sequence level in a sequence parameter set, or at a picture level in a picture parameter set, or at a tile group level in a tile group parameter set, or in an adaptation parameter set, or in a supplemental enhancement information (SEI) message.

[0363] A thirty-sixth aspect of the method according to any one of the first to thirty-fifth aspects, wherein the mapping function is expressed as the following table: [Table 39]

[0364] A thirty-seventh aspect of the method according to any one of the first to thirty-fifth aspects, wherein the mapping function is expressed as the following table: [Table 40]

[0365] A 38th aspect of the method according to any one of the 1st to 36th aspects, wherein the information of the mapping function is signalled directly or indirectly in the bitstream.

[0366] A thirty-ninth aspect of the decoder (30) comprises processing circuitry for carrying out a method according to any one of the first to thirty-eighth aspects.

[0367] A fortieth aspect of a computer program product comprising program code for carrying out a method according to any one of the first to thirty-eighth aspects.

[0368] A fortieth aspect of a decoder comprises one or more processors and a non-transitory computer readable storage medium coupled to the processors and storing programming for execution by the processors, the programming, when executed by the processors, configuring the decoder to perform a method according to any one of the first to thirty-eighth aspects.

[0369] Furthermore, the present disclosure discloses the following 25 additional aspects, which are listed as follows from the first aspect to the 25th aspect:

[0370] A first aspect of a method for obtaining a quantization parameter (QP) for a chrominance component based on a QP for a luminance component, the method being performed by a decoder, the method comprising: Get Luminance QP, deriving information for obtaining a mapping function (f) relating a luminance QP to a chrominance QP by parsing the received bitstream; Obtain a mapping function based on the obtained information; Obtain the chrominance QP based on the mapping function; It has the following.

[0371] In a second aspect of the method of the first aspect, the mapping function associates each element x of set X corresponding to a luminance QP within the allowed luminance QP range supported by the decoder (e.g., 0 to 63, or other part of the supported range, e.g., 20 to 50), or any subset of set X, to one element y of set Y corresponding to a chrominance QP within the allowed chrominance QP range supported by the decoder (e.g., 0 to 63, or other part of the supported range, e.g., 0 to 59 or 18 to 46). For example, the luminance QP range and the chrominance QP range may be the same or different.

[0372] A third aspect of the method according to the second aspect, wherein the mapping function is a monotonically increasing (non-decreasing) function.

[0373] A fourth aspect of the method according to the second aspect, wherein the set X includes a subset A in which the mapping function f is non-increasing, e.g., for any x in the set A (e.g., A={30, 39, 43}), f(x)-f(x-1)=0. For example, f(30)-f(29)=0, f(39)-f(38)=0, or f(43)-f(42)=0.

[0374] A fifth aspect of the method according to the second aspect, wherein a set X includes a subset B on which a mapping function f is increasing, i.e., f(x)-f(x-1)=c, where c is a function of x, and c(x)>=1 for any x in subset B. For example, subset B may be equal to XA, in other words subsets A and subset B are two non-overlapping subsets of X, e.g., A+B=X.

[0375] A sixth aspect of the method according to the fifth aspect, wherein the mapping function for the subset B is defined as follows: f(x)-f(x-1)=1 for any x in the subset B.

[0376] A seventh aspect of the method according to any one of the first to sixth aspects, wherein the information for obtaining the mapping function signaled in the bitstream includes a size of the subset A (sizeA) and an element a of the subset A. i The information to obtain the above is provided.

[0377] An eighth aspect of the method according to the seventh aspect, wherein the information signaled in the bitstream for obtaining the mapping function comprises a size of the subset A.

[0378] A ninth aspect of the method according to the seventh aspect, wherein the information for obtaining the mapping function signaled in the bitstream includes an element a i has a direct value of

[0379] A tenth aspect of the method according to the seventh aspect, wherein the information for obtaining the mapping function signaled in the bitstream includes an element a i The current value of and element a i-1 The difference between the preceding value of i ) with value a i is obtained as follows: for any i>0, a i =a i-1 +delta_a i .

[0380] An eleventh aspect of the method according to the seventh aspect, comprising: 0 is a 0 and starting_point_value (delta_a 0 ), and the difference (delta_a 0 ) is signaled in the bitstream, and the first value a 0 is a 0 =starting_point_value+delta_a 0 where starting_point_value is either signaled in the bitstream or is a pre-defined value, e.g. 0, 21, 30, maxQP>>1, and maxQP is the maximum QP value supported by the decoder, e.g. 63.

[0381] A twelfth aspect of a method according to any one of the seventh to eleventh aspects, wherein the information for obtaining the mapping function from the bitstream is signaled using one of the following codes: binary, unary, truncated unary, truncated binary, Golomb, or Exp-Golomb codes.

[0382] A 13th aspect of the method according to any one of the 1st to 11th aspects, wherein the mapping function is obtained using the defined functional behavior of subsets A and B, i.e., for any input argument x from subset B, the function increases by, for example, 1, such as f(x) - f(x - 1) = 1, and for any input argument x from subset A, the function is flat, such as f(x) - f(x - 1) = 0. Assuming that the first value of the mapping function corresponding to x = 0 is 0, for example, it can be implemented by repeatedly using the following pseudo-code: chroma_qp_mapping_table[0]=0; / / Initialization for(i=1;i<=maxQP;i++) / / maxQP is the maximum QP supported by the decoder { int incStep=1; / / Function increment for subset B for(j=0;j<cQpFlatSize;j++) / / cQpFlatSize is the size of subset A { if(i==cQpFlat[j]) / / cQpFlat is an array having elements of subset A { incStep=0; / / Zero function increment (flat) for subset A break; } } chroma_qp_mapping_table[i]=chroma_qp_mapping_table[i-1]+incStep; }

[0383] A 14th aspect of the method according to any one of the 4th to 12th aspects, wherein the information for obtaining the mapping function signaled within the bitstream has information for obtaining the value b of subset B, and subset A is obtained as A = X - B.

[0384] A fifteenth aspect of the method according to the second aspect, wherein the mapping function is a piecewise function and the information for obtaining the mapping function signaled in the bitstream comprises breakpoints (or change points, or pivot points) of the piecewise function.

[0385] A sixteenth aspect of a method according to the fifteenth aspect, wherein the number of breakpoints (or change points, or pivot points) and their x and y coordinates are signalled in the bitstream in a direct form or by using the difference between the current point coordinates and the previous point coordinates.

[0386] A seventeenth aspect of the method according to the fifteenth or sixteenth aspect, wherein the mapping function is a piecewise function based on a linear equation, an exponential equation, a logarithmic equation, or a combination of the above equations.

[0387] An 18th aspect of the method according to the 17th aspect, wherein parameters of the piecewise function are obtained based on the pivot points, e.g. as an example in the case of a linear equation: slope=(Ey-Dy) / (Ex-Dx), b=Dy+slope*Dx, where D(94) and E(95) are exemplary change points with coordinates Dx, Dy, and Ex, Ey respectively, and slope and b are parameters of the linear equation, e.g. y=slope*x+b.

[0388] To achieve a monotonically increasing mapping function, the slope should be non-negative, which can be achieved by applying the constraint to the deltas (Ey-Dy) and (Ex-Dx) that they have the same sign, and in particular are non-negative, e.g., greater than or equal to 0. To achieve this, an unsigned code, e.g., an unsigned integer zeroth order Exp-Golomb code, can be used to signal the difference.

[0389] A 19th aspect of the method according to any one of the 1 to 18 aspects, wherein the decoder further comprises a predetermined mapping function, and the bitstream comprises an indicator indicating whether to use the predetermined mapping function or to signal the mapping function within the bitstream.

[0390] A 20th aspect of the method according to any one of the 1 to 19th aspects, wherein the information for deriving the mapping function is signaled for both Cb and Cr components (chrominance components).

[0391] A 21st aspect of the method according to any one of the 1st to 20th aspects, wherein the information for obtaining the mapping function comprises an indicator indicating whether the mapping functions are signaled separately for the Cb and Cr components or jointly.

[0392] A 22nd aspect of a method according to any one of the 1st to 21st aspects, wherein the information for obtaining the mapping function is signaled at a sequence level within a sequence parameter set, at a picture level within a picture parameter set, or at a tile group level within a tile group parameter set within an adaptation parameter set.

[0393] A twenty-third aspect of the decoder (30) comprises processing circuitry for carrying out a method according to any one of the first to twenty-second aspects.

[0394] A twenty-fourth aspect of a computer program product comprises program code for performing a method according to any one of the first to twenty-second aspects.

[0395] A twenty-fifth aspect of a decoder comprises one or more processors and a non-transitory computer readable storage medium coupled to the processors and storing programming for execution by the processors, the programming, when executed by the processors, configuring the decoder to perform a method according to any one of the first to twenty-second aspects.

[0396] Furthermore, the present disclosure discloses the following 32 additional aspects, which are listed as follows from aspect 1 to aspect 32:

[0397] A first aspect of a method for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component, the method being performed by a decoder, the method comprising: parsing a received bitstream to obtain a luminance QP and information on a mapping function (f) relating a QP index (QPi) to a chrominance QP (QPc); obtaining a QPi based at least in part on the luminance QP; obtaining a mapping function based on the obtained information; and obtaining a QPc based on the obtained mapping function and the obtained QPi.

[0398] In a second aspect of the method of the first aspect, the mapping function associates each element x of set X corresponding to a QPi within the allowed QPi range supported by the decoder, or any subset of set X, to one element y of set Y corresponding to a QPc within the allowed QPc range supported by the decoder.

[0399] A third aspect of the method according to the second aspect, wherein the mapping function is a monotonically increasing (non-decreasing) function.

[0400] A fourth aspect of the method according to the second aspect, wherein the set X includes a subset A in which the mapping function f is non-increasing, e.g., f(x)-f(x-1)=0 for any x in the subset A.

[0401] A fifth aspect of the method according to the fourth aspect, wherein the set X includes a subset B on which the mapping function f is augmented, i.e. for any x in the subset B, f(x)-f(x-1)=c and A+B=X, where c is a natural number greater than or equal to 1.

[0402] A sixth aspect of the method according to any one of the second to fourth aspects, wherein the set X comprises a subset B on which the mapping function f is augmented, i.e. for any x in the subset B, f(x)-f(x-1)=c, where c is a natural number greater than or equal to 1.

[0403] A seventh aspect of the method, according to the fifth or sixth aspect, wherein the mapping function for the subset B is defined as follows: f(x)-f(x-1)=1 for any x in the subset B.

[0404] An eighth aspect of the method according to any one of the first to seventh aspects, wherein the information for obtaining the mapping function, which is signaled in the bitstream, includes a size of the subset A (sizeA) and an element a of the subset A. i The information to obtain the above is provided.

[0405] A ninth aspect of the method according to the eighth aspect, wherein the information signaled in the bitstream for obtaining the mapping function comprises a size of the subset A.

[0406] A tenth aspect of the method according to the eighth aspect, wherein the information for obtaining the mapping function signaled in the bitstream includes an element a i has a direct value of

[0407] An eleventh aspect of the method according to the eighth aspect, wherein the information for obtaining the mapping function signaled in the bitstream includes an element a i The current value of and element a i-1 The difference between the preceding value of i ) with value a i is obtained as follows: for any i>0, ai =a i-1 +delta_a i .

[0408] A twelfth aspect of the method according to the eighth aspect, comprising: 0 is a 0 and starting_point_value (delta_a 0 ), and the difference (delta_a 0 ) is signaled in the bitstream, and the first value a 0 is a 0 =starting_point_value+delta_a 0 where starting_point_value is either signaled in the bitstream or is a pre-defined value, e.g. 0, 21, 30, maxQPi>>1, where maxQPi is the maximum QPi value supported by the decoder, e.g. 63.

[0409] A thirteenth aspect of a method according to any one of the eighth to twelfth aspects, wherein the information for obtaining the mapping function from the bitstream is signaled using one of the following codes: binary, unary, truncated unary, truncated binary, Golomb, or Exp-Golomb codes.

[0410] A fourteenth aspect of the method according to any one of the first to eleventh aspects, wherein the mapping function is obtained using a defined functional behavior of subsets A and B, i.e. for any input argument x from subset B, e.g. f(x)-f(x-1)=1, the function increases by e.g. 1, and for any input argument x from subset A, e.g. f(x)-f(x-1)=0, the function is flat, assuming that the first value of the mapping function corresponding to x=0 is 0, which can for example be implemented iteratively using the following pseudocode: chroma_qp_mapping_table[0]=0; / / initialization for(i = 1; i <= maxQP; i++) / / maxQP is the maximum QP supported by the decoder { int incStep = 1; / / Function increment for set B for(j = 0; j < cQpFlatSize; j++) / / cQpFlatSize is the size of set A { if(i == cQpFlat[j]) / / cQpFlat is an array having elements of set A { incStep = 0; / / Zero function increment for set A (flat) break; } } chroma_qp_mapping_table[i] = chroma_qp_mapping_table[i - 1] + incStep; }

[0411] A 15th aspect of the method according to any one of the 4th to 13th aspects, wherein the information for obtaining the mapping function signaled in the bitstream has information for obtaining the value b of the subset B, and the subset A is obtained as A = X - B.

[0412] A 16th aspect of the method according to any one of the 4th to 13th aspects, wherein the subset B includes the sub - subset B k which includes elements x where the mapping function has the same increment c k : x ∈ B k and f(x) - f(x - 1) = c k when this is the case, where c k is a natural number, for example, c k is equal to 0, 1, 2, 3, 4,.... In other words, the subset B can be split into different sub - subsets according to the amount of the mapping function increment at the point x of the sub - subset Bk. k

[0413] ​A seventeenth aspect of the method according to the sixteenth aspect, wherein the information for obtaining the mapping function, which is signaled in the bitstream, is a sub-subset B k At least one size (size B k ) and sub-subset B k At least one element b of i The information to obtain the above is provided.

[0414] A 18th aspect of the method according to the 16th or 17th aspect, wherein the information for obtaining the mapping function signalled in the bitstream is a sub-subset B k The increment value of the mapping function at the point is obtained.

[0415] A nineteenth aspect of the method according to the sixteenth or seventeenth aspect, wherein the information for obtaining the mapping function signalled in the bitstream is a sub-subset B k The number of the items to be processed is stored in the memory.

[0416] A twentieth aspect of the method according to the second aspect, wherein the mapping function is a piecewise function and the information for obtaining the mapping function signaled in the bitstream comprises breakpoints (or change points, or pivot points) of the piecewise function.

[0417] A 21st aspect of a method according to the 20th aspect, wherein the number of breakpoints (or change points, or pivot points) and their x and y coordinates are signaled in the bitstream in a direct form or by using the difference between the current point coordinates and the previous point coordinates.

[0418] A twenty-second aspect of the method according to the twentieth or twenty-first aspect, wherein the mapping function is a piecewise function based on a linear equation, an exponential equation, a logarithmic equation, or a combination of the above equations.

[0419] A twenty-third aspect of the method according to the twenty-second aspect, wherein parameters of the piecewise function are obtained based on the pivot points, e.g., as an example in the case of a linear equation: slope=(Ey-Dy) / (Ex-Dx), b=Dy+slope*Dx, where D(94) and E(95) are exemplary change points with coordinates Dx, Dy, and Ex, Ey, respectively, and slope and b are parameters of the linear equation, e.g., y=slope*x+b.

[0420] A 24th aspect of the method according to any one of the 1st to 23rd aspects, wherein the decoder further comprises a predetermined mapping function, and the bitstream comprises an indicator indicating whether to use the predetermined mapping function or to signal the mapping function within the bitstream.

[0421] A 25th aspect of the method according to any one of the 1st to 24th aspects, wherein the information for deriving the mapping function is signaled for both Cb and Cr components (chrominance components).

[0422] A 26th aspect of the method according to any one of the 1st to 25th aspects, wherein the information for obtaining the mapping function comprises an indicator indicating whether the mapping functions are signaled separately for the Cb and Cr components or jointly.

[0423] A 27th aspect of a method according to any one of the 1st to 26th aspects, wherein information of the mapping function is signaled at a sequence level in a sequence parameter set, or at a picture level in a picture parameter set, or at a tile group level in a tile group parameter set, or in an adaptation parameter set, or in a supplemental enhancement information (SEI) message.

[0424] A twenty-eighth aspect of the method according to any one of the first to twenty-seventh aspects, wherein the mapping function is expressed as the following table: [Table 41]

[0425] A twenty-ninth aspect of the method according to any one of the first to twenty-seventh aspects, wherein the mapping function is expressed as the following table: [Table 42]

[0426] A thirtieth aspect of the decoder (30) comprises processing circuitry adapted to carry out a method according to any one of the first to twenty-ninth aspects.

[0427] A thirty-first aspect of a computer program product comprises program code for performing a method according to any one of the first to twenty-ninth aspects.

[0428] A thirty-second aspect of a decoder comprises one or more processors and a non-transitory computer readable storage medium coupled to the processor and storing programming for execution by the processor, the programming, when executed by the processor, configuring the decoder to perform a method according to any one of the first to twenty-ninth aspects.

[0429] The present disclosure discloses the following 41 further aspects, which are listed as follows from the first aspect to the forty-first aspect.

[0430] A first aspect of a method for obtaining a chrominance quantization parameter (QP) for a chrominance component based on a luminance QP for a luminance component, the method being performed by a decoder, the method comprising: parsing a received bitstream to obtain a luminance QP and information on a mapping function (f) relating a QP index (QPi) to a chrominance QP (QPc); obtaining a QPi based at least in part on the luminance QP; obtaining a mapping function based on the obtained information; and obtaining a QPc based on the obtained mapping function and the obtained QPi.

[0431] In a second aspect of the method of the first aspect, the mapping function associates each element x of set X corresponding to a QPi within the allowed QPi range supported by the decoder, or any subset of set X, to one element y of set Y corresponding to a QPc within the allowed QPc range supported by the decoder.

[0432] A third aspect of the method according to the second aspect, wherein the mapping function is a monotonically increasing (non-decreasing) function.

[0433] A fourth aspect of the method according to the second or third aspect, wherein the set X comprises a subset A in which the mapping function f is not increasing, e.g. For any x in a subset A, f(x)-f(x-1)=0 It is.

[0434] A fifth aspect of the method according to the fourth aspect, wherein the set X includes a subset B on which the mapping function f is augmented, i.e. for any x in the subset B, f(x)-f(x-1)=c and A+B=X, where c is a natural number greater than or equal to 1.

[0435] A sixth aspect of the method according to any one of the second to fourth aspects, wherein the set X comprises a subset B on which the mapping function f is augmented, i.e. for any x in the subset B, f(x)-f(x-1)=c, where c is a natural number greater than or equal to 1.

[0436] A seventh aspect of the method, according to the fifth or sixth aspect, wherein the mapping function for the subset B is defined as follows: f(x)-f(x-1)=1 for any x in the subset B.

[0437] An eighth aspect of the method according to any one of the first to seventh aspects, wherein the information of the mapping function is a size of the subset A (sizeA) and an element a of the subset A. i has information on.

[0438] A ninth aspect of the method according to any one of the first to eighth aspects, wherein the information of the mapping function comprises a size of the subset A.

[0439] A tenth aspect of the method according to any one of the first to ninth aspects, wherein the information of the mapping function is based on element a of the subset A. i has a direct value of

[0440] An eleventh aspect of the method according to any one of the eighth to tenth aspects, wherein the information of the mapping function is i The current value of and element a i-1 The difference between the preceding value of i ) with value a i is obtained as follows: for any i>0, a i =a i-1 +delta_a i .

[0441] A twelfth aspect of the method according to any one of the eighth to tenth aspects, wherein the information of the mapping function is a first value a 0 and starting_point_value (delta_a 0 ) and the first value a of subset A 0 However, the difference (delta_a 0 ) based on a 0 =starting_point_value+delta_a 0 where starting_point_value is either signaled in the bitstream or is a pre-defined value, e.g. 0, 21, 30, maxQPi>>1, where maxQPi is the maximum QPi value supported by the decoder, e.g. 63.

[0442] A 13th aspect of the method according to any one of the 1st to 12th aspects, wherein the information of the mapping function is signaled in a bit stream using any one of the following codes: binary, fixed length, unary, truncated unary, truncated binary, Golomb, or Exp-Golomb code.

[0443] A 14th aspect of the method according to any one of the 1st to 13th aspects, wherein the mapping function is obtained using the defined functional behavior of subsets A and B, that is, for example, for any input argument x from subset B, such as f(x) - f(x - 1) = 1, the function increases by, for example, 1 only, and for any input argument x from subset A, such as f(x) - f(x - 1) = 0, the function is flat. Assuming that the first value of the mapping function corresponding to x = 0 is 0, for example, it can be implemented by repeatedly using the following pseudo-code: chroma_qp_mapping_table[0] = 0; / / Initialization for (i = 1; i <= maxQP; i++) / / maxQP is the maximum QP supported by the decoder { int incStep = 1; / / Function increment for subset B for (j = 0; j < cQpFlatSize; j++) / / cQpFlatSize is the size of subset A { if (i == cQpFlat[j]) / / cQpFlat is an array having elements of subset A { incStep = 0; / / Zero function increment (flat) for subset A break; } } chroma_qp_mapping_table[i] = chroma_qp_mapping_table[i - 1] + incStep; }

[0444] A fifteenth aspect of the method according to any one of the fourth to fourteenth aspects, wherein the mapping function information comprises information of a value b of the subset B, the subset A being obtained as A=XB.

[0445] A sixteenth aspect of the method according to any one of the fourth to fourteenth aspects, wherein the subset B is a sub-subset B k and sub-subset B k where the mapping function is the same increment c k Contains an element x with: x∈B k Then, f(x)-f(x-1)=c k where c k is a natural number, for example, c k is equal to 0, 1, 2, 3, 4, .... In other words, the subset B may be split into different sub-subsets according to the amount of the mapping function increment at point x of the sub-subset Bk.

[0446] A seventeenth aspect of the method according to the sixteenth aspect, wherein the information of the mapping function is k At least one size (size B k ) and sub-subset B k At least one element b of i It has information that:

[0447] Aspect 18 of the method according to aspect 16 or aspect 17, wherein the information of the mapping function is k The increment value of the mapping function at the point is known.

[0448] A 19th aspect of the method according to the 16th or 17th aspect, wherein the information of the mapping function is k The number of pieces of information is

[0449] A 20th aspect of the method according to any one of the 16th to 19th aspects, further comprising: k The information) is retrieved using the following syntax: [Table 43]

[0450] A twenty-first aspect of the method according to any one of the sixteenth to nineteenth aspects, comprising: k The information) is retrieved using the following syntax: [Table 44]

[0451] A 22nd aspect of the method according to the second or third aspect, wherein the mapping function is a piecewise function and the information of the mapping function comprises breakpoints, change points or pivot points of the piecewise function.

[0452] A 23rd aspect of the method according to the 2nd or 3rd aspect, wherein the number of breakpoints, or change points, or pivot points, and their x and y coordinates are signaled in the bitstream in a direct form or by using the difference between the current point coordinates and the previous point coordinates.

[0453] A twenty-fourth aspect of the method according to the twenty-second or twenty-third aspect, wherein the mapping function is a piecewise function based on a linear equation, an exponential equation, a logarithmic equation, or a combination of the above equations.

[0454] A twenty-fifth aspect of the method according to the twenty-fourth aspect, wherein parameters of the piecewise function are obtained based on the pivot points, e.g. as an example in the case of a linear equation: slope=(Ey-Dy) / (Ex-Dx), b=Dy+slope*Dx, where D(94) and E(95) are exemplary change points with coordinates Dx, Dy, and Ex, Ey respectively, and slope and b are parameters of the linear equation, e.g. y=slope*x+b.

[0455] A 26th aspect of the method according to the second or third aspect, wherein the set X includes a subset C, and the information of the mapping function comprises information of a start index (x_start) of the subset C and an end index (x_end) of the subset C.

[0456] A 27th aspect of the method according to the 25th or 26th aspect, wherein the information of the mapping function comprises information of a delta value of the mapping function f(x)-f(x-1) for any x in the subset C.

[0457] A twenty-eighth aspect of the method according to the twenty-seventh aspect, wherein the delta value is obtained using the following syntax: [Table 45] Here, sps_qpc_cb_delta[i] represents the delta value.

[0458] A twenty-ninth aspect of the method, according to the twenty-seventh aspect, wherein the delta value is in the range of 0 to 1.

[0459] A 30th aspect of the method according to the 29th aspect, wherein the delta value is obtained using the following syntax: [Table 46] Here, sps_qpc_cb_delta[i] represents the delta value.

[0460] A thirty-first aspect of a method according to any one of the twenty-sixth to thirty-first aspects, wherein the mapping function information is signaled using one of the following codes: binary, fixed length, unary, truncated unary, truncated binary, Golomb, or Exp-Golomb codes.

[0461] A 32nd aspect of the method according to any one of the 1st to 31st aspects, wherein the decoder further comprises a predetermined mapping function, and the bitstream comprises an indicator indicating whether to use the predetermined mapping function or to signal the mapping function within the bitstream.

[0462] A thirty-third aspect of the method according to any one of the first to thirty-second aspects, wherein the mapping function information is signaled for both Cb and Cr components (chrominance components).

[0463] A thirty-fourth aspect of the method according to any one of the first to thirty-third aspects, wherein the mapping function information comprises an indicator indicating whether the mapping functions are signaled separately for the Cb and Cr components or jointly.

[0464] A 35th aspect of a method according to any one of the 1st to 34th aspects, wherein information of the mapping function is signaled at a sequence level in a sequence parameter set, or at a picture level in a picture parameter set, or at a tile group level in a tile group parameter set, or in an adaptation parameter set, or in a supplemental enhancement information (SEI) message.

[0465] A thirty-sixth aspect of the method according to any one of the first to thirty-fifth aspects, wherein the mapping function is expressed as the following table: [Table 47]

[0466] A thirty-seventh aspect of the method according to any one of the first to thirty-fifth aspects, wherein the mapping function is expressed as the following table: [Table 48]

[0467] A 38th aspect of the method according to any one of the 1st to 36th aspects, wherein the information of the mapping function is signalled directly or indirectly in the bitstream.

[0468] A thirty-ninth aspect of the decoder (30) comprises processing circuitry for carrying out a method according to any one of the first to thirty-eighth aspects.

[0469] A fortieth aspect of a computer program product comprising program code for carrying out a method according to any one of the first to thirty-eighth aspects.

[0470] A fortieth aspect of a decoder comprises one or more processors and a non-transitory computer readable storage medium coupled to the processors and storing programming for execution by the processors, the programming, when executed by the processors, configuring the decoder to perform a method according to any one of the first to thirty-eighth aspects.

Claims

1. A method performed by a decoder, comprising: Receive the bitstream, parsing the bitstream to obtain luma quantization parameters (QP) and information about a chroma QP mapping table that associates QP indices (QPi) with chrominance QPs (QPc), the values ​​of the chroma QP mapping table satisfy a mapping function, the mapping function being a piecewise mapping function, the piecewise mapping function information having pivot points of the piecewise mapping function, the information about the chroma QP mapping table including the pivot points of the piecewise mapping function, the number of the pivot points and their respective x and y coordinates being signaled in the bitstream based on a delta value between the coordinates of a current pivot point and the coordinates of a previous pivot point; obtaining a QPi based at least in part on the obtained luminance QP; obtaining a chroma QP mapping table based on the pivot point of the piecewise mapping function; Obtaining a first QPc based on the obtained chroma QP mapping table and the obtained QPi; Having said that, the chroma QP mapping table associates each element x of a set X corresponding to a QPi within a allowed QPi range supported by the decoder, or any subset of the set X, with one element y of a set Y corresponding to a QPc within a allowed QPc range supported by the decoder, the allowed QPc range being in the range 0 to 63; method.

2. The method of claim 1 , wherein the mapping function is a piecewise function based on a linear equation.

3. The method of claim 1 or 2, wherein the information of the chroma QP mapping table is signaled at a sequence level in a sequence parameter set.

4. A decoder comprising processing circuitry for carrying out the method according to any one of claims 1 to 3.

5. A computer program arranged to cause a computer to carry out the method according to any one of claims 1 to 3.

6. A decoder comprising: one or more processors; a non-transitory computer readable storage medium coupled to the processor and storing programming for execution by the processor, the programming, when executed by the processor, configuring the decoder to perform the method of any one of claims 1 to 3; and A decoder having

7. A computer readable storage medium tangibly embodied with computer program code which, when executed by a computer unit, causes the computer unit to carry out the method according to any one of claims 1 to 3.

8. a non-transitory memory storage configured to store video data in the form of a bitstream; A video decoder configured to perform the method according to any one of claims 1 to 3; A video data decoding device having the above configuration.

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