US20140286412A1 - Intra dc prediction for lossless coding in video coding - Google Patents

Intra dc prediction for lossless coding in video coding Download PDF

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US20140286412A1
US20140286412A1 US14/223,945 US201414223945A US2014286412A1 US 20140286412 A1 US20140286412 A1 US 20140286412A1 US 201414223945 A US201414223945 A US 201414223945A US 2014286412 A1 US2014286412 A1 US 2014286412A1
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sample
predictive block
reconstructed
samples
prediction
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Rajan Laxman Joshi
Joel Sole Rojals
Marta Karczewicz
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Qualcomm Inc
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Qualcomm Inc
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    • H04N19/00763—
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/46—Embedding additional information in the video signal during the compression process
    • H04N19/467—Embedding additional information in the video signal during the compression process characterised by the embedded information being invisible, e.g. watermarking
    • H04N19/00854—
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/50—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding
    • H04N19/593—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using predictive coding involving spatial prediction techniques
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/70—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by syntax aspects related to video coding, e.g. related to compression standards
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/42—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation
    • H04N19/436—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals characterised by implementation details or hardware specially adapted for video compression or decompression, e.g. dedicated software implementation using parallelised computational arrangements

Definitions

  • This disclosure relates to video coding and compression.
  • Digital video capabilities can be incorporated into a wide range of devices, including digital televisions, digital direct broadcast systems, wireless broadcast systems, personal digital assistants (PDAs), laptop or desktop computers, digital cameras, digital recording devices, digital media players, video gaming devices, video game consoles, cellular or satellite radio telephones, video teleconferencing devices, and the like.
  • Digital video devices implement video compression techniques, such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard, and extensions of such standards, to transmit, receive and store digital video information more efficiently.
  • video compression techniques such as those described in the standards defined by MPEG-2, MPEG-4, ITU-T H.263, ITU-T H.264/MPEG-4, Part 10, Advanced Video Coding (AVC), the High Efficiency Video Coding (HEVC) standard, and extensions of such standards, to transmit, receive and store digital video information more efficiently.
  • AVC
  • Video compression techniques perform spatial (intra-picture) prediction and/or temporal (inter-picture) prediction to reduce or remove redundancy inherent in video sequences.
  • a video slice may be partitioned into video blocks, which may also be referred to as treeblocks, coding units (CUs) and/or coding nodes.
  • Video blocks in an intra-coded (I) slice of a picture are encoded using spatial prediction with respect to reference samples in neighboring blocks in the same picture.
  • Video blocks in an inter-coded (P or B) slice of a picture may use spatial prediction with respect to reference samples in neighboring blocks in the same picture or temporal prediction with respect to reference samples in other reference pictures.
  • Pictures may be referred to as frames, and reference pictures may be referred to as reference frames.
  • a video coder may generate a predictive block. As part of generating the predictive block, the video coder may use at least one of a losslessly reconstructed sample to left of a current sample in a current row of the predictive block and a losslessly reconstructed sample for a row of the predictive block above the current row for DC prediction of the current sample.
  • this disclosure describes a method of decoding video data, the method comprising: generating a predictive block, wherein generating the predictive block comprises using at least one of a first losslessly reconstructed sample and a second losslessly reconstructed sample for DC prediction of a current sample, the first losslessly reconstructed sample corresponding to a sample left of the current sample in a current row of the predictive block, the second losslessly reconstructed sample corresponding to a sample in a row of the predictive block above the current row for DC prediction of the current sample; and reconstructing a coding block by adding samples of the predictive block to corresponding residual samples.
  • this disclosure describes a method of encoding video data, the method comprising: generating a predictive block, wherein generating the predictive block comprises using at least one of a first losslessly reconstructed sample and a second losslessly reconstructed sample for DC prediction of a current sample, the first losslessly reconstructed sample corresponding to a sample left of the current sample in a current row of the predictive block, the second losslessly reconstructed sample corresponding to a sample in a row of the predictive block above the current row for DC prediction of the current sample; and generating residual samples that have values equal to a difference between a sample in a coding block and a corresponding sample in the predictive block.
  • this disclosure describes a video coding device comprising: a memory storing data; and one or more processors configured to generate a predictive block, wherein generating the predictive block comprises using at least one of a first losslessly reconstructed sample and a second losslessly reconstructed sample for DC prediction of a current sample, the first losslessly reconstructed sample corresponding to a sample left of the current sample in a current row of the predictive block, the second losslessly reconstructed sample corresponding to a sample in a row of the predictive block above the current row for DC prediction of the current sample.
  • this disclosure describes a video coding device comprising means for generating a predictive block, wherein generating the predictive block comprises using at least one of a first losslessly reconstructed sample and a second losslessly reconstructed sample for DC prediction of a current sample, the first losslessly reconstructed sample corresponding to a sample left of the current sample in a current row of the predictive block, the second losslessly reconstructed sample corresponding to a sample in a row of the predictive block above the current row for DC prediction of the current sample.
  • this disclosure describes a computer-readable data storage medium having instructions stored thereon that when executed cause one or more processors to generate a predictive block, wherein generating the predictive block comprises using at least one of a losslessly reconstructed sample to left of a current sample in a current row of the predictive block and a losslessly reconstructed sample for a row of the predictive block above the current row for DC prediction of the current sample.
  • FIG. 1 is a block diagram illustrating an example video coding system that may utilize the techniques of this disclosure.
  • FIG. 2 is a conceptual diagram illustrating a block of size M (height) ⁇ N (width).
  • FIG. 3 is a conceptual diagram illustrating example intra prediction mode directions.
  • FIG. 4 is a conceptual diagram illustrating exemplary samples that may be used for prediction in video coding.
  • FIG. 5A shows a residual differential pulse code modulation (DPCM) direction for near-vertical modes.
  • DPCM differential pulse code modulation
  • FIG. 5B shows a residual DPCM direction for near-horizontal modes.
  • FIG. 6 is a block diagram illustrating an example video encoder that may implement the techniques of this disclosure.
  • FIG. 7 is a block diagram illustrating an example video decoder that may implement the techniques of this disclosure.
  • FIG. 8A is a flowchart illustrating an example operation of a video encoder, in accordance with one or more techniques of this disclosure.
  • FIG. 8B is a flowchart illustrating an example operation of a video encoder, in accordance with one or more techniques of this disclosure.
  • FIG. 9A is a flowchart illustrating an example operation of a video decoder, in accordance with one or more techniques of this disclosure.
  • FIG. 9B is a flowchart illustrating an example operation of a video decoder, in accordance with one or more techniques of this disclosure.
  • FIG. 10A is a flowchart illustrating an example video encoder operation for sign data hiding, in accordance with one or more techniques of this disclosure.
  • FIG. 10B is a flowchart illustrating an example video decoder operation for sign data hiding, in accordance with one or more techniques of this disclosure.
  • Intra prediction is a process of generating, based on sample values in a current picture, a predictive block for a video block of the current picture.
  • the video encoder does not use sample values from other pictures to generate or otherwise identify the predictive block for the video block.
  • a video encoder may use the predictive block to determine a block of residual samples (i.e., a residual block). Residual samples in the residual block may indicate the difference between samples in the predictive block and corresponding original samples of the video block.
  • the video encoder may generate a transform coefficient block by applying a transform to the residual block. The transform may convert the residual samples from a pixel domain to a transform domain. The video encoder may then quantize the transform coefficients in the transform coefficient block to reduce the bit depths of the transform coefficients.
  • the video encoder may entropy encode syntax elements representing the quantized transform coefficients and include the resulting entropy encoded syntax elements in a bitstream.
  • a video decoder may perform an inverse of this process. That is, the video decoder may entropy decode syntax elements in the bitstream to determine quantized transform coefficients. The video decoder may then inverse quantize the quantized transform coefficients to determine the transform coefficients. Furthermore, the video decoder may apply an inverse transform to the transform coefficients to determine the residual block. In addition, the video decoder may determine a predictive block (e.g., using intra prediction). The video decoder may use samples in the predictive block and corresponding residual samples in the residual block to reconstruct samples of the video block.
  • a predictive block e.g., using intra prediction
  • the application of the transform and the use of quantization causes information loss.
  • the samples of a video block reconstructed by the video decoder may not have the same level of precision as the original samples of the video block.
  • application of the transform and use of quantization may be a form of “lossy” coding.
  • the video encoder may encode a video block using lossless encoding.
  • the video encoder does not apply the transform to residual samples and does not quantize the residual samples.
  • the video decoder does not apply inverse quantization or the inverse transform.
  • the samples of the video block reconstructed by the video decoder may have the same level of precision as the original samples of the video block.
  • the video encoder may perform a type of lossy coding in which the video encoder does not apply a transform to residual samples, but does quantize the residual samples.
  • the video decoder may apply inverse quantization to the residual samples, but does not apply an inverse transform to the residual samples. Because the video encoder still applies quantization to the residual samples, the samples reconstructed by the video decoder may have less precision than the original samples, but the precision loss may potentially be less than if the transform had been applied.
  • a video coder may use intra prediction to generate a predictive block. More specifically, the video coder uses a particular intra prediction mode from among a plurality of available intra prediction modes to generate the predictive block.
  • the intra prediction modes include a plurality of directional intra prediction modes, a planar intra prediction mode, and a DC intra prediction mode.
  • the video coder may determine a DC intra prediction value.
  • the DC intra prediction value may be an average value of samples adjacent to a left edge and a top edge of the predictive block. The video coder may set each sample value in the predictive block equal to the DC intra prediction value.
  • Some techniques of this disclosure provide improvements to the DC intra prediction mode when a video coder uses lossless coding.
  • a video encoder may use original values of samples when using DC intra prediction mode to determine values of samples in a predictive block.
  • lossy coding a video decoder does not have access to the original values of samples when using DC intra prediction to determine values of samples in a predictive block.
  • lossless coding the video decoder does have access to reconstructed values of samples when using DC intra prediction to determine values in the predictive block.
  • the reconstructed values of the samples are the same as the original values of the samples.
  • the video coder may generate a predictive block. As part of generating the predictive block, the video coder may use at least one of a losslessly reconstructed sample to left of a current sample in a current row of a predictive block and a losslessly reconstructed sample for a row of the predictive block above the current row for DC prediction of the current sample. Furthermore, in some instances, this may enable the video decoder to pipeline the determination of sample values in the predictive block.
  • a video encoder may perform a form of lossy coding in which quantization is used but the transform is skipped, which may be referred to as transform skip coding.
  • the video encoder may apply a form of residual differential pulse code modulation (DPCM) to prepare the non-transformed, but quantized, residual samples for coding.
  • DPCM residual differential pulse code modulation
  • This form of residual DPCM is described in detail elsewhere in this disclosure.
  • this form of residual DPCM described in this disclosure may increase throughput of the video encoder and/or video decoder.
  • a video encoder may entropy encode syntax elements representing quantized transform coefficients.
  • the same syntax elements may be used to represent residual samples.
  • the syntax elements representing a transform coefficient or residual sample may include a sign syntax element that indicates whether the transform coefficient or residual sample is positive or negative.
  • information indicating whether a transform coefficient or residual sample is positive or negative may be embedded in values of other syntax elements for the transform coefficient or residual sample. Embedding such information in values of other syntax elements, instead of signaling sign syntax elements may be referred to as sign data hiding.
  • sign data hiding may be difficult to implement for blocks that are coded using lossy coding for which the transform is skipped and a planar intra prediction mode, a DC intra prediction mode (e.g., a DC intra prediction mode in which reconstructed samples corresponding to samples in the predictive block are used to determine value of predictive samples in the predictive block), or residual DPCM is used.
  • a DC intra prediction mode e.g., a DC intra prediction mode in which reconstructed samples corresponding to samples in the predictive block are used to determine value of predictive samples in the predictive block
  • residual DPCM residual DPCM
  • sign data hiding may introduce errors into the residual values that are compounded when residual DPCM is applied. Such errors may propagate to subsequent residual samples, resulting in a degradation of performance.
  • sign data hiding may be normatively disabled for such blocks even if one or more syntax elements indicate that sign data hiding is enabled for such blocks.
  • the video decoder determines that sign data hiding is disabled for a current block if the current block is generated using lossy coding without application of a transform to residual data and the current block is intra predicted using an intra prediction mode in which residual DPCM is used.
  • the video decoder may obtain, from the bitstream, for each respective significant value in the block, a respective syntax element indicating whether the respective significant value is positive or negative.
  • FIG. 1 is a block diagram illustrating an example video coding system 10 that may utilize the techniques of this disclosure.
  • video coder refers generically to both video encoders and video decoders.
  • video coding or “coding” may refer generically to video encoding or video decoding.
  • video coding system 10 includes a source device 12 and a destination device 14 .
  • Source device 12 generates encoded video data. Accordingly, source device 12 may be referred to as a video encoding device or a video encoding apparatus.
  • Destination device 14 may decode the encoded video data generated by source device 12 . Accordingly, destination device 14 may be referred to as a video decoding device or a video decoding apparatus.
  • Source device 12 and destination device 14 may be examples of video coding devices or video coding apparatuses.
  • Source device 12 and destination device 14 may comprise a wide range of devices, including desktop computers, mobile computing devices, notebook (e.g., laptop) computers, tablet computers, set-top boxes, telephone handsets such as so-called “smart” phones, televisions, cameras, display devices, digital media players, video gaming consoles, in-car computers, or the like.
  • desktop computers mobile computing devices
  • notebook (e.g., laptop) computers tablet computers
  • set-top boxes telephone handsets such as so-called “smart” phones
  • televisions cameras
  • display devices digital media players
  • video gaming consoles in-car computers, or the like.
  • Destination device 14 may receive encoded video data from source device 12 via a channel 16 .
  • Channel 16 may comprise one or more media or devices capable of moving the encoded video data from source device 12 to destination device 14 .
  • channel 16 may comprise one or more communication media that enable source device 12 to transmit encoded video data directly to destination device 14 in real-time.
  • source device 12 may modulate the encoded video data according to a communication standard, such as a wireless communication protocol, and may transmit the modulated video data to destination device 14 .
  • the one or more communication media may include wireless and/or wired communication media, such as a radio frequency (RF) spectrum or one or more physical transmission lines.
  • RF radio frequency
  • the one or more communication media may form part of a packet-based network, such as a local area network, a wide-area network, or a global network (e.g., the Internet).
  • Channel 16 may include various types of devices, such as routers, switches, base stations, or other equipment that facilitate communication from source device 12 to destination device 14 .
  • channel 16 may include a storage medium that stores encoded video data generated by source device 12 .
  • destination device 14 may access the storage medium, e.g., via disk access or card access.
  • the storage medium may include a variety of locally-accessed data storage media such as Blu-ray discs, DVDs, CD-ROMs, flash memory, or other suitable digital storage media for storing encoded video data.
  • channel 16 may include a file server or another intermediate storage device that stores encoded video data generated by source device 12 .
  • destination device 14 may access encoded video data stored at the file server or other intermediate storage device via streaming or download.
  • the file server may be a type of server capable of storing encoded video data and transmitting the encoded video data to destination device 14 .
  • Example file servers include web servers (e.g., for a website), file transfer protocol (FTP) servers, network attached storage (NAS) devices, local disk drives, and the like.
  • Destination device 14 may access the encoded video data through a standard data connection, such as an Internet connection.
  • a standard data connection such as an Internet connection.
  • Example types of data connections may include wireless channels (e.g., Wi-Fi connections), wired connections (e.g., DSL, cable modem, etc.), or combinations of both that are suitable for accessing encoded video data stored on a file server.
  • the transmission of encoded video data from the file server may be a streaming transmission, a download transmission, or a combination of both.
  • video coding system 10 may be configured to support one-way or two-way video transmission to support applications such as video streaming, video playback, video broadcasting, and/or video telephony.
  • source device 12 includes a video source 18 , a video encoder 20 , and an output interface 22 .
  • output interface 22 may include a modulator/demodulator (modem) and/or a transmitter.
  • Video source 18 may include a video capture device, e.g., a video camera, a video archive containing previously-captured video data, a video feed interface to receive video data from a video content provider, and/or a computer graphics system for generating video data, or a combination of such sources of video data.
  • Video encoder 20 may encode video data from video source 18 .
  • source device 12 directly transmits the encoded video data to destination device 14 via output interface 22 .
  • the encoded video data may also be stored onto a storage medium or a file server for later access by destination device 14 for decoding and/or playback.
  • destination device 14 includes an input interface 28 , a video decoder 30 , and a display device 32 .
  • input interface 28 includes a receiver and/or a modem.
  • Input interface 28 may receive encoded video data over channel 16 .
  • Display device 32 may be integrated with or may be external to destination device 14 . In general, display device 32 displays decoded video data.
  • Display device 32 may comprise a variety of display devices, such as a liquid crystal display (LCD), a plasma display, an organic light emitting diode (OLED) display, or another type of display device.
  • LCD liquid crystal display
  • OLED organic light emitting diode
  • FIG. 1 is merely an example and the techniques of this disclosure may apply to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between the video encoding device and the video decoding device.
  • data is retrieved from a local memory, streamed over a network, or the like.
  • a video encoding device may encode and store data to memory, and/or a video decoding device may retrieve and decode data from memory.
  • the video encoding and decoding is performed by devices that do not communicate with one another, but simply encode data to memory and/or retrieve and decode data from memory.
  • Video encoder 20 and video decoder 30 each may be implemented as any of a variety of suitable circuitry, such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, hardware, or any combinations thereof. If the techniques are implemented partially in software, a device may store instructions for the software in a suitable, non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Any of the foregoing (including hardware, software, a combination of hardware and software, etc.) may be considered to be one or more processors. Each of video encoder 20 and video decoder 30 may be included in one or more encoders or decoders, either of which may be integrated as part of a combined encoder/decoder (CODEC) in a respective device.
  • CODEC combined encoder/decoder
  • This disclosure may generally refer to video encoder 20 “signaling” certain information.
  • the term “signaling” may generally refer to the communication of syntax elements and/or other data used to decode the compressed video data. Such communication may occur in real- or near-real-time. Alternately, such communication may occur over a span of time, such as might occur when storing syntax elements to a computer-readable storage medium in an encoded bitstream at the time of encoding, which a video decoding device may then retrieve at any time after being stored to this medium.
  • video encoder 20 and video decoder 30 operate according to a video compression standard, such as the High Efficiency Video Coding (HEVC) standard.
  • HEVC High Efficiency Video Coding
  • a draft of the HEVC standard referred to as “HEVC Working Draft 6,” is described in Bross et al., “High Efficiency Video Coding (HEVC) text specification draft 6,” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 7th Meeting: Geneva, Switzerland, November, 2011, the entire content of which is incorporated herein by reference.
  • JCT-VC Joint Collaborative Team on Video Coding
  • HEVC Working Draft 6 is downloadable from http://phenix.int-evry.fr/jct/doc_end_user/documents/8_San%20Jose/wg11/JCTVC-H1003-v22.zip.
  • Another draft of the HEVC standard referred to as “HEVC Working Draft 9,” is described in Bross et al., “High Efficiency Video Coding (HEVC) text specification draft 9,” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 11th Meeting: Shanghai, China, October, 2012, the entire content of which is incorporated herein by reference.
  • JCT-VC Joint Collaborative Team on Video Coding
  • HEVC Working Draft 9 is downloadable from http://phenix.int-evry.fr/jct/doc_end_user/documents/11_Shanghai/wg11/JCTVC-K1003-v8.zip.
  • Another draft of HEVC referred to as “HEVC Working Draft 10,” is described in Bross et al., “High Efficiency Video Coding (HEVC) text specification draft 10 (for FDIS & Consent),” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG16 WP3 and ISO/IEC JTC1/SC29/WG11, 12th Meeting: Geneva, CH, 14-23 Jan. 2013, the entire content of which is incorporated herein by reference. As of Mar.
  • HEVC Working Draft 10 is available from http://phenix.int-evry.fr/jct/doc_end_user/documents/12_Geneva/wg11/JCTVC-L1003-v20.zip.
  • the techniques of this disclosure are not limited to any particular coding standard or technique.
  • HEVC High Efficiency Video Coding
  • JCT-VC Joint Collaborative Team on Video Coding
  • JCTVC-M1005_v2 is available at http://phenix.int-evry.fr/jct/doc_end_user/documents/13_Incheon/pending/JCTVC-M1005-v2.zip. The entire content of JCTVC-M1005_v2 is incorporated herein by reference.
  • video encoder 20 encodes video data.
  • the video data may comprise one or more pictures. Each of the pictures is a still image forming part of a video.
  • video encoder 20 may generate a bitstream.
  • the bitstream may include a sequence of bits that form a coded representation of the video data.
  • the bitstream may include coded pictures and associated data.
  • a coded picture is a coded representation of a picture.
  • the associated data may include sequence parameter sets (SPSs), picture parameter sets (PPSs), and other syntax structures.
  • SPS sequence parameter sets
  • PPSs picture parameter sets
  • a SPS may contain parameters applicable to zero or more sequences of pictures.
  • a PPS may contain parameters applicable to zero or more pictures.
  • a picture may include three sample arrays, denoted S L , S Cb and S Cr .
  • S L is a two-dimensional array (i.e., a block) of luma samples. Luma samples may also be referred to herein as “Y” samples.
  • S Cb is a two-dimensional array of Cb chrominance samples.
  • S Cr is a two-dimensional array of Cr chrominance samples. Chrominance samples may also be referred to herein as “chroma” samples.
  • Cb chrominance samples may be referred to herein as “U samples.”
  • Cr chrominance samples may be referred to herein as “V samples.”
  • video encoder 20 may down-sample the chroma arrays of a picture (i.e., S Cb and S Cr ).
  • video encoder 20 may use a YUV 4:2:0 video format, a YUV 4:2:2 video format, or a 4:4:4 video format.
  • video encoder 20 may down-sample the chroma arrays such that the chroma arrays are 1 ⁇ 2 the height and 1 ⁇ 2 the width of the luma array.
  • video encoder 20 may down-sample the chroma arrays such that the chroma arrays are 1 ⁇ 2 the width and the same height as the luma array. In the YUV 4:4:4 video format, video encoder 20 does not down-sample the chroma arrays.
  • video encoder 20 may generate a set of coding tree units (CTUs).
  • Each of the CTUs may be a coding tree block of luma samples, two corresponding coding tree blocks of chroma samples, and syntax structures used to code the samples of the coding tree blocks.
  • a coding tree block may be an N ⁇ N block of samples.
  • a CTU may also be referred to as a “tree block” or a “largest coding unit” (LCU).
  • the CTUs of HEVC may be broadly analogous to the macroblocks of other standards, such as H.264/AVC. However, a CTU is not necessarily limited to a particular size and may include one or more coding units (CUs).
  • video encoder 20 may generate encoded representations of each slice of the picture (i.e., coded slices). To generate a coded slice, video encoder 20 may encode a series of CTUs. This disclosure may refer to an encoded representation of a CTU as a coded CTU. In some examples, each of the slices includes an integer number of coded CTUs.
  • video encoder 20 may recursively perform quad-tree partitioning on the coding tree blocks of a CTU to divide the coding tree blocks into coding blocks, hence the name “coding tree units.”
  • a coding block is an N ⁇ N block of samples.
  • a CU may be a coding block of luma samples and two corresponding coding blocks of chroma samples of a picture that has a luma sample array, a Cb sample array and a Cr sample array, and syntax structures used to code the samples of the coding blocks.
  • a CU may comprise a single coding block of samples and syntax structures used to code the coding block.
  • Video encoder 20 may partition a coding block of a CU into one or more prediction blocks.
  • a prediction block may be a rectangular (i.e., square or non-square) block of samples on which the same prediction is applied.
  • a prediction unit (PU) of a CU may be a prediction block of luma samples, two corresponding prediction blocks of chroma samples of a picture, and syntax structures used to predict the prediction block samples.
  • Video encoder 20 may generate predictive luma, Cb and Cr blocks for luma, Cb and Cr prediction blocks of each PU of the CU.
  • a CU may comprise a single coding block of samples and syntax structures used to code the coding block.
  • Video encoder 20 may use intra prediction or inter prediction to generate the predictive blocks for a PU. If video encoder 20 uses intra prediction to generate the predictive blocks of a PU, video encoder 20 may generate the predictive blocks of the PU based on decoded samples of the picture associated with the PU.
  • video encoder 20 may generate the predictive blocks of the PU based on decoded samples of one or more pictures other than the picture associated with the PU.
  • Video encoder 20 may use uni-prediction or bi-prediction to generate the predictive blocks of a PU.
  • the PU may have a single motion vector.
  • the PU may have two motion vectors.
  • video encoder 20 may generate a residual block for the CU. For instance, video encoder 20 may generate a luma residual block for the CU. Each sample in the CU's luma residual block indicates a difference between a luma sample in one of the CU's predictive luma blocks and a corresponding sample in the CU's original luma coding block. In addition, video encoder 20 may generate a Cb residual block for the CU.
  • predictive blocks e.g., luma, Cb and Cr blocks
  • Each sample in the CU's Cb residual block may indicate a difference between a Cb sample in one of the CU's predictive Cb blocks and a corresponding sample in the CU's original Cb coding block.
  • Video encoder 20 may also generate a Cr residual block for the CU.
  • Each sample in the CU's Cr residual block may indicate a difference between a Cr sample in one of the CU's predictive Cr blocks and a corresponding sample in the CU's original Cr coding block.
  • video encoder 20 may use quad-tree partitioning to decompose the residual blocks of a CU into transform blocks.
  • video encoder 20 may use quad-tree partitioning to decompose luma, Cb, and Cr residual blocks of a CU into luma, Cb, and Cr transform blocks.
  • a transform block may be a rectangular block of samples on which the same transform is applied.
  • a transform unit (TU) of a CU may be a transform block of luma samples, two corresponding transform blocks of chroma samples, and syntax structures used to transform the transform block samples.
  • each TU of a CU may be associated with a luma transform block, a Cb transform block, and a Cr transform block.
  • the luma transform block associated with the TU may be a sub-block of the CU's luma residual block.
  • the Cb transform block may be a sub-block of the CU's Cb residual block.
  • the Cr transform block may be a sub-block of the CU's Cr residual block.
  • a TU may comprise a single transform block and syntax structures used to transform the transform block samples.
  • a TU size may be the size of a transform block of a TU.
  • Video encoder 20 may apply one or more transforms to a transform block of a TU to generate a coefficient block for the TU. For instance, video encoder 20 may apply one or more transforms to a luma transform block of a TU to generate a luma coefficient block for the TU. A coefficient block may be a two-dimensional array of transform coefficients. A transform coefficient may be a scalar quantity. In addition, video encoder 20 may apply one or more transforms to a Cb transform block of a TU to generate a Cb coefficient block for the TU. Video encoder 20 may apply one or more transforms to a Cr transform block of a TU to generate a Cr coefficient block for the TU.
  • video encoder 20 may quantize the coefficient block. Quantization generally refers to a process in which transform coefficients are quantized to possibly reduce the amount of data used to represent the transform coefficients, providing further compression.
  • video encoder 20 may entropy encode syntax elements indicating the quantized transform coefficients. For example, video encoder 20 may perform Context-Adaptive Binary Arithmetic Coding (CABAC) on the syntax elements indicating the quantized transform coefficients.
  • CABAC Context-Adaptive Binary Arithmetic Coding
  • Video encoder 20 may output the entropy-encoded syntax elements in a bitstream.
  • CABAC Context-Adaptive Binary Arithmetic Coding
  • Video decoder 30 may receive a bitstream generated by video encoder 20 .
  • video decoder 30 may parse the bitstream to decode syntax elements from the bitstream.
  • Video decoder 30 may reconstruct the pictures of the video data based at least in part on the syntax elements decoded from the bitstream.
  • the process to reconstruct the video data may be generally reciprocal to the process performed by video encoder 20 .
  • video decoder 30 may use motion vectors of PUs to determine predictive blocks for the PUs of a current CU.
  • video decoder 30 may inverse quantize transform coefficient blocks associated with TUs of the current CU.
  • Video decoder 30 may perform inverse transforms on the transform coefficient blocks to reconstruct transform blocks associated with the TUs of the current CU.
  • Video decoder 30 may reconstruct the coding blocks of the current CU by adding the samples of the predictive blocks for PUs of the current CU to corresponding samples of the transform blocks of the TUs of the current CU. By reconstructing the coding blocks for each CU of a picture, video decoder 30 may reconstruct the picture.
  • a video coder such as video encoder 20 or video decoder 30 , may use intra prediction to generate a predictive block for a current PU.
  • the video coder may determine values of samples in the predictive block using a set of reference samples. For instance, in HEVC intra prediction, already reconstructed samples from the top and left side neighboring blocks may be used for prediction. These reconstructed samples may be referred to as reference samples.
  • FIG. 2 illustrates reference samples of a block for HEVC intra prediction.
  • FIG. 2 is a conceptual diagram illustrating a block of size M (height) ⁇ N (width).
  • M indicates rows and N indicates columns.
  • the samples of a block are denoted by P i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1).
  • the term “samples” can refer to the original pixel values of an input component (e.g., R, G, or B in an RGB picture, Y, Cb, or Cr, in YCbCr pictures, etc.) or sample values of a component after applying a color transform to the input components.
  • the reference pixels are denoted by P ⁇ 1,j , where ⁇ 1 ⁇ j ⁇ 2N and P i, ⁇ 1 , where ⁇ 1 ⁇ i ⁇ 2M.
  • the reference samples may include a set of reference samples left of the current PU and a set of reference sample above the current PU.
  • This disclosure may refer to the set of reference samples above the current PU as the top predictor.
  • This disclosure may refer to the set of reference samples left of the current PU as the left predictor.
  • already reconstructed samples from the top and left side neighboring blocks are used for prediction (the “top” neighboring block may also be called the “above” neighboring block). These samples are referred to as reference samples.
  • a video coder using HEVC may use a specific padding process to generate missing reference samples.
  • the video coder may generate the predictive block according to an intra prediction mode from a plurality of available intra prediction modes.
  • the intra prediction modes may include a plurality of directional (i.e., angular) intra prediction modes. For instance, in some versions of HEVC, there are 33 directional intra prediction modes. Each of the directional intra prediction modes corresponds to a different direction.
  • FIG. 3 is a conceptual diagram illustrating example intra prediction mode directions.
  • the video coder may, for each respective sample of the predictive block, assign to the respective sample a value of a reference sample (or a weighted combination of reference samples) that is aligned with the respective sample in a direction corresponding to the directional intra prediction mode.
  • a video coder uses a directional (i.e., angular) intra prediction mode to generate a predictive block for a current block, the video coder may be said to be performing angular intra prediction.
  • the intra prediction modes include a DC intra prediction mode.
  • the video coder when the video coder uses DC intra prediction to generate a predictive block, the video coder may determine a mean value of the reference samples. The video coder may then determine that each sample in the predictive block has the determined mean value.
  • all samples of the predictive block have the same value. For example, assume that a padding process has been completed so that all the reference samples are available.
  • the DC prediction may be formed as:
  • the intra prediction modes include a planar intra prediction mode.
  • predSamples[x][y] may denote the value of a sample at position x, y of the prediction block.
  • the video coder may determine the samples of the predictive block as follows:
  • the value of a sample of the predictive block is an average of two linear interpolations of the value.
  • first linear interpolation as values of x increase from left to right across a row of the predictive block, a weight accorded to a reference sample left of the row decreases while a weight accorded to a reference sample above and right of a top-right corner of the predictive block increases.
  • second linear interpolation as values of y increase down a column of the predictive block, a weight accorded to a reference sample above the column diminishes while a weight accorded to a sample below and left of a bottom-left corner of the predictive block increases.
  • planar intra prediction may use samples P ⁇ 1,j where 0 ⁇ j ⁇ (N ⁇ 1), and P M, ⁇ 1 to generate a bi-linear prediction in the vertical direction.
  • samples P i, ⁇ 1 where 0 ⁇ i ⁇ (M ⁇ 1), and P ⁇ 1,N may be used to generate a bi-linear prediction in the horizontal direction.
  • T i,j V ( M ⁇ i )* P ⁇ 1,j +i*P M, ⁇ 1 ,
  • T i,j H ( N ⁇ j )* P i, ⁇ 1 +j*P ⁇ 1,N and
  • T i,j ( T i,j V +T i,j H +N )>>(log 2 N+ 1).
  • video encoder 20 and video decoder 30 implement a lossless coding mode as described herein.
  • video encoder 20 transforms (e.g., using a discrete cosine transform) and quantizes residual data (i.e., prediction error) for the block. In other words, the prediction error is transformed and quantized.
  • video encoder 20 may not apply a transform or quantization to residual data for the block. In other words, in lossless coding mode (e.g., for a CU or an entire picture), the transform and quantization steps may be skipped.
  • video encoder 20 may treat the sample values of the residual data in the same manner as quantized transform coefficients. For instance, video encoder 20 may entropy encode syntax elements representing sample values of the residual data and include the resulting data in a bitstream. Thus, the residual data does not undergo any loss of information due to transformation or quantization.
  • video decoder 30 may not apply inverse quantization or inverse transforms to the residual data for the block. Instead, video decoder 30 may entropy decode syntax elements representing sample values of the residual data and then reconstruct sample values of the block based at least in part on sample values of the residual data.
  • Several example techniques of this disclosure relate to lossless encoding. As described herein, instead of using reference samples from neighboring blocks for prediction, samples from a current block can be used for improved prediction. For instance, several example techniques of this disclosure describe modifications that may be applicable to an intra DC prediction mode for lossless coding in the HEVC standard. Furthermore, several example techniques of this disclosure describe modifications that may be applicable to an intra planar prediction mode for lossless coding in the HEVC standard. The techniques of this disclosure may also be applicable to other types of prediction, and may also be applicable to other coding standards.
  • samples from the current block can be used for improved prediction.
  • techniques for angular intra prediction for lossy coding modes as well as lossless coding modes when transform is skipped are set forth in Lan et al., “Intra and inter coding tools for screen contents,” Joint Collaborative Team on Video Coding (JCT-VC) of ITU-T SG 16 WP3 and ISO/IEC JTC1/SC29/WG11, 5 th Meeting, Geneva, CH, 16-23 March, 2011, document JCTVC-E145 (hereinafter, “JCTVC-E145”).
  • JCTVC-VC Joint Collaborative Team on Video Coding
  • JCT-VC-E145 JCTVC-E145
  • transform and quantization steps are skipped, so it may be possible to improve upon the process for determining samples of a predictive block when using the intra DC mode.
  • the samples are being processed in a raster scan along rows.
  • the same techniques can be extended to raster scan along columns (or even to diagonal or zig-zag scans, but losing some potential of parallelization of the techniques).
  • residual entropy decoding of the prediction error
  • the term “original sample” or “original sample value” may refer to either actual original sample values or reconstructed sample values (i.e., non-residual samples). Due to the raster scan along rows, all the samples from previous rows as well as all the samples to the left of the current sample from the current row are available for DC prediction.
  • One or more techniques of this disclosure take advantage of this to improve intra prediction using the DC intra prediction mode.
  • the intra prediction modes of this disclosure can replace the planar intra prediction mode or can be understood as planar intra prediction modes.
  • the intra prediction modes of this disclosure may replace the current planar mode in HEVC for lossless coding. Details described in the examples of this disclosure may be combined with one or more details of other examples of this disclosure. That is, the details may be combined in any of a wide variety of different ways to achieve still other examples.
  • a video coder e.g., video encoder 20 or video decoder 30
  • the video coder may process samples of a predictive block in a raster scan order.
  • the video coder may use a causal neighborhood of the sample of the predictive block to form a DC prediction value for the sample.
  • a causal neighborhood of a sample in a predictive block is a set of reconstructed samples (e.g., non-residual, non-predictive samples) that correspond to samples in the predictive block that have already been determined.
  • the causal neighborhood of a sample in the predictive block may include reconstructed samples that correspond to locations above and left of the sample.
  • the video coder calculates the DC prediction value, DC i,j , for a current sample P i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), as:
  • video encoder 20 may determine a DC intra prediction value (i.e., DC i,k ) for the respective sample as an average of a reconstructed value of a sample above the respective sample (i.e., P i,j ⁇ 1 ) and a reconstructed value of a sample left of the respective sample (i.e., P i ⁇ 1, j ). Because video encoder 20 is using lossless coding, the reconstructed value of the sample left of the respective sample and the reconstructed value of the sample above respective sample are same as the original values of the sample left of the respective sample and the original value of the sample above the respective sample.
  • video decoder 30 may determine a DC intra prediction value (i.e., DC i,k ) for the respective sample as an average of a reconstructed value of a sample above the respective sample (i.e., P i,j ⁇ 1 ) and a reconstructed value of a sample left of the respective sample (i.e., P i ⁇ 1,j ). Because video decoder 30 is using lossless coding, the reconstructed value of the sample above the respective sample and the reconstructed value of the sample left of the respective sample are the same as the original value of the sample above the respective sample and the original value of the sample left of the respective sample.
  • DC i,j+1 can be represented as
  • DC i,j+1 ( P i,j +P i ⁇ 1,j+1 +1)>>1, or
  • DC i,j+1 (( R i,j +(( P i,j ⁇ 1 +P i ⁇ 1,j +1)>>1)+ P i ⁇ 1,j+1 +1)>>1,
  • R i,j is the prediction residual for sample at location (i,j). Because the right bit-shift is non-linear process, there may be no way to calculate DC i,j+1 before finishing the calculation of DC i,j . For instance, it may be difficult for video decoder 30 to process multiple samples of the predictive block in parallel.
  • video decoder 30 may obtain, from a bitstream, syntax elements indicating residual sample values of the current block.
  • video decoder 30 does not need apply inverse quantization or an inverse transform to determine the residual sample values of the current block.
  • Obtaining the syntax elements from the bitstream may involve entropy decoding the syntax elements. Accordingly, when the current block is coded using lossless or lossy coding, it can be assumed that prediction residuals (i.e., the prediction error) of the current block have already been entropy decoded.
  • the prediction residuals are available for use in determining the reconstructed values of samples that video decoder 30 uses in determining the DC prediction values for samples of a predictive block for the current block. Assuming that the prediction residuals have already been entropy decoded, it may be possible to pipeline the processing of samples in different rows with a one sample delay. Thus, in accordance with one or more techniques of this disclosure, video decoder 30 may start processing of a second row of samples after one sample from the first row has been reconstructed. In this way, video decoder 30 may process multiple rows of samples in parallel. Hence, as part of generating a predictive block, a video coder may pipeline processing of samples in different rows of the predictive block, wherein a one cycle delay for DC prediction exists between rows of the predictive block.
  • a video coder may calculate a DC prediction value DC i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), as:
  • DC i,j ( P i,j ⁇ 1 +P i ⁇ 1,j ⁇ P i ⁇ 1,j ⁇ 1 ). (6)
  • video encoder 20 may determine a DC prediction value (i.e. DC i,j ) for the respective sample as a sum of a reconstructed value of a sample above the respective sample (i.e., P i,j ⁇ 1 ) and a reconstructed value of a sample left of the respective sample (i.e., P i ⁇ 1,j ), minus an original value of a sample immediately above and left of the respective sample (i.e., P i ⁇ 1,j ⁇ 1 ).
  • video decoder 30 may determine a DC prediction value (i.e.
  • DC i,j for the respective sample as a sum of a reconstructed value of a sample above the respective sample (i.e., P i,j ⁇ 1 ) and a reconstructed value of a sample left of the respective sample (i.e., P i ⁇ 1,j ), minus a reconstructed value of a sample immediately above and left of the respective sample (i.e., P i ⁇ 1,j ⁇ 1 ). Because lossless coding is being used, the reconstructed value of the samples are the same as the original values of the samples.
  • a video coder can calculate DC i,j+1 for a current sample P i,j of a predictive block without waiting for P i,j as follows.
  • DC i,j+1 can be expressed as:
  • DC i,j+1 (( P i,j ⁇ 1 +P i ⁇ 1,j ⁇ P i ⁇ 1,j ⁇ 1 )+ r i,j +P i ⁇ 1,j+1 ⁇ P i ⁇ 1,j ) (7)
  • Equation (7) may be rewritten as follows:
  • r i,j is the prediction error residual for sample P i,j .
  • the calculation of a DC intra prediction value for a particular sample at location (i, j+1) is not dependent on the reconstructed values of the samples to the left of the particular sample. Rather, the calculation of the DC intra prediction value DC i,j+1 for a particular sample may depend on the reconstructed value for the sample directly above, as well as the residual values for all the samples to the left of the current sample, and reference samples in the same row and the row above. This may allow video decoder 30 (as well as video encoder 20 ) to calculate the DC prediction values for all the samples in a row of a block in parallel assuming that the residuals for the entire row have already been decoded.
  • the reconstructed value of the samples (i.e., P i,j ⁇ 1 , P i ⁇ 1,j , and P i ⁇ 1,j ⁇ 1 ) are the same as the original values of the samples.
  • this technique may be applied to lossy coding. In that case, to maintain parallelization, it is necessary to use unclipped reconstructed value for the sample to the left for DC prediction.
  • the reconstructed samples from the row above may be clipped or unclipped. For example, for an 8-bit video sequence, the reconstructed samples are clipped to the interval [0, 255].
  • a video coder may calculate a DC prediction value DC i,j for a current sample P i,j of a predictive block, where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), as:
  • DC i,j ( P i,j ⁇ 1 +P i ⁇ 1,j +P i ⁇ 1,j ⁇ 1 +P i ⁇ 1,j+1 +2)>>2, (9)
  • DC i,j ( P i,j ⁇ 1 +P i ⁇ 1,j +P i ⁇ 1,j ⁇ 1 +P i ⁇ 1,j+1 )>>2.
  • a DC intra prediction value for the respective sample is an average of the reconstructed sample above the respective sample (i.e., P i,j ⁇ 1 ), the reconstructed sample left of the respective sample (i.e., P i ⁇ 1,j ), the reconstructed sample above and left of the respective sample (i.e., P i ⁇ 1,j ⁇ 1 ), and the reconstructed sample above and right of the respective sample (i.e., P i ⁇ 1,j+1 ).
  • the reconstructed values of the samples (i.e., P i,j ⁇ 1 , P i ⁇ 1,j , P i ⁇ 1,j ⁇ 1 , and P i ⁇ 1,j+1 ) are the same as the original values of the samples.
  • a video coder may assume that the top and top-right samples (i.e., P i ⁇ 1,j and P i ⁇ 1,j+1 , respectively) have the same value.
  • the video coder may modify the DC prediction to use only available samples.
  • a sample may be unavailable if the sample is not within the boundaries of a current slice or picture, or has not yet been coded.
  • a video coder may perform DC intra prediction on a block size smaller than the TU size. For example, irrespective of the TU size, a video coder may perform the DC intra prediction on 2 ⁇ 2 blocks. The video coder may process the 2 ⁇ 2 blocks of a predictive block in a raster scan order. In this example, for samples P 2i,2j , P 2i,2j+1 , P 2i+1,2j , and P 2i+1, 2j+1 , the video coder calculates the DC intra prediction values as:
  • the video coder can process four samples in parallel.
  • the video coder may be able to determine the DC intra prediction values of each of the four samples of a 2 ⁇ 2 block in parallel.
  • the video coder may use 4 ⁇ 4 blocks or 8 ⁇ 8 blocks instead of 2 ⁇ 2 blocks.
  • r i,j wherein 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), be the prediction residuals after performing DC intra prediction as specified in HEVC (e.g., HEVC Working Draft 10).
  • r i,j may be a prediction residual value after performing DC intra prediction as described in equation (1) above, for a 4 ⁇ 4 block
  • a video coder may then generate intermediate values s i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1).
  • the video coder may generate the intermediate values s i,j as:
  • the video coder may then generate modified residual values t i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), as follows:
  • the video encoder may entropy encode the modified residuals, t i,j , as described in regular HEVC (e.g., HEVC Working Draft 10). On the decoder side (e.g., at video decoder 30 ), this process is reversed. For example, video decoder 30 may determine,
  • Video decoder 30 may also determine,
  • a potentially better predictor can be used instead of taking simple difference.
  • a video coder may determine s i,j as follows:
  • various other examples of this disclosure can be applied for improving the DC intra prediction mode in lossy coding when the transform is skipped.
  • various other examples of this disclosure may be applied for improving the DC intra prediction mode when a video encoder does not apply a transform to residual samples of a transform block, but does quantize the residual samples of the transform block.
  • a causal neighborhood is used for calculating the DC prediction value for the current sample.
  • reconstructed (quantized) sample values in the causal neighborhood may be used. Because application of the transform is skipped, the reconstructed values in the causal neighborhood are available. It should be noted that to retain parallelization benefits, the clipping operation is not applied to reconstructed values from the current row until the processing for the entire row is complete. For the row above, either clipped or unclipped reconstructed values may be used.
  • a TU is divided into smaller blocks (e.g., 2 ⁇ 2 blocks) and a DC prediction value is calculated for each smaller block.
  • reconstructed (quantized) sample values may be used in the case of lossy coding where the transform is skipped.
  • a video coder may calculate the DC prediction value DC i,j as:
  • DC i,j ( Q ( P i,j ⁇ 1 )+ Q ( P i ⁇ 1,j ) ⁇ Q ( P i ⁇ 1,j ⁇ 1 )) (Equ. DC1)
  • equation DC1 is similar to equation (6), above, except that the sample values (i.e., P i,j ⁇ 1 , P i ⁇ 1,j , and P i ⁇ 1,j ⁇ 1 ) are quantized and then de-quantized.
  • This disclosure may refer to such samples as quantized samples or quantized versions of original samples.
  • the video coder may calculate a DC prediction value for the respective sample as a sum of a quantized version of the original sample above the respective sample (i.e., Q(P i,j ⁇ 1 ) and a quantized version of the original sample left of the respective sample (i.e., Q(P i ⁇ 1,j ), minus a quantized version of the original sample above and left of the respective sample (i.e., Q(P i ⁇ 1,j ⁇ 1 )).
  • terms of the form Q(P i,j ) are reconstructed samples.
  • the residual value r i,j is equal to the sample value P i,j minus the corresponding DC intra prediction value DC i,j .
  • the reconstructed residual after quantization and dequantization is denoted by Q(r i,j ).
  • video decoder 30 may have some desirable throughput properties on the decoder side. For example, it may be possible for video decoder 30 to calculate the reconstructed sample values for all the samples in a row (or column) of a block simultaneously. For instance, video decoder 30 may obtain the reconstructed sample values as:
  • Q(P i ⁇ 1,j ) denotes a reconstructed sample which may be appropriately clipped. For example, to appropriately clip a reconstructed value with an input bit depth of 8, the values of Q(P i ⁇ 1,j ) are clipped between 0 and 255.
  • the other values, Q(P i ⁇ 1, ⁇ 1 ) and Q(P i, ⁇ 1 ) belong to previously reconstructed blocks and are already clipped.
  • the reconstructed sample Q(P i ⁇ 1,j ) in equation DC2 is unclipped but can be clipped appropriately without affecting throughput.
  • the prediction specified in equation DC1 is only approximate if the video decoder uses equation DC2 for reconstruction.
  • the prediction in equation DC1 is only approximate because instead of Q(P i,j ⁇ 1 ), which is a clipped version, an unclipped version is used.
  • the unclipped version of Q(P i,j ⁇ 1 ) may be used on the encoder side as well to generate the DC prediction to avoid a drift between the encoder and the decoder. It is possible to use the clipped version, but then the samples may have to be reconstructed one by one, thereby affecting throughput. This is because, in that case, equation DC1 may have to be used for reconstruction.
  • the reconstruction of a sample may depend on the completion of reconstruction of a sample to the left of the sample. It has been described in this disclosure how a row of samples can be reconstructed in parallel. A similar process can be followed for reconstructing all the samples in a column in parallel. If less parallelism is desired, the summation term may be broken up into smaller chunks, thereby potentially reducing throughput but reducing the average number of additional operations needed for reconstructing a sample.
  • a video coder may generate a predictive block.
  • the video coder may use at least one of a first reconstructed sample (e.g., Q(P i ⁇ 1,j )) and a second reconstructed sample (e.g., Q(P i,j ⁇ 1 )) for DC prediction of a current sample of the predictive block.
  • the first reconstructed sample may correspond to a sample left of the current sample in the current row of the predictive block.
  • the second reconstructed sample may correspond to a sample in a row of the predictive block above the current row.
  • the video coder may reconstruct a coding block what was coded using lossy coding by adding samples of the predictive block to corresponding residual samples.
  • the video coder may determine a reconstructed value Q(P i,j ⁇ 1 ) corresponding to a sample above the current sample.
  • the video coder may determine a reconstructed value Q(P i ⁇ 1,j ) corresponding to a sample left of the current sample.
  • the video coder may also determine a reconstructed value Q(P i ⁇ 1,j ⁇ 1 ) corresponding to a sample left and above the current sample.
  • the video coder may calculate a DC prediction value DC i,j for the current sample P i,j as:
  • DC i,j ( Q ( P i,j ⁇ 1 )+ Q ( P i ⁇ 1,j ) ⁇ Q ( P i ⁇ 1,j ⁇ 1 )).
  • the video coder may, for each respective reconstructed value from among Q(P i,j ⁇ 1 ), Q(P i ⁇ 1,j ), and Q(P i ⁇ 1,j ⁇ 1 ), determine the respective reconstructed value in one of the following ways.
  • the video coder may determine the respective reconstructed value as a dequantized residual value for a given sample (e.g., Q(r i,j )) plus a DC prediction value for the corresponding sample (e.g., DC i,j ).
  • the given sample corresponds to the respective reconstructed value.
  • the video coder may clip the reconstructed value corresponding to the sample left of the given sample.
  • Another example of this disclosure proposes a modification to the prediction process for the planar mode.
  • the vertical prediction may be more accurate if the original samples from the last row are used for performing vertical prediction instead of using P M, ⁇ 1 .
  • the horizontal prediction may be more accurate if the original samples from the last column are used for performing horizontal prediction instead of using P ⁇ 1,N .
  • the use of the original samples in intra planar mode is a basic idea behind one or more examples of this disclosure.
  • the video encoder may then generate the prediction values T i,j , where 0 ⁇ i ⁇ (M ⁇ 2) and 0 ⁇ j ⁇ (N ⁇ 2), as follows:
  • T i,j V ( M ⁇ i )* P ⁇ 1,j +i*P M ⁇ 1,j ,
  • T i,j H ( N ⁇ j )* P i, ⁇ 1 +j*P i,N ⁇ 1 and
  • T i,j ( T i,j V +T i,j H +N )>>(log 2 N+ 1). (19)
  • the video encoder may generate the remaining residuals, r i,j , where 0 ⁇ i ⁇ (M ⁇ 2) and 0 ⁇ j ⁇ (N ⁇ 2), by subtracting the prediction values from the original sample values.
  • the video encoder may entropy encode the entire block of residuals, r i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), as in HEVC (e.g., HEVC Working Draft 10).
  • a video decoder (e.g., video decoder 30 ) may entropy decode the entire block of prediction residuals to generate residual values r i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1).
  • the video decoder adds residual values for the last row and column to the above prediction values to reconstruct the original sample values for the last row and column.
  • the video decoder generates the prediction values T i,j , where 0 ⁇ i ⁇ (M ⁇ 2) and 0 ⁇ j ⁇ (N ⁇ 2), exactly as on the encoder side above.
  • the video decoder adds residual values r i,j , where 0 ⁇ i ⁇ (M ⁇ 2) and 0 ⁇ j ⁇ (N ⁇ 2), to the prediction values to reconstruct the sample values for the remaining sample positions in the block.
  • the video encoder subtracts a prediction value for a position from the original sample value for the position to generate a residual value for that position.
  • the video encoder may then predict the elements of the last row and column bilinearly as:
  • T M ⁇ 1,j (( N ⁇ j )* P M ⁇ 1, ⁇ 1 +j*P M ⁇ 1,N ⁇ 1 )>>(log 2 N ),
  • T i,N ⁇ 1 ( M ⁇ i )* P ⁇ 1,N ⁇ 1 +i*P M ⁇ 1,N ⁇ 1 )>>(log 2 M ). (20)
  • the video encoder generates the prediction values T i,j , where 0 ⁇ i ⁇ (M ⁇ 2) and 0 ⁇ j ⁇ (N ⁇ 2), as follows:
  • T i,j V ( M ⁇ i )* P ⁇ 1,j +i*P M ⁇ 1,j ,
  • T i,j H ( N ⁇ j )* P i, ⁇ 1 +j*P i,N ⁇ 1 and
  • T i,j ( T i,j V +T i,j H +N )>>(log 2 N+ 1). (21)
  • the video encoder generates residual values r i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1) by subtracting the prediction values from the original sample values. Furthermore, in this example, the video encoder entropy encodes the entire block of residuals, r i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1) as in HEVC (e.g., HEVC Working Draft 10).
  • the residue distribution due to the prediction techniques of this disclosure tends to be the reverse of the common one in video compression when a transform is employed.
  • the residue has higher values at lower frequencies, and lower expected values at higher frequencies.
  • the last row and column tend to have larger values.
  • An approach to improve performance while taking advantage of the entropy coding method designed for the transform residue is to rotate the residue coming from the prediction in the examples provided above. That is, the residue is rotated 180 degrees, so the top-left part becomes the bottom-right, and vice versa. Then, this rotated residue is entropy coded.
  • the residue is obtained and then rotated 180 degrees.
  • the planar prediction process is modified as follows.
  • HEVC planar mode e.g., planar mode as described in HEVC Working Draft 10
  • P 0,0 can be predicted as (P ⁇ 1,0 +P 0, ⁇ 1 +1)>>1.
  • the remaining samples in the first column can be predicted using the left sample in the same row.
  • the remaining samples in the first row can be predicted using the above sample in the same column.
  • the planar prediction, T i,j where 1 ⁇ i ⁇ (M ⁇ 1) and 1 ⁇ j ⁇ (N ⁇ 1), is generated as follows:
  • T i,j V P i ⁇ 1,j +w v *( P i ⁇ 1,j ⁇ P i ⁇ 2,j ),
  • T i,j H P i,j ⁇ 1 +w h *( P i,j ⁇ 1 ⁇ P i,j ⁇ 2 ) and
  • T i,j ( T i,j V +T i,j H +1)>>1.
  • w v and w h are weights.
  • a value of 0.5 is used for both w v and w h since the value of 0.5 can be implemented as a bit-shift.
  • the remaining residuals i.e., r i,j , where 1 ⁇ i ⁇ (M ⁇ 1) and 1 ⁇ j ⁇ (N ⁇ 1), are generated by subtracting the prediction values from the original sample values.
  • the entire block of residuals i.e., r i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1)
  • HEVC e.g., HEVC Working Draft
  • the video decoder adds the residual values for the first row and column to the above prediction values to reconstruct the original sample values for the first row and column. Subsequently, the video decoder generates the prediction values (i.e., T i,j , where 1 ⁇ i ⁇ (M ⁇ 1) and 1 ⁇ j ⁇ (N ⁇ 1)) exactly as on the encoder side above. In this example, the video decoder adds residual values (i.e., r i,j , where 1 ⁇ i ⁇ (M ⁇ 1) and 1 ⁇ j ⁇ (N ⁇ 1)) to the prediction values to reconstruct the sample values for the remaining positions in the block.
  • the rightmost column and bottom row are predicted using a planar prediction procedure as described in the HEVC (e.g., HEVC Working Draft 10).
  • the original sample values for the rightmost column and the bottom row are then used to perform planar or angular prediction for remaining samples of the block.
  • reconstructed (quantized) sample values may be used for performing planar or angular prediction on the remaining samples.
  • the DC prediction values for the first row and column are filtered (DC prediction filtering).
  • the first row and column of the prediction values, respectively are filtered (gradient filtering).
  • the same concept is applied to angular intra prediction modes.
  • the last row and column is predicted as specified in HEVC (e.g., HEVC Working Draft 10, equation (3), etc.).
  • the original sample values for the last row and column are used to perform intra prediction in addition to the reference samples.
  • FIG. 4 shows the samples which are used for prediction. The shaded positions in FIG. 4 are the positions used as reference samples for performing the prediction.
  • video encoder 20 and video decoder 30 may perform coding that uses one or more original sample values within a block of video data to perform prediction of other sample values within the block.
  • the original sample values may correspond to a last row and a last column of the block (e.g., the bottom row and the right most column of the block).
  • original sample values may correspond to a first row and a first column of the block (e.g., the top row and the left most column).
  • FIG. 4 illustrates one example of sample values used to perform prediction of other sample values.
  • the video coder may perform a lossless coding mode, and the lossless coding mode may comprise a planar coding mode, an angular intra coding mode, or another mode.
  • the techniques may further include a rotate operation on set of residual values generated by the prediction, followed by entropy coding with respect to the rotated set of residual values.
  • DPCM differential pulse code modulation
  • residual DPCM is applied when a CU is being coded losslessly.
  • the basic idea of residual DPCM is to use the upper row pixel for predicting the current pixel for vertical mode and to use the left column pixel for predicting the current pixel for vertical mode.
  • Residual DPCM as described in JCTVC-L0117, can be described as follows.
  • the block could represent any component (e.g. luma, chroma, R, G, B, etc.).
  • the residual DPCM is applied to the residual samples, so that the modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j is obtained as follows when the intra prediction mode is vertical:
  • the modified residual samples of ⁇ tilde over (R) ⁇ are signaled to the video decoder, instead of the original residual samples R. This may be equivalent to using P i ⁇ 1,j as a prediction for P i,j for the vertical prediction mode and using P i,j ⁇ 1 as a prediction for P i,j for the horizontal prediction mode.
  • the original residual samples can be reconstructed after the modified residual samples are parsed as follows:
  • the original residual samples can be reconstructed after the modified residual samples are parsed as follows:
  • this disclosure discusses methods for extending the residual DPCM techniques proposed in JCTVC-L0117 for horizontal and vertical intra prediction modes to other angular intra prediction modes for lossless coding. Because the coding is lossless, the original neighboring samples (in causal coding order) as well as the corresponding prediction residuals are available for prediction (because transform and quantization are skipped).
  • the residual DPCM technique may be extended to other angular intra prediction modes.
  • FIG. 3 shows the intra prediction directions for different angular prediction modes (from 2 to 34). Now consider a mode between 22 and 30. For each of these modes, the prediction direction can be considered to be close to vertical (near-vertical). The numbers 22 and 30 are just examples. Other ranges (e.g., intra prediction modes between 24 and 28) may be chosen as well. Now consider that the residual r i,j , where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), is calculated as specified in HEVC (e.g., HEVC Working Draft 10).
  • the residual DPCM may be applied to the residual samples exactly as in JCTVC-L0117 to obtain the modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j as follows:
  • the prediction direction can be considered to be close to horizontal (i.e., near-horizontal).
  • the numbers 6 and 14 are just examples. In other examples, other ranges (e.g., intra prediction modes between 8 and 12) may be used.
  • the residual r i,j where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1) is calculated as specified in HEVC (e.g., HEVC Working Draft 10). That is, the prediction is performed according to the angular mode and the prediction is subtracted from the original sample values to determine the residual r i,j .
  • the residual DPCM is applied to the residual samples exactly as in JCTVC-L0117 to obtain the modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j as follows:
  • the modified residual samples of ⁇ tilde over (R) ⁇ are signaled to the decoder.
  • the original residual samples can be reconstructed after the modified residual samples are parsed as follows.
  • the intra prediction mode is near-vertical (e.g., modes 22 to 30, inclusive)
  • the original residual samples can be reconstructed as:
  • the original residual samples can be reconstructed as:
  • the residual r i,j is added to the prediction performed according to the angular mode to obtain the original samples.
  • the prediction for horizontal and vertical modes it may be possible to enable or disable the addition of a gradient term to the prediction for the first column (for vertical mode) or the first row (for horizontal mode).
  • the residual may be modified in the following way.
  • the residual r i,j where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), may be calculated as specified in HEVC Working Draft 10. That is, the prediction may be performed according to the angular mode and the prediction may be subtracted from the original sample values to get the residual r i,j .
  • a modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j may be determined as follows:
  • the modified residual samples of ⁇ tilde over (R) ⁇ are signaled to the decoder (e.g., video decoder 30 ).
  • the video decoder may reconstruct original residual samples after the video decoder parses the modified residual samples as follows.
  • the video decoder may reconstruct the original residual samples as:
  • r i,j may be added to the prediction performed according to the angular mode to obtain the original samples.
  • r i ⁇ 1,j ⁇ 1 may need to be available. This may always be true if the true residuals are calculated row-by-row or column-by-column. Thus, it may be possible to calculate the true residual r i,j for all the samples in a row (or column) in parallel.
  • the residual may be modified in the following way.
  • the residual r i,j where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), may be calculated as specified in HEVC (e.g., HEVC Working Draft 10). That is, the prediction may be performed according to the angular mode and the prediction may be subtracted from the original sample values to determine the residual r i,j .
  • a modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j may be determined as follows:
  • the modified residual samples of ⁇ tilde over (R) ⁇ may be signaled to a video decoder (e.g., video decoder 30 ).
  • the video decoder may reconstruct original residual samples after the video decoder parses the modified residual samples as follows.
  • the video decoder may reconstruct the original residual samples using the following equation:
  • r i,j may be added to the prediction performed according to the angular mode to obtain the original samples.
  • r i ⁇ 1,j+1 may need to be available. This may always be true if the true residuals are calculated row-by-row. Thus, it may be possible to calculate the true residual r i,j for all the samples in a row in parallel.
  • the residual may be modified in the following way.
  • the residual r i,j where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1) may be calculated as specified in HEVC (e.g., HEVC Working Draft 10). That is, the prediction may be performed according to the angular mode and the prediction may be subtracted from the original sample values to determine the residual r i,j .
  • a modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j may be determined as follows:
  • the modified residual samples of ⁇ tilde over (R) ⁇ may be signaled to a video decoder (e.g., video decoder 30 ).
  • the video decoder may reconstruct the original residual samples after the video decoder parses the modified residual samples as follows.
  • the video decoder may reconstruct the original residual samples according to the following equation:
  • the residual r i,j may be added to the prediction performed according to the angular mode to obtain the original samples.
  • r i+1,j ⁇ 1 may need to be available. This may always be true if the true residuals are calculated column-by-column. Thus, it may be possible to calculate the true residual r i,j for all the samples in a column in parallel.
  • the first, second, third, and fourth examples where residual DPCM techniques are extended to angular intra prediction modes for lossless coding may be employed simultaneously provided that the range of prediction modes for each embodiment do not overlap.
  • the fifth example where residual DPCM techniques are extended to angular intra prediction modes for lossless coding proposes to extend the concept of residual DPCM to the first row for a vertical or near-vertical intra prediction mode and to the first column for a horizontal or near-horizontal intra prediction mode.
  • the residual r i,j where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1) may be calculated as specified in HEVC (e.g., HEVC Working Draft 10). That is, the prediction may be performed according to the angular mode and the prediction may be subtracted from the original sample values to determine the residual r i,j .
  • a modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j may be determined as follows:
  • r ⁇ 1,j refers to the residual from the upper block. If the upper block is not available or if the upper block belongs to a different LCU, it may not be possible to not perform residual DPCM on the first row.
  • the modified residual samples of ⁇ tilde over (R) ⁇ may be signaled to the video decoder.
  • the video decoder may reconstruct the original residual samples after the video decoder parses the modified residual samples as follows.
  • the original residual samples may be reconstructed as follows:
  • This approach may be extended in a similar manner to the second, third, and fourth examples where residual DPCM techniques are extended to angular intra prediction modes for lossless coding as described above.
  • the residual DPCM method proposed in JCTVC-L0117 can also be applied to the DC intra mode (e.g., mode 1 in HEVC) and to the planar mode (e.g., mode 0 in HEVC).
  • the vertical (or horizontal) residue prediction may be applied after the DC intra prediction is done.
  • the vertical and horizontal residue prediction may both be applied: first apply the vertical (horizontal) DCPM and then apply the horizontal (vertical) DPCM to the output of the first DCPM.
  • a seventh example where residual DPCM techniques are extended to angular intra prediction modes for lossless coding is similar to the sixth example where residual DPCM techniques are extended to angular intra prediction modes for lossless coding in that two or more DPCMs can be applied on the residue.
  • the two diagonal DPCMs described in the third and fourth examples where residual DPCM techniques are extended to angular intra prediction modes for lossless coding to the planar mode and then the horizontal and vertical DPCM.
  • JCTVC-E145 discussed one way to extend these techniques to lossy intra coding when the transform is skipped.
  • JCTVC-E145 discussed one way to extend these techniques to lossy intra coding when the transform is skipped.
  • the idea proposed in JCTVC-E145 is that instead of using the reference samples for intra prediction as shown in FIG. 2 , reconstructed sample values from causal neighbors can be used to perform intra prediction.
  • this can be computationally costly as the prediction process has to be repeated for each sample.
  • near-horizontal and near-vertical intra prediction modes for a block for which transform is skipped are considered.
  • a near-vertical mode may be defined as an intra prediction mode where the prediction direction is near vertical. Examples of near-vertical modes may be all intra prediction modes between 22 and 30 as shown in FIG. 3 .
  • a near-horizontal mode may be defined as an intra prediction mode where the prediction direction is near horizontal. Examples of near-horizontal intra prediction modes may be all intra prediction modes between 6 and 14 as shown in FIG. 3 .
  • M (rows) ⁇ N (cols) the block of size
  • r i,j where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), be the prediction residual after performing intra prediction as specified in HEVC (e.g., HEVC Working Draft 10). This is shown in FIGS. 5A and 5B .
  • the block may represent any component (e.g. luma, chroma, R, G, B, etc.).
  • FIG. 5A shows a residual DPCM direction for near-vertical modes.
  • FIG. 5B shows a residual DPCM direction for near-horizontal modes.
  • Each respective square in FIGS. 5A and 5B corresponds to a respective residual sample r i,j .
  • the vertical arrows in each column of FIG. 5A show the residual DPCM direction for the near-vertical modes.
  • the horizontal arrows in each row of FIG. 5B show the residual DPCM direction for the near-horizontal modes.
  • a DPCM direction is a direction (e.g., horizontal or vertical) along with a video coder processes samples when applying residual DPCM.
  • the block of residual values may be denoted as R.
  • residual r i,j has undergone quantization and inverse quantization.
  • the residual DPCM may be applied to the residual samples to obtain an M ⁇ N array ⁇ tilde over (R) ⁇ , as follows.
  • the modified M ⁇ N array ⁇ tilde over (R) ⁇ with elements ⁇ tilde over (r) ⁇ i,j may be obtained as follows when the intra prediction mode is vertical:
  • ⁇ tilde over (r) ⁇ i,j may be obtained as:
  • the modified residual values in the leftmost column of ⁇ tilde over (R) ⁇ are equal to corresponding residual values in the leftmost column of R.
  • video encoder 20 may set a corresponding modified residual value ⁇ tilde over (r) ⁇ i,j equal to the respective residual value (i.e., r i,j ) minus a reconstructed residual value corresponding to a residual value occurring immediately left of the respective residual value (i.e., Q(r (i ⁇ 1),j) ).
  • the modified residual values in the top row of ⁇ tilde over (R) ⁇ are equal to corresponding residual values in the top row of R.
  • video encoder 20 may set the corresponding modified residual value (i.e., ⁇ tilde over (r) ⁇ i,j ) equal to the respective residual value (i.e., r i,j ) minus a reconstructed residual value corresponding to a residual value occurring immediately above the respective residual value (i.e., Q(r i,(j ⁇ 1) ).
  • the modified residual sample, ⁇ tilde over (r) ⁇ i,j is quantized to produce a quantized version of the modified residual sample, Q( ⁇ tilde over (r) ⁇ i,j ).
  • the reconstructed residual sample Q(r i,j ) is calculated as:
  • the reconstructed residual values corresponding to residual values in a leftmost column of R are equal to corresponding quantized versions of modified residual values in the leftmost column of ⁇ tilde over (R) ⁇ .
  • video encoder 20 sets the corresponding reconstructed residual value equal to the sum of the quantized version of the corresponding modified residual value in ⁇ tilde over (R) ⁇ (i.e., Q( ⁇ tilde over (r) ⁇ i,j )) and the reconstructed residual value corresponding to the residual value occurring immediately to the left of the respective residual value (i.e., Q(r i ⁇ 1,j )).
  • the reconstructed residual values corresponding to residual values in the top row of R are equal to corresponding quantized versions of modified residual values in the top row of ⁇ tilde over (R) ⁇ .
  • video encoder 20 may set the corresponding reconstructed residual value equal to a sum of the quantized version of the corresponding modified residual value in ⁇ tilde over (R) ⁇ (i.e., Q( ⁇ tilde over (r) ⁇ i,j )) and a reconstructed residual value corresponding to the residual value in R occurring immediately above the respective residual value (i.e., Q(r i,j ⁇ 1 )).
  • Video decoder 30 may add reconstructed residual sample values to the original prediction values to produce reconstructed sample values. For example, video decoder 30 may add the reconstructed residual samples Q(r i,j ) to corresponding samples of a predictive block to reconstruct sample values of a current block (e.g., a current CU).
  • a current block e.g., a current CU
  • inverse RDPCM The process of determining reconstructed residual values from residual values that are encoded using DPCM may be referred to herein as “inverse RDPCM.”
  • both video encoder 20 and video decoder 30 clip the reconstructed samples to an appropriate bitdepth.
  • the clipping operation is performed after the inverse RDPCM process to reconstruct quantized residuals.
  • ⁇ tilde over (r) ⁇ i,j may be determined as:
  • the reconstructed residual sample Q(r i,j ) may be determined as:
  • the DPCM may be applied to bit-shifted versions of the reconstructed residuals.
  • video decoder 30 may perform, for each sample, a dequantization operation, a left shift by 7, and then a right shift (e.g., after adding an offset) by (20-bit depth).
  • bit depth may refer to the number of bits used to represent a sample value or a transform coefficient.
  • a dequantization operation there is a right shift by bdShift after adding an offset.
  • section 8.6.2 of JCTVC-M1005_v2 (i.e., a draft of the range extension specification for HEVC) describes a scaling and transformation process that determines an array of residual samples based on an array of transform coefficient levels of a transform block of a TU.
  • the array of transform coefficient levels may contain residual sample values if the transform and quantization is not applied to the transform block.
  • a portion of section 8.6.2 of JCTVC-M1005_v2 is reproduced below.
  • the (nTbS) ⁇ (nTbS) array of residual samples r is derived as follows:
  • r[x][y ] ( r[x][y ]+(1 ⁇ (bdShift ⁇ 1)))>>bdShift (8-269)
  • section 8.6.2 of JCTVC-M1005_v2 specifies that section 8.6.3 of JCTVC-M1005_v2 is invoked if the transform and quantization is applied to the transform block.
  • Section 8.6.3 of JCTVC-M1005_v2 describes a scaling process for transform coefficients.
  • Section 8.6.3 of JCTVC-M1005_v2 is reproduced below.
  • variable bdShift is derived as follows:
  • d[x][y] Clip 3( ⁇ 32768,32767,((TransCoeffLevel[xTbY][yTbY][cIdx][ x][y]*m[x][y ]*levelScale[qP%6] ⁇ (qP/6))+(1 ⁇ (bdShift ⁇ 1)))>>bdShift) (8-274)
  • video decoder 30 may determine a scaled transform coefficient, d[x][y], using equation 8-274 of JCTVC-M1005_v2.
  • the Clip3( . . . ) function is defined as:
  • the inverse DPCM may be applied to the dequantized sample values before applying the left-shift.
  • the inverse DPCM is applied to samples after dequantization or after left shift by 7.
  • a right shift by (20-bit depth) after adding an offset is applied at the very end of the process to reconstruct the residuals.
  • the inverse DPCM may be applied after right shifting by an amount less than (20-bit depth) to retain better precision, before applying the remaining right shift so that the overall right shift amounts to (20-bit depth).
  • video encoder 20 does not apply a transform to residual samples of a transform block, but does quantize the residual samples of the transform block.
  • video encoder 20 may apply a form of lossy coding in which the transform is skipped.
  • video decoder 30 may determine, from syntax elements in a bitstream, quantized residual samples of the transform block and dequantize the quantized residual samples of the transform block to reconstruct the residual samples of the transform block without applying an inverse transform to the transform block.
  • gradient filtering may be modified as described herein using reconstructed (quantized) sample values instead of original sample values.
  • HEVC e.g., HEVC Working Draft 10
  • a gradient term is added to the prediction for the first column (for vertical mode) or the first row (for horizontal mode). This may be referred to as gradient filtering.
  • the addition of the gradient term could be enabled or disabled when using residual DPCM.
  • This disclosure proposes improvements to the gradient filtering for horizontal and vertical intra prediction modes when residual prediction is used.
  • the gradient filtering may be extended to other columns for vertical intra prediction mode as follows. Because the left and left-top original samples are available in lossless mode, the gradient term may be added to the prediction for any column in the vertical intra prediction mode. Thus, for vertical intra prediction mode, the prediction for sample P i,j , 0 ⁇ i ⁇ M ⁇ 1, 0 ⁇ j ⁇ N ⁇ 1 may be modified to:
  • the modified gradient filtering for vertical intra prediction mode may be applied to any component and any block size.
  • the prediction for sample P i,j is P i,j ⁇ 1
  • the gradient term for the samples in the first row may be modified to ((P ⁇ 1,j ⁇ P ⁇ 1,j ⁇ 1 )>>1).
  • the prediction for sample P 0,j , 0 ⁇ j ⁇ N ⁇ 1 may be determined by:
  • the gradient filtering may be extended to other columns for horizontal intra prediction mode as follows. Because the top and left-top original samples are always available in lossless mode, the gradient term may be added to the prediction for any row in the horizontal intra prediction mode. Thus, for horizontal intra prediction mode, the prediction for sample P i,j , 0 ⁇ i ⁇ M ⁇ 1, 0 ⁇ j ⁇ N ⁇ 1 may be given by:
  • a PPS may include a sign data hiding enabled syntax element (e.g., sign_data_hiding_enabled_flag).
  • sign data hiding enabled syntax element e.g., sign_data_hiding_enabled_flag
  • sign data hiding enabled syntax element has a particular value (e.g., 1)
  • syntax elements e.g., coeff_sign_flag syntax elements
  • video encoder 20 may signal, in a bitstream, an explicit indication (e.g., a sign_data_hiding_enabled_flag) that sign data hiding is enabled for a current picture and hence a current block within the current picture.
  • video decoder 30 may obtain, from a bitstream, an explicit indication (e.g., a sign_data_hiding_enabled_flag) that sign data hiding is enabled for a current picture and hence a current block in the current picture.
  • Section 7.3.8.11 of JCTVC-M1005_v2 is reproduced below.
  • sign_data_hiding_enabled_flag 0 specifies that sign bit hiding (i.e., sign data hiding) is disabled.
  • sign_data_hiding_enabled_flag 1 specifies that sign bit hiding is enabled.
  • This disclosure may use the terms “sign bit hiding” and “sign data hiding” interchangeably.
  • a video coder may organize syntax elements representing transform coefficients according to a sub-block scanning order. In the sub-block scanning order, the video coder divides a transform coefficient block into sub-blocks, each being 4 transform coefficients wide and 4 transform coefficients high.
  • the video coder may determine a sign hidden variable (i.e., signHidden) for each of the sub-blocks.
  • a sign hidden variable i.e., signHidden
  • the difference in positions between a first significant (i.e., non-zero) transform coefficient in a 4 ⁇ 4 sub-block of a transform coefficient block and a last significant transform coefficient in the 4 ⁇ 4 sub-block of the transform coefficient block is greater than 3 (i.e., lastSignScanPos ⁇ firstSigScanPos>3) and the transform and quantization steps are not bypassed (i.e., skipped) for the current CU (i.e., !cu_transquant_bypass_flag)
  • the video coder may determine that the sign hidden variable (i.e., signHidden) for the 4 ⁇ 4 sub-block is equal to 1. If the transform is skipped or bypassed, the transform coefficients are actually prediction residuals.
  • a sign syntax element (e.g., coeff_sign_flag[n]) for the respective transform coefficient is signaled in the bitstream if the respective transform coefficient is significant (i.e., non-zero) and if the sign_data_hiding_enabled_flag specifies that sign bit hiding is not enabled, the sign hidden variable for the 4 ⁇ 4 sub-block is not equal to 1, or the respective transform coefficient is not the first significant transform coefficient in the 4 ⁇ 4 sub-block.
  • the sign of a significant transform coefficient is not signaled if the sign_data_hiding_enabled_flag indicates that sign bit hiding is enabled, the difference in position between the first significant coefficient of the 4 ⁇ 4 sub-block and the last significant coefficient of the 4 ⁇ 4 sub-block is greater than 3, the 4 ⁇ 4 sub-block was not generated using transform and quantization bypass coding (e.g. lossless coding), and the respective transform coefficient is the first significant transform coefficient of the 4 ⁇ 4 sub-block.
  • transform and quantization bypass coding e.g. lossless coding
  • coeff_sign_flag[n] specifies the sign of a transform coefficient level for the scanning position n as follows. If coeff_sign_flag[n] is equal to 0, the corresponding transform coefficient level has a positive value. Otherwise (coeff_sign_flag[n] is equal to 1), the corresponding transform coefficient level has a negative value. When coeff_sign_flag[n] is not present, coeff_sign_flag[n] is inferred to be equal to 0.
  • video encoder 20 may embed data indicating the sign of a transform coefficient/residual sample in the value of the transform coefficient/residual sample value itself. For instance, video encoder 20 may modify one or more bits representing a transform coefficient/residual sample such that the parity information can be used by video decoder 30 to determine whether the first significant coefficient in a 4 ⁇ 4 subblock is positive or negative. For example, if the sum of absolute values of transform coefficients in a 4 ⁇ 4 subblock is even, the sign is inferred to be positive, otherwise the sign is inferred to be negative.
  • video encoder 20 may change a least significant bit of the representation of one of the quantized transform coefficient/residual samples in a 4 ⁇ 4 subblock. Consequently, a user may not be able to perceive any loss of visual quality due to video encoder 20 modifying a bit of representation of the transform coefficient/residual sample to indicate the sign of the transform coefficient/residual sample.
  • Such errors may be compounded when residual DPCM is applied because residual DPCM may rely on video decoder 30 adding together multiple transform coefficients/residual samples to determine transform coefficients/residual samples.
  • sign data hiding may actually result in degradation of performance.
  • sign data hiding may be normatively disabled. This means that even though it is indicated in a bitstream (or as a default choice) that sign data hiding is being used, sign data hiding is disabled for certain blocks.
  • a video coder may disable sign data hiding for a block if the video coder does not apply a transform to the block, if the block is intra predicted using a planar intra prediction mode or a DC intra prediction mode, or if the block is intra predicted using an intra prediction mode for with residual DPCM is applied.
  • sign data hiding may be disabled when transform is skipped and the block is intra-coded and the intra mode is planar intra prediction.
  • sign data hiding may be disabled when transform is skipped and the block is intra-coded and the intra mode is DC intra prediction.
  • sign data hiding may be disabled when transform is skipped and the block is intra-coded and the intra mode is a mode for which residual DPCM is applied.
  • video encoder 20 may determine that sign data hiding is disabled for a current block if the current block is generated using lossy coding without application of a transform (e.g., a discrete cosine transform, directional transform, or other transform) to residual data and the current block is intra predicted using an intra prediction mode in which residual DPCM is used.
  • video encoder 20 may include, in the bitstream, for each respective significant value in the current block, a respective syntax element indicating whether the respective significant value is positive or negative.
  • video decoder 30 may determine that sign data hiding is disabled for the current block if the current block is generated using lossy coding without application of a transform (e.g., a discrete cosine transform, directional transform, or other transform) to residual data and the current block is intra predicted using an intra prediction mode in which residual DPCM is used.
  • a transform e.g., a discrete cosine transform, directional transform, or other transform
  • video decoder 30 obtains, from the bitstream, for each respective significant value in the block, a respective syntax element indicating whether the respective significant value is positive or negative.
  • sign data hiding may be disabled for a block when transform is skipped, the block is intra-coded, or for all the transform-skip blocks.
  • sign data hiding may be disabled regardless of which intra prediction mode is used. For instance, a video coder may determine that sign data hiding is disabled for a current block if the current block is coded without application of the transform to the residual data of the current block, and the current block is intra coded using a DC intra prediction mode or a planar intra prediction mode.
  • FIG. 6 is a block diagram illustrating an example video encoder 20 that may implement the techniques of this disclosure.
  • FIG. 6 is provided for purposes of explanation and should not be considered limiting of the techniques as broadly exemplified and described in this disclosure.
  • this disclosure describes video encoder 20 in the context of HEVC coding.
  • the techniques of this disclosure may be applicable to other coding standards or methods.
  • video encoder 20 includes a prediction processing unit 100 , a residual generation unit 102 , a transform processing unit 104 , a quantization unit 106 , an inverse quantization unit 108 , an inverse transform processing unit 110 , a reconstruction unit 112 , a filter unit 114 , a decoded picture buffer 116 , and an entropy encoding unit 118 .
  • Prediction processing unit 100 includes an inter-prediction processing unit 120 and an intra-prediction processing unit 126 .
  • Inter-prediction processing unit 120 includes a motion estimation unit 122 and a motion compensation unit 124 .
  • video encoder 20 may include more, fewer, or different functional components.
  • Video encoder 20 may receive video data. Video encoder 20 may encode each CTU in a slice of a picture of the video data. Each of the CTUs may be associated with equally-sized luma coding tree blocks (CTBs) and corresponding CTBs of the picture. As part of encoding a CTU, prediction processing unit 100 may perform quad-tree partitioning to divide the CTBs of the CTU into progressively-smaller blocks. The smaller block may be coding blocks of CUs. For example, prediction processing unit 100 may partition a CTB associated with a CTU into four equally-sized sub-blocks, partition one or more of the sub-blocks into four equally-sized sub-sub-blocks, and so on.
  • CTBs luma coding tree blocks
  • Video encoder 20 may encode CUs of a CTU to generate encoded representations of the CUs (i.e., coded CUs).
  • prediction processing unit 100 may partition the coding blocks associated with the CU among one or more PUs of the CU.
  • each PU may be associated with a luma prediction block and corresponding chroma prediction blocks.
  • Video encoder 20 and video decoder 30 may support PUs having various sizes. As indicated above, the size of a CU may refer to the size of the luma coding block of the CU and the size of a PU may refer to the size of a luma prediction block of the PU.
  • video encoder 20 and video decoder 30 may support PU sizes of 2N ⁇ 2N or N ⁇ N for intra prediction, and symmetric PU sizes of 2N ⁇ 2N, 2N ⁇ N, N ⁇ 2N, N ⁇ N, or similar for inter prediction.
  • Video encoder 20 and video decoder 30 may also support asymmetric partitioning for PU sizes of 2N ⁇ nU, 2N ⁇ nD, nL ⁇ 2N, and nR ⁇ 2N for inter prediction.
  • Inter-prediction processing unit 120 may generate predictive data for a PU by performing inter prediction on each PU of a CU.
  • the predictive data for the PU may include a predictive sample blocks (i.e., predictive blocks) of the PU and motion information for the PU.
  • Inter-prediction unit 121 may perform different operations for a PU of a CU depending on whether the PU is in an I slice, a P slice, or a B slice. In an I slice, all PUs are intra predicted. Hence, if the PU is in an I slice, inter-prediction unit 121 does not perform inter prediction on the PU.
  • the predictive block is formed using spatial prediction from previously-encoded neighboring blocks within the same frame.
  • motion estimation unit 122 may search the reference pictures in a list of reference pictures (e.g., “RefPicList0”) for a reference region for the PU.
  • the reference region for the PU may be a region, within a reference picture, that contains samples (e.g., sample blocks) that most closely corresponds to the sample blocks of the PU.
  • Motion estimation unit 122 may generate a reference index that indicates a position in RefPicList0 of the reference picture containing the reference region for the PU.
  • motion estimation unit 122 may generate a motion vector that indicates a spatial displacement between a coding block of the PU and a reference location associated with the reference region.
  • the motion vector may be a two-dimensional vector that provides an offset from the coordinates in the current decoded picture to coordinates in a reference picture.
  • Motion estimation unit 122 may output the reference index and the motion vector as the motion information of the PU.
  • Motion compensation unit 124 may generate the predictive sample blocks of the PU based on actual or interpolated samples at the reference location indicated by the motion vector of the PU.
  • motion estimation unit 122 may perform uni-prediction or bi-prediction for the PU. To perform uni-prediction for the PU, motion estimation unit 122 may search the reference pictures of RefPicList0 or a second reference picture list (“RefPicList1”) for a reference region for the PU.
  • RefPicList0 a second reference picture list
  • Motion estimation unit 122 may output, as the motion information of the PU, a reference index that indicates a position in RefPicList0 or RefPicList1 of the reference picture that contains the reference region, a motion vector that indicates a spatial displacement between a sample block of the PU and a reference location associated with the reference region, and one or more prediction direction indicators that indicate whether the reference picture is in RefPicList0 or RefPicList1.
  • Motion compensation unit 124 may generate the predictive sample blocks of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU.
  • motion estimation unit 122 may search the reference pictures in RefPicList0 for a reference region for the PU and may also search the reference pictures in RefPicList1 for another reference region for the PU.
  • Motion estimation unit 122 may generate reference picture indexes (i.e., reference indexes) that indicate positions in RefPicList0 and RefPicList1 of the reference pictures that contain the reference regions.
  • motion estimation unit 122 may generate motion vectors that indicate spatial displacements between the reference location associated with the reference regions and a sample block of the PU.
  • the motion information of the PU may include the reference indexes and the motion vectors of the PU.
  • Motion compensation unit 124 may generate the predictive sample blocks of the PU based at least in part on actual or interpolated samples at the reference region indicated by the motion vector of the PU.
  • one or more units within prediction processing unit 100 may perform one or more of the techniques described herein as part of a video encoding process.
  • Intra-prediction processing unit 126 may generate predictive data for a PU by performing intra prediction on the PU.
  • the predictive data for the PU may include predictive blocks for the PU and various syntax elements.
  • Intra-prediction processing unit 126 may perform intra prediction on PUs in I slices, P slices, and B slices.
  • intra-prediction processing unit 126 may use multiple intra prediction modes to generate multiple sets of predictive data for the PU.
  • intra-prediction processing unit 126 may extend samples from sample blocks of neighboring PUs across the sample blocks of the PU in a direction associated with the intra prediction mode.
  • the neighboring PUs may be above, above and to the right, above and to the left, or to the left of the PU, assuming a left-to-right, top-to-bottom encoding order for PUs, CUs, and CTUs.
  • Intra-prediction processing unit 126 may use various numbers of intra prediction modes, e.g., 33 directional intra prediction modes.
  • intra-prediction processing unit 126 may implement lossless coding modes and the modifications described herein to improve such coding modes. In accordance with some techniques of this disclosure, intra-prediction processing unit 126 may use one or more original sample values within a block to perform intra DC prediction of other sample values within the block.
  • Prediction processing unit 100 may select the predictive data for PUs of a CU from among the predictive data generated by inter-prediction processing unit 120 for the PUs or the predictive data generated by intra-prediction processing unit 126 for the PUs. In some examples, prediction processing unit 100 selects the predictive data for the PUs of the CU based on rate/distortion metrics of the sets of predictive data.
  • the predictive sample blocks of the selected predictive data may be referred to herein as the selected predictive sample blocks.
  • Residual generation unit 102 may generate, based on coding blocks (e.g., the luma, Cb and Cr coding blocks) of a CU and the selected predictive blocks (e.g., luma, Cb and Cr blocks) of the PUs of the CU, residual blocks (e.g., luma, Cb and Cr residual blocks) for the CU. For instance, residual generation unit 102 may generate the residual blocks of the CU such that each sample in the residual blocks has a value equal to a difference between a sample in a coding block of the CU and a corresponding sample in a corresponding selected predictive block of a PU of the CU.
  • coding blocks e.g., the luma, Cb and Cr coding blocks
  • the selected predictive blocks e.g., luma, Cb and Cr blocks
  • residual blocks e.g., luma, Cb and Cr residual blocks
  • Transform processing unit 104 may perform quad-tree partitioning to partition the residual blocks associated with a CU into transform blocks associated with TUs of the CU.
  • a TU may be associated with a luma transform block and two chroma transform blocks.
  • the sizes and positions of the luma and chroma transform blocks of TUs of a CU may or may not be based on the sizes and positions of prediction blocks of the PUs of the CU.
  • a quad-tree structure known as a “residual quad-tree” (RQT) may include nodes associated with each of the regions.
  • the TUs of a CU may correspond to leaf nodes of the RQT.
  • Transform processing unit 104 may generate transform coefficient blocks for each TU of a CU by applying one or more transforms to the transform blocks of the TU. Transform processing unit 104 may apply various transforms to a transform block associated with a TU. For example, transform processing unit 104 may apply a discrete cosine transform (DCT), a directional transform, or a conceptually similar transform to a transform block. In some examples, transform processing unit 104 does not apply transforms to a transform block. In such examples, the transform block may be treated as a transform coefficient block.
  • DCT discrete cosine transform
  • Quantization unit 106 may quantize the transform coefficients in a coefficient block. The quantization process may reduce the bit depth associated with some or all of the transform coefficients. For example, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m.
  • Quantization unit 106 may quantize a coefficient block associated with a TU of a CU based on a quantization parameter (QP) value associated with the CU.
  • QP quantization parameter
  • Video encoder 20 may adjust the degree of quantization applied to the coefficient blocks associated with a CU by adjusting the QP value associated with the CU. Quantization may introduce loss of information, thus quantized transform coefficients may have lower precision than the original ones.
  • the following may be performed for 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), where M is a height of a block and N is the width of a block.
  • the block is a residual block that includes residual values indicating differences between sample values in a predictive block generated using intra prediction and original samples values.
  • the block is a transform skip block.
  • Residual generation unit 102 may determine a modified residual value ⁇ tilde over (r) ⁇ i,j for a residual value r i,j . If the block is coded using a vertical intra prediction mode, ⁇ tilde over (r) ⁇ i,j is defined as:
  • Q(r (i ⁇ 1),j ) denotes a reconstructed residual value for a residual value r i ⁇ 1,j one column left of the residual value r i,j . If the block is coded using a horizontal intra prediction mode, ⁇ tilde over (r) ⁇ i,j is defined as:
  • Q(r i,(j ⁇ 1 ) denotes a reconstructed residual value for a residual value r i,j ⁇ 1 one row above the residual value r i,j .
  • Quantization unit 106 may quantize the modified residual value ⁇ tilde over (r) ⁇ i,j to produce a quantized modified residual value Q( ⁇ tilde over (r) ⁇ i,j ).
  • Inverse quantization unit 108 and inverse transform processing unit 110 may apply inverse quantization and inverse transforms to a coefficient block, respectively, to reconstruct a residual block from the coefficient block.
  • Reconstruction unit 112 may add the reconstructed residual block to corresponding samples from one or more predictive blocks generated by prediction processing unit 100 to produce a reconstructed transform block associated with a TU. By reconstructing transform blocks for each TU of a CU in this way, video encoder 20 may reconstruct the coding blocks of the CU.
  • Filter unit 114 may perform one or more deblocking operations to reduce blocking artifacts in the coding blocks associated with a CU.
  • Decoded picture buffer 116 may store the reconstructed coding blocks after filter unit 114 performs the one or more deblocking operations on the reconstructed coding blocks.
  • Inter-prediction processing unit 120 may use a reference picture that contains the reconstructed coding blocks to perform inter prediction on PUs of other pictures.
  • intra-prediction processing unit 126 may use reconstructed coding blocks in decoded picture buffer 116 to perform intra prediction on other PUs in the same picture as the CU.
  • Entropy encoding unit 118 may receive data from other functional components of video encoder 20 .
  • entropy encoding unit 118 may receive coefficient blocks from quantization unit 106 and may receive syntax elements from prediction processing unit 100 .
  • Entropy encoding unit 118 may perform one or more entropy encoding operations on the data to generate entropy-encoded data.
  • entropy encoding unit 118 may perform a context-adaptive variable length coding (CAVLC) operation, a CABAC operation, a variable-to-variable (V2V) length coding operation, a syntax-based context-adaptive binary arithmetic coding (SBAC) operation, a Probability Interval Partitioning Entropy (PIPE) coding operation, an Exponential-Golomb encoding operation, or another type of entropy encoding operation on the data.
  • Video encoder 20 may output a bitstream that includes entropy-encoded data generated by entropy encoding unit 118 .
  • the bitstream may include data that represents a RQT for a CU.
  • entropy encoding unit 118 may determine that sign data hiding is disabled for a current block if the current block is generated without application of a transform to residual data and the current block is intra predicted using an intra prediction mode in which residual DPCM is used.
  • entropy encoding unit 118 may include, in the bitstream, a syntax element indicating whether a value in the current block is positive or negative.
  • Element 130 in FIG. 6 may represent a switch (or a conceptual switch) for selecting between lossless coding and lossy coding.
  • Control signal 132 may represent a signal from prediction processing unit 100 that determines the lossless or lossy coding and element 134 may represent a decoding loop that bypasses the inverse transform and inverse quantization processes.
  • lossless coding eliminates transforms and quantization.
  • lossless coding performs transforms and eliminates only the quantization process.
  • lossless coding may be implemented with the use of transforms and quantitation, but the quantization parameter may be selected so as to avoid any quantization data loss.
  • Elements 136 and 138 represent switches (or conceptual switches) that may be used to implement a transform skipping mode.
  • the residual data is not transformed by transform processing unit 104 but is quantized by quantization unit 106 .
  • the dash lines of element 136 represent two possible data paths. In one data, the residual data is quantized by quantization unit 106 and in the other data path the residual data is not quantized by quantization unit 106 .
  • the residual data is inverse quantized by inverse quantization unit 108 but is not transformed by inverse transform processing unit 110 .
  • the dash lines of element 138 represent an alternate data path where the residual data is inverse quantized by inverse quantization unit 108 but is not transformed by inverse transform processing unit 110 .
  • FIG. 7 is a block diagram illustrating an example video decoder 30 that is configured to implement the techniques of this disclosure.
  • FIG. 7 is provided for purposes of explanation and is not limiting on the techniques as broadly exemplified and described in this disclosure.
  • this disclosure describes video decoder 30 in the context of HEVC coding.
  • the techniques of this disclosure may be applicable to other coding standards or methods.
  • video decoder 30 includes an entropy decoding unit 150 , a prediction processing unit 152 , an inverse quantization unit 154 , an inverse transform processing unit 156 , a reconstruction unit 158 , a filter unit 160 , and a decoded picture buffer 162 .
  • Prediction processing unit 152 includes a motion compensation unit 164 and an intra-prediction processing unit 166 .
  • video decoder 30 may include more, fewer, or different functional components.
  • Video decoder 30 may receive a bitstream.
  • Entropy decoding unit 150 may parse the bitstream to decode syntax elements from the bitstream.
  • Entropy decoding unit 150 may entropy decode entropy-encoded syntax elements in the bitstream.
  • Prediction processing unit 152 , inverse quantization unit 154 , inverse transform processing unit 156 , reconstruction unit 158 , and filter unit 160 may generate decoded video data based on the syntax elements extracted from the bitstream.
  • the bitstream may comprise a series of NAL units.
  • the NAL units of the bitstream may include coded slice NAL units.
  • entropy decoding unit 150 may extract and entropy decode syntax elements from the coded slice NAL units.
  • Each of the coded slices may include a slice header and slice data.
  • the slice header may contain syntax elements pertaining to a slice.
  • the syntax elements in the slice header may include a syntax element that identifies a PPS associated with a picture that contains the slice.
  • entropy decoding unit 150 determines that sign data hiding is disabled for a current block if the current block is generated without application of a transform to residual data and the current block is intra predicted using an intra prediction mode in which residual DPCM is used. In such examples, when sign data hiding is disabled for the current block, entropy decoding unit 150 obtains, from the bitstream, for each respective significant value in the block, a respective syntax element indicating whether the respective significant value is positive or negative.
  • video decoder 30 may perform a reconstruction operation on a non-partitioned CU. To perform the reconstruction operation on a non-partitioned CU, video decoder 30 may perform a reconstruction operation on each TU of the CU. By performing the reconstruction operation for each TU of the CU, video decoder 30 may reconstruct residual blocks of the CU.
  • inverse quantization unit 154 may inverse quantize, i.e., de-quantize, coefficient blocks associated with the TU.
  • Inverse quantization unit 154 may use a QP value associated with the CU of the TU to determine a degree of quantization and, likewise, a degree of inverse quantization for inverse quantization unit 154 to apply. That is, the compression ratio, i.e., the ratio of the number of bits used to represent the original sequence and the compressed one, may be controlled by adjusting the value of the QP used when quantizing transform coefficients.
  • the compression ratio may also depend on the method of entropy coding employed.
  • inverse transform processing unit 156 may apply one or more inverse transforms to the coefficient block in order to generate a residual block associated with the TU.
  • inverse transform processing unit 156 may apply an inverse DCT, an inverse integer transform, an inverse Karhunen-Loeve transform (KLT), an inverse rotational transform, an inverse directional transform, or another inverse transform to the coefficient block.
  • KLT Karhunen-Loeve transform
  • intra-prediction processing unit 166 may perform intra prediction to generate predictive blocks for the PU.
  • Intra-prediction processing unit 166 may use an intra prediction mode to generate the predictive blocks (e.g., predictive luma, Cb and Cr blocks) for the PU based on the prediction blocks of spatially-neighboring PUs.
  • Intra-prediction processing unit 166 may determine the intra prediction mode for the PU based on one or more syntax elements decoded from the bitstream.
  • intra-prediction processing unit 166 may use one or more original sample values within a block to perform intra DC prediction of other sample values within the block. That is, intra-prediction processing unit 166 may generate a predictive block.
  • intra-prediction processing unit 166 may use at least one of a losslessly reconstructed sample to left of a current sample in a current row of a predictive block and a losslessly reconstructed sample for a row of the predictive block above the current row for DC prediction of the current sample
  • Prediction processing unit 152 may construct a first reference picture list (RefPicList0) and a second reference picture list (RefPicList1) based on syntax elements extracted from the bitstream. Furthermore, if a PU is encoded using inter prediction, entropy decoding unit 150 may extract motion information for the PU. Motion compensation unit 164 may determine, based on the motion information of the PU, one or more reference regions for the PU. Motion compensation unit 164 may generate, based on samples blocks at the one or more reference blocks for the PU, predictive blocks (e.g., luma, Cb and Cr blocks) for the PU. In accordance with one or more techniques of this disclosure, one or more units within prediction processing unit 152 (such as intra prediction processing unit 166 ) may perform techniques described herein as part of a video decoding process.
  • RefPicList0 first reference picture list
  • RefPicList1 second reference picture list
  • Reconstruction unit 158 may use the transform block (e.g., luma, Cb and Cr transform blocks) associated with TUs of a CU and the predictive blocks (e.g., luma, Cb and Cr predictive blocks) of the PUs of the CU, i.e., either intra-prediction data or inter-prediction data, as applicable, to reconstruct the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU.
  • reconstruction unit 158 may add samples of the luma, Cb and Cr transform blocks to corresponding samples of the predictive luma, Cb and Cr blocks to reconstruct the luma, Cb and Cr coding blocks of the CU.
  • entropy decoding unit 150 may generate a block of residual values.
  • This block may be a transform skip block.
  • the block may be a residual block that includes residual values indicating differences between original sample values and sample values in a predictive block generated using intra prediction.
  • inverse quantization unit 154 may calculate a reconstructed residual value Q(r i,j ) for a residual value r i,j in the block. If the block is coded using a vertical intra prediction mode (or, in some examples, a near-vertical intra prediction mode), Q(r i,j ) is defined as:
  • Q( ⁇ tilde over (r) ⁇ i,j ) denotes a quantized version of a modified residual value ⁇ tilde over (r) ⁇ i,j
  • the modified residual value ⁇ tilde over (r) ⁇ i,j is a modified version of the residual value r i,j
  • Q(r i ⁇ 1,j ) is a reconstructed residual value for (i.e., corresponding to) a residual value one column left of the residual value r i,j .
  • Entropy decoding unit 150 may have previously determined Q(r i ⁇ 1,j ) in the same manner that entropy decoding unit 150 determines Q(r i,j ). If the block is coded using a horizontal intra prediction mode, Q(r i,j ) is defined as:
  • Q(r i,j ⁇ 1 ) is a reconstructed residual value for a residual value one row above the residual value r i,j .
  • Entropy decoding unit 150 may have previously determined Q(r i,j ⁇ 1 ) in the same manner that entropy decoding unit 150 determines Q(r i,j ).
  • Reconstruction unit 158 may add the reconstructed residual value Q(r i,j ) to a prediction value to reconstruct a sample value.
  • Filter unit 160 may perform a deblocking operation to reduce blocking artifacts associated with the coding blocks (e.g., the luma, Cb and Cr coding blocks) of the CU.
  • Video decoder 30 may store the coding blocks (e.g., luma, Cb and Cr coding blocks) of the CU in decoded picture buffer 162 .
  • Decoded picture buffer 162 may provide reference pictures for subsequent motion compensation, intra prediction, and presentation on a display device, such as display device 32 of FIG. 1 .
  • video decoder 30 may perform, based on the blocks (e.g., luma, Cb and Cr blocks) in decoded picture buffer 162 , intra prediction or inter prediction operations on PUs of other CUs.
  • video decoder 30 may extract, from the bitstream, transform coefficient levels of the significant luma coefficient block, inverse quantize the transform coefficient levels, apply a transform to the transform coefficient levels to generate a transform block, generate, based at least in part on the transform block, a coding block, and output the coding block for display.
  • Element 170 may represent a normal coding path for lossy compression, and element 172 may represent a bypass coding path that bypasses the inverse transform and inverse quantization processes. These different paths are merely exemplary and lossless coding may be performed without any bypass.
  • lossless coding eliminates transforms and quantization.
  • lossless coding performs transforms and eliminates only the quantization process.
  • lossless coding may be implemented with the use of transforms and quantitation, but the quantization parameter may be selected so as to avoid any quantization data loss.
  • Element 174 represents an example of a path that may be used for a transform skipping mode. In a transform skipping mode, the residual data may be inverse quantized by inverse quantization unit 154 , but the inverse transforming of inverse transform processing unit 156 may be skipped. These and other examples are within the scope of this disclosure.
  • FIG. 8A is a flowchart illustrating an example operation of video encoder 20 , in accordance with one or more techniques of this disclosure.
  • operations similar to the operation of FIG. 8A may include more, fewer, or different actions.
  • one or more actions of the operation of FIG. 8A may be omitted or rearranged.
  • dashed lines indicate actions not performed in some examples.
  • video encoder 20 may generate a predictive block ( 200 ). As part of generating the predictive block, video encoder 20 may use at least one of: a losslessly reconstructed sample to left of a current sample in a current row of a predictive block and a losslessly reconstructed sample for a row of the predictive block above the current row for DC prediction of the current sample ( 202 ).
  • video decoder 30 processes samples in the predictive block in a horizontal raster scan order, a vertical raster scan order, a diagonal scan order, or a zig-zag scan order. In such examples, processing the samples in the predictive block may comprise determining DC predictions for the samples as well as reconstructing the samples losslessly.
  • video encoder 20 may generate residual samples that have values equal to a difference between a sample in a coding block and a corresponding sample in the predictive block
  • FIG. 8B is a flowchart illustrating an example operation of video decoder 30 , in accordance with one or more techniques of this disclosure.
  • operations similar to the operation of FIG. 8B may include more, fewer, or different actions.
  • one or more actions of the operation of FIG. 8B may be omitted or rearranged.
  • video decoder 30 may generate a predictive block ( 250 ). As part of generating the predictive block, video decoder 30 may use at least one of a losslessly reconstructed sample to left of a current sample in a current row of a predictive block and a losslessly reconstructed sample for a row of the predictive block above the current row for DC prediction of the current sample ( 252 ). In some examples, video decoder 30 processes samples in the predictive block in a horizontal raster scan order, a vertical raster scan order, a diagonal scan order, or a zig-zag scan order. In such examples, processing the samples in the predictive block may comprise determining DC predictions for the samples. Furthermore, in the example of FIG. 8B , video decoder 30 may reconstruct a coding block by adding samples of the predictive block to corresponding residual samples ( 254 ).
  • FIG. 9A is a flowchart illustrating an example operation of video encoder 20 , in accordance with one or more techniques of this disclosure.
  • operations similar to the operation of FIG. 9A may include more, fewer, or different actions.
  • one or more actions of the operation of FIG. 9A may be omitted or rearranged.
  • the example of FIG. 9A is explained with reference to components shown in FIG. 6 .
  • the operation of FIG. 9A may be performed by components and types of video encoders other than that shown in FIG. 6 .
  • residual generation unit 102 of video encoder 20 may generate a block of residual values ( 350 ).
  • the block of residual values is a transform skip block.
  • the block may be a residual block that includes residual values indicating differences between original sample values and sample values in a predictive block generated using intra prediction.
  • the video coder may perform the remaining actions of FIG. 9A for each location (i,j) of the block, where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), M is a height of a block, and N is the width of the block.
  • residual generation unit 102 of video encoder 20 may determine a modified residual value ⁇ tilde over (r) ⁇ i,j for a residual value r i,j in the block ( 352 ). If the block is coded using a vertical intra prediction mode, or in some examples, an intra prediction mode between 22 and 30 as defined in HEVC Working Draft 10, ⁇ tilde over (r) ⁇ i,j is defined as:
  • Q(r (i ⁇ 1),j ) denotes a reconstructed residual value for (i.e., corresponding to) a residual value r i ⁇ 1,j . If the block is coded using a horizontal intra prediction mode, or, in some examples, an intra prediction mode between 6 and 14, ⁇ tilde over (r) ⁇ i,j is defined as:
  • Q(r i,(j ⁇ 1 ) denotes a reconstructed residual value for a residual value r i,j ⁇ 1 .
  • quantization unit 106 of video encoder 20 may quantize the modified residual value ⁇ tilde over (r) ⁇ i,j to produce a quantized modified residual value Q( ⁇ tilde over (r) ⁇ i,j ) ( 354 ).
  • Video encoder 20 may signal the quantized modified residual value Q( ⁇ tilde over (r) ⁇ i,j ) in a bitstream ( 356 ).
  • video encoder 20 may generate one or more syntax elements indicating the quantized modified residual value Q( ⁇ tilde over (r) ⁇ i,j ).
  • entropy encoding unit 118 of video encoder 20 may entropy encode the one or more syntax elements and include the resulting data in the bitstream.
  • video encoder 20 may calculate a reconstructed residual value Q(r i,j ) ( 358 ). In some examples, video encoder 20 may calculate the reconstructed residual value Q(r i,j ) as part of a feedback loop to determine reconstructed sample values for use in further intra prediction or inter prediction. If the block is coded using the vertical intra prediction mode (or in some examples, a near vertical intra prediction mode), the reconstructed residual value Q(r i,j ) may be defined as:
  • Q(r i,j ) may be defined as:
  • inverse transform processing unit 110 does not apply an inverse transform to the residual value r i,j .
  • reconstruction unit 112 of video encoder 20 may add the reconstructed residual value Q(r i,j ) to a prediction value to determine a reconstructed sample value ( 360 ).
  • the prediction value may be a sample in a predictive block.
  • Prediction processing unit 100 of video encoder 20 may use the reconstructed sample value for intra prediction or inter prediction of other blocks ( 362 ).
  • FIG. 9B is a flowchart illustrating an example operation of video decoder 30 , in accordance with one or more techniques of this disclosure.
  • operations similar to the operation of FIG. 9B may include more, fewer, or different actions.
  • one or more actions of the operation of FIG. 9B may be omitted or rearranged.
  • the example of FIG. 9B is explained with reference to components shown in FIG. 7 .
  • the operation of FIG. 9B may be performed by components and types of video decoders other than that shown in FIG. 7 .
  • Video decoder 30 may perform the operation of FIG. 9B for each location (i,j) of a transform skip block, where 0 ⁇ i ⁇ (M ⁇ 1) and 0 ⁇ j ⁇ (N ⁇ 1), M is a height of a block, and N is the width of the block.
  • the block may be a residual block that includes residual values indicating differences between original sample values and sample values in a predictive block generated using intra prediction.
  • entropy decoding unit 150 of video decoder 30 may obtain, from a bitstream, one or more syntax elements indicating a modified quantized residual value Q( ⁇ tilde over (r) ⁇ i,j ) ( 400 ).
  • Entropy decoding unit 150 may entropy decode some or all of the one or more syntax elements.
  • inverse quantization unit 154 of video decoder 30 may calculate a reconstructed residual value Q(r i,j ) for a residual value r i,j ( 402 ).
  • the residual value r i,j is a bit-shifted residual value as described elsewhere in this disclosure. If the block is coded using a vertical intra prediction mode, Q(r i,j ) is defined as:
  • Q( ⁇ tilde over (r) ⁇ i,j ) denotes a quantized version of a modified residual value ⁇ tilde over (r) ⁇ i,j
  • the modified residual value ⁇ tilde over (r) ⁇ i,j is a modified version of the residual value r i,j
  • Q(r i ⁇ 1,j ) is a reconstructed residual value for a residual value one column left of the residual value r i,j .
  • Q(r i,j ⁇ 1 ) is a reconstructed residual value for a residual value one row above the residual value r i,j .
  • the modified residual value ⁇ tilde over (r) ⁇ i,j is defined as:
  • the modified residual value ⁇ tilde over (r) ⁇ i,j is defined as:
  • inverse transform processing unit 156 does not apply an inverse transform to the reconstructed residual value Q(r i,j ).
  • Reconstruction unit 158 of video decoder 30 may add the reconstructed residual value Q(r i,j ) to a prediction value to reconstruct a sample value ( 406 ).
  • the prediction value may be a sample in a predictive block.
  • FIG. 10A is a flowchart illustrating an example video encoder operation for sign data hiding, in accordance with one or more techniques of this disclosure.
  • operations similar to the operation of FIG. 10A may include more, fewer, or different actions.
  • one or more actions of the operation of FIG. 10A may be omitted or rearranged.
  • video encoder 20 generates a bitstream that includes a sequence of bits that forms a coded representation of video data ( 600 ).
  • video encoder 20 may determine that sign data hiding is disabled for a current block if the current block is generated without application of a transform to residual data and the current block is intra predicted using an intra prediction mode in which a residual DPCM technique is used ( 602 ).
  • the current block may be a 4 ⁇ 4 sub-block of a block of residual samples to which the residual DPCM technique has been applied.
  • video encoder 20 may output the bitstream ( 604 ).
  • video encoder 20 may signal, in the bitstream, for each respective significant residual value in the current block, a syntax element indicating whether the respective significant residual value is positive or negative. In such examples, when sign data hiding is not disabled for the current block, video encoder 20 may not signal, in the bitstream, a syntax element indicating whether a value of at least one significant residual value or transform coefficient in the current block is positive or negative.
  • FIG. 10B is a flowchart illustrating an example video decoder operation for sign data hiding, in accordance with one or more techniques of this disclosure.
  • operations similar to the operation of FIG. 10B may include more, fewer, or different actions.
  • one or more actions of the operation of FIG. 10B may be omitted or rearranged.
  • video decoder 30 obtains syntax elements from a bitstream that includes a sequence of bits that forms a coded representation of video data ( 650 ). As part of obtaining the syntax elements from the bitstream, video decoder 30 may determine that sign data hiding is disabled for a current block if the current block is generated without application of a transform to residual data and the current block is intra predicted using an intra prediction mode in which a residual DPCM technique is used ( 652 ). In the context of FIG. 10B , the current block may be a 4 ⁇ 4 sub-block of a block of residual samples to which the residual DPCM technique has been applied. Subsequently, in the example of FIG. 10B , video decoder 30 may reconstruct a picture of the video data based at least in part on the syntax elements obtained from the bitstream ( 654 ).
  • video decoder 30 may obtain, from the bitstream, for each respective significant residual value in the current block, a syntax element indicating whether the respective significant residual value is positive or negative. In such examples, when sign data hiding is not disabled for the current block, video decoder 30 may not obtain from the bitstream a syntax element indicating whether a value of a significant residual value in the current block is positive or negative.
  • a method of coding video data comprising: using one or more original sample values within a block of video data to perform intra DC prediction of other sample values within the block.
  • using one or more original sample values within the block to perform prediction of other sample values within the block comprises: using original sample values that occur earlier in a scan order to predict sample values that occur later in the scan order.
  • using one or more original sample values within the block to perform prediction of other sample values within the block comprises: using original sample values of a previously scanned row to predict sample values of a subsequently scanned row.
  • using one or more original sample values within the block to perform prediction of other sample values within the block comprises: using original sample values that correspond to causal neighbors of a sample to predict sample values for the sample.
  • a method of coding video data comprising: performing DC prediction on a block size that is smaller than a transform unit (TU) size.
  • TU transform unit
  • the DC prediction is performed on a 2 ⁇ 2 block size, wherein at least some TU sizes are larger than the 2 ⁇ 2 block size.
  • DC prediction values are calculated as one of: (P 2i ⁇ 1,2j +P 2i ⁇ 1,2j+1 +P 2i,2j ⁇ 1 +P 2i+1,2j ⁇ 1 +2)>>2 or (P 2i ⁇ 1,2j +P 2i ⁇ 1,2j+1 +P 2i,2j ⁇ 1 +P 2i+1,2j ⁇ 1 )>>2, wherein, 0 ⁇ i ⁇ ((M/2) ⁇ 1), 0 ⁇ j ⁇ ((N/2) ⁇ 1).
  • a method of coding video data comprising: performing DC prediction on a 2 ⁇ 2 block size regardless of a size of a transform unit (TU).
  • a method of coding video data comprising: exploiting a correlation between residuals after performing a normal DC prediction.
  • a system configured to perform the method of any of examples 1-27 or combinations thereof.
  • a non-transitory computer readable storage medium storing instructions that when executed cause one or more processors to perform the method of any of examples 1-27 or combinations thereof.
  • a video encoding device configured to perform the method of any of examples 1-24 and 27 or combinations thereof.
  • a video decoding device configured to perform the method of any of examples 1-21 and 25-27 or combinations thereof.
  • a video encoding device comprising means for performing the steps of the method of any of examples 1-24 and 27 or combinations thereof.
  • a video decoding device comprising means for performing the steps of the method of any of examples 1-21 and 25-27 or combinations thereof.
  • a method of coding video data comprising: using one or more original sample values within a block of video data to perform prediction of other sample values within the block.
  • using one or more original sample values within the block to perform prediction of other sample values within the block comprises: using original sample values corresponding to a last row and a last column of the block to perform prediction of the other sample values.
  • using one or more original sample values within the block to perform prediction of other sample values within the block comprises: using original sample values corresponding to a first row and a first column of the block to perform prediction of the other sample values.
  • FIG. 4 illustrates the samples locations of the sample values used for to perform prediction of other sample values.
  • the method further comprising: performing a rotate operation on set of residual values generated by the prediction; and performing entropy coding with respect to the rotated set of residual values.
  • a system configured to perform the method of any of examples 1-10 or combinations thereof.
  • a non-transitory computer readable storage medium storing instructions that when executed cause one or more processors to perform the method of any of examples 1-10 or combinations thereof.
  • a video encoding device configured to perform the method of any of examples 1-10 or combinations thereof.
  • a video decoding device configured to perform the method of any of examples 1-10 or combinations thereof.
  • a video encoding device comprising means for performing the steps of the method of any of examples 1-10 or combinations thereof.
  • a video decoding device comprising means for performing the steps of the method of any of examples 1-10 or combinations thereof.
  • a method of coding video data comprising: determining a modified array of residual samples; determining for a modified residual sample a dequantized version of the residual sample; and adding the dequantized version of the residual sample to a prediction value to determine a reconstructed value.
  • a method of coding video data comprising: determining a modified array of residual samples; determining for a modified residual sample a quantized version of the residual sample; and signaling in an encoded bitstream the quantized version of the residual sample.
  • a system configured to perform the method of any of examples 1-15 or combinations thereof.
  • a non-transitory computer readable storage medium storing instructions that when executed cause one or more processors to perform the method of any of examples 1-13 or combinations thereof.
  • a video encoding device configured to perform the method of any of examples 10-13 or combinations thereof.
  • a video decoding device configured to perform the method of any of examples 1-9 or combinations thereof.
  • a video encoding device comprising means for performing the steps of the method of any of examples 10-13 or combinations thereof.
  • a video decoding device comprising means for performing the steps of the method of any of examples 1-9 or combinations thereof.
  • a method for decoding video data comprising: receiving a block of video data encoded using lossless coding and intra prediction; reconstructing residual samples from the losslessly coded block of video data according to a residual differential pulse code modulation (DPCM) process; and performing intra prediction according to an intra prediction mode using the residual samples to produce reconstructed video samples, wherein the intra prediction mode is not one of a vertical intra prediction mode and a horizontal intra prediction mode.
  • DPCM residual differential pulse code modulation
  • the intra prediction mode is one of a nearly-vertical intra prediction mode and a nearly-horizontal intra prediction mode.
  • reconstructing residual samples according to the residual DPCM process comprises reconstructing residual samples according to the equation
  • r is a reconstructed residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • reconstructing residual samples according to the residual DPCM process comprises reconstructing residual samples according to the equation:
  • r is a reconstructed residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • reconstructing residual samples according to the residual DPCM process comprises reconstructing residual samples according to the equation:
  • r is a reconstructed residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the method further comprising: not reconstructing residual samples according to the residual DPCM process for a first row of the losslessly coded block of video data.
  • the method further comprising: not reconstructing residual samples according to the residual DPCM process for a first column of the losslessly coded block of video data.
  • reconstructing residual samples according to the residual DPCM processes comprises reconstructing residual samples according to one of a vertical residual DPCM process and a horizontal DPCM process.
  • reconstructing residual samples according to the residual DPCM processes comprises reconstructing residual samples according to both a vertical residual DPCM process and a horizontal DPCM process.
  • reconstructing residual samples according to the residual DPCM processes comprises reconstructing residual samples according to a diagonal DPCM process, a horizontal DPCM process, and a vertical DPCM process.
  • a method for encoding video data comprising: receiving a block of video data; performing intra prediction on the block of video data according to an intra prediction mode to produce a predictive block of samples and residual samples, wherein the intra prediction mode is not one of a vertical intra prediction mode and a horizontal intra prediction mode; and generating a losslessly coded block of video data from the residual samples using a residual differential pulse code modulation (DPCM) process.
  • DPCM residual differential pulse code modulation
  • the intra prediction mode is one of a nearly-vertical intra prediction mode and a nearly-horizontal intra prediction mode.
  • the residual DPCM process is a vertical residual DPCM process for nearly-vertical intra prediction modes
  • the residual DPCM process is a horizontal residual DPCM process for nearly-horizontal intra prediction modes
  • r is a residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • r is a residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • r is a residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the method further comprising: not generating the losslessly coded block of video data using the residual DPCM process for a first row of the block of video data.
  • the method further comprising: not generating the losslessly coded block of video data using the residual DPCM process for a first column of the block of video data.
  • the intra prediction mode is one of a DC intra prediction mode and a planar intra prediction mode
  • generating the losslessly coded block of video data from the residual samples using the residual DPCM processes comprises generating the losslessly coded block of video data from the residual samples according to one of a vertical residual DPCM process and a horizontal DPCM process.
  • the intra prediction mode is one of a DC intra prediction mode and a planar intra prediction mode
  • generating the losslessly coded block of video data from the residual samples using the residual DPCM processes comprises generating the losslessly coded block of video data from the residual samples according to both a vertical residual DPCM process and a horizontal DPCM process.
  • the intra prediction mode is a planar intra prediction mode
  • generating the losslessly coded block of video data from the residual samples using the residual DPCM processes comprises generating the losslessly coded block of video data from the residual samples according to a diagonal DPCM process, a horizontal DPCM process, and a vertical DPCM process.
  • An apparatus configured to decode video data, the apparatus comprising: means for receiving a block of video data encoded using lossless coding and intra prediction; means for reconstructing residual samples from the losslessly coded block of video data according to a residual differential pulse code modulation (DPCM) process; and means for performing intra prediction according to an intra prediction mode using the residual samples to produce reconstructed video samples, wherein the intra prediction mode is not one of a vertical intra prediction mode and a horizontal intra prediction mode.
  • DPCM residual differential pulse code modulation
  • the intra prediction mode is one of a nearly-vertical intra prediction mode and a nearly-horizontal intra prediction mode.
  • the residual DPCM process is a vertical residual DPCM process for nearly-vertical intra prediction modes
  • the residual DPCM process is a horizontal residual DPCM process for nearly-horizontal intra prediction modes
  • the intra prediction mode is a diagonal down-right intra prediction mode
  • the means for reconstructing residual samples according to the residual DPCM process comprises means for reconstructing residual samples according to the equation:
  • r is a reconstructed residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the intra prediction mode is a diagonal down-left intra prediction mode
  • the means for reconstructing residual samples according to the residual DPCM process comprises means for reconstructing residual samples according to the equation:
  • r is a reconstructed residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the intra prediction mode is a diagonal up-right intra prediction mode
  • the means for reconstructing residual samples according to the residual DPCM process comprises means for reconstructing residual samples according to the equation:
  • r is a reconstructed residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the apparatus further comprising: means for not reconstructing residual samples according the residual DPCM process for a first row of the losslessly coded block of video data.
  • the apparatus further comprising: means for not reconstructing residual samples according the residual DPCM process for a first column of the losslessly coded block of video data.
  • the intra prediction mode is one of a DC intra prediction mode and a planar intra prediction mode
  • the means for reconstructing residual samples according to the residual DPCM processes comprises means for reconstructing residual samples according to one of a vertical residual DPCM process and a horizontal DPCM process.
  • the intra prediction mode is one of a DC intra prediction mode and a planar intra prediction mode
  • the means for reconstructing residual samples according to the residual DPCM processes comprises means for reconstructing residual samples according to both a vertical residual DPCM process and a horizontal DPCM process.
  • the intra prediction mode is a planar intra prediction mode
  • the means for reconstructing residual samples according to the residual DPCM processes comprises means for reconstructing residual samples according to a diagonal DPCM process, a horizontal DPCM process, and a vertical DPCM process.
  • An apparatus configured to encode video data, the apparatus comprising: means for receiving a block of video data; means for performing intra prediction on the block of video data according to an intra prediction mode to produce residual samples, wherein the intra prediction mode is not one of a vertical intra prediction mode and a horizontal intra prediction mode; and means for generating a losslessly coded block of video data from the residual samples using a residual differential pulse code modulation (DPCM) process.
  • DPCM residual differential pulse code modulation
  • the intra prediction mode is one of a nearly-vertical intra prediction mode and a nearly-horizontal intra prediction mode.
  • the residual DPCM process is a vertical residual DPCM process for nearly-vertical intra prediction modes
  • the residual DPCM process is a horizontal residual DPCM process for nearly-horizontal intra prediction modes
  • the intra prediction mode is a diagonal down-right intra prediction mode
  • the means for generating the losslessly coded block of video data from the residual samples using the residual DPCM process comprises means for generating the losslessly coded block of video data according to the equation:
  • r is a residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the intra prediction mode is a diagonal down-right intra prediction mode
  • the means for generating the losslessly coded block of video data from the residual samples using the residual DPCM process comprises means for generating the losslessly coded block of video data according to the equation:
  • r is a residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the intra prediction mode is a diagonal down-right intra prediction mode
  • the means for generating the losslessly coded block of video data from the residual samples using the residual DPCM process comprises means for generating the losslessly coded block of video data according to the equation:
  • r is a residual sample
  • ⁇ tilde over (r) ⁇ is a sample of the losslessly coded block of video data
  • M and N define a size of the block of video data
  • i and j define a location of a sample within the block of video data.
  • the apparatus further comprising: means for not generating the losslessly coded block of video data using the residual DPCM process for a first row of the block of video data.
  • the apparatus further comprising: means for not generating the losslessly coded block of video data using the residual DPCM process for a first column of the block of video data.
  • the intra prediction mode is one of a DC intra prediction mode and a planar intra prediction mode
  • the means for generating the losslessly coded block of video data from the residual samples using the residual DPCM processes comprises means for generating the losslessly coded block of video data from the residual samples according to one of a vertical residual DPCM process and a horizontal DPCM process.
  • the intra prediction mode is one of a DC intra prediction mode and a planar intra prediction mode
  • the means for generating the losslessly coded block of video data from the residual samples using the residual DPCM processes comprises means for generating the losslessly coded block of video data from the residual samples according to both a vertical residual DPCM process and a horizontal DPCM process.
  • the intra prediction mode is a planar intra prediction mode
  • the means for generating the losslessly coded block of video data from the residual samples using the residual DPCM processes comprises means for generating the losslessly coded block of video data from the residual samples according to a diagonal DPCM process, a horizontal DPCM process, and a vertical DPCM process.
  • a video decoder configured to perform any combination of the methods of examples 1 to 13.
  • a video encoder configured to perform any combination of the methods of examples 14 to 26.
  • a computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device configured to decode video data to perform any combination of the methods of examples 1 to 13.
  • a computer-readable storage medium storing instructions that, when executed, cause one or more processors of a device configured to encode video data to perform any combination of the methods of examples 14 to 26.
  • a method of coding video data comprising: generating prediction samples for horizontal intra coding of a block of video data, wherein for every column of the block of video data, the prediction samples include a gradient term.
  • a method of coding video data comprising: generating prediction samples for vertical intra coding of a block of video data, wherein for every row of the block of video data, the prediction samples include a gradient term.
  • the method any combination of examples 1-10.
  • a system configured to perform the method of any of examples 1-10 or combinations thereof.
  • a non-transitory computer readable storage medium storing instructions that when executed cause one or more processors to perform the method of any of examples 1-10 or combinations thereof.
  • a video encoding device configured to perform the method of any of examples 1-10 or combinations thereof.
  • a video decoding device configured to perform the method of any of examples 1-10 or combinations thereof.
  • a video encoding device comprising means for performing the steps of the method of any of examples 1-10 or combinations thereof.
  • a video decoding device comprising means for performing the steps of the method of any of examples 1-10 or combinations thereof.
  • Computer-readable media may include computer-readable storage media, which corresponds to a tangible medium such as data storage media, or communication media including any medium that facilitates transfer of a computer program from one place to another, e.g., according to a communication protocol.
  • Computer-readable media generally may correspond to (1) tangible computer-readable storage media which is non-transitory or (2) a communication medium such as a signal or carrier wave.
  • Data storage media may be any available media that can be accessed by one or more computers or one or more processors to retrieve instructions, code and/or data structures for implementation of the techniques described in this disclosure.
  • a computer program product may include a computer-readable medium.
  • such computer-readable storage media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage, or other magnetic storage devices, flash memory, or any other medium that can be used to store desired program code in the form of instructions or data structures and that can be accessed by a computer.
  • any connection is properly termed a computer-readable medium.
  • a computer-readable medium For example, if instructions are transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium.
  • DSL digital subscriber line
  • Disk and disc includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk and Blu-ray disc, where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.
  • processors such as one or more digital signal processors (DSPs), general purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuitry.
  • DSPs digital signal processors
  • ASICs application specific integrated circuits
  • FPGAs field programmable logic arrays
  • processors may refer to any of the foregoing structure or any other structure suitable for implementation of the techniques described herein.
  • the functionality described herein may be provided within dedicated hardware and/or software modules configured for encoding and decoding, or incorporated in a combined codec. Also, the techniques could be fully implemented in one or more circuits or logic elements.
  • the techniques of this disclosure may be implemented in a wide variety of devices or apparatuses, including a wireless handset, an integrated circuit (IC) or a set of ICs (e.g., a chip set).
  • IC integrated circuit
  • a set of ICs e.g., a chip set.
  • Various components, modules, or units are described in this disclosure to emphasize functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, various units may be combined in a codec hardware unit or provided by a collection of interoperative hardware units, including one or more processors as described above, in conjunction with suitable software and/or firmware.

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