Patent Application
20230224454
At least one of the present embodiments generally relates to a method or an apparatus for video encoding or decoding, and more particularly, to a method or an apparatus featuring a new information being representative of at least a transform to be applied to the residue of an image block when this block is predicted by a neural network-based intra prediction mode.
To achieve high compression efficiency, image and video coding schemes usually employ 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 correlations, then the difference between an original image block and its prediction, often denoted as prediction error or prediction residual, is transformed, quantized, and entropy coded. To reconstruct the video, the compressed data are decoded by inverse processes corresponding to the entropy coding, quantization, transform, and prediction.
Recent additions to video compression technology include various industry standards, versions of the reference software and/or documentations such as Joint Exploration Model (JEM) and later VTM (Versatile Video Coding (VVC) Test Model) being developed by the JVET (Joint Video Exploration Team) group. The aim is to make further improvements to the existing HEVC (High Efficiency Video Coding) standard.
Existing methods for coding and decoding show some limitations in the choice of the one or more transform(s) to apply to the residue of an image block, for example when this block is predicted by a neural network-based intra prediction mode. Therefore, there is a need to improve the state of the art.
The drawbacks and disadvantages of the prior art are solved and addressed by the general aspects described herein.
According to a first aspect, there is provided a method. The method comprises video decoding by determining an intra prediction of an image block using at least one neural network from a context comprising pixels surrounding the image block; obtaining an information relative to a transform method to apply for decoding the image block, the transform method being adapted to a neural network-based intra prediction mode; obtaining a block of residue of the image block by applying at least one inverse transform to a block of transform coefficients according to the information relative to the transform method; and decoding the image block based on the intra prediction and the block of residue.
According to another aspect, there is provided a second method. The method comprises video encoding by determining an intra prediction of the image block using at least one neural network from a context comprising pixels surrounding the image block; obtaining an information relative to a transform method to apply for encoding the image block, said transform method being adapted to a neural network-based intra prediction mode; obtaining a block of residue from the image block and said intra prediction; obtaining a block of transform coefficients by applying at least one transform to the block of residue according to the information relative to the transform method; and encoding the block of transform coefficients.
According to another aspect, there is provided an apparatus. The apparatus comprises one or more processors, wherein the one or more processors are configured to implement the method for video decoding according to any of its variants. According to another aspect, the apparatus for video decoding comprises means for determining an intra prediction of an image block using at least one neural network from a context comprising pixels surrounding the image block; means for obtaining an information relative to a transform method to apply for decoding the image block, the transform method being adapted to a neural network-based intra prediction mode; means for obtaining a block of residue of the image block by applying at least one inverse transform to a block of transform coefficients according to the information relative to the transform method; and means for decoding the image block based on the intra prediction and the block of residue.
According to another aspect, there is provided another apparatus. The apparatus comprises one or more processors, wherein the one or more processors are configured to implement the method for video encoding according to any of its variants. According to another aspect, the apparatus for video encoding comprises means for determining an intra prediction of the image block using at least one neural network from a context comprising pixels surrounding the image block; means for obtaining an information relative to a transform method to apply for encoding the image block, said transform method being adapted to a neural network-based intra prediction mode; means for obtaining a block of residue from the image block and said intra prediction; means for obtaining a block of transform coefficients by applying at least one transform to the block of residue according to the information relative to the transform method; and means for encoding the block of transform coefficients.
According to another general aspect of at least one embodiment, the information is inferred by the at least one neural network used in intra prediction of the image block from a context comprising pixels surrounding said image block.
According to another general aspect of at least one embodiment, the information relative to a transform method is decoded/encoded in a bitstream.
According to another general aspect of at least one embodiment, the information comprises a transform group index (trGrpIdx) representative of a mapping between a neural network intra prediction mode and a group of transforms among a plurality of groups of transforms.
According to another general aspect of at least one embodiment, the information comprises a transform index (trIdx) representative of a mapping between a neural network intra prediction mode and a transform among a plurality of transforms.
According to another general aspect of at least one embodiment, the information comprises a transform macro group index (trMacroGrpIdx) representative of a mapping between a neural network intra prediction mode and a hierarchical group of transforms.
According to another general aspect of at least one embodiment, one neural network inferring the information relative to a transform method to apply for encoding the image block (or decoding the image block) further comprises one or more output data being any of a scalar, a vector, a tensor from which at least one of a transform group index (trGrpIdx), a transform index (trIdx), a transform macro group index (trMacroGrpIdx) is determined.
According to another general aspect of at least one embodiment, at least one transform among a plurality of transforms of a transform method is learned and the parameters (ϕ) of the learned transforms are signaled in the bitstream.
According to another general aspect of at least one embodiment, at least one neural network inferring information relative to a transform method to apply for encoding the image block (or decoding the image block) is learned and the parameters of the at least one neural network inferring information relative to a transform method to apply are signaled in the bitstream.
According to another general aspect of at least one embodiment, a prediction of the information relative to a transform method to apply for encoding the image block (or decoding the image block) is determined and the information relative to a transform method to apply is predictively encoded/decoded based on the prediction.
According to another general aspect of at least one embodiment, for iterative testing of the encoding parameters of a given image block, the intra prediction of the image block determined by the neural network-based intra prediction mode is saved to the memory the first time it is computed, and the intra prediction of the image block is loaded during each subsequent test.
According to another general aspect of at least one embodiment, at least one neural network inferring information relative to a transform method to apply for encoding the image block (or decoding the image block) is adapted to coding with separate luminance and chrominance tree.
According to another general aspect of at least one embodiment, for iterative testing of the encoding parameters of a given image block, the block of primary transform coefficients resulting from the application of a primary transform to the block of residue of the neural network intra prediction is saved to memory the first time it is computed, and this block of primary transform coefficients is loaded during each subsequent test that requires it
According to another general aspect of at least one embodiment, there is provided a device comprising an apparatus according to any of the decoding embodiments; and at least one of (i) an antenna configured to receive a signal, the signal including the video block, (ii) a band limiter configured to limit the received signal to a band of frequencies that includes the video block, or (iii) a display configured to display an output representative of the video block.
According to another general aspect of at least one embodiment, there is provided a non-transitory computer readable medium containing data content generated according to any of the described encoding embodiments or variants.
According to another general aspect of at least one embodiment, there is provided a signal comprising video data generated according to any of the described encoding embodiments or variants.
According to another general aspect of at least one embodiment, a bitstream is formatted to include data content generated according to any of the described encoding embodiments or variants.
According to another general aspect of at least one embodiment, there is provided a computer program product comprising instructions which, when the program is executed by a computer, cause the computer to carry out any of the described encoding/decoding embodiments or variants.
These and other aspects, features and advantages of the general aspects will become apparent from the following detailed description of exemplary embodiments, which is to be read in connection with the accompanying drawings.
In the drawings, examples of several embodiments are illustrated.
In block-based video codec, intra prediction is employed to exploit the spatial redundancy that exists in an image. For a given image block predicted in intra, the residue, as known as residual block, which corresponds to the difference between the original block and its intra prediction, is transformed and quantized, and the quantized transformed coefficients are entropy coded into the bitstream. According to different coding modes, one or more transform(s) is applied to the residual block and the one or more transform(s) is either explicitly signaled in the bitstream or derived based on available information among which intra prediction mode. The present principles relate to the signaling/deriving of the one or more transform(s) after determining the intra prediction mode predicting a given block. The term “transform(s)” refers to the primary transform(s) and, optionally, the secondary transform(s), the ternary transform(s). For example, in VVC, the transform process is composed of a primary transform picked via the Multiple Transform Selection (MTS) and, optionally, a secondary transform, called Low Frequency Non-Separable Transform (LFNST).
Recent developments of video codec also introduce deep intra prediction which infers an intra prediction of an image block using at least one neural network from a context surrounding this current image block. One of the challenges is to deal with the one or more transform(s) to apply to the residue of an image block when this block is predicted by a neural network-based intra prediction mode.
This is solved and addressed by the general aspects described herein, which are directed to an intra prediction of a current image block using at least one neural network and obtaining an information relative to at least a transform to apply to the residue of image block wherein the information is either signaled in the bitstream and/or inferred by a neural network along with the neural network intra prediction of the current block.
Advantageously, the information on the transform to apply allows to adapt the transform process to any deep intra prediction mode without having a fixed predefined mapping between a deep intra prediction mode and a transform scheme in the encoder and/or decoder. Various embodiments of adaptation are described from the signaling of transform indices according to VVC standard, the signaling of hierarchical groups of transforms, or signaling parameters of a transform or even signaling parameters of neural network inferring transforms for deep intra prediction mode allowing full configurability of the transform scheme.
In the case of an image block predicted via a deep intra prediction mode, when the indices of the transforms to be applied to the residue of prediction are signaled in the bitstream instead of using a fixed predefined mapping between the deep intra prediction mode and the transform scheme, the encoder must run additional tests to find these transform indices. If each of these additional tests implies re-computing the neural network prediction, the running time of the encoder explodes as a neural network inference requires a lot of arithmetic operations.
Similarly, if each of these additional tests implies re-computing the same primary transform coefficients resulting from the application of a given primary transform to the residue of the neural network prediction, the running time of the encoder grows noticeably. That is why, on the encoder side, for a given image block, for the deep intra prediction mode exclusively, the predicted block is saved after being computed the first time. Then, it is loaded during each subsequent test. Similarly, the primary transform coefficients resulting from the application of a given primary transform to the residue of the neural network prediction is saved after being computed the first time. Then, it is loaded during each subsequent test if needed.
Since at least some embodiments relates to the signaling of the transform(s) for a block predicted via a neural network-based intra prediction mode, MTS and the signaling of LFNST are firstly described, the neural network-based intra prediction is then introduced.
Signaling of the Transforms in VVC
The primary transform in VVC is separable. This means that the primary transform coefficients of a given Transform Block (TB) result from the application of a horizontal transform followed by a vertical transform to the difference between this TB and its prediction, called “residue of prediction”. For a luminance TB, the possible pairs of a horizontal transform and a vertical transform are
In the case of a luminance Coding Block (CB), MTS can be explicit, i.e. flags are written to the bitstream to signal the pair of transforms used by its luminance TBs, or implicit, i.e. the pair of transforms is inferred from available information.
sps_mts_enabled_flag=1 and sps_explicit_mts_intra_enabled_flag=1, which corresponds to a standard configuration. In
For a luminance CB with explicit MTS, the horizontal and vertical transforms used by its luminance TBs, denoted trTypeHorizontal and trTypeVertical respectively, are specified by mtsIdx∈{0, 1, 2, 3, 4} as shown in Table 1.
For a luminance CB predicted in intra with implicit MTS, trTypeHorizontal and trTypeVertical are inferred from the available information as shown by the right side of
LFNST is a non-separable secondary transform applied to the primary transform coefficients of a given TB predicted in intra. For TBs of sizes 4×N and N×4, there exists 8 different 16×16 LFNST matrices, N∈{4, 8, 16, 32}. For the other TB sizes, there exist 8 different 48×16 LFNST matrices. In each case, the 8 possible LFNST matrices are grouped into 4 sets of 2 LFNST matrices.
For a given CB, lfnstIdx∈{0, 1, 2} signals, in a set, which of the 2 LFNST matrices applies to the primary transform coefficients of each of its TBs. lfnstIdx=0 means that LFNST is not used. lfnstIdx∈{1, 2} refer to respectively the first and second LFNST matrices of this set. The signaling of lfnstIdx is depicted in
Now, for a given CB predicted in intra with lfnstIdx∈{1, 2}, the set of 2 LFNST matrices to be picked among the 4 possible sets is still to be determined. It is inferred from the index of the intra prediction mode selected to predict this CB, as shown in Table 2. Moreover, the decision of transposing the primary transform coefficients of each TB in this CB is also inferred from the index of the intra prediction mode selected to predict this CB as also shown in Table 2.
0, 1
2, 12
13, 23
24, 34
35, 44
45, 55
56, 80
For a luminance CB predicted via a MIP mode, i.e. mipFlag=1, if its height and width are larger than 16, lfnstIdx can belong to {1, 2} as shown on
For a chrominance CB predicted via a Cross-Component Linear Model (CCLM) mode, if lfnstIdx∈{1, 2}, LFNST for this chrominance CB is defined as follows. If the luminance CB that is collocated with this chrominance CB is predicted by a MIP mode, the index of the set of 2 LFNST matrices and the decision of transposing the primary transform coefficients of the TB of this chrominance CB are inferred from the wide angle intra mode index 0 using Table 2. Otherwise, the index of the set of 2 LFNST matrices and the decision of transposing the primary transform coefficients of the TB of this chrominance CB are inferred from the wide angle intra mode selected to predict this collocated luminance CB using Table 2.
Acceleration of the Intra Search in the Encoder of the VVC Reference Software (VTM)
In a latest version of VTM, for a given image block, the search for the intra prediction mode used to predict this block and the transform(s) to be applied to the residue of prediction is speeded up by saving and loading a given predicted block instead of re-computing this predicted block several times. To illustrate this, let us take a given image block, the intra prediction mode of index intraModeIdx∈0, 66
and analyze when the predicted block is computed/saved/loaded over the different full rate-distortion tests during the intra search of VTM. Here, the “full rate-distortion” test means the computation of the rate-distortion cost of the complete encoding of the image block predicted via the mode of index intraModeIdx. In Table 3, during “Test 0”, the predicted block given by the mode of index intraModeIdx is saved. Then, during the test of Transform Skip (TS) called “Test 1”, this predicted block is loaded. But, apart from this load and save, the same predicted block is re-computed from “Test 2” to “Test 7”. In this variant encoder, we assume that, for a given image block, the predicted block given by each intra prediction mode is not saved once and then loaded when needed as this requires to store at least n predicted blocks, incurring a large memory cost. n denotes the number of intra prediction modes involved in the full rate-distortion tests. Note that, in Table 3, all the heuristics that could stop the series of tests from “Test 0” to “Test 7” early are ignored for clarity. Note also that, in Table 3, during “Test 0”, the primary transform coefficients resulting from the application of the DCT2 horizontally and the DCT2 vertically to the residue of prediction is saved and loaded as they are first used by a heuristic comparing the Sum of Absolute Differences (SAD) of DCT2-DCT2 and the SAD of TS to decide whether “Test 1” will be skipped, then used to compute the full rate-distortion cost of “Test 0”.
Neural Network-Based Intra Prediction
A neural network for intra prediction infers from the context surrounding the current block a prediction of this current block.
In the previous work, two distinct approaches aim at integrating neural network-based intra prediction mode(s) into VVC: the integration of a single generic neural network-based intra prediction mode and the integration of multiple specialized neural network-based intra prediction modes.
An example of deep intra prediction is described in the article entitled “Iterative training of neural networks for intra prediction”, Thierry Dumas, Franck Galpin, and Philippe Bordes, arXiv:2003.06812v1, March 2020). This article describes a first approach of deep intra prediction wherein a single generic neural network-based intra prediction mode is introduced. The single neural network-based intra prediction mode is usually composed of several neural networks, each predicting blocks of a different size. For instance, the neural network in the single neural network-based mode includes 11 neural networks, each predicting blocks of a different size in T={4×4, 4×8, 8×4, 4×16, 16×4, 8×8, 8×16, 16×8, 16×16, 32×32, 64×64}. For a given W×H block, if W×H∈T, the neural network in the single neural network-based mode predicting W×H blocks is used for prediction. Otherwise, the single neural network-based mode is not able to predict this block.
In terms of signaling, fora given W×H luminance CB predicted in intra, if W×H∈T, a single flag is written to the bitstream to indicate whether the single neural network-based intra prediction mode or an intra prediction mode in VVC is selected.
The thrust of this first approach is, roughly speaking, for a given block, to have a neural network inferring from the context of this block the “direction of propagation(s)” that are the most likely to give high quality of prediction while using these directions to compute a prediction of this block from the context. To do so, the neural network must be fed with a large context. That is why, na≥4, nl≥4, na and nl growing with the size of the block.
According to a second approach, multiple specialized neural network-based intra prediction modes are introduced as with the tool Matrix Intra Prediction (MIP) in VVC. The MIP gathers specialized neural network-based intra prediction modes. MIP contains 32 modes for 4×4 luminance CBs, 16 modes for 4×8, 8×4, and 8×8 luminance CBs, and 12 modes for the other luminance CB sizes.
Unlike in the first approach, a neural network in MIP is not designed to infer from the context of a given luminance CB the “direction of propagation(s)” that are the most likely to give high quality of prediction. Instead, the “direction of propagation” is found by the encoder search among the different MIP modes. That is why, in MIP, the context of a luminance CB is small, and the neural networks do not need a large capacity of representation. Consequently, the context of a luminance CB only comprises a line of W decoded pixels above it and a line of H decoded pixels on its left side. Besides, each neural network in MIP has a single layer, without non-linearity, without bias, which amounts to a linear transformation.
Now, when integrating a neural network-based intra prediction mode into a block-based video codec with existing transforms, one of the challenges is to deal with the signaling of the transforms that are inferred from existing intra prediction modes. Note that these transforms can be a series of individual transforms (like MTS and LFNST in VVC), or a transform in a large set of adaptive transforms.
This problem is well illustrated by LFNST. The set of 2 LFNST matrices of index i was trained on examples, each example being the primary transform coefficients obtained by applying (DCT2, DCT2) to the residue resulting from the prediction of a block via an intra prediction mode whose index belongs to the range Ri, i∈0, 3
. For instance, R3=
24, 34
∪
35, 44
, the primary transform coefficients being transposed if the intra prediction mode index belongs to
35, 44
This justifies the mapping in Table 2. However, the skilled in the art faces an issue while trying to infer the index of the set of 2 LFNST matrices for a block predicted via a new neural network-based intra prediction mode.
This problem is critical when the single neural network-based intra prediction mode is integrated into the video codec. Indeed, as a neural network in this mode can infer from the context of a block the “direction of propagation(s)” that are the most likely to give high quality of prediction, from the prediction of one block to the prediction of another block, this mode can yield different directions of propagation. Therefore, the systematic inference of the same set of 2 LFNST matrices from the index of the neural network-based intra prediction mode underperforms in terms of rate-distortion.
This is solved and addressed by the general aspects described herein, which are directed to an intra prediction of an image block using at least one neural network and obtaining an information relative to at least a transform method to apply to the residue of the neural network prediction if this transform is primary, or to the block of transform coefficients obtained by applying other transforms to the residue of the neural network prediction if this transform is not primary. In at least one embodiment, for a given block predicted via a neural network-based intra prediction mode, all the transform indices that are commonly inferred from the index of the selected intra prediction mode are signaled by writing flags to the bitstream. Alternatively, in at least another embodiment, each neural network involved in the neural network-based intra prediction mode is trained at inferring, from the context of a block, the transform indices that are commonly inferred from the index of the selected intra prediction mode. Then, on both the encoder and decoder sides, for a given block predicted via a neural network-based intra prediction mode, the neural network used for prediction directly returns the needed transform indices.
Various embodiments of the generic encoding or decoding method are described in the following.
Signaling the Transform Indices that are Usually Inferred from the Selected Intra Prediction Mode Index
0, n−1
of a group of transforms is determined. If a given block is predicted via the intra prediction mode of index i⊂
0, m−1
, the used transform belongs to the group of index trGrpIdx=mappingIntraTrGrp(i). Then, in this group, the index of the used transform (belonging to
0, p−1
is optionally written to the bitstream. The exemplary mapping of
According to a first variant embodiment, the coding of the index trGrpIdx is compatible with any code. As previously described, if a block is predicted by the added neural network-based intra prediction mode, the index trGrpIdx of the group including the used transform is encoded and decoded via a truncated binary code. The truncated binary code can be replaced by any other code. For instance, it can be replaced by a unary code.
According to a second variant embodiment, the transforms are no longer grouped. The notion of groups of transforms is removed. In this case, the video codec contains m intra prediction modes and n transforms.
0, n−1
of a transform. If a given block is predicted via the intra prediction mode of index i∈
0, m−1
, the transform of index trIdx=mappingIntraTr(i) is used for the given block. If a block is predicted by the added neural network-based intra prediction mode, the index trIdx of the used transform is written to the bitstream.
According to a third variant embodiment, the transforms can be grouped hierarchically. 0, n−1
of a macro group. If a given block is predicted via the intra prediction mode of index i∈
0, m−1
the used transform will belong to the macro group of index trMacroGrpIdx=mappingIntraTrMacroGrp(i). Then, in this macro group, the index of the sub-group containing the used transform is optionally signaled by writing a flag to the bitstream. Finally, in the used sub-group, the index of the used transform is optionally written to the bitstream. If a block is predicted by the added neural network-based intra prediction mode, the index trMacroGrpIdx of the macro group containing the used transform is written to the bitstream.
According to a fourth variant embodiment, the approach described by
0, 6
in
According to a fifth variant embodiment, the transforms are learned and signaled. In the previous approaches, the transforms are assumed to be fixed at both the encoder and decoder sides throughout the encoding and decoding. However, according to another variant embodiment, the different transforms are learned on the encoder side. Then, the transform parameters are transmitted from the encoder to the decoder. Finally, the decoder retrieves the transforms by reading their parameters from the bitstream. This variant embodiment is advantageously compatible with the signaling of transforms from the encoder to the decoder.
Neural Network-Based Mode Inferring the Transform Indices
According to at least another embodiment, the information on the one or more transform(s) to be applied is inferred at both the encoder and decoder. Considering the non-limiting example of generic mapping of 0, n−1
of the group containing the used transform is not written to the bitstream. Instead, it is inferred from the context of this block by the neural network-based intra prediction mode.
0, p−1
) is optionally written to the bitstream. Alternatively, it may be inferred from available information. The resulting secondary transform coefficients T1 are fed into the quantizer (320).
0, p−1
) is read from the bitstream if the encoder wrote it into the bitstream. It is inferred from available information if the encoder did so. The inverse primary transform (415) computes the reconstructed residue {tilde over (R)} from {tilde over (T)}0. Finally, the reconstructed block is {tilde over (Y)}={tilde over (R)}+Ŷ.
According to a first variant embodiment, the transforms are no longer grouped. Indeed, the notion of groups of transforms is removed. This corresponds to the generic case presented with reference to 0, n−1
of a transform. According to this first variant, if a block is predicted by the added neural network-based intra prediction mode, the index trIdx∈
0, n−1
of the used transform is not written to the bitstream. Instead, it is inferred from the context of this block by the neural network-based intra prediction mode. This inference on the encoder side (500) is described in
According to a second variant embodiment, the transforms are grouped hierarchically. This corresponds to the generic case presented with reference to 0, n−1
of a macro group. According to this second variant, if a block is predicted by the added neural network-based intra prediction mode, the index trMacroGrpIdx∈
0, n−1
of the macro group containing the used transform is not written to the bitstream. Instead, it is inferred from the context of this block by the neural network-based intra prediction mode. This inference on the encoder and decoder sides can be straightforwardly deduced from
According to a third variant embodiment, the indices of different types of transforms are inferred from neural network-based intra prediction mode. In the case of a block predicted by the added neural network-based intra prediction mode, the indices of several different used transforms can be inferred from the context of this block by the neural network-based mode.
The portion of the encoder (700) resulting from the combination is depicted in 0, p−1
) is optionally written to the bitstream. Alternatively, it may be inferred from available information. The resulting secondary transform coefficients T1 are fed into the quantizer (706).
The portion of the decoder (800) resulting from the combination is shown on 0, p−1
) is read from the bitstream if the encoder wrote it into the bitstream. It is inferred from available information if the encoder did so. The inverse primary transform (804) of index trIdx computes the reconstructed residue {tilde over (R)} from {tilde over (T)}0. Finally, the reconstructed block is {tilde over (Y)}={tilde over (R)}+Ŷ.
In
According to a fourth variant embodiment, various additional inputs are fed into the neural network-based intra prediction mode. The additional of inputs does not modify the core of the disclosed approach. These additional inputs can be
Note that, for any other block that is either partially or fully included in the context of the current block, if this block is predicted in intra, the index of the intra prediction mode used to predict this block can also be fed into the neural network-based intra prediction mode.
According to a fifth variant embodiment, the output of the neural network-based intra prediction changes.
For example, in the third variant embodiment, if the neural network-based intra prediction mode returns the vector P0∈(+)n
+)n
According to a sixth variant embodiment, additional outputs are returned by the neural network-based intra prediction. The additional of outputs does not change the core of the proposed approach. These additional outputs can be
According to a seventh variant embodiment, the inference of the transform indices by the neural network-based intra prediction mode can be straightforwardly applied to VVC.
Let the current luminance CB be predicted by the added neural network-based intra prediction mode. In this case, mtsIdx∈{0, 1, 2, 3, 4} is inferred from the context of the CB by the neural network-based intra prediction mode instead of being written to the bitstream as shown on 0, 6
of the used group of a set of 2 LFNST matrices and the decision of transposing the primary transform coefficients (c.f. Table 4) is inferred from the context of the CB by the neural network-based intra prediction mode as shown on
Note that, in
For the sake of clarity, we consider in the following that the neural network-based intra prediction mode is applied to determine a prediction of a given CB, not a TB. In other words, although the neural network-based intra prediction is compatible with a tool such as ISP in VVC, the exemplary embodiments are described for the case where a CB is equivalent to a TB, that is a tool such as ISP is disabled.
According to an eighth variant embodiment, the inference of the transform indices by the neural network-based mode is applied to VVC, and, for the current CB predicted by the neural network-based intra prediction mode, the index trGrpIdxlfnstIdx=1∈0, 6
used when lfnstIdx is equal to 1 and the index trGrpIdxlfnstIdx=2∈
0, 6
used when lfnstIdx is equal to 2 are inferred from the context of the current CB by the neural network-based intra prediction mode instead of trGrpIdx.
According to a ninth variant embodiment, the approach described above wherein the neural network-based mode infers the transforms indices is generalized to the case of transforms that are learned on the encoder side. Then, the transform parameters are transmitted from the encoder to the decoder. Finally, the decoder recovers the learned transforms by reading their parameters from the bitstream.
A non-limiting example of the third variant embodiment adapted to transmitted learned transforms is described below. In this example, it is assumed that only the primary transforms are learned. It is also assumed that the primary transforms for a given frame are learned before encoding this frame, using data from the past reconstructed frames.
0, p−1
) is eventually written to the bitstream. Alternatively, it may be inferred from available information. The resulting secondary transform coefficients T1 are fed into the quantizer.
0, p−1
) is read from the bitstream if the encoder wrote it into the bitstream. It is inferred from available information if the encoder did so. The inverse primary transform (1005) of index trIdx and parameters ϕ(trIdx) computes the reconstructed residue {tilde over (R)} from {tilde over (T)}0. Finally, the reconstructed block is {tilde over (Y)}={tilde over (R)}+Ŷ.
This example can be straightforwardly extended to the case of transmitted learned secondary transforms, transmitted learned ternary transforms, and so on. Note that, in the above example, the transforms are learned for a given frame, before encoding this frame. This can be straightforwardly extended to the case of transforms learned at a different level. For instance, the transforms can be learned for a given group of t frames, before encoding this group. Also note that, in the above example, a learned transform and its inverse transform have different parameters. But, they can be identical. Finally, unlike in the above example, only a subset of the transforms of a given type can be learned, the remaining transforms of this type being fixed and known at both the encoder and decoder sides throughout the encoding and the decoding.
According to a tenth variant embodiment, the learned neural network-based intra prediction mode itself is transmitted to the decoder. In the different propositions of the previous embodiments and its variants, instead of learning the neural network-based intra prediction mode offline and fixing it at both the encoder and decoder sides throughout the encoding and decoding, this mode can be learned on the encoder side. Then, its parameters are transmitted from the encoder to the decoder. Finally, the decoder recovers the neural network-based intra prediction mode by reading its parameters from the bitstream.
On
According to an eleventh variant embodiment, the inference of the transform indices by the neural network-based mode is applied to VVC for a CU in separate tree in luminance and chrominance wherein a current chrominance CB is predicted by a CCLM mode. Advantageously, the index (trGrpIdxY) representative of a group of 2 LFNST matrices with the decision of transposing the primary transform coefficients is inferred for luminance component and a transform method to apply for decoding the chrominance components of the image block is determined from said index (trGrpIdxY) representative of a group of 2 LFNST matrices with the decision of transposing the primary transform coefficients of a collocated luminance components according to the value of the respective lfnstIdx.
According to a twelfth variant embodiment, for a CU in separate tree in chrominance, if the current chrominance CB is predicted by a CCLM mode, if the LFNST index for this CU lfnstIdxC∈{1, 2}, LFNST for the current chrominance CB is defined as follows. If the index idxModeLuma of the intra prediction mode selected to predict the luminance CB that is collocated with the current chrominance CB is equal to the index NN_IDX of the neural network-based intra prediction mode, LFNST for the current chrominance CB is defined via Table 2 using wide angle intra prediction mode index t, where t is the wide angle intra prediction mode index of any non-MIP intra prediction mode in VVC, t being fixed at both the encoder and decoder sides. Otherwise, LFNST for the current chrominance CB is defined as in VVC.
Neural Network-Based Mode Predicting the Transform Indices
In the section “Neural network-based mode inferring the transform indices”, the neural network-based intra prediction mode infers from the context of the current block a prediction of this block and the needed transform indices. Differently, any transform index inferred by the neural network-based intra prediction mode can be replaced by a prediction of this transform index. This replacement can apply to any of the twelve variant embodiments in the section “Neural network-based mode inferring the transform indices”. To be more precise, the third, seven, and eight variant embodiments in the section “Neural network-based mode inferring the transform indices” are adapted to the current case below.
According to a first variant embodiment of the predictive coding of transform indices, an adaptation of the third variant embodiment in the section “Neural network-based mode inferring the transform indices” is illustrated in
0, p−1
) is eventually written to the bitstream. Alternatively, it may be inferred from available information. The resulting secondary transform coefficients T1 are fed into the quantizer (1106). A first predictive encoder (1107) encodes trIdx with respect to predTrIdx, yielding the bits Aremainder written to the bitstream. A second predictive encoder (1108) encodes trGrpIdx with respect to predTrGrpIdx, yielding the bits Bremainder written to the bitstream.
0, p−1
) is read from the bitstream if the encoder wrote it into the bitstream. It is inferred from available information if the encoder did so. The inverse primary transform (1204) of index trIdx computes the reconstructed residue {tilde over (R)} from {tilde over (T)}0. Finally, the reconstructed block is {tilde over (Y)}={tilde over (R)}+Ŷ.
According to a second variant embodiment of the predictive coding of transform indices, an adaptation of the seventh variant embodiment in the section “Neural network-based mode inferring the transform indices” is presented in
According to a third variant embodiment of the predictive coding of transform indices, an adaptation of the eighth variant embodiment in the section “Neural network-based mode inferring the transform indices” is illustrated in
In the embodiment presented in
To circumvent the above-mentioned large coding cost, according to a fourth variant embodiment of the predictive coding of transform indices, for a CU in separate tree in chrominance, its blue chrominance CB and its red chrominance CB share the same trGrpIdxC. The predictive encoding of trGrpIdxC with respect to predTrGrpIdxC
According to a fifth variant embodiment, for a CU in separate tree in chrominance, the blue chrominance CB and the red chrominance CB share the same trGrpIdxC. The predictive encoding of trGrpIdxC with respect to predTrGrpIdxC
According to a sixth variant embodiment, the eleventh variant embodiment in “Neural network-based mode inferring the transform indices” can be adapted to the case of the neural network-based mode predicting the transform indices by simply replacing trGrpIdxlfnstIdx=1Y by predTrGrpIdxlfnstIdx=1Y and trGrpIdxlfnstIdx=2Y by predTrGrpIdxlfnstIdx=2Y in
According to a seventh variant embodiment, the twelfth variant embodiment in “Neural network-based mode inferring the transform indices” can be applied to the case of the neural network-based mode predicting the transform indices without modifying the description.
Use of the Mappings in Tables 2 and 4 During the Neural Network-Based Inference/Prediction of the Transform Indices
In the sections “Neural network-based mode inferring the transform indices” and “Neural network-based mode predicting the transform indices”, the neural network-based intra prediction mode returns vectors from which either the transform indices or predictions of the transform indices are computed without any intermediate predefined mapping. Alternatively, the neural network-based intra prediction mode can return vectors, and either the transform indices or predictions of the transform indices are obtained from these vectors using at least one intermediate predefined mapping.
In a first variant embodiment, the neural network-based intra prediction mode returns vectors in which a coefficient represents the probability of the index of an intra prediction mode in VVC, excluding the MIP modes. Either the transform indices or predictions of the transform indices are obtained from these vectors first using the mapping in VVC from an intra prediction mode index to its wide angle intra prediction mode index, then using Tables 2 and 4.
Acceleration of the Encoder Intra Search Involving the Neural Network-Based Intra Prediction Mode
For a given block predicted via a neural network-based intra prediction mode, when the transform indices are signaled instead of being inferred from the index of the selected intra prediction mode, the encoder search for trGrpIdx increases the encoder running time. The same goes when the neural network-based mode predicts the transform indices as illustrated on
According to a first variant embodiment, the acceleration of the encoder intra search involving the neural network-based intra prediction mode is applied to VVC featuring the neural network-based intra prediction mode, and the fourth variant embodiment in Section “Signaling the transform indices that are usually inferred from the selected intra prediction mode index” is re-used. Then, the tests computing the rate-distortion costs of the complete encodings of a given block predicted via the neural network-based intra prediction mode are shown in Table 5. Note that, in Table 5, all the heuristics that can stop the series of tests from “Test 0” to “Test 19” early are ignored for clarity. Note also that, in Table 5, the primary transform coefficients resulting from the application of the DCT2 horizontally and the DCT2 vertically to the residue of the neural network intra prediction are saved to memory following their first computation and loaded during each subsequent test as the combination of the DCT2 horizontally and the DCT2 vertically is the most frequently used primary transform.
According to a second variant embodiment, the acceleration of the encoder intra search involving the neural network-based intra prediction mode is applied to VVC featuring the neural network-based intra prediction mode, and the approach described in Section “Neural network-based mode predicting the transform indices” and illustrated on
According to a third variant embodiment, the acceleration of the encoder intra search involving the neural network-based intra prediction mode is applied to VVC featuring the neural network-based intra prediction mode, and the approach illustrated in
From the above three variant embodiments, the proposed acceleration of the encoder intra search involving the neural network-based intra prediction mode can be straightforwardly extended to any case described in this disclosure.
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.
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.
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. Additionally, terms such as “first”, “second”, etc. may be used in various embodiments to modify an element, component, step, operation, etc., such as, for example, a “first decoding” and a “second decoding”. Use of such terms does not imply an ordering to the modified operations unless specifically required. So, in this example, the first decoding need not be performed before the second decoding, and may occur, for example, before, during, or in an overlapping time period with the second decoding.
Various methods and other aspects described in this application can be used to modify modules, for example, the intra prediction, transform modules, and/or inverse transform modules (160, 260, 125, 150, 250), of a video encoder 100 and decoder 200 as shown in
Various numeric values are used in the present application, for example, the number of transforms, the number of transform level, the indices of transforms. The specific values are for example purposes and the aspects described are not limited to these specific values.
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 pre-processing, 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 (110) 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).
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 pre-encoding processing and signaled in the bitstream.
The system 2000 includes at least one processor 2010 configured to execute instructions loaded therein for implementing, for example, the various aspects described in this document. Processor 2010 can include embedded memory, input output interface, and various other circuitries as known in the art. The system 2000 includes at least one memory 2020 (e.g., a volatile memory device, and/or a non-volatile memory device). System 2000 includes a storage device 2040, 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 2040 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 2000 includes an encoder/decoder module 2030 configured, for example, to process data to provide an encoded video or decoded video, and the encoder/decoder module 2030 can include its own processor and memory. The encoder/decoder module 2030 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 2030 can be implemented as a separate element of system 2000 or can be incorporated within processor 2010 as a combination of hardware and software as known to those skilled in the art.
Program code to be loaded onto processor 2010 or encoder/decoder 2030 to perform the various aspects described in this document can be stored in storage device 2040 and subsequently loaded onto memory 2020 for execution by processor 2010. In accordance with various embodiments, one or more of processor 2010, memory 2020, storage device 2040, and encoder/decoder module 2030 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 2010 and/or the encoder/decoder module 2030 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 2010 or the encoder/decoder module 2030) is used for one or more of these functions. The external memory can be the memory 2020 and/or the storage device 2040, 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 VVC (Versatile Video Coding, a new standard being developed by JVET, the Joint Video Experts Team).
The input to the elements of system 2000 can be provided through various input devices as indicated in block 2005. 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
In various embodiments, the input devices of block 2005 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 2000 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 2010 as necessary. Similarly, aspects of USB or HDMI interface processing can be implemented within separate interface ICs or within processor 2010 as necessary. The demodulated, error corrected, and demultiplexed stream is provided to various processing elements, including, for example, processor 2010, and encoder/decoder 2030 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 2000 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 2015, for example, an internal bus as known in the art, including the Inter-IC (12C) bus, wiring, and printed circuit boards. The system 2000 includes communication interface 2050 that enables communication with other devices via communication channel 2090. The communication interface 2050 can include, but is not limited to, a transceiver configured to transmit and to receive data over communication channel 2090. The communication interface 2050 can include, but is not limited to, a modem or network card and the communication channel 2090 can be implemented, for example, within a wired and/or a wireless medium.
Data is streamed, or otherwise provided, to the system 2000, in various embodiments, using a wireless network such as a Wi-Fi network, for example IEEE 802.11 (IEEE refers to the Institute of Electrical and Electronics Engineers). The Wi-Fi signal of these embodiments is received over the communications channel 2090 and the communications interface 2050 which are adapted for Wi-Fi communications. The communications channel 2090 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 2000 using a set-top box that delivers the data over the HDMI connection of the input block 2005. Still other embodiments provide streamed data to the system 2000 using the RF connection of the input block 2005. 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 2000 can provide an output signal to various output devices, including a display 2065, speakers 2075, and other peripheral devices 2085. The display 2065 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 2065 can be for a television, a tablet, a laptop, a cell phone (mobile phone), or other device. The display 2065 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 2085 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 2085 that provide a function based on the output of the system 2000. For example, a disk player performs the function of playing the output of the system 2000.
In various embodiments, control signals are communicated between the system 2000 and the display 2065, speakers 2075, or other peripheral devices 2085 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 2000 via dedicated connections through respective interfaces 2065, 2075, and 2085. Alternatively, the output devices can be connected to system 2000 using the communications channel 2090 via the communications interface 2050. The display 2065 and speakers 2075 can be integrated in a single unit with the other components of system 2000 in an electronic device such as, for example, a television. In various embodiments, the display interface 2065 includes a display driver, such as, for example, a timing controller (T Con) chip.
The display 2065 and speaker 2075 can alternatively be separate from one or more of the other components, for example, if the RF portion of input 2005 is part of a separate set-top box. In various embodiments in which the display 2065 and speakers 2075 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 2010 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 2020 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 2010 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, comprising intra predicting an image block using at least one neural network from a context comprising pixels surrounding said image block, wherein said intra predicting further comprises obtaining an information relative to at least a transform to apply to the image block, and wherein, for a decoder, obtaining such transform information comprises decoding an information signaled in the bitstream or inferring transforms using the at least one neural network for intra prediction or any combination of both features.
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, intra predicting an image block using at least one neural network from a context comprising pixels surrounding said image block, wherein said intra predicting further comprises obtaining an information relative to at least a transform to apply to the image block, and wherein, for an encoder, obtaining such transform information comprises signaling an information in the bitstream or inferring transforms using the at least one neural network for intra prediction or any combination of both features.
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, mappingIntraTrGrp, trGrpIdx, nnFlag 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.
Various embodiments refer to rate distortion optimization. In particular, during the encoding process, the balance or trade-off between the rate and distortion is usually considered, often given the constraints of computational complexity. The rate distortion optimization is usually formulated as minimizing a rate distortion function, which is a weighted sum of the rate and of the distortion. There are different approaches to solve the rate distortion optimization problem. For example, the approaches may be based on an extensive testing of all encoding options, including all considered modes or coding parameters values, with a complete evaluation of their coding cost and related distortion of the reconstructed signal after coding and decoding. Faster approaches may also be used, to save encoding complexity, in particular with computation of an approximated distortion based on the prediction or the prediction residual signal, not the reconstructed one. Mix of these two approaches can also be used, such as by using an approximated distortion for only some of the possible encoding options, and a complete distortion for other encoding options. Other approaches only evaluate a subset of the possible encoding options. More generally, many approaches employ any of a variety of techniques to perform the optimization, but the optimization is not necessarily a complete evaluation of both the coding cost and related distortion.
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 “/”, “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 transform. 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, across various claim categories and types. 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:
| Number | Date | Country | Kind |
|---|---|---|---|
| 20305668.4 | Jun 2020 | EP | regional |
| 20306137.9 | Sep 2020 | EP | regional |
| 21305378.8 | Mar 2021 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/065209 | 6/8/2021 | WO |
