Quantization parameter signaling

Abstract

To provide a method, an apparatus, a program, and a program-based device for deriving and signaling luma (luminance) and / or chroma (saturation) quantization parameters (QP) of a video signal.SOLUTION: A first method is to directly transmit a user-defined chroma quantization parameter (Qpc) table in high-level syntax. This leads to more flexible and efficient QP control for future codec developments and video content coding. A second method is to signal luma QP and chroma QP independently. This method eliminates the need for a Qpc table and the dependency on chroma quantization parameters on luma QP.SELECTED DRAWING: Figure 5A

Description

[Technical field]

[0001] The present disclosure relates to deriving and signaling quantization parameters when encoding video signals, and more particularly to methods, apparatus, computer programs, and computer-program-based devices for deriving and signaling luma and / or chroma quantization parameters of a video signal.

[0002] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 62 / 853,352, filed May 28, 2019, which is incorporated herein by reference. [Background technology]

[0003] Quantization parameter (QP) is a type of parameter used in video bitstream to adjust quality and bitrate. In general, a lower QP value set during encoding results in higher quality of the encoded video at the expense of more consumed bits required, and a QP of 0 means no quantization. Meanwhile, the higher the value of QP, the lower the quality of the encoded video and the fewer bits consumed. Furthermore, a decoder uses the QP value when reconstructing video content from the encoded video.

[0004] Versatile Video Coding (VVC) is a standard being developed by the Joint Video Exploration Team (JVET) to code both standard dynamic range (SDR) and high dynamic range (HDR) content. In the current (2019) VVC specification, the signaling of quantization parameters for luma and chroma components is handled differently.

[0005] For the luma component, a delta quantization parameter (QP), which denotes the difference between successive quantization parameter values, is signaled and added to the initial QP value for each slice.

[0006] For chroma, the chroma quantization parameter (Qpc) is derived from the luma QP with chroma offset values ​​(qPi) using a chroma quantization parameter table. As an example, FIG. 1 shows a table (100) containing different values ​​of Qpc as a function of the luma quantization parameter with chroma offset qPi. The data shown in the table (100) corresponds to a specific chroma format. According to the VVC standard, the chroma format is based on the variable chroma_format_idc, which ranges from 0 to 3. The table (100) corresponds to a chroma_format_idc value of 1, which represents the chroma format (4:2:0).

[0007] The table (100) in FIG. 1 is inherited from the High Efficiency Video Coding (HEVC) standard and is designed for SDR content only. However, when HDR Perceptual Quantization (PQ) content was first considered in JCT-VC, it was concluded that the default SDR Qpc table was not suitable for HDR content because it would result in chroma artifacts at low bitrates, especially in achromatic regions. As a result, a non-normative encoder optimization using a variable called ChromaQPOffset was introduced into the HDR Common Test Conditions (CTC) for HDR PQ content. In general, ChromaQPOffset is signaled in the Picture Parameter Set (PPS) to indicate a difference from the luma QP value, which indicates that a constant value is used based on the input QP. However, there are cases where the QP varies over a picture and a constant offset cannot accommodate it.

[0008] In the first version of HEVC, there were separate QP offsets for each of the two chroma components at the slice level. However, at the coding unit (CU) level, a delta QP was applied to all three components with chroma passing through a mapping table based on the luma QP. In the Range Extensions (Rext) version, separate chroma QP control was introduced at the CU level via chroma QP offset lists specified for Cb and Cr, respectively.

[0009] <Derivation of quantization parameters in the current VVC standard> In this process, the luma quantization parameter Qp' Y and the chroma quantization parameter Qp' Cb and Qp' Cr The luma quantization parameter Qp Y The initial value of is derived as follows: SliceQp Y =26+init_qp_minus26+slice_qp_delta qP Y_PREV represents the previous luma quantization parameter for the current coding unit. If the current quantization group is the first quantization group of a slice or brick, qP Y_PREV is set to SliceQpY. Otherwise, qP Y_PREV is the luma quantization parameter Qp of the last luma coding unit of the previous quantization group in decoding order. Y is set equal to

[0010] qP Y_PRED represents the predicted luma quantization parameter of the current coding unit. If the current quantization group is the first quantization group in a CTB row in a brick and the top coding unit is available, qP Y_PRED Top CU Qp Y otherwise, qP Y_PRED =(qP Y_A +qP Y_B +1)>>1 Here, if the left coding block is not the first coding block of the left quantization group, or if the left coding block is unavailable, qP Y_A qP Y_PREV If the top coding block is not the first coding block in the top quantization group, or if the top coding block is not available, then qP Y_B qP Y_PREV is set to.

[0011] Variable Qp per coding unit Y is derived as follows:

number

[0012] Luma quantization parameter Qp' Y can be derived as follows: Qp′ Y = Qp Y +QpBdOffset Y If ChromaArrayType is not 0 and treeType is SINGLE_TREE or DUAL_TREE_CHROMA, the following applies: If treeType is equal to DUAL_TREE_CHROMA, the variable QpY is set equal to the luma quantization parameter QpY of the current luma coding unit that covers the luminance position (xCb+cbWidth / 2, yCb+cbHeight / 2). Variable qP Cb and qP Cr is derived as follows:

number

number

[0013] Current video content is not the same as the SDR content for which the original default SDR Qpc table was designed. As an example, the luma and chroma components of SDR and HDR content may be encoded using Y'CbCr or ICtCp signal formats. For HDR content, the situation is more complicated. HDR content may further be encoded using HLG or PQ transfer characteristics. It may be beneficial to signal different chroma quantization parameters for different chroma component types and transfer characteristics. It may also be beneficial to signal different chroma quantization parameters for two different chroma components, Cb and Cr or Ct and Cp. It may also be beneficial to signal chroma quantization parameters in a content-dependent manner. The disclosed method and apparatus address the above-mentioned problems and needs.

[0014] The device and method according to the present disclosure provide a solution to the problem of deriving a chroma QP (QPc) for HDR content. Additionally, a device and method for signaling such derived chroma QP for HDR are also disclosed. According to a first aspect of the present disclosure, a method for decoding an encoded video bitstream is disclosed, the method comprising the steps of: a) extracting a chroma quantization parameter (Qpc) table that maps a luma quantization parameter (Qp) having a chroma QP offset value qP(i) to a corresponding chroma Qp value Qpc(i), where i) "i" is an index of a table entry ranging from startID to endID, ii) startID is an integer greater than or equal to 1 and less than N, N is the total number of Qpc table entries, and iii) endID is an integer greater than startID and 1 and less than or equal to N; and b) generating a decoded output signal based on the extracted Qpc table and the encoded video bitstream, where the encoded bitstream includes a table identifier, and in a first case the table identifier indicates the presence of a default table, and in a second case the encoded video bitstream further includes one or more elements signaled in a high level syntax, the one or more elements being encoded based on a) two or more chroma Qp values, or b) a combination of one or more chroma Qp values ​​and one or more luma Qp with chroma offset values.

[0015] According to a second aspect of the present disclosure, a method for decoding an encoded stream of a video signal includes extracting a luma quantization parameter (Qps), a first chroma component Qps, and a second chroma component Qps from the encoded stream; and generating the output decoded video signal based on the extracted luma components, the first chroma component, and the second chroma component Qp and the encoded video bitstream, the encoded video stream including a plurality of elements signaled in a high level syntax, the plurality of elements being encoded based on a combination of the luma Qps, the first chroma component, and the second chroma component Qps, the first chroma component Qps being derived based on a predicted value of the first chroma component Qps and a bit depth of a first chroma component sample of the video signal, and the second chroma component Qps being derived based on a predicted value of the second chroma component Qps and a bit depth of a second chroma component sample of the video signal. [Brief description of the drawings]

[0016] [Figure 1] 1 shows an example of a table containing different values ​​of the chroma quantization parameter as a function of the luma quantization parameter. [Diagram 2] 1 illustrates an example HDR Qpc table according to an embodiment of the present disclosure. [Diagram 3] 1 illustrates an exemplary Qpc table according to an embodiment of the present disclosure. [Figure 4A] 1 shows an example Qpc table for HDR PQ content type. [Figure 4B] 1 shows an example Qpc table for an HDR Hybrid-Long Gamma (HLG) content type. [Figure 5A] 5B illustrates an exemplary SDR Qpc mapping function-based luma quantization parameter. [Figure 5B] 5A illustrates an exemplary SDR Qpc mapping function-based luma quantization parameter (continued from FIG. 5A ). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] <Definition> Throughout this document, technical terms used related to video encoding and decoding are defined according to Versatile Vide Coding (draft 5), document JVET-N1001-v3, Joint Video Experts Team (JVET) of ITU-T SG 16 WP 3, and ISO / IEC JTC 1 / SC 29 / WG 11, 14th Meeting: Geneva, CH, 19-27 March 2019.

[0018] <Description> <1. Deriving Chroma PQ based on user-defined Qpc table> According to an embodiment of the present disclosure, the chroma QP of HDR content may be determined using a user-defined Qpc table. FIG. 2 shows a table (200) representing an example HDR Qpc table according to an embodiment of the present disclosure. The table (200) serves essentially the same purpose for HDR content as the default SDR Qpc table specified in the current VVC serves for SDR content. Those skilled in the art will appreciate that the disclosed approach based on a user-defined Qpc table for HDR content unifies codec design for all SDR and HDR signal types and leads to more flexible and efficient QP control for future codec developments.

[0019] According to one embodiment of the present disclosure, the HDR Qpc table as described may be directly signaled in high level syntax such as video parameter set (VPS), signal parameter set (SPS), PPS, adaptation parameter set (APS), slice header, and SEI message. To reduce signaling overhead, and according to other embodiments of the present disclosure, a default Qpc table may be used as a normative table in the standard specification or as a non-normative example in the standard specification.

[0020] Referring to FIG. 2, in the SPS, a new syntax element chroma_qp_table_idc may be added. If the value of chroma_qp_table_idc is equal to 0, it refers to the original SDR Qpc table in the VVC specification text (see table (100) in FIG. 1). If the value of chroma_qp_table_idc is equal to 1, it refers to table (200) in FIG. 2. According to one embodiment of the present disclosure, the variable chroma_qp_table_idc is an indication of an index into the array of Qpc as a function of qPi when ChromaArrayType is equal to 1. The value of chroma_qp_table_idc may be in the range from 0 to 1.

[0021] According to further embodiments of the present disclosure, one Qpc table can be signaled and shared for both Cb and Cr, or two separate tables designed for Cb and Cr respectively can be signaled. To reduce signaling overhead, each Qpc table can be differentially coded, approximated with a piecewise linear function, run-length coded, coded with Lempel-Ziv-Welch (LZW) or similar algorithm, or coded with a mixture of the above mentioned techniques.

[0022] The above Qpc tables may be used for HDR content with HLG or PQ transfer characteristics. With reference to Figures 1-2, it can be seen that from tables (100, 200) and Qpc tables designed for other content types such as HLG, some Qpc values ​​are equal to qPi or can be directly derived by subtracting a constant value. To save coding bits, the range of table elements that needs to be signaled in the bitstream can be specified by a start index and an end index [startID, endID].

[0023] In the following, various methods for signaling chroma QP values ​​according to the teachings of this disclosure are described. Throughout this disclosure, the term "delta Qp", also denoted as "dQp", is used to describe the difference between two consecutive QP values.

[0024] <Method 1a> In this method, the difference between two adjacent Qpc entries in [startID,endID] is encoded: dQpc[i]=Qpc[i]-Qpc[i-1] (1)

[0025] In general, the SDR and HDR Qpc tables according to the teachings of this disclosure may only include dQp values ​​of 0 and 1. Delta QP values ​​can be directly signaled. Alternatively, codewords can be composed of multiple delta QP values. For example, delta QP values ​​of Cb and Cr pairs with the same index value may be combined. As another example, delta QP values ​​of two consecutive index values ​​can be combined for Cb, and similarly for Cr. Optionally, the sequence of codewords constructed from delta QP value combinations can be further compressed using methods such as Huffman coding or other lossless compression algorithms. For delta Qpc values ​​other than 0 and 1, the syntax can specify a maximum delta value. In some cases, startID and endID may be constrained to be even or odd values ​​to reduce the number of bits that need to be signaled.

[0026] In the following description of the further embodiment, differences from the previously described embodiment will be mainly described. Therefore, features common to both embodiments will be omitted in the following description, and it should be considered that the features of the previously described embodiment are also implemented or at least can be implemented in the further embodiment, unless otherwise required in the following description.

[0027] <Method 1b> In this way, the difference value between each pair of {qPi,Qpc} in [startID,endID] may be encoded as follows: dQp[i]=qPi[i]-Qpc[i] (2) The delta QP value between qPi and Qpc may range from 0 to 18. This indicates that method 1a may be more suitable for encoding than method 1b.

[0028] <Method 1c> The method is based on fitting the qPi to Qpc mapping curve through a piecewise linear function defined as:

number

number

[0029] <Method 1d> In this method, run-length coding may be used to encode the dQpc[i] values ​​defined in equation (1). As an example, referring to table (100) in FIG. 1, the delta Qp values ​​are derived as a sequence of 0s and 1s. The delta values ​​(0 or 1) may be coded along with a count of the resulting values. FIG. 3 shows table (300), which is an exemplary illustration of a Qpc table based on this method.

[0030] According to an embodiment of the present disclosure, one default Qpc table may be predefined for each of different signal types, such as SDR, PQ, and HLG content. Figures 4A-4B show tables (400A, 400B) representing example Qpc tables for HDR PQ and HLG content, respectively. In the absence of a user-defined Qpc table, the encoder and decoder may apply the default Qpc table instead. An embodiment of the present disclosure may assume that a user-defined Qpc is not signaled. This approach has the advantage of saving more bits.

[0031] The following table corresponds to method 1a above and shows an example syntax of the SPS and tile group header raw byte sequence payload (RBSB), where syntax elements according to the teachings of the present disclosure are depicted in italic font in contrast to other existing syntax elements. A detailed description of the various syntax elements will now be provided. A default QPc table can be specified in the SPS by signaling a default QPc table type index. If no default table is provided, a predefined QPc table may be transmitted in the SPS along with a delta QP value between two adjacent table elements. One or more alternative QPc tables for use in a slice may be signaled in the PPS to override the QPc table in the SPS.

[0032] [Table 1-1]

[0033] [Table 1-2]

[0034] [Table 1-3]

[0035] Setting sps_default_qpc_table_flag to 1 uses the default chroma quantization parameter table and therefore no Qpc table needs to be sent. Instead, an index is signaled indicating which default Qpc table to use. sps_default_qpc_table_flag equal to 0 specifies that no default Qpc table is defined and must be sent in the SPS.

[0036] default_qpc_table_type_idx indicates which default Qpc table to use when sps_default_qpc_table_flag is 1. When default_qpc_table_type_idx is 0 and pps_slice_qpc_table_present_flag is 0, it indicates that one or more default SDR Qpc tables are used. When default_qpc_table_type_idx is equal to 1 and pps_slice_qpc_table_present_flag is equal to 0, it indicates that one or more HDR PQ Qpc tables are used. When default_qpc_table_type_idx is equal to 2 and pps_slice_qpc_table_present_flag is equal to 0, it indicates that one or more default HLG Qpc tables are used. When default_qpc_table_type_idx is 3, it is reserved for future use.

[0037] sps_separate_qpc_table_enable_flag, when set to 1, specifies that Cb and Cr use separate Qpc tables. sps_cr_qp_delta[i] and sps_cr_qp_gap_idx are defined and signaled in the SPS, and slice_cr_qp_delta[i] and slice_cr_qp_gap_idx are defined in the slice header. sps_separate_qpc_table_enable_flag, when set to 0, specifies that Cb and Cr use the same Qpc table.

[0038] sps_qpc_table_start_index_div2 specifies the start index for signaling delta QP values ​​in Qpc table elements. It is defined as an even integer between 0 and 63. For table elements with index less than sps_qpc_table_start_index_div2*2, Qpc is set to the same value as qPi.

[0039] sps_qpc_table_end_index_div2 specifies the end index before signaling delta QP values ​​in Qpc table elements. It is defined as an even number between 0 and 63. For table elements with index larger than sps_qpc_table_end_index_div2*2, sps_cb_qp_delta[i] and sps_cr_qp_delta[i] are set to 1. sps_cb_qp_delta[i] specifies the delta value between spsQpcb[i] and spsQpcb[i-1] in sps_cb_qp_delta[0] to construct the quantization parameter table for Cb defined in SPS. The i-th entry of the quantization parameter table for Cb in SPS is derived as follows: spsQpcb[i]=sps_cb_qp_delta[i]+spsQpcb[i-1]

[0040] sps_cr_qp_delta[i] specifies the delta value of spsQpcr[i] and spsQpcr[i-1] centered on sps_cr_qp_delta[0] to construct the quantization parameter table of Cr defined in SPS. The i-th entry of the quantization parameter table of Cr in SPS is derived as follows: spsQpcr[i]=sps_cr_qp_delta[i]+spsQpcr[i-1]

[0041] If pps_slice_qpc_table_present_flag is 1, it specifies that the quantization parameter tables for the Cb and Cr components of the current slice are present and defined in the slice header. If pps_slice_qpc_table_present_flag is 0, it specifies that the quantization parameter tables for the Cb and Cr components of the current slice are not present in the slice header and the default quantization parameter tables are applied to Cb and Cr.

[0042] slice_cb_qp_delta[i] specifies the delta value by slice_cb_qp_delta[0] between sliceQpcb[i] and sliceQpcb[i-1] to construct the slice quantization parameter table for Cb. The ith entry of the slice Qpc table for Cb component is derived as follows: sliceQpcb[i]=slice_cb_qp_delta[i]+sliceQpcb[i-1]

[0043] slice_cr_qp_delta[i] is defined when sps_separate_qpc_table_enable_flag is 1, and specifies the delta value between sliceQpcr[i] and sliceQpcr[i-1] for constructing the slice quantization parameter table for Cr as slice_cr_qp_delta[0]. The i-th entry of the slice Qpc table for the Cr component is derived as follows: sliceQpcr[i]=slice_cr_qp_delta[i]+sliceQpcr[i-1]

[0044] <2. Derive chroma QP independently from luma QP> According to further embodiments of the present disclosure, the luma Qps and chroma Qps may be signaled independently. Such an approach has the advantage of eliminating the dependency of the chroma QP on the luma QP. In the following, the derivation of the chroma QP according to the embodiments of the present disclosure is described in detail.

[0045] The initial values ​​of the chroma quantization parameters of slices SliceQpCb and SliceQpCr can be derived as follows: SliceQpCb=26+init_qp_minus26+slice_cb_qp_delta (3) SliceQpCr=26+init_qp_minus26+slice_cr_qp_delta (4) If the current quantization group is the first quantization group of a slice or brick, qP Cb_PREV and qP Cr_PREV are set to SliceQpCb and SliceQpCr, respectively. Otherwise, qP Cb_PREV and qP Cr_PREV is set equal to the chroma quantization parameter Qpc of the last chroma coding unit of the previous quantization group in decoding order.

[0046] qP Cb_PRED and qP Cr_PRED is the predicted chroma quantization parameter for the current coding unit. If the current quantization group is the first quantization group in a CTB row in a brick and the top coding unit is available, qP Cb_PRED and qP Cr_PRED Set Qpc of the top CU, otherwise, qP Cb_PRED =(qP Cb_A +qP Cb_B +1)>>1 (5) qP Cr_PRED =(qPCr_A +qP Cr_B +1)>>1 (6) Here, qP Cb_A and qP Cr_A is qP if the left coding block is not the first coding block in the left quantization group, or if the left coding block is not available, respectively. Cb_PREV and qP Cr_PREV , and qP if the top coded block is not the first coded block in the top quantization group or if the top coded block is not available, respectively. Cb_B and qP Cr_B qP Cb_PREV and qP Cr_PREV is set to.

[0047] The variables QpCb and QpCr for each coding unit can be derived as follows:

number

number

[0048] Chroma quantization parameter Qp´ Cb and Qp´ Cr can be derived as follows: Qp′Cb=QpCb+QpBdOffsetC (9) Qp′Cr=QpCr+QpBdOffsetC (10) The difference value between the quantization parameter of the current coding unit and its prediction, CuCbQpDeltaVal and CuCrQpDeltaVal, may be specified at the transform unit layer. There are several ways to code the delta QP value.

[0049] In the following, an exemplary method according to the teachings of the present disclosure is described. Also, the difference between the QP of each color component (e.g., luma, chroma Cb, and chroma Cr) and its predicted value is abbreviated as dPQ' to distinguish it from dPQ, which indicates the difference between successive QPs in the context of the Qpc table, as described above.

[0050] <Method 2a> In this method, the dQPs of three color components, luma, chromaCb, and chromaCr, are encoded, represented by the variables CuQpDeltaVal, CuCbQpDeltaVal, and CuCrQpDeltaVal, respectively.

[0051] The following description of the further embodiment focuses on the differences between it and the previously described embodiment. Features common to both embodiments are therefore omitted from the following description, and it should therefore be assumed that features of the previously described embodiment are implemented, or at least can be implemented, in the further embodiment, unless the following description requires otherwise.

[0052] <Method 2b> In this method, dQP' of the luma component CuQpDeltaVal is coded. Furthermore, the difference between dQp' of each chroma component and luma dQp' is coded according to: CbdQpDeltaVal=CuCbQpDeltaVal-CuQpDeltaVal (11) CrdQpDeltaVal=CuCrQpDeltaVal-CuQpDeltaVal (12)

[0053] <Method 2c> In this method, the element CrCbdQpDeltaVal is defined as follows: CrCbdQpDeltaVal=CuCrQpDeltaVal-CuCbQpDeltaVal (13) where elements CuCrQpDeltaVal and CuCbQpDeltaVal have the same definitions as in method 2c above.

[0054] <Method 2d> In this method, the element CrCbdQpDeltaVal is defined as follows: CrCbdQpDeltaVal=CuCrQpDeltaVal-CuCbQpDeltaVal where elements CuCrQpDeltaVal and CuCbQpDeltaVal have the same definitions as in method 2c above.

[0055] <Method 2e> In this method, the difference value from the chroma QP and luma QP is defined as follows: dQp′Cb=Qp′Y-Qp′Cb (14) dQp′Cr=Qp′Y-Qp′Cr (15) The signaling for method 2e is similar to method 2a, without the need to signal slice_cb_qp_delta and slice_cr_qp_delta (see below) in the slice header.

[0056] The following table shows an example syntax for the Row Byte Sequence Payload (RBSB) for SPS and Tile Group Header, corresponding to Method 2a above, where syntax elements according to the teachings of this disclosure are shown in italics in contrast to other existing syntax elements, followed by a detailed description of the various syntax elements.

[0057] [Table 2-1]

[0058] [Table 2-2]

[0059] [Table 2-3]

[0060] [Table 2-4]

[0061] [Table 2-5]

[0062] The methods and systems described in this disclosure may be implemented in hardware, software, firmware, or any combination thereof. Features described as blocks, modules, or components may be implemented together (e.g., in a logic device such as an integrated logic device) or separately (e.g., as separate connected logic devices). The software portions of the methods of this disclosure may comprise a computer-readable medium comprising instructions that, when executed, at least partially perform the described methods. The computer-readable medium may include, for example, a random access memory (RAM) and / or a read-only memory (ROM). The instructions may be executed by a processor (e.g., a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable logic array (FPGA), a graphics processing unit (GPU), or a general-purpose GPU).

[0063] A number of embodiments of the present disclosure have been described. Nevertheless, it will be understood that various modifications can be made without departing from the spirit and scope of the disclosure. Accordingly, other embodiments are within the scope of the following claims.

[0064] The above examples are provided to those of ordinary skill in the art as a complete disclosure and description of how to make and use the embodiments of the present disclosure, and are not intended to limit the scope of what the inventors regard as their disclosure.

[0065] Modifications of the above-described modes for carrying out the methods and systems disclosed herein that are obvious to those skilled in the art are intended to be within the scope of the following claims. All patents and publications mentioned in this specification are indicative of the level of skill of those skilled in the art to which this disclosure pertains. All references cited in this disclosure are incorporated by reference to the same extent as if each reference was individually incorporated by reference in its entirety.

[0066] Of course, it is to be understood that the present disclosure is not limited to the particular method or system, as the particular method or system may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. As used herein and in the appended claims, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. The term "plurality" includes two or more referents unless the content clearly dictates otherwise. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

Claims

[Claim 1] 1. An apparatus for reconstructing encoded data, comprising: The apparatus comprises: means for receiving an encoded bitstream including one or more encoded images, each image including a luma component, a first chroma component and a second chroma component; extracting syntax parameters from the encoded bitstream to determine a chroma quantization parameter (QP) table, the chroma QP table mapping input luma QP values ​​to corresponding chroma QP values; means for decoding the one or more encoded images based on the chroma QP table, the syntax parameters including a starting luma QP value and one or more offset parameters, and for determining a mapping from the luma QP values ​​to the chroma QP values ​​using a piecewise linear representation; 13. An apparatus comprising:

Images