RU2848190C2 - Reporting quantisation parameters - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention relates to image encoding/decoding and more specifically to methods of reporting quantisation parameters (QP) of brightness and/or colour of a video signal. Disclosed method of reporting quantisation parameters for SDR and HDR content in video coding is described using two approaches. First approach is to send the user-defined Qpc table directly in the high-level syntax. It results in more flexible and efficient QP control for development of future codecs and coding of video content. Second approach is to report brightness and colour QP independently. This approach eliminates the need for Qpc-tables and removes dependency of chromaticity quantisation parameter on luminance QP.

EFFECT: high encoding/decoding efficiency by reporting chroma quantisation parameters in a content-dependent manner.

9 cl, 5 dwg

Description

Cross-references to related applications

This application claims priority to U.S. Provisional Patent Application No. 62/853,352, filed May 28, 2019, which is incorporated herein by reference.

Field of technology to which the invention relates

The present disclosure relates to extracting and communicating quantization parameters in video signal coding, and more particularly to methods, equipment, a computer program, and a device based on a computer program for extracting and communicating quantization parameters of the luminance and/or chrominance of a video signal.

State of the art

The quantization parameter (QP) is a type of parameter used in a video bitstream to regulate the quality and bit rate. Generally, a lower QP value specified during encoding results in higher encoded video quality at the expense of a higher bit rate, while a QP of 0 means no quantization. Conversely, a higher QP value results in lower encoded video quality and lower bit rates. Additionally, the decoder uses QP values when reconstructing video content from the encoded video.

The Versatile Video Coding (VVC) standard is a standard being developed by the Joint Video Engineering Task Force (JVET) that encodes both standard dynamic range (SDR) and high dynamic range (HDR) content. In the current (2019) VVC specification, the communication of quantization parameters for the luminance and chrominance components is handled differently.

For the luminance component, the delta quantization parameter (QP), which denotes the difference between successive quantization parameter values, is signaled and summed with the initial QP values for each slice.

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

Table (100) in Fig. 1 is inherited from the High Efficiency Video Coding (HEVC) standard and is designed only for SDR content. However, when HDR content based on perceptual quantization (PQ) was initially studied in JCT-VC, it was concluded that the default SDR Qpc table is not suitable for HDR content, since it leads to chroma artifacts at low bit rates, particularly in achromatic areas. Therefore, a non-normative encoder optimization using a variable called ChromaQPOffset is introduced in the HDR Common Test Conditions (CTC) for HDR PQ content. By generally specifying the difference relative to the luminance QP value, ChromaQPOffset is signaled in the frame parameter set (PPS), which means that a constant value is used based on the input QP. However, there are cases where the QP varies across the frame and this cannot be handled by a constant offset.

In the first version of HEVC, different QP offsets were provided for each of the two chroma components at the slice level. However, at the coding unit (CU) level, delta QP is applied to all three components, with chroma also passing through a mapping table based on the luma QP. In the range extension (Rext) version, separate chroma QP control is introduced at the CU level through lists of chroma QP offsets specified for Cb and Cr, respectively.

Extracting quantization parameters in the current VVC standard

In this process, the luma quantization parameter Qp' _Y and the chroma quantization parameters Qp' _Cb and Qp' _Cr are extracted. The initial value of the luma quantization parameter Qp' _Y for a slice is extracted as follows:

SliceQp _Y =26+init_qp_minus26+slice_qp_delta

- qP _{Y_PREV} represents the previous luma quantization parameter for the current coding unit. qP _{Y_PREV} is set to SliceQp _Y if the current quantization group is the first quantization group in a slice or block. Otherwise, qP _{Y_PREV} is set to the luma quantization parameter Qp _Y of the last luma coding unit in the previous quantization group in decoding order.

- qP _{Y_PRED} represents the predicted luma quantization parameter for the current coding unit. If the current quantization group is the first quantization group in the CTB row in the block, and the upper coding unit is available, set qP _{Y_PRED} to the Qp _Y of the upper CU; otherwise:

qP _{Y_PRED} =(qP _{Y_A} +qP _{Y_B} +1)>>1,

where qP _{Y_A} is set to qP _{Y_PREV} if the left coding block is not the first coding block in the left quantization group or if the left coding block is not available; qP _{Y_B} is set to qP _{Y_PREV} if the top coding block is not the first coding block in the top quantization group or if the top coding block is not available.

The variable Qp _Y for each coding unit is extracted as follows:

Qp _Y =((qP _{Y_PRED} +CuQpDeltaVal+64+2*QpBdOffset _Y )%(64+QpBdOffset _Y ))-QpBdOffset _Y

CuQpDeltaVal is specified with cu_qp_delta_abs and cu_qp_delta_sign_flag in the transformation unit layer.

The brightness quantization parameter Qp' _Y is extracted as follows:

Qp' _Y = Qp _Y + QpBdOffset _Y

When ChromaArrayType is not 0 and treeType is SINGLE_TREE or DUAL_TREE_CHROMA, the following applies:

- When treeType is DUAL_TREE_CHROMA, the Qp variable_Yis set equal to the parameter Qp_Ybrightness quantization current luma encoding unit, which covers the luma location (xCb+cbWidth/2, yCb+cbHeight/2).

- The variables qP _Cb and qP _Cr are extracted as follows:

qPi _Cb =Clip3(-QpBdOffset _C , 69, Qp _Y +pps_cb_qp_offset+slice_cb_qp_offset)

qPi _Cr =Clip3(-QpBdOffset _C , 69, Qp _Y +pps_cr_qp_offset+slice_cr_qp_offset)

- If ChromaArrayType is 1, the variables qP _Cb and qP _Cr are set to the value of Qp _C as specified in Table 1 (shown again below for convenience) based on the index qPi, which is equal to qPiC _b and qPiC _r , respectively.

Otherwise, the variables qP _Cb and qP _Cr are set equal to Min(qPi, 63), based on the index qPi, which is equal to qPi _Cb and qPi _Cr , respectively.

- The chromaticity quantization parameters for Cb and Cr, Qp' _Cb and Qp' _Cr , are extracted as follows:

Qp'C _b = qP _Cb + QpBdOffset _C

Qp'C _r = qP _Cr + QpBdOffset _C

The essence of the invention

Current video content is not identical to the SDR content for which the original default SDR Qpc table is designed. As one example, the luma and chroma components for SDR and HDR content can be encoded using Y'CbCr or ICtCp signal formats. For HDR content, the situation is more complex. HDR content can additionally be encoded using HLG or PQ transfer characteristics. It may be advantageous to communicate different chroma quantization parameters for different types of chroma components and transfer characteristics. It may also be advantageous to communicate different chroma quantization parameters for two different chroma components, Cb and Cr or Ct and Cp. It may also be advantageous to communicate chroma quantization parameters in a content-dependent manner. The disclosed methods and devices address the above problems and requirements.

English: Devices and methods according to the present disclosure provide solutions to the problem of chroma QP (QPc) extraction for HDR content. Additionally, devices and methods for reporting such extracted chroma QP for HDR are also disclosed. According to a first aspect of the present disclosure, a method is disclosed for decoding an encoded video bitstream, comprising: a) retrieving a chroma quantization parameter (Qpc) table mapping a luma quantization parameter (Qp) with luma QP offset values qP(i) to corresponding chroma Qp values Qpc(i), wherein: i) "i" is an index of table entries in the range from startID to endID; ii) startID is an integer greater than or equal to 1 and less than N, N is the total number of Qpc table entries; and iii) endID is an integer greater than startID and 1 and less than or equal to N; and b) generating a decoded output signal based on the retrieved Qpc table and the encoded video bitstream; wherein the encoded bitstream comprises a table identifier, and wherein: in the first case: the table identifier indicates the presence of a default table; and in the second case: the encoded video bitstream further comprises one or more elements signalled in a high-level syntax, wherein the one or more elements are encoded based on a combination of one of a) two or more chroma Qp values or b) one or more chroma Qp values with one or more luminance Qp values with chroma offset values.

According to a second aspect of the present disclosure, a method is disclosed for decoding an encoded video signal stream, comprising: extracting, from the encoded stream, luminance quantization parameters (Qps), Qps of first chroma components and Qps of second chroma components; and generating an output decoded video signal based on the extracted Qps of luminance, the first and second chroma components and the encoded video bit stream; wherein: the encoded video stream comprises a plurality of elements signaled in a high-level syntax; the plurality of elements are encoded based on a combination of Qps of luminance, Qps of first and second chroma components; Qps of the first chroma components are extracted based on the predicted Qps values of the first chroma components and the bit depth of samples of the first chroma component of the video signal; and Qps of the second chroma components are extracted based on the predicted Qps values of the second chroma components and the bit depth of samples of the second chroma component of the video signal.

Brief description of the drawings

Fig. 1 shows an example of a table containing different values of the chroma quantization parameters as a function of the luminance quantization parameter.

Fig. 2 shows an exemplary HDR Qpc table in accordance with an embodiment of the present disclosure.

Fig. 3 shows an exemplary Qpc table in accordance with an embodiment of the present disclosure.

Fig. 4A shows an exemplary Qpc table for the HDR PQ content type.

Fig. 4B shows an example Qpc table for the hybrid long gamma (HLG) HDR content type.

Fig. 5 shows an exemplary SDR Qpc mapping function based on luminance quantization parameters.

Implementation of the invention

Definitions

In this document, the technical terms used related to video coding and decoding are defined according to the Universal Video Coding Standard (Draft 5), document JVET-N1001-v3, Joint Video Experts Group (JVET) ITU-T SG 16 WP 3 and ISO/IEC JTC 1/SC 29/WG 11, 14th Conference: Geneva, CH, 19–27 March 2019.

Description

1. Extraction of PQ chroma based on user-defined Qpc tables

According to embodiments of the present disclosure, the chroma QP for HDR content can be determined using a user-defined Qpc table. Fig. 2 shows a table (200) representing an exemplary HDR Qpc table according to an embodiment of the present disclosure. The table (200) serves a substantially identical purpose for HDR content as the default SDR Qpc table specified in the current VVC serves for SDR content. Those skilled in the art will appreciate that the disclosed approach based on a user-defined Qpc table for HDR content should unify the codec design solution for all types of SDR and HDR signals and lead to more flexible and efficient QP management for the development of future codecs.

According to an embodiment of the present disclosure, the HDR Qpc table, as described, can be communicated directly in a high-level syntax, for example, in a video parameter set (VPS), in a signal parameter set (SPS), in a PPS, in an adaptation parameter set (APS), in a slice header and in an SEI message, etc. In order to reduce the amount of transmitted service information and according to other embodiments of the present disclosure, the Qpc tables by default can be used as normative tables in standard specifications or as non-normative examples in standard specifications.

With reference to Fig. 2 and in the SPS, a new syntax element chroma_qp_table_idc may be added. The value of chroma_qp_table_idc, equal to 0, refers to the original SDR Qpc table in the text of the VVC specification, see table (100) in Fig. 1. When the value of chroma_qp_table_idc is equal to 1, it refers to the table (200) in Fig. 2. According to an embodiment of the present disclosure, the variable chroma_qp_table_idc is an indicator of the index to the Qpc array as a function of qPi for ChromaArrayType equal to 1. The value of chroma_qp_table_idc may be in the range of 0-1, inclusive.

According to additional embodiments of the present disclosure, either a single Qpc table may be communicated and shared by both Cb and Cr, or two separate tables, designed for Cb and Cr, respectively, may be communicated. To reduce the amount of transmitted overhead, each Qpc table may be differentially encoded, approximated using a piecewise linear function, run-length encoded, encoded using the Lempel-Ziv-Welch (LZW) code or similar algorithms, or encoded using a combination of the above technologies.

The Qpc table described above can be used for HDR content using the HLG or PQ transfer function. Returning to 1-2, from the (100, 200) tables and Qpc tables designed for other content types, such as HLG, it should be noted that some Qpc values are either equal to qPi or can be extracted directly by subtracting a constant value. To reduce the number of coding bits, the range of table elements to be reported in the bitstream can be specified using the start and end indices [startID, endID].

Various methods for communicating QP chromaticity values are described below, in accordance with the teachings of this disclosure. Throughout this disclosure, the term "delta Qp," also represented as "dQp," is used to describe the difference between two consecutive QP values.

Method 1a

In this method, the difference between two adjacent Qpc records in [startID, endID] is encoded:

dQpC[i]=Qp _C [i]-QpC[i-1] (1)

In general, SDR and HDR Qpc tables according to the teachings of the present disclosure may include only dQp values of 0 and 1. Delta Qpc values may be reported directly. Alternatively, codewords may consist of multiple delta Qpc values. For example, the delta Qpc values of Cb and Cr pairs having the same index value may be combined. As another example, the delta Qpc values of two consecutive index values may be combined for Cb and similarly for Cr. Optionally, codeword sequences composed of combinations of delta Qpc values may be further compressed using methods such as Huffman coding or other lossless compression algorithms. For delta Qpc values other than 0 and 1, the maximum delta value may be specified in the syntax. In some cases, startID and endID may be constrained to be even or odd values to reduce the number of bits that must be reported.

The following descriptions of additional embodiments focus on the differences between them and the embodiment described above. Therefore, features common to both embodiments are omitted from the following description, and it should therefore be assumed that the features of the embodiment described above are implemented or at least can be implemented in the additional embodiment, unless the following description requires otherwise.

Method 1b

In this method, the difference value between each pair {qPi, Qpc} in [startID, endID] can be encoded:

dQp[i]=qPi[i]-Qp _C [i] (2)

The delta QP values between qPi and Qpc can range from 0 to 18, which indicates that method 1a may be more convenient to encode than method 1b.

Method 1c

This method is based on fitting the Qpc-mapping curve from qPi through a piecewise linear function defined as follows:

,

Where , .

Method 1d

In this method, run-length coding can be used to encode the dQpC[i] values specified in formula (1). Referring to table (100) in Fig. 1, as an example, the delta Qp values are extracted as a sequence of 0 and 1. The delta values (0 or 1) along with a counter of consecutive values can be encoded. Fig. 3 shows table (300), which is an exemplary illustration of a Qpc table based on this method.

According to an embodiment of the present disclosure, one default Qpc table can be predefined for each of the different signal types, such as SDR PQ and HLG content. Figs. 4A-4B show tables (400A, 400B) representing exemplary Qpc tables for HDR PQ and HLG content, respectively. If a user-defined Qpc table is not present, the encoder and decoder can instead use the default Qpc table. Embodiments according to the present disclosure can be envisaged in which user-defined Qpc _Cs are not communicated. This approach has the advantage of reducing a larger number of bits.

The following table corresponds to the above method 1a and shows an exemplary syntax of the primary data byte sequence (RBSB) for the SPS and tile group header, wherein the syntax elements in accordance with the teachings of the present disclosure are illustrated in italic font, unlike other existing syntax elements. A detailed description of the various syntax elements is provided below. The default Qpc table can be indicated in the SPS using the default Qpc table type message. If the default table is not provided, a predefined Qpc table can be sent to the SPS with the delta QP values between two adjacent table elements. One or more alternative Qpc tables for use in a slice can be signaled in the PPS to override the SPS Qpc table.

- sps_default_qpc_table_flag equal to 1 indicates that the default chroma quantization parameter table should be used, and therefore there is no need to send a QPC table. Instead, an index is signaled to indicate which default QPC table should be used; sps_default_qpc_table_flag equal to 0 indicates that no default QPC tables are specified and should be sent to the SPS.

- default_qpc_table_type_idx specifies which default Qpc table should be used when sps_default_qpc_table_flag is 1; default_qpc_table_type_idx equal to 0 and pps_slice_qpc_table_present_flag equal to 0 specify that one or more default SDR Qpc tables should be used; default_qpc_table_type_idx equal to 1 and pps_slice_qpc_table_present_flag equal to 0 specify that one or more default HDR PQ Qpc tables should be used; default_qpc_table_type_idx equal to 2 and pps_slice_qpc_table_present_flag equal to 0 specify that one or more default HLG Qpc tables should be used; default_qpc_table_type_idx equal to 3 is reserved for future use.

- sps_separate_qpc_table_enable_flag equal to 1 indicates that Cb and Cr use separate Qpc tables; sps_cr_qp_delta[i] and sps_cr_qp_gap_idx are set and reported in SPS, slice_cr_qp_delta[i] and slice_cr_qp_gap_idx are set in the slice header; sps_separate_qpc_table_enable_flag equal to 0 indicates that Cb and Cr use identical Qpc table.

- sps_qpc_table_start_index_div2 specifies the starting index from which Qpc table elements should be reported with delta QP values. It is specified as an even number from 0 to 63. For table elements with an index less than sps_qpc_table_start_index_div2*2, QpC is set equal to the same value as qPi.

- sps_qpc_table_end_index_div2 specifies the ending index up to which Qpc table elements should be reported with QP delta values. It is specified as an even number from 0 to 63. For table elements with an index greater than sps_qpc_table_end_index_div2*2, sps_cb_qp_delta[i] and sps_cr_qp_delta[i] are set to 1.

- sps_cb_qp_delta[i] specifies the delta values between spsQpcb[i] and spsQpcb[i-1], with sps_cb_qp_delta[0], to construct the quantization parameter table for Cb specified in SPS; the i-th entry of the Cb quantization parameter table in SPS is retrieved as follows: spsQpcb[i]=sps_cb_qp_delta[i]+spsQpcb[i-1].

- sps_cr_qp_delta[i] specifies the delta values between spsQpcr[i] and spsQpcr[i-1], with sps_cr_qp_delta[0], to construct the quantization parameter table for Cr specified in SPS; the i-th entry of the Cr quantization parameter table in SPS is retrieved as follows: spsQpcr[i]=sps_cr_qp_delta[i]+spsQpcr[i-1].

- pps_slice_qpc_table_present_flag equal to 1 indicates that the quantization parameter tables for the Cb and Cr components for the current slice are present and specified in the slice header; pps_slice_qpc_table_present_flag equal to 0 indicates that the quantization parameter tables for the Cb and Cr components for the current slice are not present in the slice header, and the default quantization parameter tables are applied for Cb and Cr.

- slice_cb_qp_delta[i] specifies the delta values between sliceQpcb[i] and sliceQpcb[i-1], with slice_cb_qp_delta[0], to construct the quantization parameter table for slices for Cb; the i-th entry of the Qpc table for slices for a Cb component is retrieved as follows: sliceQpcb[i]=slice_cb_qp_delta[i]+sliceQpcb[i-1].

- slice_cr_qp_delta[i] is set when sps_separate_qpc_table_enable_flag is 1, which specifies delta values between sliceQpcr[i] and sliceQpcr[i-1], with slice_cr_qp_delta[0], to constitute the quantization parameter table for slices for Cr; the i-th entry of the Qpc table for slices for the Cr component is retrieved as follows: sliceQpcr[i]=slice_cr_qp_delta[i]+sliceQpcr[i-1].

2. Extraction of chroma QP independent of luminance QP

According to additional embodiments of the present disclosure, the luma and chroma QPs may be reported independently. This approach has the advantage of eliminating the dependence of the chroma QP on the luma QP. The extraction of the chroma QP in accordance with embodiments of the present disclosure is described in detail below.

The initial values of the chroma quantization parameter for a slice, SliceQp _Cb and SliceQp _Cr , can be extracted as follows:

SliceQp _Cb =26+init_qp_minus26+slice_cb_qp_delta (3)

SliceQp _Cr =26+init_qp_minus26+slice_cr_qp_delta (4)

- qP _{Cb_PREV} and qP _{Cr_PREV} are set equal to SliceQp _Cb and SliceQp _Cr , respectively, if the current quantization group is the first quantization group in a slice or block. Otherwise, qP _{Cb_PREV} and qP _{Cr_PREV} are set equal to the chroma quantization parameter QpC of the last chroma coding unit in the previous quantization group in decoding order.

- qP _{Cb_PRED} and qP _{Cr_PRED} represent the predicted chroma quantization parameters for the current coding unit. If the current quantization group is the first quantization group in the CTB row in the block, and the upper coding unit is available, set qP _{Cb_PRED} and qP _{Cr_PRED} to be the Qp _C of the upper CU; otherwise:

qP _{Cb_PRED} =(qP _{Cb_A} +qP _{Cb_B} +1)>>1 (5)

qP _{Cr_PRED} =(qP _{Cr_A} +qP _{Cr_B} +1)>>1 (6),

where qP _{Cb_A} and qP _{Cr_A} are set equal to qP _{Cb_PREV} and qP _{Cr_PREV} , respectively, if the left coding block is not the first coding block in the left quantization group or if the left coding block is not available; qP _{Cb_B} and qP _{Cr_B} are set equal to qP _{Cb_PREV} and qP _{Cr_PREV} , respectively, if the upper coding block is not the first coding block in the upper quantization group or if the upper coding block is not available.

The variable QpCb and QpCr for each coding unit can be extracted as follows:

QpCb=((qPCb_PRED+CuCbQpDeltaVal+64+2*QpBdOffsetC)%(64+QpBdOffsetC))-QpBdOffsetC (7)

QpCr=((qPCr_PRED+CuCrQpDeltaVal+64+2*QpBdOffsetC)%(64+QpBdOffsetC))-QpBdOffsetC (8)

The chroma quantization parameters Qp' _Cb and Qp' _Cr are then extracted as follows:

Qp' _Cb =Qp _Cb +QpBdOffset _C (9)

Qp' _Cr =Qp _Cr +QpBdOffset _C (10)

The difference values between the current coding unit's quantization parameter and its prediction, CuCbQpDeltaVal and CuCrQpDeltaVal, can be specified in the transform unit layer. Several ways to encode delta QP values are available.

In the following, exemplary methods consistent with the teachings of the present disclosure are described. Furthermore, the difference between the QP of each color component (e.g., luminance, chroma Cb, and chroma Cr) and its predicted value is abbreviated as dPQ' to distinguish it from dPQ, which indicates, as described above, the difference between successive QPs in the context of Qpc tables.

Method 2a

In this method, the dQPs of the three color components, luma, chroma Cb, and chroma Cr, as represented by the variables CuQpDeltaVal, CuCbQpDeltaVal, and CuCrQpDeltaVal, respectively, are encoded.

The following descriptions of additional embodiments focus on the differences between them and the embodiment described above. Therefore, features common to both embodiments are omitted from the following description, and it should therefore be assumed that the features of the embodiment described above are implemented or at least can be implemented in the additional embodiment, unless the following description requires otherwise.

Method 2b

In this method, the dQp' of the luminance component, CuQpDeltaVal, is encoded. Additionally, the difference between the dQp' of each chrominance component and the dQp' of the luminance is encoded as follows:

CbdQpDeltaVal=CuCbQpDeltaVal-CuQpDeltaVal (11)

CrdQpDeltaVal=CuCrQpDeltaVal-CuQpDeltaVal (12)

Method 2c

In this method, the CrCbdQpDeltaVal element is as given below:

CrCbdQpDeltaVal=CuCrQpDeltaVal-CuCbQpDeltaVal (13)

is encoded, with the elements CuCrQpDeltaVal and CuCbQpDeltaVal having the same definition as in the case of method 2c described above.

Method 2d

In this method, the CrCbdQpDeltaVal element is as given below:

CrCbdQpDeltaVal=CuCrQpDeltaVal-CuCbQpDeltaVal

is encoded, with the elements CuCrQpDeltaVal and CuCbQpDeltaVal having the same definition as in the case of method 2c described above.

Method 2e

In this method, the difference values from the chroma QP and the luminance QP are given as:

dQp' _Cb =Qp' _Y -Qp' _Cb (14)

dQp' _Cr =Qp' _Y -Qp' _Cr (15)

are encoded. Signaling for method 2e is similar to method 2a, without the need to report slice_cb_qp_delta and slice_cr_qp_delta (see below) in the slice header.

The following table corresponds to the above method 2a and shows an exemplary syntax of the primary data byte sequence (RBSB) for the SPS and tile group header, with the syntax elements in accordance with the teachings of this disclosure illustrated in italics, unlike other existing syntax elements. A detailed description of the various syntax elements follows.

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

A number of embodiments of the disclosure have been described. However, it should be understood that various modifications can be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the appended claims.

The examples set forth above are provided to those skilled in the art as a complete disclosure and description of how to make and use embodiments of the disclosure, and are not intended to limit the scope to what the inventor(s) consider their disclosure to be.

Modifications to the above-described modes for implementing the methods and systems disclosed herein that are obvious to those skilled in the art are intended to fall within the scope of the appended claims. All patents and publications cited in the detailed description indicate levels of skill in the art to which the disclosure pertains. All materials cited in this disclosure are incorporated by reference to the extent that each material is individually incorporated by reference in its entirety.

It should be understood that the disclosure is not limited to specific methods or systems, which may, of course, vary. It should also be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in this detailed description and the appended claims, the singular forms "a" and "an" include multiple reference entities unless the context clearly dictates otherwise. The term "a" or "a" includes two or more reference entities unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the disclosure pertains.

Provision 1. A method for decoding an encoded video bit stream, wherein the method comprises the steps of:

a) extracting a chromaticity quantization parameter (Qpc) table mapping the quantization parameter (Qp) of the luminance with the values qP(i) of the luminance offset QP to the corresponding Qp-values Qpc(i) of the chromaticity, wherein:

i) "i" represents the index of the table records ranging from startID to endID;

ii) startID is an integer greater than or equal to 1 and less than N, N being the total number of records of the Qpc table; and

iii) endID is an integer greater than startID and 1 and less than or equal to N; and

b) generate a decoded output signal based on the extracted Qpc table and the encoded video bit stream;

wherein the encoded bit stream contains a table identifier, and wherein:

in the first case:

- the table identifier indicates the presence of the default table; and

in the second case:

- the encoded video bit stream further comprises one or more elements signalled in a high-level syntax, wherein the one or more elements are encoded based on a combination of one of a) two or more chroma Qp values or b) one or more chroma Qp values with one or more luminance Qp values with chroma offset values.

Provision 2. The method according to Provision 1, wherein the video signal corresponding to the encoded video bit stream comprises a first chrominance component and a second chrominance component.

Provision 3. The method according to Provision 2, wherein the first chromaticity component and the second chromaticity component share an identical Qpc table.

Provision 4. The method according to Provision 2, wherein the Qpc table comprises a first and a second Qpc table corresponding to the first and second chromaticity components, respectively.

Provision 5. The method according to Provision 1, wherein the combination of one or more Qp-color values comprises differences between successive Qp-parameter values.

Provision 6. The method according to Provision 4, in which:

the first array with elements dQpc1(j) of the first array, j=startID+1, ..., endID is extracted according to dQpc1(j)=Qpc1(j)-Qpc1(j-1), where Qpc1 represents the first color component;

the second array with elements dQpc2(j) of the second array, j=startID+1, ..., endID is retrieved according to dQpc2(j)=Qpc2(j)-Qpc2(j-1), where Qpc2 represents the second color component; and

a combination of two or more Qp chromaticity values comprises one or more pairs of array elements, wherein each pair of array elements comprises an element of the first array and an element of the second array, wherein the elements of the first and second arrays have an identical index.

Provision 7. The method according to Provision 4, in which:

the first array with elements dQpc1(j) of the first array, j=startID+1, ..., endID is extracted according to dQpc1(j)=Qpc1(j)-Qpc1(j-1), where Qpc1 represents the first color component;

the second array with elements dQpc2(j) of the second array, j=startID+1, ..., endID is retrieved according to dQpc2(j)=Qpc2(j)-Qpc2(j-1), where Qpc2 represents the second color component; and

a combination of two or more Qp chromaticity values contains:

two consecutive index values of the first array; and

two consecutive index values of the second array.

Provision 8. The method according to Provision 6 or 7, wherein the combination of two or more Qp values is encoded based on a Huffman coding scheme or a lossless compression algorithm.

Provision 9. The method according to Provision 1, wherein the combination of one or more chroma Qp values with one or more luminance Qp values with chroma offset values comprises differences between the luminance Qp values with chroma offset values and the corresponding chroma Qp values.

Provision 10. The method according to Provision 1, in which:

the combination of one or more Qp chroma values with one or more Qp luminance values with chroma offset values comprises Qp(startID), Qp(endID), Qpc(startID) and Qpc(endID); and

QP luminance parameters with QP chromaticity offsets are mapped to Qp chromaticity parameters based on a piecewise linear function defined over Qp(startID), Qp(endID), Qpc(startID), and Qpc(endID).

Provision 11. The method according to Provision 5, wherein the combination of two or more Qp values is encoded using a run-length encoding scheme.

Provision 12. The method of Provision 1, wherein the default table comprises one table for single dynamic range (SDR) content, one table for perceptual quantization (PQ)-based high dynamic range (HDR) content, and one table for hybrid long gamma (HLG) content.

Provision 13. A method for decoding an encoded video signal stream, wherein the method comprises the steps of:

extract, from the encoded stream, the luminance quantization parameters (Qps), Qps of the first chrominance components and Qps of the second chrominance components; and

generate an output decoded video signal based on the extracted luminance, Qps of the first and second color components and the encoded video bit stream;

in this case:

- the encoded video stream contains a set of elements signaled in high-level syntax;

- a set of elements are encoded based on a combination of Qps of luminance, Qps of the first and second chroma components;

- the Qps of the first chrominance components are extracted based on the predicted Qps values of the first chrominance components and the bit depth of the first chrominance component samples of the video signal; and

- The Qps of the second chroma components are extracted based on the predicted Qps values of the second chroma components and the bit depth of the second chroma component samples of the video signal.

Provision 14. The method according to Provision 13, wherein the combination of Qps of luminance, Qps of first and second chromaticity components comprises:

differences of successive Qps of the first color components;

differences of successive Qps of the second color components; and

differences between successive Qps of brightness.

Provision 15. The method according to Provision 13, in which:

the first array is extracted according to CuC1QpDeltaVal(i)=Qpc1(i)-predQpc1(i), i=1, ..., N, where Qpc1 and predQpc1 represent the QP of the first chroma component and the predicted value Qp of the first chroma component, and N is an integer representing the total number of Qpc samples;

the second array is extracted according to CuC2QpDeltaVal(i)=Qpc2(i)-predQpc2(i), i=1, ..., N, where Qpc2 and predQpc2 represent the QP of the second color component and the predicted value Qp of the second color component;

the combination of Qps of luminance, Qps of the first and second chromaticity components contains:

the third array, defined as CuQpDeltaVal(i)=Qp1(i)-predQp1(i), i=1, ..., N, where Qp1 and predQp1 represent the luminance QP and the predicted luminance Qp;

the fourth array, defined as follows: C1dQpDeltaVal(i)=CuC1QpDeltaVal(i)-CuQpDeltaVal(i), i=1, ..., N; and

the fifth array, defined as follows: C2dQpDeltaVal(i)=CuC2QpDeltaVal(i)-CuQpDeltaVal(i), i=1, ..., N.

Provision 16. The method according to Provision 13, in which:

the first array is extracted according to CuC2QpDeltaVal(i)=Qpc2(i)-predQpc2(i), i=1, ..., N, where Qpc2 and predQpc2 represent the QP of the second chroma component and the predicted value Qp of the second chroma component, and N is an integer representing the total number of Qpc samples; and

the combination of Qps of luminance, Qps of the first and second chromaticity components contains:

the second array, defined as CuQpDeltaVal(i)=Qp1(i)-predQp1(i), i=1, ..., N, where Qp1 and predQp1 represent the luminance QP and the predicted luminance Qp;

a third array defined as CuC1QpDeltaVal(i)=Qpc1(i)-predQpc1(i), i=1, ..., N, where Qpc1 and predQpc1 represent the QP of the first chroma component and the predicted value Qp of the first chroma component, and N is an integer representing the total number of Qpc samples; and

the fourth array is defined as C1C2dQpDeltaVal(i)=CuC2QpDeltaVal(i)-CuC1QpDeltaVal(i), i=1, ..., N.

Provision 17. The method according to Provision 13, in which:

the first array is extracted according to CuC1QpDeltaVal(i)=Qpc1(i)-predQpc1(i), i=1, ..., N, where Qpc1 and predQpc1 represent the QP of the second chromaticity component and the predicted value Qp of the second chromaticity component, and N is an integer representing the total number of Qpc samples; and

the combination of Qps of luminance, Qps of the first and second chromaticity components contains:

the second array, defined as CuQpDeltaVal(i)=Qp1(i)-predQp1(i), i=1, ..., N, where Qp and predQp represent the luminance QP and the predicted luminance value Qp;

a third array defined as CuC2QpDeltaVal(i)=Qpc2(i)-predQpc2(i), i=1, ..., N, where Qpc2 and predQpc2 represent the QP of the second chroma component and the predicted value Qp of the second chroma component, and N is an integer representing the total number of Qpc samples; and

the fourth array is defined as C1C2dQpDeltaVal(i)=CuC1QpDeltaVal(i)-CuC2QpDeltaVal(i), i=1, ..., N.

Provision 18. The method according to Provision 13, in which:

the combination of Qps of luminance, Qps of the first and second chromaticity components contains:

a first array defined as dQpc1(i)=Qp1(i)-Qpc1(i), and in which i=1, ..., N, Qp1 and Qpc1 represent the luminance Qp and the first chrominance component Qp1, respectively, N represents the total number of luminance samples Qp; and

the second array, defined as dQpc2(i)=Qp1(i)-Qpc2(i), and in which i=1, ..., N, Qp1 and Qpc2 represent the luminance Qp and the second chrominance component Qp2, respectively.

Claims (17)

1. A method for recovering encoded data using a processor, the method comprising the steps of: receiving an encoded bit stream comprising one or more encoded frames, each frame comprising a luminance component, a first chrominance component and a second chrominance component; extracting syntax parameters from the encoded bitstream to determine a chroma quantization parameter (QP) table, wherein the chroma QP table maps input luma QP values to corresponding chroma QP values; and decoding said one or more encoded frames based on a chroma QP table, wherein the syntax parameters comprise an initial luminance QP value and one or more offset parameters for determining a mapping of luminance QP values to chroma QP values using a piecewise linear representation. 2. The method according to claim 1, wherein said one or more offset parameters comprise a chroma delta QP parameter dQpc[i] = Qpc[i] - Qpc[i-1], where i denotes an index value, and Qpc[i-1] and Qpc[i] denote successive chroma QP values. 3. The method according to claim 1, wherein the syntax parameters further comprise a flag indicating whether the first chroma component and the second chroma component share a common chroma QP table, or whether the first chroma component and the second chroma component have different chroma QP tables. 4. A non-volatile, machine-readable recording medium on which are stored program codes that, when executed by a computer, cause the computer to generate a bit stream for decoding an image, wherein the bit stream comprises: a coded frame section comprising an encoded sequence of video frames, each frame comprising a luminance component, a first chrominance component and a second chrominance component; and a bitstream parameter section including coded syntax parameters for defining a chroma quantization parameter (QP) table, wherein the chroma QP table maps input luminance QP values to corresponding chroma QP values, wherein the syntax parameters comprise an initial luminance QP value and one or more offset parameters for defining a mapping of luminance QP values to chroma QP values using a piecewise linear representation. 5. The non-volatile computer-readable recording medium of claim 4, wherein said one or more offset parameters comprise a delta QP chroma parameter dQpc[i] = Qpc[i] - Qpc[i-1], where i denotes an index value and Qpc[i-1] and Qpc[i] denote successive QP chroma values. 6. The non-volatile machine-readable recording medium according to claim 4, wherein the syntax parameters further comprise a flag indicating whether the first chroma component and the second chroma component share a common chroma QP table, or whether the first chroma component and the second chroma component have different chroma QP tables. 7. A method for encoding a sequence of video frames to form an encoded video bit stream, the method comprising the steps of: receiving a sequence of frames, each frame containing a luminance component, a first chrominance component, and a second chrominance component; encoding a sequence of video frames using luma quantization parameter (QP) values and chroma QP values to form an encoded video bitstream; and encoding signal parameters in an encoded video bitstream for a decoder to determine a chroma QP table, wherein the chroma QP table maps input luminance QP values to corresponding chroma QP values, wherein the signal parameters comprise an initial luminance QP value and one or more offset parameters for determining a mapping of luminance QP values to chroma QP values using a piecewise linear representation. 8. The method according to claim 7, wherein said one or more offset parameters comprise a chroma delta QP parameter dQpc[i] = Qpc[i] - Qpc[i-1], where i denotes an index value, and Qpc[i-1] and Qpc[i] denote successive chroma QP values. 9. The method according to claim 7, wherein the signal parameters further comprise a flag indicating whether the first chrominance component and the second chrominance component share a common chrominance QP table, or whether the first chrominance component and the second chrominance component have different chrominance QP tables.