Varying quantization parameter values based on resolution variations

Abstract

A method for encoding or decoding a region of a picture included in a video stream is provided. The method includes obtaining a first value of a luma quantization parameter (QP) of a luma component; and determining a first value of Chroma QP for the Chroma component based on the first value of Luma QP. The method further includes obtaining a second value of brightness QP; and determining a second value of Chroma QP based on the second value of Luma QP. The method further includes encoding or decoding a region of the picture at a second resolution using a second value of luma QP and a second value of chroma QP.

Description

Technical Field

[0001] Embodiments related to changing quantization parameter (QP) values based on resolution changes are disclosed. Background Art

[0002] Video, Pictures, and Picture Resolution

[0003] A video sequence consists of a series of pictures. Each picture consists of one or more components. Each component can be described as a two-dimensional rectangular array of sample values. Typically, a picture consists of three components: a luminance component Y, where the sample values are luminance values; and two chrominance components Cb and Cr, where the sample values are chrominance values.

[0004] The resolution of a picture generally refers to the size of the luminance component of the picture. For example, a picture with a resolution of 1920x1080 means that the width of the luminance component of the picture is 1920 and the height of the luminance component of the picture is 1080.

[0005] Parameter Sets, Slice Headers, and Picture Headers

[0006] Versatile Video Coding (VVC) specifies three types of parameter sets: Picture Parameter Set (PPS), Sequence Parameter Set (SPS), and Video Parameter Set (VPS). The PPS includes data common to the entire picture, the SPS includes data common to the coded layer video sequence (CVS), and the VPS includes data common to multiple CLVSs (e.g., data of multiple layers in a bitstream).

[0007] The concept of a slice is to divide a picture into independently encoded slices, where the decoding of one slice in a picture is independent of other slices in the same picture. Each slice has a slice header that includes syntax elements. When decoding the slice, the slice header values decoded from these syntax elements are used.

[0008] In VVC, a coded picture contains a picture header. The picture header contains parameters common to all slices of the coded picture.

[0009] Coding Units and Coding Blocks

[0010] A block is a two-dimensional array of samples. In video coding, each component is divided into blocks, and the coded video bitstream includes a series of coded blocks. In video coding, a picture is usually divided into units that cover specific regions of the picture.

[0011] Each unit consists of all blocks from all components that make up that particular region, and each block belongs entirely to one unit. Coding units (CUs) in VVC are examples of units. In VVC, a CU can be recursively split into smaller CUs. The CU at the top level is called a coding tree unit (CTU). A CU usually contains three coding blocks, namely one coding block for luma and two coding blocks for chroma. The size of the luma coding block is the same as that of the CU. In the current VVC (i.e., version 1), the size of a CU can be from 4x4 to 128x128.

[0012] Intra prediction

[0013] In intra prediction (also known as spatial prediction), previously decoded blocks within the same picture are used to predict a block. Samples within the current block are predicted using samples from previously decoded blocks within the same picture. A picture consisting only of intra-predicted blocks is called an intra picture.

[0014] Inter prediction and motion compensation

[0015] In inter prediction (also known as temporal prediction), blocks from previously decoded pictures are used to predict blocks in the current picture. Samples within the current block are predicted using samples from blocks in previously decoded pictures. A picture that allows inter-predicted blocks is called an inter picture. The previously decoded pictures used for inter prediction are called reference pictures.

[0016] Residual, transform, and quantization

[0017] Then, the difference between the samples of the source block (containing the original samples) and the samples of the prediction block (also known as the residual block) is usually compressed through a spatial transform to eliminate further redundancy. Then, the transform coefficients are quantized by a quantization parameter (QP) to control the fidelity of the residual block and thus the bitrate required to compress the block. The coding block flag (CBF) is used to indicate whether there are any non-zero quantized transform coefficients. Then, all coding parameters are entropy-coded at the encoder and decoded at the decoder. If the coding block flag is 1 and then added to the prediction block, the reconstructed block can be derived by inverse quantizing and inverse-transforming the quantized transform coefficients.

[0018] Picture downscaling and upscaling

[0019] In video coding, the current picture with the current resolution can be rescaled to a different target resolution. A rescaling filter is usually involved in the rescaling process.

[0020] When the target resolution is less than the current resolution, the resizing operation is commonly referred to as downsampling. The resizing filter used in downsampling is typically a low-pass filter, which is used to reduce the risk of introducing aliasing artifacts in the downsampled image. During downsampling, high-frequency details present in the source resolution are sometimes lost.

[0021] When the target resolution is greater than the current resolution, the resizing operation is called upsampling. If the current image has previously been downsampled from another original image at a higher resolution, the upsampling process generally cannot fully recover or reproduce the high-frequency details present in the original image.

[0022] Adaptive video streaming

[0023] In adaptive streaming, a video sequence is typically divided into segments that are 1 to 5 seconds long each. These segments are encoded at various resolutions and qualities such that several segments cover each given time interval. Then, all segments are typically stored on the server side. When a decoder wants to display the video corresponding to a specific time interval, it can select one of the many segments with varying bitrates and qualities. The decoder typically determines which segment to request based on preferences or the resolution of the transmission capabilities. This means that the video quality can be increased or decreased during playback according to the network throughput; when the network throughput is high, the decoder selects high-bitrate segments that offer high quality and / or high resolution; when the network throughput is low, the resolution, quality, and bitrate are decreased, but still provide a smooth playback experience without stopping for buffering.

[0024] In the case of pre-recorded content, the encoding of adaptive streaming can be performed once, and then the segments can be stored on the server to satisfy many decoder playback requests. In this case, the encoding does not have to be real-time. Some adaptive streaming systems allow live content. In this case, the encoder must be able to encode faster than real-time because several segments must be produced within the same time interval. As in the case of pre-recorded content, these segments are then stored on the server, and then several viewers (clients) can request and decode these segments. Some of these clients may have poor network throughput and will request low-bitrate segments within a specific time interval, while other clients can enjoy high network throughput and will request high-bitrate segments within the same time interval.

[0025] In video conferencing, especially when only two users are communicating point-to-point (as opposed to multi-point), the resolution or quality can be adjusted to match the current transmission channel throughput. Compared to adaptive streaming, there is no need to create several segments within the same time interval and thus the encoding speed does not need to be higher than real-time speed: if the bitrate is too high, the decoder can signal this information to the encoder, which can then reduce the quality or resolution of subsequent frames, resulting in a lower bitrate for these future frames.

[0026] VVC and Reference Picture Resampling (RPR)

[0027] Versatile Video Coding (VVC) is a block-based video codec standardized by the International Telecommunication Union - Telecommunication (ITU-T) and the Moving Picture Experts Group (MPEG), which uses both temporal prediction and spatial prediction. Spatial prediction is achieved using intra (I) prediction within the current picture. Temporal prediction is achieved using unidirectional inter (P) prediction or bidirectional inter (B) prediction at the block level based on previously decoded reference pictures. In the encoder, the difference between the original sample data and the predicted sample data (referred to as the residual) is transformed into the frequency domain, quantized, and then entropy coded before being sent together with necessary prediction parameters such as prediction mode and motion vectors. The decoder performs entropy decoding, inverse quantization, and inverse transformation to obtain the residual, and then adds the residual to the intra prediction or inter prediction to reconstruct the picture.

[0028] RPR is a VVC tool that can be used to enable switching between different resolutions in a video bitstream without using intra pictures to encode the start of a new sequence. This provides greater flexibility for adjusting the resolution to control the bitrate, which can be used for, e.g., video conferencing or adaptive streaming. As part of the inter prediction of the current picture, RPR can utilize previously encoded pictures by resizing a previously encoded picture with a resolution lower or higher than the resolution of the current picture to be encoded to the resolution of the current picture.

[0029] Hierarchical B-picture coding structure

[0030] In a configuration commonly referred to as the "random access configuration", intra-coded pictures are positioned at fixed intervals (such as per second). The pictures between intra pictures are typically encoded using the hierarchical B-picture structure.

[0031] The following Figure 9An example of a hierarchical structure of 8 pictures is shown. First, picture 0 is encoded, and then picture 8 is encoded using picture 0 as its reference picture. Then picture 4 is encoded using pictures 8 and 0 as reference pictures. Then pictures 2 and 6 are encoded similarly. Finally, pictures 1, 3, 5, and 7 are encoded. Pictures 1, 3, 5, and 7 are referred to as the highest hierarchical level, pictures 2, 4, and 6 are referred to as the second-highest hierarchical level, and picture 4 is referred to as the second-lowest level and picture 8 is referred to as the lowest level. Generally, pictures 1, 3, 5, and 7 are not used as references for any other pictures. They are called non-reference pictures. In video coding, a hierarchical structure of 16 or 32 pictures is also commonly used.

[0032] QP Control in VVC

[0033] In the sequence parameter set (SPS), the luminance-to-chroma QP mapping table is signaled, and then ChromaQpTable is defined, which has the chroma QP corresponding to the given luminance QP.

[0034] From SPS

[0035]

[0036] sps_joint_cbcr_enabled_flag being equal to 1 specifies that joint coding of chroma residuals is enabled for CLVS. sps_joint_cbcr_enabled_flag being equal to 0 specifies that joint coding of chroma residuals is disabled for CLVS. When absent, the value of sps_joint_cbcr_enabled_flag is inferred to be equal to 0.

[0037] sps_same_qp_table_for_chroma_flag being equal to 1 specifies that only one chroma QP mapping table is signaled, and this table applies to both Cb and Cr residuals, and additionally applies to joint Cb - Cr residuals when sps_joint_cbcr_enabled_flag is equal to 1.

[0038] sps_same_qp_table_for_chroma_flag being equal to 0 specifies that there are two chroma QP mapping tables, one for Cb and one for Cr, and one additionally for joint Cb - Cr when sps_joint_cbcr_enabled_flag is equal to 1. When absent, the value of sps_same_qp_table_for_chroma_flag is inferred to be equal to 1.

[0039] sps_qp_table_start_minus26[i] plus 26 specifies the starting luma and chroma QPs for describing the i-th chroma QP mapping table. The value of sps_qp_table_start_minus26[i] shall be in the range of -26 - QpBdOffset to 36, inclusive of -26 - QpBdOffset and 36. When not present, the value of sps_qp_table_start_minus26[i] is inferred to be equal to 0.

[0040] sps_num_points_in_qp_table_minus1[i] plus 1 specifies the number of points for describing the i-th chroma QP mapping table. The value of sps_num_points_in_qp_table_minus1[i] shall be in the range of 0 to 36 - sps_qp_table_start_minus26[i], inclusive of 0 and 36 - sps_qp_table_start_minus26[i]. When not present, the value of sps_num_points_in_qp_table_minus1[0] is inferred to be equal to 0.

[0041] sps_delta_qp_in_val_minus1[i][j] specifies the incremental value for deriving the input coordinates of the j-th pivot point of the i-th chroma QP mapping table. When not present, the value of sps_delta_qp_in_val_minus1[0][j] is inferred to be equal to 0.

[0042] sps_delta_qp_diff_val[i][j] specifies the incremental value for deriving the output coordinates of the j-th pivot point of the i-th chroma QP mapping table.

[0043] The i-th chroma QP mapping table ChromaQpTable[i] (where i = 0..numQpTables - 1) is derived as follows:

[0044]

[0045] When sps_same_qp_table_for_chroma_flag is equal to 1, ChromaQpTable[1][k] and ChromaQpTable[2][k] are set to be equal to ChromaQpTable[0][k], where k is in the range of -QpBdOffset to 63, inclusive of -QpBdOffset and 63.

[0046] The initial QP can be signaled together with one or more QP offset values for chrominance components in the Picture Parameter Set (PPS), and then refined in the slice and / or picture header.

[0047] From PPS:

[0048]

[0049] pps_init_qp_minus26 plus 26 specifies the SliceQp of each slice that references the PPS Y initial value. When decoding a non-zero value of ph_qp_delta, the SliceQp Y initial value is modified at the picture level, or when decoding a non-zero value of sh_qp_delta, the SliceQp Y initial value is modified at the slice level. The value of pps_init_qp_minus26 shall be in the range of -(26 + QpBdOffset) to +37, inclusive of -(26 + QpBdOffset) and +37.

[0050] From picture header

[0051]

[0052] ph_qp_delta specifies the Qp Y initial value to be used for the coded blocks in the picture until modified by the value of CuQpDeltaVal in the coding unit layer.

[0053] When pps_qp_delta_info_in_ph_flag is equal to 1, the initial value of the quantization parameter SliceQp Y for all slices of the picture Y is derived as follows:

[0054] SliceQp Y = 26 + pps_init_qp_minus26 + ph_qp_delta(2)

[0055] SliceQp Y value shall be in the range of -QpBdOffset to +63, inclusive of -QpBdOffset and +63.

[0056] From slice header

[0057]

[0058] sh_qp_delta specifies the Qp for the coded blocks in the sliceY The initial value until it is modified by the value of CuQpDeltaVal in the coding unit layer.

[0059] When pps_qp_delta_info_in_ph_flag is equal to 0, the Qp of this slice Y The initial value of the quantization parameter SliceQp Y Is derived as follows:

[0060] SliceQp Y = 26 + pps_init_qp_minus26 + sh_qp_delta(3)

[0061] SliceQp Y The value should be in the range of -QpBdOffset to +63, including -QpBdOffset and +63.

[0062] From the transform unit syntax

[0063]

[0064] Luma QP (Qp Y ) is first derived from the slice QP and then predicted based on the luma QP of adjacent blocks. The variable Qp Y Is derived as follows:

[0065] Qp Y = ((qP Y_PRED + CuQpDeltaVal + 64 + 2 * QpBdOffset) % (64 + QpBdOffset)) - QpBdOffset (4)

[0066] Where the variable qP Y_PREV Is derived as follows:

[0067] - If one or more of the following conditions are true, then qP Y_PREV Is set to be equal to SliceQ pY :

[0068] - The current quantization group is the first quantization group in the slice.

[0069] - The current quantization group is the first quantization group in the tile.

[0070] - Otherwise, qP Y_PREV Is set to be equal to the luma quantization parameter Q of the last luma coding unit in the previous quantization group in decoding order PY .

[0071] Luma quantization parameter Q P'YIs derived as follows:

[0072] Qp' Y = Qp Y + QpBdOffset(5)

[0073] The chroma QP is derived as follows:

[0074] The variable qP Cb , qP Cr and qP CbCr are derived as follows:

[0075] qP Chroma = Clip3(-QpBdOffset, 63, Qp Y )(6)

[0076] qP Cb = ChromaQpTable[0][qP Chroma (7)

[0077] qP Cr = ChromaQpTable[1][qP Chroma (8)

[0078] qP CbCr = ChromaQpTable[2][qP Chroma (9)

[0079] The chroma luminance parameters Q P'Cb and Qp' Cr for the Cb and Cr components, as well as the joint Cb - Cr coded Qp' CbCr are derived as follows:

[0080] Qp' Cb = Clip3(-QpBdOffset, 63, qP Cb + pps_cb_qp_offset + sh_cb_qp_offset + CuQpOffset Cb ) + QpBdOffset(10)

[0081] Qp' Cr = Clip3(-QpBdOffset, 63, qP Cr + pps_cr_qp_offset + sh_cr_qp_offset + CuQpOffset Cr ) + QpBdOffset(11)

[0082] Qp' CbCr=Clip3(-QpBdOffset, 63, qP CbCr +pps_joint_cbcr_qp_offset_value+ sh_joint_cbcr_qp_offset + CuQpOffset CbCr ) + QpBdOffset(12)

[0083] Therefore, it can be seen that the luma QP (Qp Y ) is first used to derive the chroma QP via the ChromaQpTable. Then, the chroma Cb QP can be adjusted by pps_cb_qp_offset + sh_cb_qp_offset + CuQpOffsetCb to obtain the final chroma QP for the chroma component Cb, and the chroma Cr QP can be adjusted by pps_cr_qp_offset + sh_cr_qp_offset + CuQpOffsetCr to obtain the final chroma QP for the chroma component Cr.

[0084] The variable CuQpOffset Cb , CuQpOffset Cr and CuQpOffset CbCr are derived as follows:

[0085] - If cu_chroma_qp_offset_flag is equal to 1, the following terms apply:

[0086] CuQpOffset Cb =pps_cb_qp_offset_list[cu_chroma_qp_offset_idx](13)

[0087] CuQpOffset Cr =pps_cr_qp_offset_list[cu_chroma_qp_offset_idx](14)

[0088] CuQpOffset CbCr =pps_joint_cbcr_qp_offset_list[cu_chroma_qp_offset_idx](15)

[0089] - Otherwise (cu_chroma_qp_offset_flag is equal to 0), CuQpOffset Cb , CuQpOffset Cr and CuQpOffset CbCr are all set to be equal to 0.

[0090] pps_cb_qp_offset and pps_cr_qp_offset are chrominance QP offsets that can be defined in PPS, sh_cb_qp_offset and sh_cr_qp_offset are chrominance QP offsets that can be defined in the slice header, and CuQpOffsetCb and CuQpOffsetCr are chrominance QP offsets that can be defined based on blocks. The combined chrominance QP offset can also be a supplement to per-component chrominance QP offset control.

[0091] GOP-based RPR control for encoding resolution

[0092] Under GOP-based control of the encoding resolution, the reduced resolution is encoded at a finer quantization level to allow a similar amount of bits as when encoding at full resolution. For a quarter resolution (0.5 in both dimensions), the QP is reduced by -6 (since this corresponds to halving the quantization step). For encoding at 4 / 9 resolution (2 / 3 in both dimensions), the QP is reduced by -4, and when encoding at 8 / 10 resolution (4 / 5 in both dimensions), the QP is reduced by -2.

[0093] Scalable coding

[0094] VVC and HEVC also support encoding different resolutions with dependencies such that the encoding of a lower resolution can be used to predict a higher resolution, and then the higher resolution is encoded. In scalable coding, it has been shown that by encoding at a lower QP (finer quantization) in the base layer with a quarter resolution than in the enhancement layer with full resolution, the benefits of scalable coding superior to single-layer coding can be achieved in some cases. When encoding at a quarter resolution, the QP difference is similar to the QP difference of GOP-based RPR control. For example, for 2x scalability, the QP in the base layer is approximately -6 lower than the QP in the enhancement layer. Summary of the invention

[0095] There are certain challenges currently. For example, in VVC, a luminance QP to chrominance QP mapping table is used to retrieve the chrominance QP value based on the value of the luminance QP. However, in this mapping table, the chrominance QP value mapped to the luminance QP value is different from the luminance QP value. For example, when the value of the luminance QP is equal to 30, the chrominance QP value corresponding to this luminance QP value can be equal to 32 instead of 30. This is problematic, especially when the resolution of the picture to be encoded and / or decoded changes from one resolution to another. For example, if the resolution of the picture to be encoded and / or decoded changes from one resolution to another, the luminance QP value and the chrominance QP value need to change by a desired amount according to the resolution change to maintain a similar relative bit amount spent on luminance and chrominance when encoding at the other resolution. However, since the new value of the chrominance QP (associated with the new resolution) is determined based on the new value of the luminance QP (associated with the new resolution), the new value of the chrominance QP can be different from changing the old value of the chrominance QP by a desired amount (meaning the new value of the chrominance QP ≠ the old value of the chrominance QP + the desired amount).

[0096] Thus, in one aspect of the embodiments of the present disclosure, a method for encoding or decoding a region of a picture included in a video stream is provided, where the region of the picture can be encoded in either a first resolution and / or a second resolution. The method includes obtaining a first value of a luminance quantization parameter (QP) of a luminance component, where the first value of the luminance QP is associated with the first resolution; the method further includes: based on the first value of the luminance QP, determining a first value of a chrominance QP of a chrominance component, where the first value of the chrominance QP is associated with the first resolution. The method further includes obtaining a second value of the luminance QP, where the second value of the luminance QP is associated with the second resolution. The method further includes: based on the second value of the luminance QP, determining a second value of the chrominance QP, where the second value of the chrominance QP is associated with the second resolution. The method further includes using the second value of the luminance QP and the second value of the chrominance QP to encode or decode the region of the picture at the second resolution, where the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the difference between the first value of the chrominance QP and the second value of the chrominance QP.

[0097] In another aspect, a method for encoding or decoding a region of a picture included in a video stream is provided, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution. The method includes: obtaining a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; based on the first value of the luminance QP, determining a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution; and obtaining a configured luminance QP change value associated with a change from the first resolution to the second resolution. The method further includes: based on the first value of the luminance QP and the configured luminance QP change value, determining a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution. The method further includes: obtaining a configured chrominance QP change value associated with a change from the first resolution to the second resolution, wherein the configured chrominance QP change value is different from the configured luminance QP change value. The method further includes: based on the second value of the luminance QP and / or the configured chrominance QP change value, determining a second value of the chrominance QP, wherein the second value of the chrominance QP is associated with the second resolution. The method further includes using the second value of the luminance QP and the second value of the chrominance QP to encode or decode the region of the picture in the second resolution, wherein a difference between the first value of the luminance QP and the second value of the luminance QP is the same as the configured luminance QP change value, and a difference between the first value of the chrominance QP and the second value of the chrominance QP is the same as the configured chrominance QP change value.

[0098] In another aspect, a method for encoding or decoding a region of a picture included in a video stream is provided, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution. The method includes obtaining a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; the method includes: obtaining a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution. The method includes: determining to encode the video in the second resolution; and based on the determination, retrieving a configured luminance QP change value associated with a change from the first resolution to the second resolution and a configured chrominance QP change value associated with a change from the first resolution to the second resolution. The method further includes: generating a second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value; generating a second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value; and using the second value of the luminance QP and the second value of the chrominance QP to encode or decode the region of the picture in the second resolution.

[0099] In another aspect, a computer program including instructions is provided, which when executed by a processing circuit, causes the processing circuit to execute the method of any one of the above embodiments.

[0100] On the other hand, there is provided a carrier including the computer program of the above embodiment, wherein the carrier is one of an electrical signal, an optical signal, a radio signal, and a computer-readable storage medium.

[0101] On the other hand, there is provided an apparatus for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution. The apparatus is configured to obtain a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; the apparatus is further configured to: based on the first value of the luminance QP, determine a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution; obtain a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution; and based on the second value of the luminance QP, determine a second value of the chrominance QP, wherein the second value of the chrominance QP is associated with the second resolution. The apparatus is further configured to use the second value of the luminance QP and the second value of the chrominance QP to encode or decode the region of the picture in the second resolution, wherein a difference between the first value of the luminance QP and the second value of the luminance QP is the same as a difference between the first value of the chrominance QP and the second value of the chrominance QP.

[0102] On the other hand, there is provided an apparatus for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution. The apparatus is configured to obtain a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; the apparatus is configured to: based on the first value of the luminance QP, determine a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution. The apparatus is configured to: obtain a configured luminance QP change value associated with a change from the first resolution to the second resolution; based on the first value of the luminance QP and the configured luminance QP change value, determine a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution; and obtain a configured chrominance QP change value associated with a change from the first resolution to the second resolution, wherein the configured chrominance QP change value is different from the configured luminance QP change value. The apparatus is configured to: based on the second value of the luminance QP and / or the configured chrominance QP change value, determine a second value of the chrominance QP, wherein the second value of the chrominance QP is associated with the second resolution; and use the second value of the luminance QP and the second value of the chrominance QP to encode or decode the region of the picture in the second resolution, wherein the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the configured luminance QP change value, and the difference between the first value of the chrominance QP and the second value of the chrominance QP is the same as the configured chrominance QP change value.

[0103] On the other hand, there is provided an apparatus for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution. The apparatus is configured to: obtain a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; obtain a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution; and determine to encode the video in the second resolution. The apparatus is further configured to: based on the determination, retrieve a configured luminance QP change value associated with a change from the first resolution to the second resolution and a configured chrominance QP change value associated with a change from the first resolution to the second resolution; generate a second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value; generate a second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value; and use the second value of the luminance QP and the second value of the chrominance QP to encode or decode the region of the picture in the second resolution.

[0104] On the other hand, there is provided an apparatus, the apparatus comprising: a processing circuit; and

[0105] A memory including instructions executable by the processing circuitry, whereby the apparatus is operable to perform the method of any one of the above embodiments.

[0106] Embodiments of the present disclosure allow for generating correct / desired QP values for chrominance components, thereby improving the performance of video encoding and decoding.

[0107] The accompanying drawings, which are included herein and form a part of this specification, illustrate various embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0108] The accompanying drawings, which are included herein and form a part of this specification, illustrate various embodiments.

[0109] Figure 1A A system according to some embodiments is shown

[0110] Figure 1B A system according to some embodiments is shown.

[0111] Figure 1C A system according to some embodiments is shown.

[0112] Figure 2 A schematic block diagram of an encoder according to some embodiments is shown.

[0113] Figure 3 A schematic block diagram of a decoder according to some embodiments is shown.

[0114] Figure 4 An example of a picture included in a video bitstream is shown.

[0115] Figure 5 A process according to some embodiments is shown.

[0116] Figure 6 A process according to some embodiments is shown.

[0117] Figure 7 A process according to some embodiments is shown.

[0118] Figure 8 An apparatus according to some embodiments is shown.

[0119] Figure 9 An example of a hierarchical structure of an 8-picture structure using two reference pictures for each picture is shown and temporal layers 0 to 3 are shown. DETAILED DESCRIPTION

[0120] Figure 1AFIG. 0 shows system 100 according to some embodiments. System 100 includes a first entity 102, a second entity 104, and a network 110. The first entity 102 is configured to send a video stream (also known as "video bitstream", "bitstream", "encoded video") 106 to the second entity 104.

[0121] The first entity 102 can be any computing device (e.g., a network node such as a server) capable of encoding video using an encoder 112 and sending the encoded video to the second entity 104 via the network 110. The second entity 104 can be any computing device (e.g., a network node, a user device such as a mobile phone, a laptop computer, a tablet computer, a vehicle, etc.) capable of receiving the encoded video and decoding the encoded video using a decoder 114. The first entity 102 and the second entity 104 can be a single physical entity or a combination of multiple physical entities. The multiple physical entities can be located at the same location or can be distributed in the cloud.

[0122] In some embodiments, as Figure 1B shown, the first entity 102 is a video stream server 132, and the second entity 104 is a video stream client (e.g., a user equipment (UE) 134). The UE 134 can be any one of a desktop computer, a laptop computer, a tablet computer, a mobile phone, or any other computing device. The video stream server 132 is capable of sending a video bitstream 136 (e.g., a YouTube™ video stream) to the video stream client 134. Upon receiving the video bitstream 136, the UE 134 can decode the received video bitstream 136, thereby generating and displaying the video for the video stream.

[0123] In other embodiments, as Figure 1C shown, the first entity 102 and the second entity 104 are a first UE 152 and a second UE 154. For example, the first UE 152 can be a provider of a video conference session or a caller in a video chat, and the second UE 154 can be a responder to the video conference session or a responder to the video chat. In the Figure 1C embodiment shown, the first UE 152 is capable of sending a video bitstream 156 for a video conference (e.g., Zoom™, Skype™, MS Teams™, etc.) or a video chat (e.g., Facetime™) to the second UE 154. Upon receiving the video bitstream 156, the second UE 154 can decode the received video bitstream 156, thereby generating and displaying the video for the video conference session or the video chat.

[0124] Figure 2FIG. 0 shows a schematic block diagram of an encoder 112 according to some embodiments. The encoder 112 is configured to encode blocks of pixel values (hereinafter referred to as "blocks") in video frames of a source video 202. In the encoder 112, a motion estimator 250 performs motion estimation based on blocks that have been provided in the same frame or a previous frame to predict a current block (e.g., a block included in a video frame of the source video 202). In the case of inter-frame prediction, the result of the motion estimation is a motion or displacement vector associated with a reference block. The motion vector is used by a motion compensator 250 to output an inter-frame prediction of the block.

[0125] An intra-frame predictor 249 calculates an intra-frame prediction of the current block. The outputs from the motion estimator / compensator 250 and the intra-frame predictor 249 are input to a selector 251, which selects either an intra-frame prediction or an inter-frame prediction for the current block. The output from the selector 251 is input to an error calculator in the form of an adder 241, which also receives the pixel values of the current block. The adder 241 calculates and outputs a residual that is the difference in pixel values between the block and its prediction. This error is transformed in a transformer 242 (such as by a discrete cosine transform) and quantized by a quantizer 243 (thereby generating a value of a QP parameter), and then encoded in an encoder 244 (such as by an entropy encoder). In inter-frame coding, the estimated motion vector is taken to the encoder 244 to produce an encoded representation of the current block.

[0126] The transformed and quantized residual of the current block is also provided to an inverse quantizer 245 and an inverse transformer 246 to retrieve the original residual. This error is added by an adder 247 to the block prediction output from the motion compensator 250 or the intra-frame predictor 249 to create a reconstructed sample block 280 that can be used for prediction and encoding of the next block. The reconstructed sample block 280 is processed by a filter 230 in order to perform filtering to counteract any blocking artifacts. The output from the filter 230 (e.g., a neural network-based filter), i.e., output data 290, is then temporarily stored in a frame buffer 248, in which the output can be used by the intra-frame predictor 249 and the motion estimator / compensator 250.

[0127] In some embodiments, the encoder 112 may further include a sample adaptive offset (SAO) unit 270 and / or an adaptive loop filter (ALF) 272. The SAO unit 270 and the ALF 272 may be configured to: receive the output data 290 from the filter 230, perform additional filtering on the output data 290, and provide the filtered output data to the buffer 248.

[0128] Although in Figure 2In the illustrated embodiment, filter 230 is disposed between SAO unit 270 and adder 247. However, in other embodiments, filter 230 may replace SAO unit 270 and / or ALF 272. Alternatively, in other embodiments, filter 230 may be disposed between buffer 248 and motion compensator 250. Additionally, in some embodiments, a deblocking filter (not shown) may be disposed between filter 230 and adder 247 such that the reconstructed sample block 280 undergoes deblocking processing and is then provided to filter 230. Further, in other embodiments, filter 230 may act as a deblocking filter.

[0129] Figure 3 FIG. 4 is a schematic block diagram of decoder 114 according to some embodiments. Decoder 114 includes a decoder 361 (such as an entropy decoder) that decodes the encoded representation of a block to obtain a set of quantized and transformed residuals. These residuals are dequantized in inverse quantizer 362 and inverse-transformed by inverse transform 363 to obtain a set of residuals. These residuals are added to the pixel values of the reference block in adder 364. Depending on whether inter-frame prediction or intra-frame prediction is performed, the reference block is determined by motion estimator / compensator 367 or intra-frame predictor 366.

[0130] Accordingly, selector 368 is interconnected to adder 364 and motion estimator / compensator 367 and intra-frame predictor 366. The resulting decoded block 380 output from adder 364 is input to filter unit 330 to filter any blocking artifacts. The filtered block 390 is output from filter 330 and is further preferably temporarily provided to frame buffer 365 and can be used as a reference block for subsequent blocks to be decoded.

[0131] Frame buffer (e.g., decoded picture buffer (DPB)) 365 is thus connected to motion estimator / compensator 367 such that the stored pixel blocks are available to motion estimator / compensator 367. The output of adder 364 is preferably also provided to intra-frame predictor 366 to be used as an unfiltered reference block.

[0132] In some embodiments, decoder 114 may include SAO unit 380 and / or ALF 382. SAO unit 380 and ALF 382 may be configured to receive output data 390 from filter 330, perform additional filtering on output data 390, and provide the filtered output data to buffer 365.

[0133] Although in Figure 3In the illustrated embodiment, the filter 330 is disposed between the SAO unit 380 and the adder 364. However, in other embodiments, the filter 330 may replace the SAO unit 380 and / or the ALF 382. Alternatively, in other embodiments, the filter 330 may be disposed between the buffer 365 and the motion compensator 367. In addition, in some embodiments, a deblocking filter (not shown) may be disposed between the filter 330 and the adder 364 such that the reconstructed sample block 380 undergoes deblocking processing and is then provided to the filter 330.

[0134] As discussed above, when encoding a video or decoding a video bitstream, a quantization parameter (QP) may be used (e.g., the quantizer 243 included in the encoder 112 and the inverse quantizer 362 included in the decoder 114). The value of the QP may be set differently depending on the resolution of at least one region of the picture for which encoding or decoding using the value of the QP is to be applied. Examples of at least one region of the picture include the entire picture, slices, etc. For ease of explanation, the embodiments of the present disclosure are generally described with respect to the entire picture. However, these embodiments are equally applicable to any region within the picture (which means that, in the following description, the word "picture" may be replaced by "region of the picture" such as a slice).

[0135] In Figure 1B In the illustrated scenario, if the video stream server 132 wants to send a video stream 136 including a picture with a resolution of 4K (3840x2160) to the video stream client 134, the QP value of the luminance component is set to 36 and the QP value of the chrominance component is set to 36. On the other hand, if the video stream server 132 wants to send a video stream 136 including a picture with a resolution of 1920x2160 to the video stream client 134, the QP value of the luminance component is set to 30 and the QP value of the chrominance component is set to 30. In the present disclosure, the QP of the luminance component is referred to as the luminance QP, and the QP of the chrominance component is referred to as the chrominance QP.

[0136] Since the desired (configured or ideal) values of the luminance and chrominance QPs may vary depending on the resolution of the picture (for which encoding or decoding using the value of the QP is to be applied), when the resolution of the picture included in the video stream 136 changes from one resolution (e.g., 4K) to another resolution (e.g., 1920x2160), it is desirable to adjust the values of the luminance QP and the chrominance QP accordingly.

[0137] However, there is a scenario where even if the resolution of the pictures included in the video stream 136 changes from one resolution (e.g., 4K) to another resolution (e.g., 1920x2160), the value of the chrominance QP cannot be correctly changed. For example, in the prior art, by using mapping data (e.g., a mapping table), the value of the chrominance QP for the current picture resolution is determined based on the value of the luminance QP for the current picture resolution. The concept of the mapping table is shown below.

[0138]

[0139] However, as shown above, the mapping table may not output the expected value of the chrominance QP for a given resolution. For example, although the expected value of the chrominance QP for a resolution of 1920x2160 is 30, the mapping table may output 32, which is a non-expected value of the chrominance QP for this resolution.

[0140] Therefore, in an embodiment of the present disclosure, the encoder 112 or the decoder 114 is configured to generate an expected value of the chrominance QP for a given picture resolution. For example, in the above scenario, according to an embodiment of the present disclosure, the encoder 112 or the decoder 114 is configured to generate 30 (instead of 32) as the value of the chrominance QP for a resolution of 1920x2160.

[0141] Figure 4 A first picture 402 having a first resolution A (e.g., 4K (i.e., 3840x2160)) and a second picture 406 having a second resolution B (e.g., 1920x2160) are shown. The first picture 402 may include a region 404 (e.g., a slice), and the second picture 406 may include a region 408 (e.g., a slice). Each of the first picture 402 and the second picture 406 may include different color components. Examples of color components are Y (luminance), Cb (chrominance B), and Cr (chrominance R).

[0142] The first picture 402 or the region 404 has an expected bit rate given by a first expected value of the luminance QP or a first expected value of the chrominance QP. Similarly, the second picture 406 or the region 408 has an expected bit rate given by a second expected value of the luminance QP or a second expected value of the chrominance QP. The difference (desiredQPchange) between the first expected value of the luminance QP and the second expected value of the luminance QP may correspond to a first expected QP difference (also known as an expected QP change value or a configured QP change value).

[0143] Similarly, the difference between the first expected value of the chroma QP and the second expected value of the chroma QP may correspond to a second expected QP difference. In some embodiments, the first expected QP difference and the second expected QP difference are the same. However, in other embodiments, the first expected QP difference and the second expected QP difference are different.

[0144] When the second resolution is 1 / 2x in two dimensions, 2 / 3x in two dimensions, and 4 / 5x in two dimensions compared to the first resolution, examples of the expected QP difference (when switching from the first resolution A to the second resolution B) are -6, -4, and -2. Similarly, when the second resolution is 2x in two dimensions, 1.5x in two dimensions, or 1.25x in two dimensions compared to the first resolution, the expected QP difference can be 6, 4, and 2. As described above, the above values are provided as examples, and other expected QP differences can be used.

[0145] Return reference Figure 1B , assume that the video stream server 132 sends a video stream 136 to the video stream client 134, and the video stream 136 includes a first picture 402 with a resolution A (e.g., 4K). The video stream 136 may include a first expected value of the luminance QP for the resolution A (e.g., 36).

[0146] Upon receiving the video stream 136, the decoder 114 may use a mapping table (e.g., provided below) to find the mapped value of the chroma QP corresponding to the first expected value of the luminance QP (e.g., 36) (e.g., 36).

[0147]

[0148] Then, the decoder 114 may decode the first picture 402 or at least the region 404 included in the first picture 402 using the first expected value of the luminance QP and the mapped value of the chroma QP.

[0149] Let us further assume that the operation of the video stream server 132 has changed such that the video stream server 132 now sends a video stream 136 to the video stream client 134, and the video stream 136 includes a second picture 406 with a resolution B (1902x2160). The video stream 136 now includes a second expected value of the luminance QP corresponding to the resolution B (e.g., 30).

[0150] Upon receiving the video stream 136, the decoder 114 may use a mapping table (e.g., provided below) to find the mapped value of the chroma QP corresponding to the second expected value of the luminance QP (e.g., 30) (e.g., 32).

[0151]

[0152] However, the mapped value of the chrominance QP obtained (e.g., 32) may not be the expected value of the chrominance QP for resolution B (e.g., 1920x2160). Here, the mapped value of the chrominance QP is also referred to as the non-expected value of the chrominance QP. In other words, the encoding operation performed by the encoder 112 using the mapped value of the chrominance QP or the decoding operation performed by the decoder 114 using the mapped value of the chrominance QP may not be as good as the encoding operation performed by the encoder 112 using the second expected value of the chrominance QP or the decoding operation performed by the decoder 114 using the second expected value of the chrominance QP.

[0153] Thus, in some embodiments, the encoder 112 or the decoder 114 may be configured to: generate a second expected value of the chrominance QP for resolution B (e.g., 30), even if the mapped value of the chrominance QP is not equal to the second expected value.

[0154] More specifically, in some embodiments, the encoder 112 included in the video stream server 132 may be configured to include a chrominance QP offset value in the bitstream 136, which can be used to convert the mapped value of the chrominance QP for resolution B (e.g., 32) to the second expected value of the chrominance QP (e.g., 30).

[0155] When the resolution of the picture included in the bitstream 136 changes from resolution A (e.g., 4K) to resolution B (1920x2160), there are various ways to calculate the chrominance QP offset value to be used. In one example, the chrominance QP offset value can be calculated as follows: chrominance QP offset value (e.g., -2) = the first expected QP value of the chrominance QP for resolution A (e.g., 36) - the mapped QP value of the chrominance QP for resolution B (e.g., 32) + the desired QP change value ("desiredQPchange") (e.g., -6). In some embodiments, the desired QP change value can be set to be equal to the first expected QP value of the luma QP for resolution A (e.g., 36) - the second expected QP value of the luma QP for resolution B (e.g., 30).

[0156] After calculating the chrominance QP offset value, the encoder 112 may send the chrominance QP offset value to the decoder 114. In some embodiments, the chrominance QP offset value may be included in the bitstream 136. The offset value can be signaled for Cb and Cr by enabling the slice chrominance QP offset flag (setting pps_slice_chroma_qp_offsets_present_flag to 1), or the offset value can be signaled as a slice chrominance QP change, and then the chrominance QP offset (sh_cb_qp_offset, sh_cr_qp_offset) is set.

[0157] After receiving the bitstream 136, which includes a second expected value of the luminance QP for resolution B, a chrominance QP offset value, and / or an expected QP change value, the decoder 114 may calculate a second expected value of the chrominance QP for resolution B based on the second expected value of the luminance QP for resolution B and the chrominance QP offset value. More specifically, first, the decoder 114 may determine a mapped value of the chrominance QP for resolution B (e.g., 32) based on the second expected value of the luminance QP for resolution B (e.g., 30) by using a mapping table (e.g., provided below) for resolution B (e.g., 1920x2160).

[0158]

[0159] After determining the mapped value of the chrominance QP for resolution B (e.g., 32), the decoder 114 may calculate a second expected value of the chrominance QP for resolution B (e.g., 30) based on the mapped value of the chrominance QP for resolution B and the chrominance QP offset value. For example, the second expected value of the chrominance QP for resolution B may be calculated as follows: the second expected value of the chrominance QP for resolution B (e.g., 30) = the mapped value of the chrominance QP for resolution B (e.g., 32) + the chrominance QP offset value (e.g., -2).

[0160] After calculating the second expected value of the chrominance QP for resolution B, the decoder 114 may decode the second picture 406 or at least the region 408 included in the second picture 406 by using the second expected value of the chrominance QP for resolution B (e.g., 30) and the second expected value of the luminance QP for resolution B (e.g., 30).

[0161] Code examples of an encoder that performs group of pictures (GOP)-based reference picture resampling (RPR) for reduced resolutions 0.5, 2 / 3, and 4.5 (in both dimensions) are provided below:

[0162]

[0163]

[0164]

[0165] In the above embodiments, a common expected QP change value is used for both the luminance component and the chrominance component. However, in other embodiments, two different expected QP change values may be provided for the luminance component and the chrominance component (e.g., in a case where it is desired to increase the chrominance component more than the luminance component by changing the QP value more). An example of different expected QP change values for the luminance component and the chrominance component is shown below.

[0166]

[0167] In some embodiments, the encoder 112 or the decoder 114 may determine how to generate a second expected value of the luminance QP and the chrominance QP based only on the resolution of a picture or a region of a picture included in or to be included in the bitstream 136. For example, the encoder 112 or the decoder 114 may detect that the resolution of the picture has changed from resolution A to resolution B, and upon making this detection, the encoder 112 or the decoder 114 may determine an expected QP change value of the luminance QP and / or the chrominance QP. There are different ways for the encoder 112 or the decoder 114 to determine the expected QP change value of the luminance QP and / or the chrominance QP.

[0168] In one example, a mapping table (such as the mapping table provided above) may be stored in the encoder 112 or the decoder 114, and the encoder 112 or the decoder 114 may use this mapping table to retrieve the expected QP change values of the luminance QP and the chrominance QP based on the amount of change in the picture resolution or the region resolution, and use the retrieved values to change the QP values.

[0169] Note that in the case of determining the expected QP change values of the luminance QP and the chrominance QP based only on detecting a change in the resolution of a region of a picture, as described above, the expected QP change values are applied to the luminance QP value and / or the chrominance QP value for that region.

[0170] More specifically, as described above, although the embodiments of the present disclosure are illustrated for an entire picture, these embodiments are equally applicable to a part (region) of a picture (e.g., a slice or a block of a picture such as a CU or a CTB). In the case where an embodiment is applied to a region of a picture, different luminance QP values may be provided for different regions of the same picture, and different chrominance QP values may be provided for different regions of the same picture. For example, a picture may include a first region having a first size (i.e., a first resolution) and a second region having a second size (i.e., a second resolution). In such a case, a first value of the luminance QP and a first value of the chrominance QP may be provided for the first region, and a second value of the luminance QP and a second value of the chrominance QP may be provided for the second region. In such a case, the expected QP change values discussed above are derived based only on the resolution changes of the respective parts of the entire picture.

[0171] In some embodiments, encoding or decoding the first picture 402, at least the region 404 in the first picture 402, the second picture 406, or at least the region 408 in the second picture 406 using the expected value of the luminance QP and the expected value of the chrominance QP may be performed for reference picture resampling (RPR) or scalable coding.

[0172] Figure 5 A process 500 for encoding or decoding a region of a picture included in a video stream is shown, where the region of the picture can be encoded in either a first resolution and / or a second resolution. Process 500 may start at step s502. Step s502 includes obtaining a first value of a luminance quantization parameter (QP) of a luminance component, where the first value of the luminance QP is associated with the first resolution. Step s504 includes determining, based on the first value of the luminance QP, a first value of a chrominance QP of a chrominance component, where the first value of the chrominance QP is associated with the first resolution. Step s506 includes obtaining a second value of the luminance QP, where the second value of the luminance QP is associated with the second resolution. Step s508 includes determining, based on the second value of the luminance QP, a second value of the chrominance QP, where the second value of the chrominance QP is associated with the second resolution. Step s510 includes encoding or decoding the region of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP, where the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the difference between the first value of the chrominance QP and the second value of the chrominance QP.

[0173] In some embodiments, the region of the picture is the entire picture or a part of the picture.

[0174] In some embodiments, process 500 includes obtaining a chrominance QP offset value for adjusting the value of the chrominance QP, where the second value of the chrominance QP associated with the second resolution is determined based on the chrominance QP offset value.

[0175] In some embodiments, determining the second value of the chrominance QP includes retrieving, based on the second value of the luminance QP, a mapped value of the chrominance QP that is mapped to the second value of the luminance QP using mapping data; and combining the mapped value of the chrominance QP and the chrominance QP offset value to generate the second value of the chrominance QP.

[0176] In some embodiments, the second value of the chrominance QP = the mapped value of the chrominance QP + the chrominance QP offset value.

[0177] In some embodiments, the chrominance QP offset value is included in a picture header or a slice header of the video stream.

[0178] In some embodiments, the region of the picture is a first part of the picture, the chrominance QP offset value is only for the first part of the picture, the picture includes a second part, and a different QP offset value is provided for the second part of the picture.

[0179] In some embodiments, the chrominance QP offset value is set such that: chrominance QP offset value = first value of chrominance QP - mapped value of chrominance QP + configured QP change value, and the configured QP change value is equal to the difference between the first value of the luminance QP and the second value of the luminance QP.

[0180] In some embodiments, when the second resolution is , , or times that of the first resolution, the differences between the first value of the luminance QP and the second value of the luminance QP are respectively set to -6, -4, or -2.

[0181] In some embodiments, when the second resolution is 2 times, 1.5 times, or 1.25 times that of the first resolution, the differences between the first value of the luminance QP and the second value of the luminance QP are respectively set to 6, 4, or 2.

[0182] In some embodiments, the picture is at least partially predicted by reference picture resampling (RPR) or encoded using scalable coding.

[0183] Figure 6 Process 600 for encoding or decoding a region of a picture included in a video stream is shown, where the region of the picture can be encoded in either the first resolution and / or the second resolution. Process 600 may start at step s602. Step s602 includes obtaining a first value of the luminance quantization parameter (QP) of the luminance component, where the first value of the luminance QP is associated with the first resolution. Step s604 includes determining, based on the first value of the luminance QP, a first value of the chrominance QP of the chrominance component, where the first value of the chrominance QP is associated with the first resolution. Step s606 includes obtaining a configured luminance QP change value of the luminance QP associated with the change from the first resolution to the second resolution. Step s608 includes determining, based on the first value of the luminance QP and the configured luminance QP change value, a second value of the luminance QP, where the second value of the luminance QP is associated with the second resolution. Step s610 includes obtaining a configured chrominance QP change value of the chrominance QP associated with the change from the first resolution to the second resolution, where the configured chrominance QP change value is different from the configured luminance QP change value. Step s612 includes determining, based on the second value of the luminance QP and / or the configured chrominance QP change value, a second value of the chrominance QP, where the second value of the chrominance QP is associated with the second resolution. Step s614 includes encoding or decoding the region of the picture at the second resolution using the second value of the luminance QP and the second value of the chrominance QP, where the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the configured luminance QP change value, and the difference between the first value of the chrominance QP and the second value of the chrominance QP is the same as the configured chrominance QP change value.

[0184] In some embodiments, the region of the picture is the entire picture or a part of the picture.

[0185] In some embodiments, process 600 includes obtaining a chrominance QP offset value for adjusting the value of chrominance QP, wherein a second value of chrominance QP associated with a second resolution is determined based on the chrominance QP offset value.

[0186] In some embodiments, determining the second value of chrominance QP includes: retrieving a mapped value of chrominance QP mapped to the second value of luminance QP based on the second value of luminance QP using mapping data; and combining the mapped value of chrominance QP and the chrominance QP offset value to generate the second value of chrominance QP.

[0187] In some embodiments, the second value of chrominance QP = the mapped value of chrominance QP + the chrominance QP offset value.

[0188] In some embodiments, the chrominance QP offset value is included in the picture header or slice header of the video stream.

[0189] In some embodiments, the region of the picture is the first part of the picture, the chrominance QP offset value is only for the first part of the picture, the picture includes a second part, and a different QP offset value is provided for the second part of the picture.

[0190] In some embodiments, the chrominance QP offset value is set such that the chrominance QP offset value = the first value of chrominance QP - the mapped value of chrominance QP + the configured chrominance QP change value.

[0191] In some embodiments, when the second resolution is , , or of the first resolution, the configured chrominance QP change values are -5, -3, or -1 respectively, and when the second resolution is , , or of the first resolution, the configured luminance QP change values are -6, -4, or -2 respectively.

[0192] In some embodiments, when the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured chrominance QP change values are 5, 3, or 1 respectively, and when the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured luminance QP change values are 6, 4, or 2 respectively.

[0193] In some embodiments, the picture is at least partially predicted by reference picture resampling (RPR) or encoded using scalable coding.

[0194] Figure 7 A process for encoding or decoding an image region included in a video stream is shown, where the region of the picture can be encoded at either a first resolution and / or a second resolution. Process 700 may begin at step s702. Step s702 includes obtaining a first value of the luminance quantization parameter (QP) of the luminance component, where the first value of the luminance QP is associated with the first resolution. Step s702 includes: obtaining a first value of the chrominance QP of the chrominance component, where the first value of the chrominance QP is associated with the first resolution. Step s706 includes determining to encode the video at the second resolution. Step s708 includes: based on this determination, retrieving a configured luminance QP change value associated with the change from the first resolution to the second resolution and a configured chrominance QP change value associated with the change from the first resolution to the second resolution; Step s710 includes generating a second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value. Step s712 includes generating a second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value. Step s714 includes encoding or decoding the region of the picture at the second resolution using the second value of the luminance QP and the second value of the chrominance QP.

[0195] In some embodiments, the region of the picture is the entire picture or a part of the picture.

[0196] In some embodiments, the configured luminance QP change value is the same as the configured chrominance QP change value, and when the second resolution is , , or of the first resolution, the configured luminance QP change values are -6, -4, or -2 respectively.

[0197] In some embodiments, the configured luminance QP change value is the same as the configured chrominance QP change value, and when the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured luminance QP change values are 6, 4, or 2 respectively.

[0198] In some embodiments, when the second resolution is , , or of the first resolution, the configured chrominance QP change values are -5, -3, or -1 respectively, and when the second resolution is , , or of the first resolution, the configured luminance QP change values are -6, -4, or -2 respectively.

[0199] In some embodiments, when the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured chroma QP change values are 5, 3, or 1 respectively, and when the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured luma QP change values are 6, 4, or 2 respectively.

[0200] In some embodiments, the picture is predicted at least in part by reference picture resampling (RPR) or is coded using scalable coding.

[0201] Figure 8 is a block diagram of apparatus 800 for implementing encoder 112, decoder 114, or components included in encoder 112 or decoder 114 (e.g., Figure 2 249, 250 as shown, Figure 3 366, 367 as shown). When apparatus 800 implements a decoder, apparatus 800 may be referred to as "decoding apparatus 800", and when apparatus 800 implements an encoder, apparatus 800 may be referred to as "encoding apparatus 800". As Figure 8As shown, apparatus 800 may include: processing circuitry (PC) 802, which may include one or more processors (P) 855 (e.g., general microprocessors and / or one or more other processors such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), etc.), which may be co-located in a single housing or a single data center or may be geographically distributed (i.e., apparatus 800 may be a distributed computing apparatus); at least one network interface 848, which includes a transmitter (Tx) 845 and a receiver (Rx) 847 for enabling apparatus 800 to send data to and receive data from other nodes connected to network 110 (e.g., an Internet Protocol (IP) network), where network interface 848 is (directly or indirectly) connected to network 110 (e.g., network interface 848 may be wirelessly connected to network 110, in which case network interface 448 is connected to an antenna arrangement); and a storage unit (aka "data storage system") 808, which may include one or more non-volatile storage devices and / or one or more volatile storage devices. In embodiments where PC 802 includes a programmable processor, a computer program product (CPP) 841 may be provided. CPP 841 includes a computer-readable medium (CRM) 842 that stores a computer program (CP) 843 including computer-readable instructions (CRI) 844. CRM 842 may be a non-transitory computer-readable medium such as a magnetic medium (e.g., a hard disk), an optical medium, a storage device (e.g., random access memory, flash memory), etc. In some embodiments, CRI 844 of computer program 843 is configured such that when executed by PC 802, CRI causes apparatus 800 to perform the steps described herein (e.g., the steps described herein with reference to the flowcharts). In other embodiments, apparatus 800 may be configured to perform the steps described herein without code. That is, for example, PC 802 may consist of only one or more ASICs. Thus, the features of the embodiments described herein may be implemented in hardware and / or software fashion.

[0202] Overview of Embodiments

[0203] A1. A method (500) for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture may be encoded in either a first resolution and / or a second resolution, the method comprising:

[0204] obtaining (s502) a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution;

[0205] Determine (s504) a first value of the chrominance QP for the chrominance component based on the first value of the luminance QP, wherein the first value of the chrominance QP is associated with the first resolution;

[0206] Obtain (s506) a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution;

[0207] Determine (s508) a second value of the chrominance QP based on the second value of the luminance QP, wherein the second value of the chrominance QP is associated with the second resolution; and

[0208] Encode or decode (s510) the region of the picture at the second resolution using the second value of the luminance QP and the second value of the chrominance QP, wherein

[0209] the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the difference between the first value of the chrominance QP and the second value of the chrominance QP.

[0210] A1a. The method according to embodiment A1, wherein the region of the picture is the entire picture or a part of the picture.

[0211] A2. The method according to embodiment A1 or A1a, comprising:

[0212] Obtain a chrominance QP offset value for adjusting the value of the chrominance QP, wherein

[0213] the second value of the chrominance QP associated with the second resolution is determined based on the chrominance QP offset value.

[0214] A3. The method according to embodiment A2, wherein determining the second value of the chrominance QP comprises:

[0215] Based on the second value of the luminance QP, use mapping data to retrieve a mapped value of the chrominance QP, the mapped value being mapped to the second value of the luminance QP; and

[0216] Combine the mapped value of the chrominance QP with the chrominance QP offset value to generate the second value of the chrominance QP.

[0217] A4. The method according to embodiment A2 or A3, wherein the second value of the chrominance QP = the mapped value of the chrominance QP + the chrominance QP offset value.

[0218] A5. The method according to any one of embodiments A2 to A4, wherein the chrominance QP offset value is included in the picture header or slice header of the video stream.

[0219] A5a. A method according to any one of embodiments A2 to A5, wherein,

[0220] The region of the picture is the first part of the picture,

[0221] The chrominance QP offset value is only applicable to the first part of the picture,

[0222] The picture includes a second part, and

[0223] A different QP offset value is provided for the second part of the picture.

[0224] A6. A method according to any one of embodiments A2 to A5a, wherein,

[0225] The chrominance QP offset value is set such that the chrominance QP offset value = the first value of the chrominance QP - the mapped value of the chrominance QP + the configured QP change value, and

[0226] The configured QP change value is equal to the difference between the first value of the luminance QP and the second value of the luminance QP.

[0227] A7. A method according to any one of embodiments A1 to A6, wherein, when the second resolution is 、 、or of the first resolution, the difference between the first value of the luminance QP and the second value of the luminance QP is set to -6, -4 or -2 respectively.

[0228] A8. A method according to any one of embodiments A1 to A6, wherein, when the second resolution is 2 times, 1.5 times or 1.25 times the first resolution, the difference between the first value of the luminance QP and the second value of the luminance QP is set to 6, 4 or 2 respectively.

[0229] A9. A method according to any one of embodiments A1 to A8, wherein the picture is at least partially predicted by reference picture resampling (RPR) or encoded using scalable coding.

[0230] B1. A method (600) for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution, the method comprising:

[0231] Obtaining (s602) a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution;

[0232] Determine (s604) a first value of the chrominance QP for the chrominance component based on the first value of the luminance QP, wherein the first value of the chrominance QP is associated with the first resolution;

[0233] Obtain (s606) a configured luminance QP change value of the luminance QP associated with the change from the first resolution to the second resolution;

[0234] Determine (s608) a second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value, wherein the second value of the luminance QP is associated with the second resolution;

[0235] Obtain (s610) a configured chrominance QP change value of the chrominance QP associated with the change from the first resolution to the second resolution, wherein the configured chrominance QP change value is different from the configured luminance QP change value;

[0236] Determine (s612) a second value of the chrominance QP based on the second value of the luminance QP and / or the configured chrominance QP change value, wherein the second value of the chrominance QP is associated with the second resolution; and

[0237] Encode or decode (s614) the region of the picture at the second resolution using the second value of the luminance QP and the second value of the chrominance QP, wherein

[0238] the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the configured luminance QP change value, and

[0239] the difference between the first value of the chrominance QP and the second value of the chrominance QP is the same as the configured chrominance QP change value.

[0240] B1a. A method according to embodiment B1, wherein the region of the picture is the entire picture or a part of the picture.

[0241] B2. A method according to embodiment B1 or B1a, comprising:

[0242] Obtain a chrominance QP offset value for adjusting the value of the chrominance QP, wherein

[0243] the second value of the chrominance QP associated with the second resolution is determined based on the chrominance QP offset value.

[0244] B3. A method according to embodiment B2, wherein determining the second value of the chrominance QP comprises:

[0245] Using the mapping data, retrieve a mapped value of the chrominance QP that is mapped to the second value of the luminance QP, based on the second value of the luminance QP; and

[0246] Combine the mapped value of the chrominance QP with the chrominance QP offset value to generate a second value of the chrominance QP.

[0247] B4. The method according to embodiment B2 or B3, wherein the second value of the chrominance QP = the mapped value of the chrominance QP + the chrominance QP offset value.

[0248] B5. The method according to any one of embodiments B2 to B4, wherein the chrominance QP offset value is included in a picture header or a slice header of the video stream.

[0249] B5a. The method according to any one of embodiments B2 to B5, wherein

[0250] the region of the picture is a first part of the picture,

[0251] the chrominance QP offset value is only applicable to the first part of the picture,

[0252] the picture includes a second part, and

[0253] a different QP offset value is provided for the second part of the picture.

[0254] B6. The method according to any one of embodiments B2 to B5a, wherein

[0255] the chrominance QP offset value is set such that the chrominance QP offset value = the first value of the chrominance QP - the mapped value of the chrominance QP + a configured chrominance QP change value, and

[0256] B7. The method according to any one of embodiments B1 to B7, wherein

[0257] when the second resolution is 、 、or of the first resolution, the configured chrominance QP change values are -5, -3, or -1 respectively, and

[0258] when the second resolution is 、 or of the first resolution, the configured luminance QP change values are -6, -4, or -2 respectively.

[0259] B8. The method according to any one of embodiments B1 to B6, wherein

[0260] When the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured chrominance QP change values are 5, 3, or 1 respectively, and

[0261] When the second resolution is 2 times, 1.5 times, or 1.25 times the first resolution, the configured luminance QP change values are 6, 4, or 2 respectively.

[0262] B9. The method according to any one of embodiments B1 to B8, wherein the picture is at least partially predicted by reference picture resampling (RPR) or encoded using scalable coding.

[0263] C1. A method (700) for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution, the method comprising:

[0264] Obtaining (s702) a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution;

[0265] Obtaining (s704) a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution;

[0266] Determining (s706) to encode the video in the second resolution;

[0267] Based on the determination, retrieving (s708) a configured luminance QP change value associated with the change from the first resolution to the second resolution and a configured chrominance QP change value associated with the change from the first resolution to the second resolution;

[0268] Generating (s710) a second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value;

[0269] Generating (s712) a second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value; and

[0270] Encoding or decoding (s714) the region of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP.

[0271] C1a. The method according to embodiment C1, wherein the region of the picture is the entire picture or a part of the picture.

[0272] The method according to embodiment C1 or C1a, wherein,

[0273] the configured luminance QP change value is the same as the configured chrominance QP change value, and

[0274] when the second resolution is , or of the first resolution, the configured luminance QP change values are -6, -4, or -2, respectively.

[0275] The method according to embodiment C1 or C1a, wherein,

[0276] the configured luminance QP change value is the same as the configured chrominance QP change value, and

[0277] when the second resolution is 2 times, 1.5 times, or 1.25 times that of the first resolution, the configured luminance QP change values are 6, 4, or 2, respectively.

[0278] The method according to embodiment C1 or C1a, wherein,

[0279] when the second resolution is , , or of the first resolution, the configured chrominance QP change values are -5, -3, or -1, respectively, and

[0280] when the second resolution is , or of the first resolution, the configured luminance QP change values are -6, -4, or -2, respectively.

[0281] The method according to embodiment C1 or C1a, wherein,

[0282] when the second resolution is 2 times, 1.5 times, or 1.25 times that of the first resolution, the configured chrominance QP change values are 5, 3, or 1, respectively, and

[0283] when the second resolution is 2 times, 1.5 times, or 1.25 times that of the first resolution, the configured luminance QP change values are 6, 4, or 2, respectively.

[0284] The method according to any one of embodiments C1 to C5, wherein the picture is predicted at least in part by reference picture resampling (RPR) or encoded using scalable coding.

[0285] D1. A computer program (800) comprising instructions (844) which, when executed by a processing circuit (802), cause the processing circuit to perform a method according to any one of embodiments A1 to C6.

[0286] D2. A carrier containing the computer program according to embodiment D1, wherein the carrier is one of an electrical signal, an optical signal, a radio signal, and a computer-readable storage medium.

[0287] E1. A device (800) for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution, and the device is configured to:

[0288] obtain (s502) a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution;

[0289] based on the first value of the luminance QP, determine (s504) a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution;

[0290] obtain (s506) a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution;

[0291] based on the second value of the luminance QP, determine (s508) a second value of the chrominance QP, wherein the second value of the chrominance QP is associated with the second resolution; and

[0292] encode or decode (s510) the region of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP, wherein

[0293] the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the difference between the first value of the chrominance QP and the second value of the chrominance QP.

[0294] E2. The device according to embodiment E1, wherein the device is further configured to perform a method according to any one of embodiments A2 to A9.

[0295] F1. A device (800) for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution, and the device is configured to:

[0296] Obtain (s602) a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution;

[0297] Based on the first value of the luminance QP, determine (s604) a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution;

[0298] Obtain (s606) a configured luminance QP change value of the luminance QP associated with the change from the first resolution to the second resolution;

[0299] Based on the first value of the luminance QP and the configured luminance QP change value, determine (s608) a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution;

[0300] Obtain (s610) a configured chrominance QP change value of the chrominance QP associated with the change from the first resolution to the second resolution, wherein the configured chrominance QP change value is different from the configured luminance QP change value;

[0301] Based on the second value of the luminance QP and / or the configured chrominance QP change value, determine (s612) a second value of the chrominance QP, wherein the second value of the chrominance QP is associated with the second resolution; and

[0302] Encode or decode (s614) the region of the picture at the second resolution using the second value of the luminance QP and the second value of the chrominance QP, wherein

[0303] the difference between the first value of the luminance QP and the second value of the luminance QP is the same as the configured luminance QP change value, and

[0304] the difference between the first value of the chrominance QP and the second value of the chrominance QP is the same as the configured chrominance QP change value.

[0305] F2. The apparatus according to embodiment F1, wherein the apparatus is further configured to perform the method according to any one of embodiments B2 to B9.

[0306] G1. An apparatus (800) for encoding or decoding a region of a picture included in a video stream, wherein the region of the picture can be encoded in either a first resolution and / or a second resolution, the apparatus being configured to:

[0307] Obtain (s702) a first value of a luminance quantization parameter (QP) of a luminance component, wherein the first value of the luminance QP is associated with the first resolution;

[0308] Obtain (s704) a first value of the chrominance QP of the chrominance component, where the first value of the chrominance QP is associated with the first resolution;

[0309] Determine (s706) to encode the video at the second resolution;

[0310] Based on the determination, retrieve (s708) a configured luma QP change value associated with the change from the first resolution to the second resolution and a configured chrominance QP change value associated with the change from the first resolution to the second resolution;

[0311] Generate (s710) a second value of the luma QP based on the first value of the luma QP and the configured luma QP change value;

[0312] Generate (s712) a second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value; and

[0313] Encode or decode (s714) the region of the picture at the second resolution using the second value of the luma QP and the second value of the chrominance QP.

[0314] G2. The apparatus according to embodiment G1, wherein the apparatus is further configured to perform the method according to any one of embodiments C2 to C6.

[0315] H1. An apparatus (800) comprising:

[0316] Processing circuitry (802); and

[0317] A memory (841) containing instructions executable by the processing circuitry, whereby the apparatus is operable to perform the method according to any one of embodiments A1 to C6.

[0318] Although various embodiments are described herein, it should be understood that they are presented by way of example and not limitation. Thus, the breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments. Further, any combination of the above elements in all possible variations is included in the present disclosure, unless otherwise indicated or clearly conflicts with the context in some other way.

[0319] Additionally, although the processes described above and shown in the figures are shown as a series of steps, they are for illustrative purposes only. Thus, it is contemplated that some steps may be added, some steps may be omitted, the order of steps may be rearranged, and some steps may be performed in parallel.

Claims

1. A method (500) for encoding or decoding a region of a picture included in a video stream, wherein, The region of the picture can be encoded in either a first resolution and / or a second resolution, and the method includes: Obtaining (s502) a first value of a luminance quantization parameter QP of a luminance component, where the first value of the luminance QP is associated with the first resolution; Based on the first value of the luminance QP, determining (s504) a first value of a chrominance QP of a chrominance component, where the first value of the chrominance QP is associated with the first resolution; Obtaining (s506) a second value of the luminance QP, where the second value of the luminance QP is associated with the second resolution; Based on the second value of the luminance QP, determining (s508) a second value of the chrominance QP, where the second value of the chrominance QP is associated with the second resolution; and Encoding or decoding (s510) the region of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP, where The difference between the first value of the luminance QP and the second value of the luminance QP is the same as the difference between the first value of the chrominance QP and the second value of the chrominance QP.

2. The method according to claim 1, wherein The region of the picture is the entire picture or a part of the picture.

3. The method according to claim 1 or 2, including: Obtaining a chrominance QP offset value for adjusting the value of the chrominance QP, where The second value of the chrominance QP associated with the second resolution is determined based on the chrominance QP offset value.

4. The method according to claim 3, wherein, Determining the second value of the chrominance QP includes: Based on the second value of the luminance QP, using mapping data to retrieve a mapped value of the chrominance QP, the mapped value being mapped to the second value of the luminance QP; and Combining the mapped value of the chrominance QP with the chrominance QP offset value to generate the second value of the chrominance QP.

5. The method according to claim 3 or 4, wherein The second value of the chrominance QP = the mapped value of the chrominance QP + the chrominance QP offset value.

6. The method according to any one of claims 3 to 5, wherein The chrominance QP offset value is included in the picture header or slice header of the video stream.

7. The method according to any one of claims 3 to 6, where The region of the picture is the first part of the picture, The chrominance QP offset value is only applicable to the first part of the picture, The picture includes a second part, and A different QP offset value is provided for the second part of the picture.

8. The method according to any one of claims 3 to 7, where The chrominance QP offset value is set such that the chrominance QP offset value = the first value of the chrominance QP - the mapped value of the chrominance QP + a configured QP change value, and The configured QP change value is equal to the difference between the first value of the luminance QP and the second value of the luminance QP.

9. The method according to any one of claims 1 to 8, wherein In the case where the second resolution is 1 / 2, 2 / 3, or 4 / 5 of the first resolution, the difference between the first value of the luminance QP and the second value of the luminance QP is set to -6, -4, or -2 respectively.

10. The method according to any one of claims 1 to 8, wherein, When the second resolution is 2 times, 1.5 times or 1.25 times the first resolution, the difference between the first value of the luminance QP and the second value of the luminance QP is set to 6, 4 or 2 respectively.

11. The method according to any one of claims 1 to 10, wherein The picture is at least partially predicted by reference picture resampling RPR or encoded using scalable coding.

12. A method (700) for encoding or decoding a region of a picture included in a video stream, wherein, An area of the picture can be encoded in either the first resolution and / or the second resolution, and the method includes: Obtaining (s702) a first value of a luminance quantization parameter QP of a luminance component, where the first value of the luminance QP is associated with the first resolution; Obtaining (s704) a first value of a chrominance QP of a chrominance component, where the first value of the chrominance QP is associated with the first resolution; Determining (s706) to encode the video in the second resolution; Based on the determination, retrieving (s708) a configured luminance QP change value associated with the change from the first resolution to the second resolution and a configured chrominance QP change value associated with the change from the first resolution to the second resolution; Generating (s710) the second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value; Generating (s712) the second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value; and Encoding or decoding (s714) the area of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP.

13. The method according to claim 12, wherein, The area of the picture is the entire picture or a part of the picture.

14. The method according to claim 12 or 13, wherein, the configured luminance QP change value is the same as the configured chrominance QP change value, and when the second resolution is 1 / 2, 2 / 3 or 4 / 5 of the first resolution, the configured luminance QP change value is -6, -4 or -2 respectively.

15. The method according to claim 12 or 13, wherein, the configured luminance QP change value is the same as the configured chrominance QP change value, and when the second resolution is 2 times, 1.5 times or 1.25 times the first resolution, the configured luminance QP change value is 6, 4 or 2 respectively.

16. The method according to claim 12 or 13, wherein, when the second resolution is 1 / 2, 2 / 3, or 4 / 5 of the first resolution, the configured chrominance QP change value is -5, -3 or -1 respectively, and when the second resolution is 1 / 2, 2 / 3 or 4 / 5 of the first resolution, the configured luminance QP change value is -6, -4 or -2 respectively.

17. The method according to claim 12 or 13, wherein, when the second resolution is 2 times, 1.5 times or 1.25 times the first resolution, the configured chrominance QP change value is 5, 3 or 1 respectively, When the second resolution is 2 times, 1.5 times or 1.25 times the first resolution, the configured brightness QP change values are 6, 4 or 2 respectively.

18. The method according to any one of claims 12 to 17, wherein, The picture is at least partially predicted by reference picture resampling RPR or encoded using scalable coding.

19. A computer program (800) comprising instructions (844) which, when executed by a processing circuit (802), cause the processing circuit to perform the method according to any one of claims 1 to 18.

20. A carrier including the computer program according to claim 19, wherein, The carrier is one of an electrical signal, an optical signal, a radio signal and a computer-readable storage medium.

21. An apparatus (800) for encoding or decoding a region of a picture included in a video stream, wherein, An area of the picture can be encoded in either a first resolution and / or a second resolution, and the apparatus is configured to: Obtain (s502) a first value of a luminance quantization parameter QP of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; Based on the first value of the luminance QP, determine (s504) a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution; Obtain (s506) a second value of the luminance QP, wherein the second value of the luminance QP is associated with the second resolution; Based on the second value of the luminance QP, determine (s508) a second value of the chrominance QP, wherein the second value of the chrominance QP is associated with the second resolution; and Encode or decode (s510) the area of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP, wherein The difference between the first value of the luminance QP and the second value of the luminance QP is the same as the difference between the first value of the chrominance QP and the second value of the chrominance QP.

22. The apparatus according to claim 21, wherein, The apparatus is further configured to perform the method according to any one of claims 2 to 11.

23. An apparatus (800) for encoding or decoding a region of a picture included in a video stream, wherein, An area of the picture can be encoded in either a first resolution and / or a second resolution, and the apparatus is configured to: Obtain (s702) a first value of a luminance quantization parameter QP of a luminance component, wherein the first value of the luminance QP is associated with the first resolution; Obtain (s704) a first value of a chrominance QP of a chrominance component, wherein the first value of the chrominance QP is associated with the first resolution; Determine (s706) to encode the video in the second resolution; Based on the determination, retrieve (s708) a configured luminance QP change value associated with the change from the first resolution to the second resolution and a configured chrominance QP change value associated with the change from the first resolution to the second resolution; Generate (s710) the second value of the luminance QP based on the first value of the luminance QP and the configured luminance QP change value; Generate (s712) the second value of the chrominance QP based on the first value of the chrominance QP and the configured chrominance QP change value; and Encode or decode (s714) the area of the picture in the second resolution using the second value of the luminance QP and the second value of the chrominance QP.

24. The device according to claim 23, wherein, The apparatus is further configured to perform the method according to any one of claims 13 to 18.

25. An apparatus (800) comprising: processing circuitry (802); and a memory (841) containing instructions executable by the processing circuitry, whereby the apparatus is operable to perform the method according to any one of claims 1 to 18.

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