WO2023099249A1

WO2023099249A1 - Downsample phase indication

Info

Publication number: WO2023099249A1
Application number: PCT/EP2022/082532
Authority: WO
Inventors: Philippe Bordes; Tangi POIRIER; Philippe DE LAGRANGE; Fabrice Urban
Original assignee: Interdigital Vc Holdings France, Sas
Priority date: 2021-11-30
Filing date: 2022-11-21
Publication date: 2023-06-08

Abstract

In an encoded video stream, information is included as one or more syntax elements to indicate information to permit resizing of reference pictures. In one embodiment, this information can comprise original picture size, scaling factor, and phase. In another embodiment, phase information for horizontal and vertical directions is included. In another embodiment, information for multiple picture parameter sets is included.

Description

DOWNSAMPLE PHASE INDICATION

TECHNICAL FIELD

At least one of the present embodiments generally relates to a method or an apparatus for video encoding or decoding, compression or decompression.

BACKGROUND

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 correlation, then the differences between the original image and the predicted image, often denoted as prediction errors or prediction residuals, are 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.

SUMMARY

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 for improving the coding efficiency when image resizing is used.

According to a first aspect, there is provided a method. The method comprises steps for determining at least one syntax element for a picture comprising information indicative of at least one of an original size or a down-sampling phase of said picture; resampling said picture in correspondence with said at least one syntax element to generate a resampled picture; and, encoding video picture data for the picture, said video picture data comprising said determined at least one syntax element corresponding to the resampled picture

According to a second aspect, there is provided another method. The method comprises steps for parsing video picture data for at least one syntax element comprising information indicative of at least one of an original size or a down-sampling phase; resizing a reconstructed picture using said at least one syntax element; and, decoding the video picture data using the resized reconstructed picture. According to another aspect, there is provided an apparatus. The apparatus comprises a processor. The processor can be configured to encode a block of a video or decode a bitstream by executing any of the aforementioned methods.

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 a 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 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.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates a standard, generic video compression scheme.

Figure 2 illustrates a standard, generic video decompression scheme.

Figure 3 illustrates usage of reference picture resizing in encoder (left) and decoder (right).

Figure 4 illustrates an example of down-sampling using co-sited approach (left) and centered approach (right). Figure 5 illustrates an example mismatch when down-sampling and up-sampling phases are not the same.

Figure 6 illustrates one embodiment of creation of SEI containing down-sampling phases for several picture sizes (PPSs).

Figure 7 illustrates one embodiment of usage of proposed SEI at decoding/client side (PPSs).

Figure 8 illustrates one embodiment of a method under the described aspects.

Figure 9 illustrates another embodiment of a method under the described aspects.

Figure 10 illustrates one embodiment of an apparatus under the described aspects.

Figure 11 shows a processor based system for encoding/decoding under the general described aspects.

DETAILED DESCRIPTION

The embodiments described here are in the field of video compression and generally relate to video encoding and decoding and more specifically aims to improve the coding efficiency of resampled video signals.

Figure 1 illustrates an example of a block-based hybrid video encoder 100. 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 (Coding Units). 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 (210) 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 such as the picture partitioning information, are entropy coded (145) to output a bitstream. The encoder can skip the transform and apply quantization directly to the nontransformed 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)/ALF (Adaptive Loop Filter) filtering to reduce encoding artifacts. The filtered image is stored in a reference picture buffer (180).

Figure 2 illustrates a block diagram of an example video decoder 200. 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 Figure 1. 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, prediction modes, 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). Note that, for a given picture, the contents of the reference picture buffer 280 on the decoder 200 side is identical to the contents of the reference picture buffer 180 on the encoder 100 side for the same picture.

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.

Reference Picture Re-scaling (RPR)

In the Versatile Video Coding (VVC) standard, the picture-based re-scaling feature is named Reference Picture Resampling (RPR). Given an original video sequence composed of pictures of size (width x height), the encoder may choose for each frame which resolution (picture size) to use for coding the frame. Different picture parameter sets (PPS) are coded in the bit-stream with the possible sizes of the pictures and the slice/picture header indicates which PPS to use to decode the current video coding layer (VCL) encapsulated into network abstraction layer (NAL) unit. The SPS contains the maximum picture size.

The down-sampler and the up-sampler functions (440, 540 in Figure 3) used as pre- or post-processing respectively are not specified by the standard.

For each frame, the encoder chooses whether to encode at original or down-sized resolution (ex: picture width/height divided by 2). The choice can be made with two passes encoding or considering spatial and temporal activity in the original pictures. Consequently, the decoded picture buffer (DPB, 180, 280) can contain pictures with different size from the current picture size.

In case one reference picture in the DPB has size different from the current picture size, the re-scaling (430/530) (up-scale or down-scale) of the reference block to build the prediction block is made implicitly during the motion compensation process (170, 275).

Stream switching

The stream-switching technique allows for dynamically switching from one off-line encoded stream to another, to adapt to the variable channel bandwidth. Traditionally, the stream switch points correspond to pre-defined temporal locations that coincide with random access (RAP) points, such as intra random access point (IRAP for HEVC) or clear random access (CRA for HEVC, WC) for example without (or with few dependencies) with VCL NAL units situated before the RAP in the bit-stream. In MPEG video standards (AVC, HEVC, WC), the video data is encapsulated into NAL units (network abstraction layer) whose header indicates a NAL unit type (ex: IRAP, CRA). At the server side, several instance of video bit-streams, encoded at different bitrates and/or different picture size (or picture resolution) are created off-line. The client may seamlessly switch from one stream to another depending on its available bandwidth and capability, next up-sampling the reconstructed picture before display (540).

When producing down-sampled versions of a video sequence it is possible to perform that operation with any arbitrary phase relationship between the original video and the down-sampled video. For example, the co-sited approach aligns the mid-position of the top-left corner of the original video with the position of the top-left corner of the down-sampled video as illustrated for one dimension in Figure 4 (left). The centered approach aligns the center of the original video with the center of the down-sampled video as illustrated for one dimension in Figure 4 (right).

The problem occurs when down-sampling is performed using one approach (e.g., centered) and the up-sampling is performed using a different approach (e.g., co-sited) which will cause the content to shift position relative to the position in the original video as illustrated in Figure 5 and jeopardize seamless transition at switching point.

In many video bit-streams encoded with MPEG standards (ex: AVC, HEVC, WC), the client has no mean to infer the down-sampling phase. In another approach, it is proposed to add a new SEI (Supplemental Enhancement Information) message to Versatile Video Coding supplemental enhancement information messages for coded video bitstreams (ITU-T H.274 | ISO/IEC 23002-7). The proposed SEI message contains a single syntax element that indicates the suggested phase indication of the video to be used for up-sampling typically.

Table 1: SEI message syntax.

Table 2: specification of “ phase _idc ” proposed in another approach

However, the syntax of the prior approach has several limitations/issues:

- Both luma and chroma could have a phase shift in down-sampling, that may be different. Chroma location type would also have impact on the correct downsampling filter phase to be used for chroma.

- The syntax “co-sited/centered” doesn’t handle cases with other phases such as ! phase for example. Also, the proposal implicitly considers 2:1 down-sampling only. For other down-sampling ratios (ex: 3:2 down-sampling), it might be necessary to indicate which pixel positions are co-sited. Further, it may be necessary to allow different positions for horizontal and vertical direction.

- The syntax does not indicate the down-sampling ratio so that the decoder can inversely up-sample with the right ratio.

- The syntax does not consider the context of RPR where several PPS may be present in bit-stream, with different picture sizes and down-sampling phases potentially. It is not clear if the SEI should be sent for each chunk, or at each switch point. Also, one should avoid sending several times the same SEI.

According to the general aspects herein, it is proposed here to signal both the down-sampling phase (horizontally and vertically) and the original picture size to allow the client (decoder) to seamless up-sample the reconstructed video, even at switching point transitions with different reconstructed picture sizes. The signaling may be related to each PPS. Also, the proposed syntax reduces overhead and allows avoiding sending same information multiple times.

In one embodiment, it is proposed high level syntax (HLS) for signaling the downsampling phase (for the decoder to use same phase at up-sampling operation, 760), the preferred display size (which may correspond to the original picture size) and in relation with various PPS that may be present in RPR stream possibly. In the following example, the specified HLS is described as part or whole of a supplemental enhancement information (SEI) message, but it is not limited to SEI and could be transported with another NAL unit packet (e.g., PPS or slice/picture header).

Figure 6 (600) depicts the creation of multiple instances of bit-streams, corresponding to different picture size. The Figure 7 (700) depicts the corresponding client side (decoder) implementing stream switching feature, so that the client may select the stream (picture size) that better fulfill its current bandwidth and resource capability.

The syntaxes and semantics provided are given as example of information that could be signaled. Any variant with some values implicitly/explicitly coded should be considered. The proposed syntax allows reducing overhead and avoiding sending same information multiple times. Typically, the SEI, SPS and PPSs are sent out-of-band or at session start, so that they are not duplicated, even if the client operates multiple streams switching.

Embodiment 1 - Signaling original picture size

The syntax may include signaling allowing retrieving the original picture size (or preferred output display size) or the current picture size ratio (with respect to the original picture size). In a variant, the syntax may indicate implicitly or explicitly whether the original picture size is specified by the sequence parameters set (SPS) (e.g. sps_pic_width_max_in_luma_samples, sps_pic_height_max_in_luma_samples in WC) or if it is signaled by the syntax, as depicted in example of Table 3.

In that way, the decoder can determine the reconstructed pictures ratio and select the appropriate up-sampling filter.

Table 3: example of syntax and semantics for original picture size.

orig_pic_size_specified_by_sps_flag equal to 1 indicates the original picture size for up-sampling reconstructed pictures is indicated by SPS parameters. orig_pic_size_specified_by_sps_flag equal to 0 indicates the original picture size for up- sampling reconstructed pictures is signaled in the current SEI message. In a variant, the part A in Table 3 is optional or is not present. In this case the value of orig_pic_size_specified_by_sps_flag may have implicit value (true or false). If it is false, the part B is always present, else the part B is not present. In another variant, parts A and B are not present. orig_pic_width_in_luma_samples specify the width of the original picture size in units of luma samples. orig_pic_width_in_luma_samples shall not be equal to 0. orig_pic_height_in_luma_samples specify the height of the original picture size in units of luma samples. orig_pic_height_in_luma_samples shall not be equal to 0. phase_idc[0] and phase_idc[1] indicates the horizontal and vertical sampling grid alignment (a.k.a. down-sampling phase) of the reconstructed pictures with respect to the original picture width and height respectively. The grid resolution may be pre-defined, for example 8 or 16 phase positions for instance. In a variant, one signal only one phase indicator that allow to derive the down-sampling phase both horizontally and vertically as in Table 1 , for example.

In another variant, the current picture scaling ratio is signaled (scaling_ratio_hor, scaling_ratio_ver) and the values of (orig_pic_width_in_luma_samples, orig_pic_height_in_luma_samples^>) are derived from the current picture size (pic_width_in_luma_samples, pic_height_in_luma_samples^>) specified in PPS or from max picture size specified in SPS: orig_pic_width_in_luma_samples = pic_width_in_luma_samples x scaling_ratio_hor orig_pic_height_in_luma_samples = pic_height_in_luma_samples x scaling_ratio_ver

The phase_idc[] specifies the luma down-sampling phases. The chroma downsampling phase can be derived using the SPS syntax elements (sps_chroma_horizontal_collocated_flag, ps_chroma_ vertical_collocated_flag) wh i ch semantic in VVC is the following:

- sps_chroma_horizontal_collocated_flag equal to 1 specifies that prediction processes operate in a manner designed for chroma sample positions that are not horizontally shifted relative to corresponding luma sample positions. sps_chroma_horizontal_collocated_flag equal to 0 specifies that prediction processes operate in a manner designed for chroma sample positions that are shifted to the right by 0.5 in units of luma samples relative to corresponding luma sample positions. When sps_chroma_horizontal_collocated_flag is not present, it is inferred to be equal to 1 .

- sps_chroma_vertical_collocated_flag equal to 1 specifies that prediction processes operate in a manner designed for chroma sample positions that are not vertically shifted relative to corresponding luma sample positions. sps_chroma_vertical_collocated_flag equal to 0 specifies that prediction processes operate in a manner designed for chroma sample positions that are shifted downward by 0.5 in units of luma samples relative to corresponding luma sample positions. When sps_chroma_vertical_collocated_flag is not present, it is inferred to be equal to 1 .

In a variant, the values (sps_chroma_horizontal_collocated_flag, ps_chroma_vertical_collocated_flag) are coded in the SEI.

Embodiment 2 - Compatibility with RPR signaling

In VVC, the reconstructed picture size may be different for each picture. The SPS contains the maximal picture size, and several picture parameters sets (PPS) with different identifiers (ppsjd or pps_pic_parameter_set_id^>) may be coded in the bitstream (610). In the slice or picture header, a syntax element indicates the pps identifier (ppsjd) (ex: ph_pic_parameter_set_id in the picture header) of the PPS which is active and which allows deriving the size of the reconstructed picture (740).

A server implementing stream-switching (600) would encode several instances (N) of bit-streams that may differ with picture size. Each bit-stream may include one SPS and one PPS. Advantageously, each instance may share same SPS but have different value of ppsjd so that any PPS may be sent only once per session (first use of PPS(i), 730) (at session start for example) rather that to be sent for each chunk or at each stream switching.

In this embodiment, similarly and advantageously, the SEI may include the downsampling information corresponding to several PPS (pps_id). In a variant, it may be sent only once (640, 710) rather than to be sent for each chunk or at each stream switching, as depicted in example of Table 4. In another variant, part A and/or part B is/are not present.

Table 4: example of syntax and semantics for multiple PPS.

num_pps_down_sampling_phase_minus1 plus 1 indicates the number of PPS for which down-sampling phase is specified. pps_id[ i ] specifies the value of the pps_pic_parameter_set_id of the i^th PPS. phase_idc[ i ][ ] specifies the value of the down-sampling phases indicator of the pictures using PPS with pps_pic_parameter_set_id equal to pps_id[ i ].

Embodiment 3 - Signaling luma/chroma down-sampling phase independently In case of the down-sampling phase of the chroma is not equal to the downsampling phase of the luma, and if it cannot be derived from SPS syntax elements (sps_chroma_horizontal_collocated_flag, sps_chroma_vertical_collocated_flag), then down-sampling phase of the chroma may be explicitly signaled in the SEI as in example of Table 5 or Table 6:

Table 5: example of syntax specifying down-sampling phase for chroma.

chroma_phase_present_flag specifies whether chroma phase information is present in the SEI. In a variant, if part C is not present it may be inferred. If inferred to false, then the part D is not present. phase_chroma_idc[ i ][ ] specifies the value of the down-sampling phases indicators of the chroma components for pictures using PPS with pps_pic_parameter_set_id equal to pps_id[ i ].

Table 6: example of syntax specifying down-sampling phase for chroma.

Similarly, to the SPS syntax elements (sps_chroma_horizontal_collocated_flag, ps_chroma_vertical_collocated_flag), the semantics of

(downsampled_chroma_horizontal_collocated_flag, downsampled_chroma_vertical_collocated_flag) are the following:

- downsampled_chroma_horizontal_collocated_flag[i] equal to 1 specifies that down-sampled chroma sample positions in original picture are not horizontally shifted relative to corresponding luma sample positions. downsampled_chroma_horizontal_collocated_flag equal to 0 specifies that down- sampled chroma sample positions are shifted to the right by 0.5 in units of luma samples relative to corresponding luma sample positions in original picture. When downsampled_chroma_horizontal_collocated_flag is not present, it is inferred to be equal to 1.

- downsampled_chroma_vertical_collocated_flag[i] equal to 1 specifies that down- sampled chroma sample positions in original picture are not vertically shifted relative to corresponding luma sample positions. downsampled_chroma_vertical_collocated_flag equal to 0 specifies that down- sampled chroma sample positions that are shifted downward by 0.5 in units of luma samples relative to corresponding luma sample positions in original picture. When downsampled_chroma_vertical_collocated_flag is not present, it is inferred to be equal to 1.

One embodiment of a method 800 under the general aspects described here is shown in Figure 8. The method commences at start block 801 and control proceeds to block 810 for determining at least one syntax element for a picture comprising information indicative of an original size or down-sampling phase of said picture. Control proceeds from block 810 to block 820 for resampling said picture in correspondence with said at least one syntax element to generate a resampled picture. Control proceeds from block 820 to block 830 for encoding video picture data for the picture, said video picture data comprising said determined at least one syntax element corresponding to the resampled picture.

One embodiment of a method 900 under the general aspects described here is shown in Figure 9. The method commences at start block 901 and control proceeds to block 910 for parsing video picture data for at least one syntax element comprising information indicative of an original picture size or down-sampling phase. Control proceeds from block 910 to block 920 for resizing a reconstructed picture using said at least one syntax element. Control proceeds from block 920 to block 930 for decoding the video picture data using the resized reconstructed picture.

Figure 7 shows one embodiment of an apparatus 700 for encoding, decoding, compressing, or decompressing video data using any of the aforementioned embodiments. The apparatus comprises Processor 710 and can be interconnected to a memory 720 through at least one port. Both Processor 710 and memory 720 can also have one or more additional interconnections to external connections.

Processor 710 is also configured to either insert or receive information in a bitstream and, either compressing, encoding, or decoding using any of the described aspects.

The embodiments described here include 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. Figures 1 , 2, and 11 provide some embodiments, but other embodiments are contemplated and the discussion of Figures 1 , 2, 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.

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 intra prediction, entropy coding, and/or decoding modules (160, 360, 145, 330), of a video encoder 100 and decoder 200 as shown in Figure 1 and Figure 2. Moreover, the present aspects are not limited to WC or HEVC, and can be applied, for example, to other standards and recommendations, whether preexisting 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. The specific values are for example purposes and the aspects described are not limited to these specific values.

Figure 1 illustrates an encoder 100. 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 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).

Figure 2 illustrates a block diagram of a video decoder 200. 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 Figure 1. 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). Inloop 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.

Figure 11 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 1130. 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 Figure 11 , include composite video.

In various embodiments, the input devices of block 1130 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, bandlimiters, 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 les 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 I nter-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 802.11 (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 1130. Still other embodiments provide streamed data to the system 1000 using the RF connection of the input block 1130. 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 1110, and other peripheral devices 1120. The display 1100 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 1100 can be for a television, a tablet, a laptop, a cell phone (mobile phone), or another device. The display 1100 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 1120 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 1120 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 1100, speakers 1110, or other peripheral devices 1120 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 1100 and speakers 1110 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 1100 and speaker 1110 can alternatively be separate from one or more of the other components, for example, if the RF portion of input 1130 is part of a separate set-top box. In various embodiments in which the display 1100 and speakers 1110 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 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.

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 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.

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 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 may refer to parametric models or 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. It can be measured through a Rate Distortion Optimization (RDO) metric, or through Least Mean Square (LMS), Mean of Absolute Errors (MAE), or other such measurements. 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 transforms, coding modes or flags. In this way, in an embodiment the same transform, parameter, or mode 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.

The preceding sections describe a number of embodiments, across various claim categories and types. 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:

• Using syntax to indicate at least one of an original picture size, a rescaling/resizing ration, a phase offset, each in either a horizontal or vertical direction, for either luminance, chrominance, or both.

• A bitstream or signal that includes one or more syntax elements to perform the above functions, or variations thereof.

• A bitstream or signal that includes syntax conveying information generated according to any of the embodiments described.

• Creating and/or transmitting and/or receiving and/or decoding according to any of the embodiments described.

• A method, process, apparatus, medium storing instructions, medium storing data, or signal according to any of the embodiments described.

• Inserting in the signaling syntax elements that enable the decoder to determine decoding information 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 transform method(s) according to any of the embodiments described.

• A TV, set-top box, cell phone, tablet, or other electronic device that performs transform method(s) determination 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, bandlimits, or tunes (e.g. using a tuner) a channel to receive a signal including an encoded image, and performs transform method(s) 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 transform method(s).

Claims

27 CLAIMS

1. A method, comprising: determining at least one syntax element for a picture comprising information indicative of at least one of an original size or a down-sampling phase of said picture; resampling said picture in correspondence with said at least one syntax element to generate a resampled picture; and, encoding video picture data for the picture, said video picture data comprising said determined at least one syntax element corresponding to the resampled picture.

2.. An apparatus, comprising: a processor, configured to perform: determining at least one syntax element for a picture comprising information indicative of at least one of an original size or a down-sampling phase of said picture; resampling said picture in correspondence with said at least one syntax element to generate a resampled picture; and, encoding video picture data for the picture, said video picture data comprising said determined at least one syntax element corresponding to the resampled picture.

3. A method, comprising: parsing video picture data for at least one syntax element comprising information indicative of at least one of an original size or a down-sampling phase; and, resizing a reconstructed picture using said at least one syntax element; and, decoding the video picture data using the resized reconstructed picture.

4. An apparatus, comprising: a processor, configured to perform: parsing video picture data for at least one syntax element comprising information indicative of at least one of an original size or a down-sampling phase; and, resizing a reconstructed picture using said at least one syntax element; and, decoding the video picture data using the resized reconstructed picture.

5. The method of claim 1 or 3, or apparatus of claim 2 or 4, wherein said at least one syntax element further comprises phase information.

6. The method or apparatus of claim 5, wherein said phase information comprises horizontal information, vertical information, luminance phase and chrominance phase.

7. The method of any one of claims 1 , 3 or 5, or apparatus of any one of claims 2, 4 or 5, wherein said at least one syntax element is indicative of a location of original picture size data.

8. The method or apparatus of claim 7, wherein said location comprises a sequence parameter set and said at least one syntax element.

9. The method of any one of claims 1 , 3 or 5 through 8, or apparatus of any one of claims 2, 4 or 5 through 8, wherein information of said at least one of an original size or a down-sampling phase of said picture comprises a picture scaling ratio.

10. The method, or apparatus of claim 7, wherein supplemental enhancement information comprises down-sampling information corresponding to several picture parameter sets.

11 . The method or apparatus of claim 10, wherein supplemental enhancement information for all pictures is sent in a same message.

12. A device comprising: an apparatus according to Claim 4; and at least one of (i) an antenna configured to receive a signal, the signal including its coding unit, (ii) a band limiter configured to limit the received signal to a band of frequencies that includes the coding unit, and (iii) a display configured to display an output representative of a coding unit.

13. A non-transitory computer readable medium containing data content generated according to the method of any one of claims 1 and 5 to 11 , or by the apparatus of any of claims 2 and 5 to 11 , for playback using a processor.

14. A signal comprising video data generated according to the method of any one of claims 1 and 5 to 11 , or by the apparatus of any of claims 2 and 5 to 11 , for playback using a processor.

15. A computer program product comprising instructions which, when its program is executed by a computer, cause the computer to carry out the method of any of Claims 1 , 3 and 5 to 11.