Patent Application
20170055003
Not applicable.
Not applicable.
The amount of video data needed to depict even a relatively short film can be substantial, which may result in difficulties when the data is to be streamed or otherwise communicated across a communications network with limited bandwidth capacity. Thus, video data is generally compressed prior to being communicated across modern day telecommunications networks. Video compression devices often use software and/or hardware at the source to code the video data prior to transmission, thereby decreasing the quantity of data needed to represent digital video images. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and ever increasing demands of higher video quality, improved compression and decompression techniques that improve image quality without increasing bit-rates are desirable.
In one embodiment, the disclosure includes an encoding apparatus having a processor and a transmitter. The processor is configured to receive a video frame including screen content, generate a block containing an index map of colors for screen content in the video frame, where the block includes a first string of index values and a second string of the index values immediately below the first string, and encode a second string palette_run_type flag corresponding to the second string without referencing a first string palette_run_type flag corresponding to the first string and using a single available context. The transmitter is operably coupled to the processor and configured to transmit the second string palette_run_type flag in a bitstream to a decoding apparatus.
In another embodiment, the disclosure includes a method of encoding. The method includes receiving, by a receiver, a video frame including screen content, generating, by a processor operably coupled to the receiver, a block containing an index map of colors for screen content in the video frame, wherein the block includes a first string of index values and a second string of the index values immediately below the first string, encoding, by the processor, a second string palette_run_type flag corresponding to the second string without referencing a first string palette_run_type flag corresponding to the first string and using a single available context, and transmitting, by a transmitter operably coupled to the processor, the second string palette_run_type flag in a bitstream to a decoding apparatus.
In yet another embodiment, the disclosure includes a decoding apparatus including a receiver and a processor. The receiver is configured to receive a second palette_run_type flag in a bitstream, where the second palette_run_type flag was encoded without referencing a first string palette_run_type flag corresponding to the first string and using a single available context. The processor is operably coupled to the receiver and configured to decode the second palette_run_type flag in the bitstream using the single available context.
These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.
For a more complete understanding of this disclosure, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description, wherein like reference numerals represent like parts.
It should be understood at the outset that, although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.
Typically, video media involves displaying a sequence of still images or frames in relatively quick succession, thereby causing a viewer to perceive motion. Each frame may comprise a plurality of picture elements or pixels, each of which may represent a single reference point in the frame. During digital processing, each pixel may be assigned an integer value (e.g., 0, 1, . . . or 255) that represents an image quality or characteristic, such as luminance or chrominance, at the corresponding reference point. In use, an image or video frame may comprise a large amount of pixels (e.g., 2,073,600 pixels in a 1920×1080 frame). Thus, it may be cumbersome and inefficient to encode and decode (referred to hereinafter simply as code) each pixel independently. To improve coding efficiency, a video frame is usually broken into a plurality of rectangular blocks or macroblocks, which may serve as basic units of processing such as prediction, transform, and quantization. For example, a typical N×N block may comprise N2 pixels, where N is an integer greater than one and is often a multiple of four.
In the International Telecommunications Union (ITU) Telecommunications Standardization Sector (ITU-T) and the International Organization for Standardization (ISO)/International Electrotechnical Commission (IEC), new block concepts were introduced for High Efficiency Video Coding (HEVC). For example, coding unit (CU) may refer to a sub-partitioning of a video frame into rectangular blocks of equal or variable size. In HEVC, a CU may replace macroblock structure of previous standards. Depending on a mode of inter or intra prediction, a CU may comprise one or more prediction units (PUs), each of which may serve as a basic unit of prediction. For example, for intra prediction, an 8×8 CU may be symmetrically split into four 4×4 PUs. For another example, for an inter prediction, a 64×64 CU may be asymmetrically split into a 16×64 PU and a 48×64 PU. Similarly, a PU may comprise one or more transform units (TUs), each of which may serve as a basic unit for transform and/or quantization. For example, a 32×32 PU may be symmetrically split into four 16×16 TUs. Multiple TUs of one PU may share a same prediction mode, but may be transformed separately. Herein, the term block may generally refer to any of a macroblock, CU, PU, or TU.
Depending on the application, a block may be coded in either a lossless mode (e.g., no distortion or information loss) or a lossy mode (e.g., with distortion). In use, high quality videos (e.g., with YUV subsampling of 4:4:4) may be coded using a lossless mode, while low quality videos (e.g., with YUV subsampling of 4:2:0) may be coded using a lossy mode. As used herein, the Y component in YUV refers to the brightness of the color (the luminance or luma) while the U and V components refer to the color itself (the chroma). Sometimes, a single video frame or slice (e.g., with YUV subsampling of either 4:4:4 or 4:2:0) may employ both lossless and lossy modes to code a plurality of regions, which may be rectangular or irregular in shape. Each region may comprise a plurality of blocks. For example, a compound video may comprise a combination of different types of contents, such as text and computer graphic content (e.g., non-camera-captured images) and natural-view content (e.g., camera-captured video). In a compound frame, regions of texts and graphics may be coded in a lossless mode, while regions of natural-view content may be coded in a lossy mode. Lossless coding of texts and graphics may be desired in, for example, computer screen sharing applications, since lossy coding may lead to poor quality or fidelity of texts and graphics, which may cause eye fatigue.
With the rapid and continuous advancements made in semiconductors, networking, communications, displays, computers, and devices such as tablets and smart phones, many applications call for HEVC-based compression/coding solutions that can efficiently compress the non-camera-captured video content at high visual quality. This non-camera-captured video content, which may be referred to herein as screen content, may include computer generated graphics, text with typical motion commonly seen in applications such as window switching and moving, text scrolling, and the like. In many cases, the non-camera-captured video content provides clear textures and sharp edges with distinct colors at high contrast and may have a 4:4:4 color sampling format.
Current HEVC screen content coding introduces a palette mode to more efficiently represent computer screens. The palette mode is described in R. Joshi and J. Xu, Working Draft 2 of HEVC Screen Content Coding, MPEG-N14969/JCTVC-S1005, Strasbourg, FR, October 2014 (HEVC SCC), which is incorporated herein by this reference. The palette mode is also utilized in the Screen Content Coding Test Model (SCM) 2.0 reference software.
Despite the efficiency provided by the palette mode within the current HEVC framework, there is still room for improvement. Disclosed herein are systems and methods for improved video coding. The disclosure provides a simplified entropy (e.g., lossless) coding scheme. To reduce the overall complexity, the coding scheme encodes a flag (e.g., a palette_run_type_flag) without referring to the run_type (e.g., COPY_ABOVE) of a flag for an above index (e.g., a string above the current string). As a result, the inventive coding scheme needs only a single context. Using the new coding scheme will reduce the total number of contexts for the entire codec, and also made the encoding and decoding process simpler.
The current HEVC SCC draft utilizes a run-based one dimensional (1-D) string copy. Even so, two dimensional (2-D) string copy methods have been proposed in W. Wang, Z. Ma, M. Xu, H. Yu, “Non-CE6: 2-D Index Map Coding of Palette Mode in HEVC SCC,” JCTVC-S0151, Strasbourg, FR, October 2014, and U.S. Provisional Patent Application No. 62/060,450 entitled, “On Improved Palette Mode in HEVC SCC,” filed October 2014, which are incorporated herein by this reference. While not fully described herein for the sake of brevity, those skilled in the art will appreciate that the 2-D string copy methods may default to a run based 1-D string copy method in some circumstances.
When index mode coding in palette mode using the 1-D string method, two main parts are involved for each CU. Those two parts are color table processing and index map coding. By way of example, the index map coding for the 1-D string method may utilize a COPY_ABOVE mode, where COPY_ABOVE is applied to indicate whether the current string is identical to the indices from the string directly above the current string.
The palette_run_type flag indicates whether any index values in the string above the current string have been copied. If a portion of the string above has been copied, the palette_run_type flag is set to a first binary number (e.g., 1) representing the COPY_ABOVE_MODE. If the string above has not been copied, the palette_run_type flag is set to a second binary number (e.g., 0) representing the COPY_INDEX_MODE. When encoding the top string 102, the palette_run_type flag is set to 0 by default because there are no strings disposed above the top string 102. The index value is the particular number value (e.g., 1, 2, 3, or 4) represented within the string in the block 100. The run value is how many consecutive index values may be copied. For example, if the run value is set to 1, a single index value is copied, if the run value is set to 2, two consecutive index values are copied, if the run value is set to 3, three consecutive run values are copied, and so on. So, to encode the top string 102 having the index values 1, 2, 3, 4, the following syntax is used: palette_run_type_flag-0, index value=1, run value=1, palette_run_type_flag=0, index value=2, run value=1, palette_run_type_flag=0, index value=3, run value=1, and palette_run_type_flag=0, index value=4, run value=1.
To encode the next string 104 having index values 1, 2, 2, 2, the following syntax is used: palette_run_type_flag=1, run value=2, palette_run_type_flag=0, index value=2, run value=2. To encode the next string 106 having index values 1, 3, 2, 2, the following syntax is used: palette_run_type_flag=1, run value=1, palette_run_type_flag=0, index value=3, run value=1, and palette_run_type_flag-0, index value=2, run value=2. To encode the bottom string 108 having the index values 2, 3, 2, 2, the following syntax is used: palette_run_type_flag=0, index value=2, run value=1, palette_run_type_flag=1, run value=3.
Currently, the palette_run_type_flag is encoded by context adaptive binary arithmetic coding (CABAC) using a context model with two different contexts (e.g., context A and context B). When deciding the correct context for coding a current palette_run_type_flag, the value of the flag for the string (or row) immediately above the current string is considered. For example, if the value of the palette_run_type_flag for the string immediately above the current string has a value of 1, then the current palette_run_type_flag is coded in the bitstream using context A. If, however, value of the palette_run_type_flag for the string immediately above the current string has a value of 0, then the current palette_run_type flag is coded in the bitstream using context B. If there is no string disposed immediately above the current string, then the palette_run_type_flag is coded in the bitstream using a default context (e.g., context B). Thus, conventional encoding of the palette_run_type_flag relies upon the use of two different contexts depending on the value for the palette_run_type_flag of the string immediately above the current string.
It has been discovered, however, that there is little correlation between the value of the palette_run_type_flag for the current string and the value of the palette_run_type_flag for the string immediately above the current string. Therefore, the predictive context model described above is not necessary when encoding the palette_run_type_flag. To reduce the overall codec complexity, a simplified context model is proposed whereby the palette_run_type_flag for a current string is encoded without referencing the palette_run_type_flag of an adjacent string. Because encoding of the palette_run_type_flag for a current string is performed without regard for the palette_run_type_flag of an adjacent string (e.g., the string immediately above the current string), only a single context is needed for encoding. In other words, the simplified context model proposed herein only needs one context model in order to encode the palette_run_type_flag for a current string. Where the block (e.g., block 100 of
In block 206, a second string palette_run_type flag corresponding to the second string is encoded by a processor without referencing a first string palette_run_type flag corresponding to the first string and using a single available context. In an embodiment, the single available context is based on the CABAC model. In block 208, the second string palette_run_type flag is transmitted in a bitstream to a decoding apparatus. It should be recognized by those skilled in the art upon reviewing this disclosure that subsequent string palette_run_type flags corresponding to subsequent strings may also be encoded without referencing an adjacent string palette_run_type flag corresponding to an adjacent string and using the single available context.
The RDO module 310 may be configured to coordinate or make logic decisions for one or more of other modules. For example, based on one or more previously encoded frames, the RDO module 310 may determine how a current frame (or slice) being encoded is partitioned into a plurality of CUs, and how a CU is partitioned into one or more PUs and TUs. As noted above, CU, PU, and TU are various types of blocks used in HEVC. In addition, the RDO module 310 may determine how the current frame is to be predicted. The current frame may be predicted via inter and/or intra prediction. For intra prediction, there are a plurality of available prediction modes or directions in HEVC (e.g., 34 modes for the Y component and six modes (including linear mode (LM)) for the U or V component), and an optimal mode may be determined by the RDO module 310. For example, the RDO module 310 may calculate a sum of absolute error (SAE) for each prediction mode, and select a prediction mode that results in the smallest SAE.
In an embodiment, the prediction module 320 is configured to generate a prediction block for a current block from the input video. The prediction module 320 may utilize either reference frames for inter prediction or reference pixels in the current frame for intra prediction. The prediction block comprises a plurality of predicted pixel samples, each of which may be generated based on a plurality of reconstructed luma samples located in a corresponding reconstructed luma block, and a plurality of reconstructed chroma samples located in a corresponding reconstructed chroma block.
Upon generation of the prediction block for the current block, the current block may be subtracted by the prediction block, or vice versa, to generate a residual block. The residual block may be fed into the transform module 330, which may convert residual samples into a matrix of transform coefficients via a two-dimensional (2-D) orthogonal transform, such as a discrete cosine transform (DCT). Then, the matrix of transform coefficients may be quantized by the quantization module 340 before being fed into the entropy encoder 350. The quantization module 340 may alter the scale of the transform coefficients and round them to integers, which may reduce the number of non-zero transform coefficients. As a result, a compression ratio may be increased. In an embodiment, the entropy encoder 350 is configured to implement the inventive concepts disclosed herein.
Quantized transform coefficients may be scanned and encoded by the entropy encoder 350 into an encoded bitstream. Further, to facilitate continuous encoding of blocks, the quantized transform coefficients may also be fed into the de-quantization module 360 to recover the original scale of the transform coefficients. Then, the inverse transform module 370 may perform the inverse of the transform module 330 and generate a noisy version of the original residual block. Then, the lossy residual block may be fed into the reconstruction module 380, which may generate reconstructed samples for intra prediction of future blocks. If desired, filtering may be performed on the reconstructed samples before they are used for intra prediction. In an embodiment, the encoder 300 and/or the palette creation and index map processing module 390 of
It should be noted that
The schemes described above may be implemented on any general-purpose network component, such as a computer or network component with sufficient processing power, memory resources, and network throughput capability to handle the necessary workload placed upon it.
The secondary storage 604 is typically comprised of one or more disk drives or tape drives and is used for non-volatile storage of data and as an over-flow data storage device if the RAM 608 is not large enough to hold all working data. The secondary storage 604 may be used to store programs that are loaded into the RAM 608 when such programs are selected for execution. The ROM 606 is used to store instructions and perhaps data that are read during program execution. The ROM 606 is a non-volatile memory device that typically has a small memory capacity relative to the larger memory capacity of the secondary storage 604. The RAM 608 is used to store volatile data and perhaps to store instructions. Access to both the ROM 606 and the RAM 608 is typically faster than to the secondary storage 604. One or more of the memory devices disclosed herein (e.g., RAM 608, etc.) may store the software, programming, and/or instructions that, when executed by the logic unit 520 and/or processor 602, implement method 200 of
The terms network “element,” “node,” “component,” “module,” and/or similar terms may be interchangeably used to generally describe a network device and do not have a particular or special meaning unless otherwise specifically stated and/or claimed within the disclosure.
While several embodiments have been provided in the present disclosure, it may be understood that the disclosed systems and methods might be embodied in many other specific forms without departing from the spirit or scope of the present disclosure. The present examples are to be considered as illustrative and not restrictive, and the intention is not to be limited to the details given herein. For example, the various elements or components may be combined or integrated in another system or certain features may be omitted, or not implemented.
In addition, techniques, systems, subsystems, and methods described and illustrated in the various embodiments as discrete or separate may be combined or integrated with other systems, modules, techniques, or methods without departing from the scope of the present disclosure. Other items shown or discussed as coupled or directly coupled or communicating with each other may be indirectly coupled or communicating through some interface, device, or intermediate component whether electrically, mechanically, or otherwise. Other examples of changes, substitutions, and alterations are ascertainable by one skilled in the art and may be made without departing from the spirit and scope disclosed herein.
