WO2020117781A1

WO2020117781A1 - Method and apparatus for video encoding and decoding with adjusting the quantization parameter to block size

Info

Publication number: WO2020117781A1
Application number: PCT/US2019/064206
Authority: WO
Inventors: Philippe DE LAGRANGE; Fabrice Leleannec; Karam NASER
Original assignee: Interdigital Vc Holdings, Inc.
Priority date: 2018-12-04
Filing date: 2019-12-03
Publication date: 2020-06-11

Abstract

Different implementations are described, particularly implementations for video encoding and decoding are presented with adjusting the quantization parameter to block size. According to an implementation, in a method for decoding a block of an image, a quantizing parameter offset is determined for the block according to an indication relative to the size of the block; the quantizing parameter is adjusted by adding the quantizing parameter offset to a quantizing parameter previously determined; then a block of quantized transform coefficients is inverse-transformed using the adjusted quantizing parameter and the block of image is reconstructed. In variant implementations, an indication relative to the size of the block is function of a surface or a split depth for the block. In other variant implementations, the quantizing parameter offset is obtained from a table wherein the table is either known from the decoder or signaled in the bitstream.

Description

Method and apparatus for video encoding and decoding

with adjusting the quantization parameter to block size

TECHNICAL FIELD

At least one of the present embodiments generally relates to, e.g., a method or an apparatus for video encoding or decoding, and more particularly, to a method or an apparatus with determining a local quantizing parameter offset for a block according to an indication relative to the size of the block and adjusting the quantizing parameter for the block.

BACKGROUND

The technical field of the one or more implementations is generally related to video compression. At least some embodiments relate to improving compression efficiency compared to existing video compression systems such as HEVC (HEVC refers to High Efficiency Video Coding, also known as H.265 and MPEG-H Part 2 described in "ITU-T H.265 Telecommunication standardization sector of ITU (10/2014), series H: audiovisual and multimedia systems, infrastructure of audiovisual services - coding of moving video, High efficiency video coding, Recommendation ITU-T H.265"), or compared to under development video compression systems such as WC (Versatile Video Coding, a new standard being developed by JVET, the Joint Video Experts Team).

To achieve high compression efficiency, image and video coding schemes usually employ partitioning of an image, prediction, including motion vector prediction, and transform to leverage spatial and temporal redundancy in the video content. Generally, intra or inter prediction is used to exploit the intra or inter frame correlation, then the differences between the original image and the predicted image, often denoted as prediction errors or prediction residuals, are transformed into frequency-domain coefficients, the coefficients are quantized, and entropy coded. To reconstruct the video, the compressed data are decoded by inverse processes corresponding to the entropy decoding, inverse quantization, inverse transform, and prediction.

The quantization consists in dividing each coefficient by a specific quantization factor (Qstep). In general, a pre-defined or transmitted table allows converting one quantization parameter index (QP index) into a corresponding quantization factor, and only the QP index is coded in the bitstream. More generally, the quantization factor (QStep), the quantization parameter (QP) or the quantization parameter index (QP index) refer to a same object used in quantization. In an embodiment, the quantization parameter is locally adjusted by specifying an offset from the quantization parameter (QP) of the current picture or slice (QPslice). This local QP offset is specified, for example, for each block (AVC video coding standard), or group of blocks (a quantization group QG in HEVC or WC). Indeed, to save bits, the local QP offset is coded and decoded in a differential way: a QP predictor is typically computed, then the difference (qp_delta or delta_qp) between predictor and actual QP is computed and transmitted. For HEVC, the QP predictor is the average QP of left and top neighboring blocks when available. Then, the difference delta_qp (or qp_delta without distinction) is coded through two syntax elements, namely cu_qp_delta_abs and cu_qp_delta_sign_flag, which respectively signal the magnitude and sign of the delta_qp. They are CABAC coded. Therefore, the smaller magnitude, the smaller rate cost.

It is desirable to improve compression efficiency with the coding/decoding of local QP offset with regard to a better prediction of QP (less magnitude of delta_qp to code) or allowing a coarser granularity of QP (less delta_qp to code).

SUMMARY

The purpose of the invention is to overcome at least one of the disadvantages of the prior art. For this purpose, according to a general aspect of at least one embodiment, a method for encoding a block in an image encoding is presented. The method comprises determining a quantizing parameter offset for the block according to an indication relative to the size of the block; adjusting for the block, a quantizing parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block; quantizing the block of transform coefficients of the image block using the adjusted quantizing parameter; and encoding the block of quantized transform coefficients.

According to another general aspect of at least one embodiment, a method for decoding a block of an image is presented, comprising decoding a quantizing parameter offset for the block according to an indication relative to the size of said block; adjusting for the block, a quantizing parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block; inverse-quantizing a block of quantized transform coefficients using the adjusted quantizing parameter to obtain a block of transform coefficients; and reconstructing the block from the block of transform coefficients.

According to another general aspect of at least one embodiment, an apparatus for video encoding is presented comprising means for implementing any one of the embodiments of the encoding method.

According to another general aspect of at least one embodiment, an apparatus for video decoding is presented comprising means for implementing any one of the embodiments of the decoding method. According to another general aspect of at least one embodiment, an apparatus for video encoding is provided, comprising one or more processors, and at least one memory. The one or more processors is configured to implement to any one of the embodiments of the encoding method.

According to another general aspect of at least one embodiment, an apparatus for video decoding is provided, comprising one or more processors and at least one memory. The one or more processors is configured to implement to any one of the embodiments of the decoding method.

According to another general aspect of at least one embodiment, determining an indication relative to the size of the block further comprises determining a surface for the block. In a variant embodiment, an index in table of quantizing parameter offsets is determined from a function applied to the surface of said block. In other variant embodiments, the function is one of log2 of a ratio between the surface of the block and a minimum surface of a block, log2 of a ratio between the surface of block and a maximum surface of a block, log2 of a ratio surface block to a minimum surface of a quantization group.

According to another general aspect of at least one embodiment, determining an indication relative to the size of the block further comprises determining a split depth for the block. In a variant embodiment, an index in table of quantizing parameter offsets is determined from a function applied to the split depth of the block. In other variant embodiments, the function is function is a difference between the split depth for the block to and the minimum split depth of a quantization group.

According to another general aspect of at least one embodiment, the table of quantizing parameter offsets is signaled in at least one of a SPS message, a PPS message, a picture header, a slice header.

According to another general aspect of at least one embodiment, a scaling factor is determined, and the quantizing parameter offset for the block is scaled using the scaling factor then; adjusting the quantizing parameter comprises adding the scaled quantizing parameter offset to a quantizing parameter previously determined for the block.

According to another general aspect of at least one embodiment, a non-transitory computer readable medium is presented containing data content generated according to the method or the apparatus of any of the preceding descriptions.

According to another general aspect of at least one embodiment, a signal or a bitstream is provided comprising video data generated according to the method or the apparatus of any of the preceding descriptions. One or more of the present embodiments also provide a computer readable storage medium having stored thereon instructions for encoding or decoding video data according to any of the methods described above. The present embodiments also provide a computer readable storage medium having stored thereon a bitstream generated according to the methods described above. The present embodiments also provide a method and apparatus for transmitting the bitstream generated according to the methods described above. The present embodiments also provide a computer program product including instructions for performing any of the methods described.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of an encoding method according to a general aspect of at least one embodiment.

FIG. 2 illustrates an example of a decoding method according to a general aspect of at least one embodiment.

FIG. 3 illustrates an example of picture split into coding blocks.

FIG. 4 illustrates an example of delta-QP based on luma variance.

FIG. 5 illustrates an example of implicit delta-QP based on split depth according to a second embodiment.

FIG. 6 illustrates an example of implicit delta-QP based on block area according to a first embodiment.

FIG. 7 illustrates an example of a general flowchart using QP-offset table.

FIG. 8 illustrates another example of a general flowchart using QP-offset table.

FIG 9 illustrates a block diagram of an embodiment of video encoder in which various aspects of the embodiments may be implemented.

FIG. 10 illustrates a block diagram of an embodiment of video decoder in which various aspects of the embodiments may be implemented.

FIG. 1 1 illustrates a block diagram of an example apparatus in which various aspects of the embodiments may be implemented.

DETAILED DESCRIPTION

It is to be understood that the figures and descriptions have been simplified to illustrate elements that are relevant for a clear understanding of the present principles, while eliminating, for purposes of clarity, many other elements found in typical encoding and/or decoding devices. It will be understood that, although the terms first and second may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

The various embodiments are described with respect to the encoding/decoding of an image. They may be applied to encode/decode a part of image, such as a slice or a tile, a tile group or a whole sequence of images.

Various methods are described above, and each of the methods comprises one or more steps or actions for achieving the described method. Unless a specific order of steps or actions is required for proper operation of the method, the order and/or use of specific steps and/or actions may be modified or combined.

At least one embodiment of the present principles addresses the issue of improving compression efficiency with regards to quantization using a local QP offset. As exposed above, a local QP offset (qp_delta) is specified, for example, for each block (AVC), or group of blocks (the quantization group QG in HEVC). In HEVC, the size of a quantization group is determined with a maximum split depth ( diff_cu_qp_delta_depth syntax element from Picture Parameter Set). All blocks resulting from further splits of the Coding Units CU belong to the same quantization group and share the same QP.. However, a fine granularity is needed for better visual results of local QP adaptation. But fine granularity means higher coding cost of QP offsets. This cost can become a significant part of picture bit cost.

At least one embodiment of the present principles proposes to add or adjust a prediction for a local QP offset based on the current block size. The feature“current block size” is to be taken in a general meaning and according to non-limiting embodiments, the feature“current block size” comprises an information representative of the size of a current block size obtained from a split depth, a block surface, a number of samples, a block’s width or height.

Advantageously, the present principles increase the efficiency of prior art methods in the signaling of the block quantization parameter in a block-based video codec where multiple block sizes and rectangular shapes are supported.

In the following, a generic embodiment for a coding method and a generic embodiment for a decoding method are disclosed that comprise adjusting the quantization parameter QP to block size. Then, various embodiments are described wherein adjusting the QP is based on the block surface, or wherein adjusting the QP is based on the block split depth, or wherein the dynamic range of the QP is improved. The various embodiments are compatible with the encoding/decoding method and they can be used individually or in any combination.

Generic embodiments for a codinq/decodinq method usinq QP adapted to block size According to at least one embodiment, a differential term, called offset in the following, is incorporated in the computation of the QP used to code/decode a block or coding unit (CU), and which depends on the size of the coded block. Advantageously, this differential term introduces a fine granularity in QP derivation process resulting in better perceptual visual quality in the compression. This differential term is distinct from the coded difference (delta_QP) between the predicted QP and actual QP of a block since related to the block size.

According to a particular embodiment, this newly introduced differential term, noted QP offset or QPo_ffset, is obtained from a table storing different values of QPo_ffset, the values being addressed by an index and the table index depending on the block size. According to another particular embodiment, the differential term QP offset is online computed based on the block size.

According to a first embodiment, the block size is determined from the surface of the block.

According to a second embodiment, the block size is determined from the depth of the block in the coding tree path leading to that block. According to a non-limiting example, the coding tree path is defined according to the HEVC video compression system. According to another non-limiting example, the coding tree path is defined according to the WC video compression system.

Figure 1 illustrates an example of an encoding method according to a general aspect of at least one embodiment. In the encoding method, the determining of a QP is modified according to the present principles. The steps S1 10, S120, S130, S140 and S150 are for instance implemented in the quantization module 130 of the encoder of figure 9. The step S160 is for instance implemented in the entropy coder 145 of the encoder of figure 9.

In a first step S110, a block of transform coefficients in a coding method is accessed. In a second step S120 a quantization parameter (defining a quantization factor) is determined based on a derivation process. Advantageously, the derivation process of the QP is modified to locally adapt QP with a QP_offset depending on the block size. The modified determining S120 of a QP thus comprising determining S130 a quantization parameter offset QP_0ffSetforthe block according to an indication relative to the size of the block and adjusting S140 the quantization parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block. An example of the determining S120 of QP is exposed in a detailed embodiment in the following. Besides, various embodiments are also exposed hereafter wherein the QP_offset is implicitly determined from the block size for instance by accessing a value in a table or from a calculation using the block size. Then in a step S150, the block of transform coefficients is quantized using the adjusted QP, entropy coded in a step S160 and output as a signal to a decoder.

Figure 2 illustrates an example of a decoding method according to a general aspect of at least one embodiment. In the decoding method, the determining of a QP is modified according to the present principles. The steps S210, S220, S230, S240 and S250 are for instance implemented in the inverse quantization module 140 of the encoder of figure 9 or in the inverse quantization module 240 of the decoder of figure 10.

In a first step S210, after entropy decoding and partitioning into blocks, a block of quantized transform coefficients in a decoding method is accessed. In a second step S220 a quantization parameter (defining a quantization factor) is determined based on a derivation process. Advantageously, the derivation process of the QP is modified to locally adapt QP with a QP_0ffSet depending on the block size. The modified determining S220 of a QP thus comprising determining S230 a quantization parameter offset QP_0ffSet for the block according to an indication relative to the size of the block and adjusting S240 the quantization parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block. Similar to the determining S120 of QP for the encoding, the determining S220 of QP for the decoding is further exposed in a detailed embodiment. According to various embodiments also exposed hereafter, the QP_0ffSet is implicitly determined from the block size for instance by accessing a value in a table. For example, a table of offsets is transmitted to the decoder. The decoder then builds an index based on current block size and uses it to derive a QP_0ffSet from the table. In a variant, the QP_0ffSet is computed from the block size. Then in a step S250, the block of quantized transform coefficients is inverse-quantized using the adjusted QP, and the block of image pixels is reconstructed in a step S260 and output for instance to a display.

According to the present principles the QP derivation process is modified to adapt the QP to the block size. In perceptual video coding, a significant correlation between block size and QP-delta has been observed by the inventors. For instance, Figure 3 illustrates an example of a picture split into coding blocks and Figure 4 illustrates an example of delta-QP based on luma variance. In Figure 4, the lighter the block is, the higher the delta-QP for the block is. QP local adjustment is often correlated to the block size, because small blocks are often used for small details. This is illustrated by the correlation between block size and QP values observed on Figure 4. Besides, detailed areas, hence with high activity (e.g. luma variance, contrast), are usually encoded with higher QP for psycho- visual adaptation reasons, because the human eye is less sensitive to small variations in high activity areas. Advantageously, the present principles therefore allow:

either to reduce QP coding granularity by using coarser QGs (thus saving coding bits), and refine with size-based offsets for blocks smaller than QGs;

or to predict QP-delta using block size, when useful (smaller QP-delta, meaning less bits).

or both.

According to a particular embodiment, an implicit QP offset is retrieved from a table, using an index based on block size (taken in a broad sense). According to a particular embodiment, an index in a table of QP offset values is determined from a function applied to the block size. For example, the index is a logarithmic function applied to a ratio between block surface and CTU surface, being equal to log2(CTU surface) - log2(current block surface). Figure 6 illustrates an example of implicit delta-QP based on block area according to a first embodiment. In another example, the index is equal to a split depth. Figure 5 illustrates an example of implicit delta-QP based on split depth according to a second embodiment. As previously, in Figure 5 and in Figure 6, the lighter the block is, the higher the implicit delta-QP for the block. Advantageously, a better correlation is observed with the first embodiment wherein block size is interpreted as a block area (log2(CTU surface) - log2(current block surface)).

The advantage of the proposed methods against the prior art is that for a given typical QP allocation to optimize the perceptual video coding of a given picture, the rate cost associated with the signaling of the Quantization Parameters is reduced. By typical QP allocation, one means, for instance, a classical and known perceptual video coding method, where the QPs of various coding blocks are decided as a function of the spatial activity of the original signal in the block.

A first embodiment wherein QP offset is based on the block surface

According to a first embodiment, determining a quantizing parameter offset QP_0ffSet comprises determining an indication of a surface for the block. Firstly, this section describes various embodiments wherein the QP_0ffSet is retrieved from a table based on the indication of a surface for the block including various embodiments for specification of the QP_0ffSet table and the signaling of the QP_0ffSet table. Next, some embodiments for automated QP_0ffSet computed as a function of the block size are disclosed. Finally, the decoder and encoder side process to compute the CU final QP as a function of the QP_0ffSet is detailed. Figure 7 illustrates an example of a general flowchart using QP offset table. According to various embodiments, the method 700 of figure 7 is implemented in the determining of QP S120 of an encoding method or in the determining of QP S220 of a decoding method. Thus, in a first step S710, to determine a QP_0ffSet based on block size, a table is accessed in which a plurality of QP_0ffSet values are stored. The plurality of QP_0ffSet values are respectively determined according to an indication of the block size, and for instance in this embodiment, according to an indication of a surface for the block. In a variant, a QPo_ffset among the plurality of QP_offset in the table is accessed through an index. Thus, a step S720, an index in a table of quantizing parameter offsets QP_offset is determined from a function applied to the surface of the block. Various embodiments of such function are detailed hereafter. Then, a step S730, the quantizing parameter offset QP_0ffSet for the block is retrieved from the table through the determined index and used for adjusting the QP for the block in a step S740. In following, various embodiments of table specification and indexing are described.

According to a particular characteristic of the first embodiment, the table is pre-defined, i.e. the table is a priori known by the encoder and decoder. Advantageously no syntax element relative to the table is needed in the coded-bit-stream. In the first embodiment, the proposed table of QP_offset values is defined as a function of the block surface. The block surfaces supported by the codec are all the power-of-2 integers comprised between the minimum CU surface, i.e. 4x4=2⁴ in Luma component, and the whole CTU surface, for instance

128x128=2¹⁴. However, the minimum block surface and maximum block surface are not limited to those numerical examples and any other values defined by a codec for minimum block surface and maximum block surface are compatible with the present principles. According to a first variant, the quantizing parameter offsets in the table and the indexing are defined as a function of the block surface. In a non-limiting example, the function is a log2 of a ratio between the surface of the block and the minimum surface of a block, the pre-defined

table of QP_0ffSet values typically takes the form of Table 1. The variable Log2S is defined as follows:

Log2S = log2(width X height ) — log2(min_width X minjieight) , where width and height are the sizes of the considered rectangular CU (current block), and min_width and minjieight are the dimensions of the minimum CU size (for instance min_width and minjieight are equal to 4 in the above numerical example).

Table 1 : table of values as a function of the CU/MinCU surface ratio

For each entry Log2S of the table, an associated QP_0ffSet value is specified by the table.

According to another non-limiting example, the function is a log2 of a ratio between the surface of the block and the maximum surface of a block, the entry to the above table then consists in the log2 of the surface ratio between the maximum CU size (i.e. CTU surface) and the surface of the CU being processed (current block). In such case, the table of QP_0ffset may take the form of table 2.

Table 2: table of QP_nf^t values as a function of the CTU/CU surface ratio.

In another non-limiting example, the function is a log2 of a ratio between the surface block and the surface of the quantization group (QG) of the block. The pre-defined table of QP_0ffSet values are then defined based on the surface ratio of the considered block over the surface of quantization group QG for instance defined by a standard such as WC. The skilled in the art will easily adapt such ratio, for instance to HEVC, by considering CTU_surface / 4^Adiff_cu_qp_delta_depth wherein the syntax element diff_cu_qp_delta_depth defined the quantization group size in HEVC.

Table 3 and Table 4 illustrate various non-limiting numerical examples QPoffset values as a function of the block surface ratio over the QG size.

Table 3: table of QPo_ffset values as a function of the block surface relative to the QG surface

Table 4: table of values as a function of the block surface relative to the QG surface

According to a second variant, the quantizing offsets in the table and the indexing are further defined as a function of the QG size itself as illustrated in table 5.

Table 5: table of values as a function of the block surface relative to the QG surface

and of the QG surface itself

In a variant, the reference QG size can be the one of the current quantization group, with the table limited to smaller blocks (resulting from current quantization group subdivision), i.e. negative indexes.

According to another particular characteristic of the first embodiment, the table is signaled in the bitstream. Thus, unlike in the embodiment where the table of QP_offset is a set of pre-defined values of QPoffset, which is commonly known in advance by the encoder and the decoder, the table is signaled from the encoder to the decoder. Advantageously, the table of QP_offset is renewable in the decoder. According to another particular characteristic of the first embodiment, a default QP_offset table is advantageously pre-defined as described above. Moreover, according to a high-level syntax flag QPOffsetTableCoded, a table different from the default one may be signaled in the bitstream. If true, then the coded table of QP_0ffSet may appear after the flag QPOffsetTableCoded flag. A SPS syntax table is modified as marked up in bold in Table 6. Table 6 illustrates a SPS syntax table modified wherein the QPOffsetTableCoded flag here takes the form of the SPS syntax element sp^s_qp_off^set_table_preset_flag and each coded QP_0ffSet value takes the form of the syntax elements sps_block_size_qp_offset[ i ].

Table 6: Example of modified SPS syntax table

In table 6, numBlockSizeQpOffset is equal to the number of elements in the array of QP_0ffSet, i.e. 6 here. The table for all possible block sizes could also be transmitted by defining numBlockSizeQpOffset = 2*(log2_ctu_size_minus2

log2_min_luma_coding_block_size_minus2).

In yet another variant, the length of the table can be transmitted using the syntax element num_block_size_qp_offset_minus2, as illustrated in the table 7 in bold:

Table 7 : Example of modified SPS table syntax with explicit length

According to yet other variants, the table of QP_0ffSet is coded in the PPS or in the slice header or in the tile group or in some tile header or any other header container present in the considered video coding system. According to a non-limiting example, a PPS syntax table is modified as marked up in bold for signaling the QP_0ffSet table are indicated below in table 8.

Table 8: Example of modified PPS syntax table

An example of semantics for the PPS table is as followed:

num_block_size_qp_offset specifies the number of pps_block_size_qp_offset[ i ] that are present in the PPS. If zero or one, no pps_block_size_qp_offset[ i ] are coded and all values are inferred to zero. The value of num_block_size_qp_offset shall be in the range is 0 to 2*(log2_ctu_size_minus2 - log2_min_luma_coding_block_size_minus2) + 1 , inclusive.

pps_block_size_qp_offset[ i ] specifies the offset array used to derive the modified QP. After num_block_size_qp_offset elements are decoded, the array is extended to 2*(log2_ctu_size_minus2 - log2_min_luma_coding_block_size_minus2) + 1 elements by repeating the last decoded value. The value of pps_block_size_qp_offset[ i ] shall be in the range -( 32 + QpBdOffset / 2 ) to +( 31 + QpBdOffset / 2 ), inclusive wherein the QpBdOffset is the value of the quantization parameter range offset (for both luma and chroma) and is a function of the bit depth bit_depth_minus8 of the samples (QpBdOffset = 6 * bit_depth_minus8).

In a variant, the table size (num_block_size_qp_offset) is also defined by default by the specification (e.g. 6, or full length derived from other parameters, e.g. maxSubdiv+ 1). In that case, a coding flag (pps_block_size_qp_offset_present_flag) is specified, e.g. as follows in table 9.

Table 9 : Example of PPS syntax table with explicit length Advantageously, the QP offset table signalled in the PPS allows to adapt the values of the QP offset table to at least one of picture type, a hierarchy level, a picture-level QP.

Furthermore, according to another variant, the QP_0ffSet values of the table are coded in a differential way from value to value, knowing that they are ranked in increasing or decreasing order, depending on the embodiment of previous section used to specify the table. This differential coding limits the rate cost associated to the coding of the table of QP_0ffSet values.

According to another particular characteristic of the first embodiment wherein the table of QP_offset is a set of pre-defined values of QP_0ffSet known by the encoder and decoder, the values of QP_offset retrieved from the pre-defined are further scaled. Figure 8 illustrates an example of a general flowchart using QP offset table with scaling. Even if described for a pre-defined table of QP offset, the present scaling is not limited to this embodiment, and will be easily adapted to the embodiments wherein the QP offset is online computed or retrieved from signaled tables. According to various embodiments, the method 800 of figure 8 is implemented in the determining of QP S120 of an encoding method or in the determining of QP S220 of a decoding method. In a first step S810, a table is accessed in which a plurality of QP_offset values are stored. The plurality of QP_offset values ( bloc _size_qp_offset[\] ) and indexes are respectively determined according to an indication of the block size according toany of the variants described for the specification of a table and index based on a block surface. In a step S820, the index i for the current block is determined from a function applied to the surface of the block. In a step S830, the scaling parameters for the current block are determined. The scaling parameters for instance comprise a scaling factor qp_offset_scale and a normalizing factor qp_offset_shift. In a variant the scaling factor qp_offset_scale is signaled in the bitstream at at least one of the SPS level, PPS level, slice/tile level, or CTU level. In a variant, the normalizing factor qp_offset_shift is fixed, for instance known in advance by both encoder and decoder. In another variant, the normalizing factor qp_offset_shift is transmitted by other means, for instance in the bitstream as done for qp_offset_scale. A scaling factor advantageously allows modifying the dynamic range of QP offset which is highly dependent on coding quality level (picture-level QP), on intra complexity, and temporal complexity (rate control). Then, in a step S840, the quantizing parameter offset QP_offset for the block is retrieved from the table through the determined index and used for adjusting the QP for the block in a step S860. Besides, according to the characteristic of the present embodiment, the retrieved quantizing parameter offset block_size_qp_offset[i] for index i for the block is scaled according to:

QP_offset = ( block_size_qp_offset[\]^*qp_offset_scale ) » qp_offset_shift.

Then in a step 860, the scaled QP_offset is used for adjusting the QP for the block. This variant advantageously further improves adaptation to specific areas in the image (text/banners, logos, faces, grass, ...). Accordingly, it is desirable to control it at sub-picture level where different adaptation rules are applied.

To that end, according to another characteristic, a control syntax element is added at the CTU level, conditioned to a higher-level enabling flag (e.g. slice, PPS, or SPS), like slice_qp_offset_scale_enabled_flag. In a particular variant, an index to a scaling factor table is signaled as marked up in bold in the table below. Advantageously, the indexing in a table allows the scaling factor being more flexible than an enable flag, and consistent with what can be done at picture level. Actually, QP dynamic range is key to psychovisual quality and encoders often make use of a scaling factor as part of the adaptation rules, which highly depends on spatial and temporal complexity of the video content. The scaling factor table is designed so that more frequent factors are coded first (requiring less bits for the index).

Table 10: blockSize Qp Offset Scaler syntax

ctb_sz_qp_offset_scaler specifies the scaling factor used when applying block-size-based implicit QP offset. When not present, blockSizeQpOffsetScale is inferred to the default value (1 « blockSizeQpOffsetShift). When present, blockSizeQpOffsetScale is computed as follows:

blockSizeQpOffsetScale = blockSizeQpOffsetScaleTable[ ctb_sz_qp_offset_scaler ] In a particular variant, ctb_sz_qp_offset_scaler is coded with arithmetic coding, in a way similar to the coding of delta_qp which is coded through the syntax element cu_qp_delta_abs representative of the magnitude of the delta_qp. According to a non-limiting example, blockSizeQpOffsetShift is defined by the specification, e.g. 3.

According to a non-limiting example, blockSizeQpOffsetScaleTable specifies possible scaling factors and is defined by default in the specification as illustrated for example in table 1 1 :

Table 1 1 : blockSizeQpOffsetScaleTable syntax

This table could be extended to values greater than (1 « blockSizeQpOffsetShift) to allow greater than 1 scaling factors (e.g. up to 15).

According to another characteristic for the first embodiment, the QP₀ff_Set is directly computed as a function of the block size. Thus, unlike in the previous embodiment, no table and indexing are used. According to a particular variant, QPoffset value is computed following an affine relationship between the block size and the QPoffset. The following equations illustrate 2 exemplary affine relationships:

QPoffset = (size_index^*a - b) » c Or:

QPoffset = (sizejndex - b)^*a » c

Where sizejndex is obtained as the log2 of the surface ratio between the current CU surface and the Quantization Group surface as in the previous example of block size. Moreover, a and b are integer values, which are coded in the in some header data container, for instance the PPS, slice header, CTU header data. The value c is a constant, typically equal to 8, 6 or 4 for example. According to other non-limiting values, if c is equal to 4, according to a first variant, a is equal to -8 et b is equal to -48. According a second non-limiting variant, if c is equal to 4, a is equal to -1 et b is equal to 3. In any of the steps S140, S240, S740 or S860, the block final QP, respectively used in the quantization or dequantization by the encoder or the decoder, is computed as a function of the QP_offset. This section describes how the block final QP, noted QPy, is adjusted by adding the quantizing parameter offset QP_offset to a quantizing parameter previously determined QP’y for the block. First, the quantizing parameter QP’y of a CU is usually computed as: QP’y = pred_QP + delta_QP

Where pred_QP is the predicted value of the QP and delta_QP is the coded QP difference (or QP_delta) associated to the current block/CU.

According to the present principles, the block size dependent QP_offset is then used to adjust the final QP value in in the coding/decoding of the considered CU: QPy = QP’y + QPoffset

Where QP_offset is the differential term proposed in the present principles.

According to a variant, the final computed QP_Y is used for the block coding, stored on the CU- level, and used for the prediction of the QP of subsequent CUs to encode or decode in the current picture. According to another variant, the final computed QP_Y is only used as a temporary QP values for the quantization/inverse quantization steps in the current CU, as well as for the deblocking filtering step. However, it is not used as a reference QP value for the prediction of subsequent CU in the current picture.

A second embodiment wherein QP offset is based on the CU depth

According to a second embodiment, determining a quantizing parameter offset QP_0ffSet comprises determining an indication of a split depth for the block. The different variants described for the first embodiment are easily derivable for this second embodiment as detailed hereafter for the tables of QP_0ffSet values. Naturally, the block size is not limited to those 2 detailed embodiments and the index related to block size is for instance, in the context of 360° projection into account, log2(block height) for equi-rectangular projection ERP.

This section describes various embodiments wherein the QP_0ffSet is retrieved from a table based on the indication of a split depth for the block including the different specifications of the QP_offset table and signaling of the QP_offset table. Then, the final QP computation, in the case of a table of QP_offset indexed as a function of the depth, is the same as that of first embodiment. In a HEVC, a delta_qp is defined at the level of the quantization group and the quantization group is determined by its split depth in the coding unit ( diff_cu_qp_delta_depth ). In a latest approach of WC, the coding of the delta_QP is also defined at the level of the quantization group but the depth of a quantization group (CuQpDeltaSubdiv) is determined as a function of both the split depth in the coding unit CU and the block area (cbSubdiv) to compensate for binary or ternary tree. Basically, during the parsing of the coding tree and the CTU splitting process on the decoder side, each time a coding tree node is encountered with an overall CU depth (quad-tree depth + binary/ternary tree depth) less or equal to an SPS-coded value “diff_cu_qp_delta_depth“ or“CuQpDeltaSubdiv”, then the delta_QP of the Quantization Group corresponding to the picture area covered by the current coding tree node is marked as not yet coded. In that state, when decoding the first TU (transform unit) contained in that area, a delta QP value is decoded, and it applies to subsequent CUs contained in the considered picture area.

According to the second embodiment, the table of QP_offset values is defined as a function of the split depth of the block/CU. In a typical video codec, the picture is recursively split into square or rectangular blocks (also named Coding Units or Transform Units). The split depth of a current block thus refers to the number of recursive splits for obtaining the current block, called depth. In most recent approach, the split can be more complex. Thus, by depth of the CU, cbSubdiv, one means the cumulated quad-tree plus binary/ternary depth compensated with block area. A first variant for table specification consists in defining some positive QPoffset values for CU depths, respectively depth or cbSubdiv, which are higher than the quantization group depth, respectively diff_cu_qp_delta_depth in HEVC or CuQpDeltaSubdiv in WC. This typically takes the form of table 12, which provides exemplary QP offset values as a function of the difference between the depth of a CU and the quantization group’s depth, when positive.

Table 12: table of values as a function of the CU depth level relative to the quantization

group depth level, when the CU depth is higher than the depth of the minimum QG

According to another variant, some negative QP_offset values are assigned to some CU, when the depth of the CU is lower than the depth associated to the smallest quantization group (hence the maximum split depth). Exemplary QP_offset for that variant are given on table 13:

j

Table 13: table of QPo_ffset values according to the CIJ depth relative to the Quantization group depth level, when the CU depth is lower than the depth of the minimum QG

In a third, variant, a combination of the two above variants may be used, as is illustrated on the example of table 14:

Table 14: table of QP_nftset values according to the CL) depth relative to the Quantization group depth level, when the CU depth is lower or higher than the depth of the minimum QG

A last variant forthe specification of the table of the QP_offset may consists in a 2D QP_offset tables, where the QP_offset depends both on the CU depth relative to the smallest quantization group and on the value the smallest quantization group itself. An exemplary 2D table is given on table 15:

Table 15: table of values according to the CU depth relative to the quantization group

depth level and according to the QG depth itself

As for the first embodiment, the second embodiment is compatible with any of the variants for signaling a QPoffset table. For instance, the table of QP_offset is signaled in the bit-stream and table of SPS is modified as illustrated in bold in the following table 16:

Table 16: Example of modified SPS syntax table

As described for the corresponding first embodiment, in table 16. the QPOffsetTableCoded flag here takes the form of the proposed SPS syntax element ^sps_qp_off^set_table_preset_flag. Each coded QPoffset value takes the form of the syntax elements sps_block_dept_qp_offset[ i ]. numRelativeDepths is equal to the number of elements in the array of QPoffset, i.e. 4 here. Additional variant with multiple tables

According to some further variant, multiple pre-defined or transmitted tables of QP_0ffSet values are used. One table out of the multiple available tables is chosen on the encoder side. An index identifying the chosen table is transmitted in the bit-stream, on the sequence (SPS), PPS, slice, tile-group, tile, CTU, quantization group or CU level. This variant advantageously improve flexibility around dQP dynamic range, and adaptation to specific areas in the image (text/banners, logos, faces, grass, ...).

Additional Embodiments and Information

This application describes a variety of aspects, including tools, features, embodiments, models, approaches, etc. Many of these aspects are described with specificity and, at least to show the individual characteristics, are often described in a manner that may sound limiting. However, this is for purposes of clarity in description, and does not limit the application or scope of those aspects. Indeed, all of the different aspects can be combined and interchanged to provide further aspects. Moreover, the aspects can be combined and interchanged with aspects described in earlier filings as well.

The aspects described and contemplated in this application can be implemented in many different forms. FIGs. 9, 10 and 1 1 below provide some embodiments, but other embodiments are contemplated and the discussion of FIGs. 9, 10 and 11 does not limit the breadth of the implementations. At least one of the aspects generally relates to video encoding and decoding, and at least one other aspect generally relates to transmitting a bitstream generated or encoded. These and other aspects can be implemented as a method, an apparatus, a computer readable storage medium having stored thereon instructions for encoding or decoding video data according to any of the methods described, and/or a computer readable storage medium having stored thereon a bitstream generated according to any of the methods described.

In the present application, the terms “reconstructed” and “decoded” may be used interchangeably, the terms“pixel” and“sample” may be used interchangeably, the terms “image,”“picture” and“frame” may be used interchangeably. Usually, but not necessarily, the term“reconstructed” is used at the encoder side while“decoded” is used at the decoder side. The terms HDR (high dynamic range) and SDR (standard dynamic range) are used in this disclosure. Those terms often convey specific values of dynamic range to those of ordinary skill in the art. However, additional embodiments are also intended in which a reference to HDR is understood to mean“higher dynamic range” and a reference to SDR is understood to mean “lower dynamic range”. Such additional embodiments are not constrained by any specific values of dynamic range that might often be associated with the terms“high dynamic range” and“standard dynamic range”.

Various methods are described herein, and each of the methods comprises one or more steps or actions for achieving the described method. Unless a specific order of steps or actions is required for proper operation of the method, the order and/or use of specific steps and/or actions may be modified or combined.

Various methods and other aspects described in this application can be used to modify modules, for example, the quantization and inverse-quantization modules (130, 140, 240), of a video encoder 100 and decoder 200 as shown in FIG. 9 and FIG. 10. Moreover, the present aspects are not limited to WC or HEVC, and can be applied, for example, to other standards and recommendations, whether pre-existing or future-developed, and extensions of any such standards and recommendations (including WC and HEVC). Unless indicated otherwise, or technically precluded, the aspects described in this application can be used individually or in combination.

Various numeric values are used in the present application, for example, the QP_0ffSet values defined in the tables. The specific values are for example purposes and the aspects described are not limited to these specific values.

FIG. 9 illustrates an encoder 100 for instance implementing the encoding method 100 of FIG. 1. Variations of this encoder 100 are contemplated, but the encoder 100 is described below for purposes of clarity without describing all expected variations.

Before being encoded, the video sequence may go through pre-encoding processing (101), for example, applying a color transform to the input color picture (e.g., conversion from RGB 4:4:4 to YCbCr 4:2:0), or performing a remapping of the input picture components in order to get a signal distribution more resilient to compression (for instance using a histogram equalization of one of the color components). Metadata can be associated with the preprocessing and attached to the bitstream.

In the encoder 100, a picture is encoded by the encoder elements as described below. The picture to be encoded is partitioned (102) and processed in units of, for example, CUs. Each unit is encoded using, for example, either an intra or inter mode. When a unit is encoded in an intra mode, it performs intra prediction (160). In an inter mode, motion estimation (175) and compensation (170) are performed. The encoder decides (105) which one of the intra mode or inter mode to use for encoding the unit, and indicates the intra/inter decision by, for example, a prediction mode flag. Prediction residuals are calculated, for example, by subtracting (1 10) the predicted block from the original image block.

The prediction residuals are then transformed (125) and quantized (130). The quantized transform coefficients, as well as motion vectors and other syntax elements, are entropy coded (145) to output a bitstream. The encoder can skip the transform and apply quantization directly to the non-transformed residual signal. The encoder can bypass both transform and quantization, i.e., the residual is coded directly without the application of the transform or quantization processes.

The encoder decodes an encoded block to provide a reference for further predictions. The quantized transform coefficients are de-quantized (140) and inverse transformed (150) to decode prediction residuals. Combining (155) the decoded prediction residuals and the predicted block, an image block is reconstructed. In-loop filters (165) are applied to the reconstructed picture to perform, for example, deblocking/SAO (Sample Adaptive Offset) filtering to reduce encoding artifacts. The filtered image is stored at a reference picture buffer (180).

FIG. 10 illustrates a block diagram of a video decoder 200 for instance implementing the decoding method 200 of FIG. 2. In the decoder 200, a bitstream is decoded by the decoder elements as described below. Video decoder 200 generally performs a decoding pass reciprocal to the encoding pass as described in FIG. 9. The encoder 100 also generally performs video decoding as part of encoding video data.

In particular, the input of the decoder includes a video bitstream, which can be generated by video encoder 100. The bitstream is first entropy decoded (230) to obtain transform coefficients, motion vectors, and other coded information. The picture partition information indicates how the picture is partitioned. The decoder may therefore divide (235) the picture according to the decoded picture partitioning information. The transform coefficients are de- quantized (240) and inverse transformed (250) to decode the prediction residuals. Combining (255) the decoded prediction residuals and the predicted block, an image block is reconstructed. The predicted block can be obtained (270) from intra prediction (260) or motion-compensated prediction (i.e., inter prediction) (275). In-loop filters (265) are applied to the reconstructed image. The filtered image is stored at a reference picture buffer (280). The decoded picture can further go through post-decoding processing (285), for example, an inverse color transform (e.g. conversion from YCbCr 4:2:0 to RGB 4:4:4) or an inverse remapping performing the inverse of the remapping process performed in the pre-encoding processing (101). The post-decoding processing can use metadata derived in the preencoding processing and signaled in the bitstream. FIG. 1 1 illustrates a block diagram of an example of a system in which various aspects and embodiments are implemented. System 1000 can be embodied as a device including the various components described below and is configured to perform one or more of the aspects described in this document. Examples of such devices, include, but are not limited to, various electronic devices such as personal computers, laptop computers, smartphones, tablet computers, digital multimedia set top boxes, digital television receivers, personal video recording systems, connected home appliances, and servers. Elements of system 1000, singly or in combination, can be embodied in a single integrated circuit (IC), multiple ICs, and/or discrete components. For example, in at least one embodiment, the processing and encoder/decoder elements of system 1000 are distributed across multiple ICs and/or discrete components. In various embodiments, the system 1000 is communicatively coupled to one or more other systems, or other electronic devices, via, for example, a communications bus or through dedicated input and/or output ports. In various embodiments, the system 1000 is configured to implement one or more of the aspects described in this document.

The system 1000 includes at least one processor 1010 configured to execute instructions loaded therein for implementing, for example, the various aspects described in this document. Processor 1010 can include embedded memory, input output interface, and various other circuitries as known in the art. The system 1000 includes at least one memory 1020 (e.g., a volatile memory device, and/or a non-volatile memory device). System 1000 includes a storage device 1040, which can include non-volatile memory and/or volatile memory, including, but not limited to, Electrically Erasable Programmable Read-Only Memory (EEPROM), Read-Only Memory (ROM), Programmable Read-Only Memory (PROM), Random Access Memory (RAM), Dynamic Random Access Memory (DRAM), Static Random Access Memory (SRAM), flash, magnetic disk drive, and/or optical disk drive. The storage device 1040 can include an internal storage device, an attached storage device (including detachable and non-detachable storage devices), and/or a network accessible storage device, as non-limiting examples.

System 1000 includes an encoder/decoder module 1030 configured, for example, to process data to provide an encoded video or decoded video, and the encoder/decoder module 1030 can include its own processor and memory. The encoder/decoder module 1030 represents module(s) that can be included in a device to perform the encoding and/or decoding functions. As is known, a device can include one or both of the encoding and decoding modules. Additionally, encoder/decoder module 1030 can be implemented as a separate element of system 1000 or can be incorporated within processor 1010 as a combination of hardware and software as known to those skilled in the art. Program code to be loaded onto processor 1010 or encoder/decoder 1030 to perform the various aspects described in this document can be stored in storage device 1040 and subsequently loaded onto memory 1020 for execution by processor 1010. In accordance with various embodiments, one or more of processor 1010, memory 1020, storage device 1040, and encoder/decoder module 1030 can store one or more of various items during the performance of the processes described in this document. Such stored items can include, but are not limited to, the input video, the decoded video or portions of the decoded video, the bitstream, matrices, variables, and intermediate or final results from the processing of equations, formulas, operations, and operational logic.

In some embodiments, memory inside of the processor 1010 and/or the encoder/decoder module 1030 is used to store instructions and to provide working memory for processing that is needed during encoding or decoding. In other embodiments, however, a memory external to the processing device (for example, the processing device can be either the processor 1010 or the encoder/decoder module 1030) is used for one or more of these functions. The external memory can be the memory 1020 and/or the storage device 1040, for example, a dynamic volatile memory and/or a non-volatile flash memory. In several embodiments, an external non-volatile flash memory is used to store the operating system of, for example, a television. In at least one embodiment, a fast external dynamic volatile memory such as a RAM is used as working memory for video coding and decoding operations, such as for MPEG-2 (MPEG refers to the Moving Picture Experts Group, MPEG-2 is also referred to as ISO/IEC 13818, and 13818-1 is also known as H.222, and 13818-2 is also known as H.262), HEVC (HEVC refers to High Efficiency Video Coding, also known as H.265 and MPEG-H Part 2), or WC (Versatile Video Coding, a new standard being developed by JVET, the Joint Video Experts Team).

The input to the elements of system 1000 can be provided through various input devices as indicated in block 1 130. Such input devices include, but are not limited to, (i) a radio frequency (RF) portion that receives an RF signal transmitted, for example, over the air by a broadcaster, (ii) a Component (COMP) input terminal (or a set of COMP input terminals), (iii) a Universal Serial Bus (USB) input terminal, and/or (iv) a High Definition Multimedia Interface (HDMI) input terminal. Other examples, not shown in FIG. 10, include composite video.

In various embodiments, the input devices of block 1 130 have associated respective input processing elements as known in the art. For example, the RF portion can be associated with elements suitable for (i) selecting a desired frequency (also referred to as selecting a signal, or band-limiting a signal to a band of frequencies), (ii) downconverting the selected signal, (iii) band-limiting again to a narrower band of frequencies to select (for example) a signal frequency band which can be referred to as a channel in certain embodiments, (iv) demodulating the downconverted and band-limited signal, (v) performing error correction, and (vi) demultiplexing to select the desired stream of data packets. The RF portion of various embodiments includes one or more elements to perform these functions, for example, frequency selectors, signal selectors, band-limiters, channel selectors, filters, downconverters, demodulators, error correctors, and demultiplexers. The RF portion can include a tuner that performs various of these functions, including, for example, downconverting the received signal to a lower frequency (for example, an intermediate frequency or a near-baseband frequency) or to baseband. In one set-top box embodiment, the RF portion and its associated input processing element receives an RF signal transmitted over a wired (for example, cable) medium, and performs frequency selection by filtering, downconverting, and filtering again to a desired frequency band. Various embodiments rearrange the order of the above-described (and other) elements, remove some of these elements, and/or add other elements performing similar or different functions. Adding elements can include inserting elements in between existing elements, such as, for example, inserting amplifiers and an analog-to-digital converter. In various embodiments, the RF portion includes an antenna.

Additionally, the USB and/or HDMI terminals can include respective interface processors for connecting system 1000 to other electronic devices across USB and/or HDMI connections. It is to be understood that various aspects of input processing, for example, Reed-Solomon error correction, can be implemented, for example, within a separate input processing IC or within processor 1010 as necessary. Similarly, aspects of USB or HDMI interface processing can be implemented within separate interface ICs or within processor 1010 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor 1010, and encoder/decoder 1030 operating in combination with the memory and storage elements to process the datastream as necessary for presentation on an output device.

Various elements of system 1000 can be provided within an integrated housing, Within the integrated housing, the various elements can be interconnected and transmit data therebetween using suitable connection arrangement, for example, an internal bus as known in the art, including the Inter-IC (I2C) bus, wiring, and printed circuit boards.

The system 1000 includes communication interface 1050 that enables communication with other devices via communication channel 1060. The communication interface 1050 can include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel 1060. The communication interface 1050 can include, but is not limited to, a modem or network card and the communication channel 1060 can be implemented, for example, within a wired and/or a wireless medium.

Data is streamed, or otherwise provided, to the system 1000, in various embodiments, using a wireless network such as a Wi-Fi network, for example IEEE 802.1 1 (IEEE refers to the Institute of Electrical and Electronics Engineers). The Wi-Fi signal of these embodiments is received over the communications channel 1060 and the communications interface 1050 which are adapted for Wi-Fi communications. The communications channel 1060 of these embodiments is typically connected to an access point or router that provides access to external networks including the Internet for allowing streaming applications and other over- the-top communications. Other embodiments provide streamed data to the system 1000 using a set-top box that delivers the data over the HDMI connection of the input block 1 130. Still other embodiments provide streamed data to the system 1000 using the RF connection of the input block 1 130. As indicated above, various embodiments provide data in a non-streaming manner. Additionally, various embodiments use wireless networks other than Wi-Fi, for example a cellular network or a Bluetooth network.

The system 1000 can provide an output signal to various output devices, including a display 1100, speakers 1 1 10, and other peripheral devices 1 120. The display 1 100 of various embodiments includes one or more of, for example, a touchscreen display, an organic light- emitting diode (OLED) display, a curved display, and/or a foldable display. The display 1 100 can be for a television, a tablet, a laptop, a cell phone (mobile phone), or other device. The display 1 100 can also be integrated with other components (for example, as in a smart phone), or separate (for example, an external monitor for a laptop). The other peripheral devices 1 120 include, in various examples of embodiments, one or more of a stand-alone digital video disc (or digital versatile disc) (DVR, for both terms), a disk player, a stereo system, and/or a lighting system. Various embodiments use one or more peripheral devices 1 120 that provide a function based on the output of the system 1000. For example, a disk player performs the function of playing the output of the system 1000.

In various embodiments, control signals are communicated between the system 1000 and the display 1 100, speakers 11 10, or other peripheral devices 1 120 using signaling such as AV.Link, Consumer Electronics Control (CEC), or other communications protocols that enable device-to-device control with or without user intervention. The output devices can be communicatively coupled to system 1000 via dedicated connections through respective interfaces 1070, 1080, and 1090. Alternatively, the output devices can be connected to system 1000 using the communications channel 1060 via the communications interface 1050. The display 1 100 and speakers 1 1 10 can be integrated in a single unit with the other components of system 1000 in an electronic device such as, for example, a television. In various embodiments, the display interface 1070 includes a display driver, such as, for example, a timing controller (T Con) chip.

The display 1 100 and speaker 1 1 10 can alternatively be separate from one or more of the other components, for example, if the RF portion of input 1 130 is part of a separate set-top box. In various embodiments in which the display 1 100 and speakers 1 1 10 are external components, the output signal can be provided via dedicated output connections, including, for example, HDMI ports, USB ports, or COMP outputs.

The embodiments can be carried out by computer software implemented by the processor 1010 or by hardware, or by a combination of hardware and software. As a non-limiting example, the embodiments can be implemented by one or more integrated circuits. The memory 1020 can be of any type appropriate to the technical environment and can be implemented using any appropriate data storage technology, such as optical memory devices, magnetic memory devices, semiconductor-based memory devices, fixed memory, and removable memory, as non-limiting examples. The processor 1010 can be of any type appropriate to the technical environment, and can encompass one or more of microprocessors, general purpose computers, special purpose computers, and processors based on a multi-core architecture, as non-limiting examples.

Various implementations involve decoding. “Decoding”, as used in this application, can encompass all or part of the processes performed, for example, on a received encoded sequence in order to produce a final output suitable for display. In various embodiments, such processes include one or more of the processes typically performed by a decoder, for example, entropy decoding, inverse quantization, inverse transformation, and differential decoding. In various embodiments, such processes also, or alternatively, include processes performed by a decoder of various implementations described in this application, for example, determining a quantization parameter QP wherein the QP is adapted to the block size, inverse- quantizing the block of transform coefficients, and reconstructed the image block.

As further examples, in one embodiment“decoding” refers only to entropy decoding, in another embodiment “decoding” refers only to differential decoding, and in another embodiment“decoding” refers to a combination of entropy decoding and differential decoding. Whether the phrase “decoding process” is intended to refer specifically to a subset of operations or generally to the broader decoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art. Various implementations involve encoding. In an analogous way to the above discussion about“decoding”,“encoding” as used in this application can encompass all or part of the processes performed, for example, on an input video sequence in order to produce an encoded bitstream. In various embodiments, such processes include one or more of the processes typically performed by an encoder, for example, partitioning, differential encoding, transformation, quantization, and entropy encoding. In various embodiments, such processes also, or alternatively, include processes performed by an encoder of various implementations described in this application, for example, determining a quantization parameter QP wherein the QP is adapted to the block size, quantizing the block of transform coefficients, and entropy coding the quantized transform coefficients.

As further examples, in one embodiment“encoding” refers only to entropy encoding, in another embodiment “encoding” refers only to differential encoding, and in another embodiment“encoding” refers to a combination of differential encoding and entropy encoding. Whether the phrase “encoding process” is intended to refer specifically to a subset of operations or generally to the broader encoding process will be clear based on the context of the specific descriptions and is believed to be well understood by those skilled in the art.

Note that the syntax elements as used herein, for example, delta_qp, are descriptive terms. As such, they do not preclude the use of other syntax element names.

When a figure is presented as a flow diagram, it should be understood that it also provides a block diagram of a corresponding apparatus. Similarly, when a figure is presented as a block diagram, it should be understood that it also provides a flow diagram of a corresponding method/process.

The implementations and aspects described herein can be implemented in, for example, a method or a process, an apparatus, a software program, a data stream, or a signal. Even if only discussed in the context of a single form of implementation (for example, discussed only as a method), the implementation of features discussed can also be implemented in other forms (for example, an apparatus or program). An apparatus can be implemented in, for example, appropriate hardware, software, and firmware. The methods can be implemented in, for example, , a processor, which refers to processing devices in general, including, for example, a computer, a microprocessor, an integrated circuit, or a programmable logic device. Processors also include communication devices, such as, for example, computers, cell phones, portable/personal digital assistants ("PDAs"), and other devices that facilitate communication of information between end-users.

Reference to “one embodiment” or “an embodiment” or “one implementation” or “an implementation”, as well as other variations thereof, means that a particular feature, structure, characteristic, and so forth described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrase“in one embodiment” or“in an embodiment” or “in one implementation” or “in an implementation”, as well any other variations, appearing in various places throughout this application are not necessarily all referring to the same embodiment.

Additionally, this application may refer to “determining” various pieces of information. Determining the information can include one or more of, for example, estimating the information, calculating the information, predicting the information, or retrieving the information from memory.

Further, this application may refer to“accessing” various pieces of information. Accessing the information can include one or more of, for example, receiving the information, retrieving the information (for example, from memory), storing the information, moving the information, copying the information, calculating the information, determining the information, predicting the information, or estimating the information.

Additionally, this application may refer to“receiving” various pieces of information. Receiving is, as with“accessing”, intended to be a broad term. Receiving the information can include one or more of, for example, accessing the information, or retrieving the information (for example, from memory). Further, “receiving” is typically involved, in one way or another, during operations such as, for example, storing the information, processing the information, transmitting the information, moving the information, copying the information, erasing the information, calculating the information, determining the information, predicting the information, or estimating the information.

It is to be appreciated that the use of any of the following 7”,“and/or”, and“at least one of, for example, in the cases of“A/B”,“A and/or B” and“at least one of A and B”, is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of both options (A and B). As a further example, in the cases of“A, B, and/or C” and“at least one of A, B, and C”, such phrasing is intended to encompass the selection of the first listed option (A) only, or the selection of the second listed option (B) only, or the selection of the third listed option (C) only, or the selection of the first and the second listed options (A and B) only, or the selection of the first and third listed options (A and C) only, or the selection of the second and third listed options (B and C) only, or the selection of all three options (A and B and C). This may be extended, as is clear to one of ordinary skill in this and related arts, for as many items as are listed.

Also, as used herein, the word“signal” refers to, among other things, indicating something to a corresponding decoder. For example, in certain embodiments the encoder signals a particular one of a plurality of parameters for QP prediction method or tables. In this way, in an embodiment the same parameter is used at both the encoder side and the decoder side. Thus, for example, an encoder can transmit (explicit signaling) a particular parameter to the decoder so that the decoder can use the same particular parameter. Conversely, if the decoder already has the particular parameter as well as others, then signaling can be used without transmitting (implicit signaling) to simply allow the decoder to know and select the particular parameter. By avoiding transmission of any actual functions, a bit savings is realized in various embodiments. It is to be appreciated that signaling can be accomplished in a variety of ways. For example, one or more syntax elements, flags, and so forth are used to signal information to a corresponding decoder in various embodiments. While the preceding relates to the verb form of the word“signal”, the word“signal” can also be used herein as a noun.

As will be evident to one of ordinary skill in the art, implementations can produce a variety of signals formatted to carry information that can be, for example, stored or transmitted. The information can include, for example, instructions for performing a method, or data produced by one of the described implementations. For example, a signal can be formatted to carry the bitstream of a described embodiment. Such a signal can be formatted, for example, as an electromagnetic wave (for example, using a radio frequency portion of spectrum) or as a baseband signal. The formatting can include, for example, encoding a data stream and modulating a carrier with the encoded data stream. The information that the signal carries can be, for example, analog or digital information. The signal can be transmitted over a variety of different wired or wireless links, as is known. The signal can be stored on a processor- readable medium.

We describe a number of embodiments. Features of these embodiments can be provided alone or in any combination. Further, embodiments can include one or more of the following features, devices, or aspects, alone or in any combination, across various claim categories and types:

• Modifying the dQP / QP / QP_0ffset prediction and/or derivation process applied in the decoder and/or encoder,

• Enabling several advanced QP derivation methods in the decoder and/or encoder,

• Determining a QP_0ffSet according to an indication relative to the block size in the decoder and/or encoder,

• Determining a QP_0ffSet wherein the block surface is used to derive an indication relative to the block size in the decoder and/or encoder,

• Determining a QP_0ffSet wherein the block depth in a recursive block split is used to derive an indication relative to the block size in the decoder and/or encoder,

• An indication relative to the block size in the decoder and/or encode is an index in a QPo_ffset table, • Determining a QP_0ffSet further comprises scaling the QP_0ffSet for increasing/decreasing the dynamic range,

• Inserting in the signalling syntax elements that enable the decoder to identify the QP derivation method to use,

• Selecting, based on these syntax elements, the QP derivation method to apply at the decoder,

• Applying the QP derivation method for deriving the QP at the decoder,

• Adapting residues at an encoder according to any of the embodiments discussed,

• A bitstream or signal that includes one or more of the described syntax elements, or variations thereof,

• Inserting in the signaling syntax elements that enable the decoder to adapt residues in a manner corresponding to that used by an encoder,

• Creating and/or transmitting and/or receiving and/or decoding a bitstream or signal that includes one or more of the described syntax elements, or variations thereof,

• A TV, set-top box, cell phone, tablet, or other electronic device that performs adaptation of quantization parameter according to any of the embodiments described,

• A TV, set-top box, cell phone, tablet, or other electronic device that performs adaptation of quantization parameter according to any of the embodiments described, and that displays (e.g. using a monitor, screen, or other type of display) a resulting image,

• A TV, set-top box, cell phone, tablet, or other electronic device that selects (e.g. using a tuner) a channel to receive a signal including an encoded image, and performs adaptation of quantization parameters according to any of the embodiments described,

• A TV, set-top box, cell phone, tablet, or other electronic device that receives (e.g. using an antenna) a signal over the air that includes an encoded image, and performs adaptation of quantization parameters according to any of the embodiments described.

Claims

1. A method for encoding a block in an image, said method comprising:

determining (S130) a quantizing parameter offset for said block according to an indication relative to the size of said block;

adjusting (S140) for the block, a quantizing parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block;

quantizing (S150) the block of transform coefficients of the image block using said adjusted quantizing parameter; and

encoding (S160) said block of quantized transform coefficients.

2. A method for decoding a block of an image, said method comprising:

determining (S230) a quantizing parameter offset for said block according to an indication relative to the size of said block;

adjusting (S240) for the block, a quantizing parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block;

inverse-quantizing (S250) a block of quantized transform coefficients using said adjusted quantizing parameter to obtain a block of transform coefficients; and

reconstructing (S260) said block from said block of transform coefficients.

3. An apparatus for encoding a block of an image, said apparatus comprising at least one processor configured to:

determine a quantizing parameter offset for said block according to an indication relative to the size of said block;

adjust for the block, a quantizing parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block;

quantize the block of transform coefficients of the image block using said adjusted quantizing parameter; and

encode said block of quantized transform coefficients.

4. An apparatus for decoding a block in an image, said apparatus comprising at least one processor configured to:

determine a quantizing parameter offset for said block according to an indication relative to the size of said block; adjust for the block, a quantizing parameter by adding the quantizing parameter offset to a quantizing parameter previously determined for the block;

inverse-quantize a block of quantized transform coefficients using said adjusted quantizing parameter to obtain a block of transform coefficients; and

reconstructing (S260) said block from said block of transform coefficients.

5. A method according to claim 1 or 2, or an apparatus according to claim 3 or 4, wherein said determining of a quantizing parameter offset according to an indication relative to the size of said block further comprises determining a surface for said block.

6. A method according to claim 5, or an apparatus according to claim 5, wherein determining a quantizing parameter offset for said block further comprises determining an index in table of quantizing parameter offsets from a function applied to said surface of said block.

7. A method according to claim 6, or an apparatus according to claim 6, wherein said function is one of log2 of a ratio between the surface of said block and a minimum surface of a block, log2 of a ratio between the surface of said block and a maximum surface of a block, log2 of a ratio surface block to a minimum surface of a quantization group.

8. A method according to claim 1 or 2, or an apparatus according to claim 3 or 4, wherein said determining of a quantizing parameter according to an indication relative to the size of said block comprises determining a split depth for said block.

9. A method according to claim 8, or an apparatus according to claim 8, wherein determining a quantizing parameter offset for said block further comprises determining an index in table of quantizing parameter offsets from a function applied to said split depth for said block.

10. A method according to claim 9, or an apparatus according to claim 9, wherein said function is one of difference between the split depth for said block to and the minimum split depth of a quantization group.

11. A method according to any of claims 6, 7, 9 or 10, or an apparatus according to claim 6, 7, 9 or 10, wherein said table of quantizing parameter offsets is signaled in at least one of a SPS message, a PPS message, a picture header, a slice header.

12. A method according to any of claims 1 , 2 or 5-1 1 , or an apparatus according to any of claims 3, 4-1 1 , further comprising determining a scaling factor for the quantizing parameter offset, scaling said quantizing parameter offset for said block using said scaling factor and; wherein adjusting the quantizing parameter comprises adding the scaled quantizing parameter offset to a quantizing parameter previously determined for the block.

13. A bitstream, wherein the bitstream is formed according to the method of any one of claims 1 and 5-12, or the apparatus of any one of claims 3 and 5-12.

14. A non-transitory computer readable medium containing data content generated according to the method of any one of claims 1 and 5-12, orthe apparatus of any one of claims

3 and 5-12.

15. A computer program comprising software code instructions for performing the methods according to any one of claims 1 , 2 or 5 -12 when the computer program is executed by one or several processors.