Weighting factor reuse across components in weighted inter-prediction

Abstract

A determining is made that block-level adaptive weighted prediction (BAWP) is to be performed with respect to a luma component of a current block and a chroma component of the current block. A luma weight αγ and a luma offset βγ are obtained for the luma component. An offset β is obtained for the chroma component using the luma weight αγ. Final prediction blocks for the luma component and the chroma component are obtained based on the luma weight αγ, the luma offset βγ, and the offset β.

Description

WEIGHTING FACTOR REUSE ACROSS COMPONENTS IN WEIGHTED INTER-PREDICTIONBACKGROUND

[0001] Digital video streams may represent video using a sequence of frames or still images. Digital video can be used for various applications including, for example, video conferencing, high-definition video entertainment, video advertisements, or sharing of usergenerated videos. A digital video stream can contain a large amount of data and consume a significant amount of computing or communication resources of a computing device for processing, transmission, or storage of the video data. Various approaches have been proposed to reduce the amount of data in video streams, including encoding or decoding techniques.SUMMARY

[0002] A system of one or more computers can be configured to perform particular operations or actions by virtue of having software, firmware, hardware, or a combination of them installed on the system that in operation causes or cause the system to perform the actions. One or more computer programs can be configured to perform particular operations or actions by virtue of including instructions that, when executed by data processing apparatus, cause the apparatus to perform the actions. One general aspect includes a method. The method includes determining that block-level adaptive weighted prediction (BAWP) is to be performed with respect to a luma component of a current block and a chroma component of the current block; obtaining a luma weight ay and a luma offset Py for the luma component; obtaining an offset P for the chroma component using the luma weight ay; and obtaining final prediction blocks for the luma component and the chroma component based on the luma weight ay, the luma offset Py, and the offset p. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0003] Implementations may include one or more of the following features.

[0004] The method where obtaining the final prediction blocks for the luma component and the chroma component based on the luma weight ay, the luma offset Py, and the offset P may include obtaining a first final prediction block for the luma component based on the luma weight ay and the luma offset Py; and obtaining a second final prediction block for thechroma component based on the luma weight ay and the offset p.

[0005] The chroma component can be at least one of a chroma U component or chroma V component of the current block.

[0006] Obtaining the luma weight ay may include obtaining the luma weight ay and the luma offset Py by minimizing a summation of squared errors between reconstructed luma pixels and reference luma pixels.

[0007] Obtaining the offset P for the chroma component using the luma weight ay may include obtaining the offset P for the chroma component by minimizing a summation of squared errors between reconstructed chroma pixels and reference chroma pixels.

[0008] The method may include setting a chroma weight for the chroma component to the luma weight ay.

[0009] The method may include decoding, from a compressed bitstream, a first flag indicating that BAWP is to be performed with respect to the luma component; and decoding, from the compressed bitstream, a second flag indicating that BAWP is to be performed with respect to the luma component.

[0010] An encoder may have performed rate-distortion checks to determine that BAWP is to be performed with respect to the luma component and the chroma component.

[0011] Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium. Implementations may include a non-transitory computer-readable storage medium having stored thereon an encoded bitstream that is configured for decoding by the method.

[0012] Another general aspect includes a method. The method includes determining that a block-level adaptive weighted prediction (BAWP) is to be performed with respect to a first color component and a second color component of a current block; obtaining a weight a and a first offset pi for the first color component, obtaining a second offset P2 for the second color component, obtaining a first final prediction block of the first color component using BAWP based on the weight a and the first offset pi, and obtaining a second final prediction block of the second color component using BAWP based on the weight a and the second offset P2. Other embodiments of this aspect include corresponding computer systems, apparatus, and computer programs recorded on one or more computer storage devices, each configured to perform the actions of the methods.

[0013] Implementations may include one or more of the following features.

[0014] The method where the first color component is a luma Y color component, and the second color component is at least one of a chroma U or V component, where the weight a isobtained based on pixel values of a luma Y plane of the current block, where the second final prediction block is obtained based on the weight a, and where the second offset P2 is obtained using pixel values of a color plane corresponding the second color component.

[0015] The first color component can be a chroma U component and the second color component can be a chroma V component.

[0016] Obtaining the second offset P2 for the second color component may include setting the second offset P2 to the first offset pi.

[0017] The first color component can be a luma Y component and the second color component includes a chroma U component and a chroma V component, and the weight a and the first offset pi can be obtained using respective pixel values from a luma Y plane, a chroma U plane, and a chroma V plane of the current block.

[0018] The second offset P2 can be set to the first offset pi.

[0019] The weight a can be obtained by minimizing a summation of squared errors between reconstructed pixels and reference pixels for the first color component.

[0020] The method may include decoding, from a compressed bitstream, a first flag indicating that BAWP is to be performed with respect to the first color component; and decoding, from the compressed bitstream, a second flag indicating that BAWP is to be performed with respect to the second color component.

[0021] The first final prediction block can be obtained by applying the weight a and the first offset pi to an intermediate prediction block for the first color component.

[0022] The second final prediction block can be obtained by applying the weight a and the second offset P2 to an intermediate prediction block for the second color component.

[0023] Implementations of the described techniques may include hardware, a method or process, or computer software on a computer-accessible medium. Implementations may include a non-transitory computer-readable storage medium having stored thereon an encoded bitstream that is configured for decoding by the method.

[0024] These and other aspects of the present disclosure are disclosed in the following detailed description of the embodiments, the appended claims, and the accompanying figures. It will be appreciated that aspects can be implemented in any convenient form. For example, aspects may be implemented by appropriate computer programs which may be carried on appropriate carrier media which may be tangible carrier media (e.g. disks) or intangible carrier media (e.g. communications signals). Aspects may also be implemented using suitable apparatus which may take the form of programmable computers running computer programs arranged to implement the methods and / or techniques disclosed herein. Aspects can becombined such that features described in the context of one aspect may be implemented in another aspect.BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The description herein makes reference to the accompanying drawings described below, wherein like reference numerals refer to like parts throughout the several views.

[0026] FIG. l is a schematic of a video encoding and decoding system.

[0027] FIG. 2 is a block diagram of an example of a computing device that can implement a transmitting station or a receiving station.

[0028] FIG. 3 is a diagram of a typical video stream to be encoded and subsequently decoded.

[0029] FIG. 4 is a block diagram of an encoder.

[0030] FIG. 5 is a block diagram of a decoder.

[0031] FIG. 6 is a block diagram of a representation of a portion of a frame.

[0032] FIG. 7 is a flowchart of an example of a technique for applying BAWP when decoding a current block.

[0033] FIG. 8 illustrates an example of causal neighboring samples of a current block.

[0034] FIG. 9 is a flowchart of an example of a technique for applying BAWP when decoding a current block.DETAILED DESCRIPTION

[0035] Compression schemes related to coding video streams may include breaking images (i.e., original or source images) into blocks and generating a digital video output bitstream using one or more techniques to limit the information included in the output. Video compression exploits spatial and temporal correlations in the frames of the video signal to achieve a good compression (i.e., coding) efficiency.

[0036] A received encoded bitstream can be decoded to re-create the blocks and the source images from the limited information. Encoding a video stream, or a portion thereof, such as a frame or a block, can include using temporal or spatial similarities in the video stream to improve coding efficiency. For example, a current block of a video stream may be encoded based on identifying a difference (residual) between previously coded pixel values and those in the current block. In this way, only the residual and parameters used to generate the residual need be added to the encoded bitstream. The residual may be encoded using alossy quantization step. Decoding (i.e., reconstructing) an encoded block from such a residual often results in a distortion between the original and the reconstructed block.

[0037] Encoding using spatial similarities is known as intra prediction. Using an intraprediction mode, intra prediction can attempt to predict the pixel values of a current block of a current frame of a video stream using pixels peripheral to the current block. The pixels peripheral to the current blocks are pixels within the current frame but that are outside the current block. The pixels peripheral to the block can be pixels adjacent to the current block. Which pixels peripheral to the block are used can depend on the intra-prediction mode and / or a scan order of the blocks of a frame. For example, in a raster scan order, peripheral pixels above a current block (i.e., the block being encoded or decoded) and / or peripheral pixels to the left of the current block may be used.

[0038] Encoding using temporal similarities is known as inter prediction. Inter prediction uses a motion vector that represents the temporal displacement of a previously coded block relative to the current block. The motion vector can be identified using a method of motion estimation, such as a motion search. In the motion search, a portion of a reference frame can be translated to a succession of locations to form a predictor block that can be subtracted from a portion of a current frame to form a series of residuals. The horizontal and / or vertical translations corresponding to the location having, e.g., the smallest residual can be selected as the motion vector. The motion vector can be encoded in the encoded bitstream along with an indication of the reference frame.

[0039] Compression efficiency, with respect to temporal correlations, can be achieved by forming a reference frame prediction of a frame (i.e., blocks therein) to be encoded and only encoding the difference between blocks of the current frame and predictions therefor using motion compensation (e.g., inter-frame prediction). However, when there are temporal brightness or color variations due to factors like illumination changes, fade-in / out effects, camera flashes, and the like, motion compensation may not produce optimal results.

[0040] A technique for improving the inter prediction efficiency is block-level adaptive weighted prediction (BAWP). Improving the inter prediction efficiency, in this context, means improving the prediction accuracy (e.g., generating an enhanced prediction block). To illustrate, and as is known, decoding a current block includes generating a prediction block for the current block and adding a residual block (which may be decoded from a compressed bitstream) to the prediction block. When it is determined that BAWP is to be applied when decoding a current block, a prediction block Predorg(obtained using any conventionalprediction technique and according to a prediction mode associated with the current block) is considered to be an intermediate prediction block and is enhanced to obtain a (final) prediction block Predbawp.

[0041] To obtain Predbawpfor a color component (e.g., one of the Luma Y, chroma U, or chroma V color components) of a current block, a weight factor a (also referred to herein as a weight or a weight value) and an offset / 3 (also referred to herein as an offset value) are derived, at the decoder, based on the causal neighboring samples of the current block. When the BAWP mode is applied, the final prediction block Predbawpis attained using equation (1), where Predorgis the (intermediate) prediction block obtained according to a prediction mode, a is a weight factor, and / 3 is an offset.Predbawpcc ■ P edorg+ [3 (1)

[0042] BAWP may be applied to more than one of the color components of many blocks of the video sequence. As such, for each of blocks for which BAWP is to be performed and for each of the color components to which BAWP is to be applied for that block, respective a and / 3 parameters are calculated. For example, if BAWP were to be applied to each of the Y, U, and V components of a block, then ay, ?Y, au, / u, av, and ?v would have to be calculated at the decoder. Calculating the weights and offsets for many color components of many blocks can significantly degrade encoder and decoder performance. Experiments have shown that when BAWP is applied to more than just the luminance Y component, decoding performance is 102% as compared to when BAWP is applied to only the luminance Y component.

[0043] Implementations of cross-component weighting factor reuse calculate the weight factor a on the luma Y plane using Luma pixel values, and then applies the same factor a to the chroma U and chroma V planes. The offset / 3 can be independently determined for each color plane where BAWP is to be implemented. Different variations of reusing the weight factor a and the offset / 3 are also described.

[0044] Cross-component weighting factor reuse simplifies the computation involved in determining the weight factor a, which is a primary complexity of the BAWP algorithm at the decoder. As a result, coding time can be brought back to approximately 100% when the weight factor a is utilized across color components. In other words, even if BAWP is applied to more than just the luma Y component of blocks, the performance of the decoder can be roughly equivalent to when BAWP is applied solely to the luma Y component. Furthermore, the average BD-rate for certain test sets is reported to be -0.12% with cross-componentweighting factor reuse, compared to -0.13% when the weight factor is not reused. As such, by sharing the weight factor amongst color components computation complexity is reduced (especially at the decoder side), as compared to separately computing weight factors for each of the color components, while keeping the coding efficiency gain almost unchanged.

[0045] The intuition behind reusing the weighting factor stems from the relationship between YUV and RGB color spaces. YUV signals are typically derived from the red, green, and blue components of an image. Y represents the overall brightness or luminance, while U and V are calculated as scaled differences between Y and the blue (B) and red (R) values, respectively. In most cases, when there are changes in luminance (Y) within natural content, it is likely that U and V will follow the same scaling factor as Y, but with different offsets based on the conversion formula. Therefore, when reconstructing pixels within a block, using the same weight factor but different offsets for each color component (or plane) can yield resultant pixel values that better align with the source pixel values. However, in some instances, and to further reduce computational complexity (albeit at the potential expense of the peak signal-to-noise ratio (PSNR)), it is also possible to reuse the offset values as well.

[0046] While the description herein is mainly described with respect to one color space, namely, the YUV color space, the disclosure is not so limited. Although terminology such as luma and chroma planes, or Y / U / V planes are used, the disclosure herein can be easily extended to other color formats, such as the YCoCg, YCbCr, RGB, or other color spaces. Additionally, according to the teachings herein, more planes can be included in a compressed bitstream. For example, the planes may include a transparency plane in addition to the luma and chroma planes or a depth plane in addition to the red, green, and blue planes.

[0047] Additionally, while this disclosure mainly describes the reuse of the weigh factor, in some implementations, the offset can also be reused. For example, the weight factor and offset value obtained for the luma Y component may also be used for at least one of the chroma U and chroma V components. As another example, the weight factor and offset value may be obtained for one of the chroma U using the chroma U pixel samples or for the chromaV component using the chroma V pixel samples and used for other of the chroma componentV or U. Other examples are also described herein.

[0048] Further details of techniques for cross-component weighting factor reuse are described herein with initial reference to a system in which they can be implemented. FIG. 1 is a schematic of a video encoding and decoding system 100. A transmitting station 102 can be, for example, a computer having an internal configuration of hardware such as that described in FIG. 2. However, other implementations of the transmitting station 102 arepossible. For example, the processing of the transmitting station 102 can be distributed among multiple devices.

[0049] A network 104 can connect the transmitting station 102 and a receiving station 106 for encoding and decoding of the video stream. Specifically, the video stream can be encoded in the transmitting station 102, and the encoded video stream can be decoded in the receiving station 106. The network 104 can be, for example, the Internet. The network 104 can also be a local area network (LAN), wide area network (WAN), virtual private network (VPN), cellular telephone network, or any other means of transferring the video stream from the transmitting station 102 to, in this example, the receiving station 106.

[0050] The receiving station 106, in one example, can be a computer having an internal configuration of hardware such as that described in FIG. 2. However, other suitable implementations of the receiving station 106 are possible. For example, the processing of the receiving station 106 can be distributed among multiple devices.

[0051] Other implementations of the video encoding and decoding system 100 are possible. For example, an implementation can omit the network 104. In another implementation, a video stream can be encoded and then stored for transmission at a later time to the receiving station 106 or any other device having memory. In one implementation, the receiving station 106 receives (e.g., via the network 104, a computer bus, and / or some communication pathway) the encoded video stream and stores the video stream for later decoding. In an example implementation, a real-time transport protocol (RTP) is used for transmission of the encoded video over the network 104. In another implementation, a transport protocol other than RTP may be used (e.g., a Hypertext Transfer Protocol-based (HTTP -based) video streaming protocol).

[0052] When used in a video conferencing system, for example, the transmitting station 102 and / or the receiving station 106 may include the ability to both encode and decode a video stream as described below. For example, the receiving station 106 could be a video conference participant who receives an encoded video bitstream from a video conference server (e.g., the transmitting station 102) to decode and view and further encodes and transmits his or her own video bitstream to the video conference server for decoding and viewing by other participants.

[0053] FIG. 2 is a block diagram of an example of a computing device 200 that can implement a transmitting station or a receiving station. For example, the computing device 200 can implement one or both of the transmitting station 102 and the receiving station 106 of FIG. 1. The computing device 200 can be in the form of a computing system includingmultiple computing devices, or in the form of one computing device, for example, a mobile phone, a tablet computer, a laptop computer, a notebook computer, a desktop computer, and the like.

[0054] A processor 202 in the computing device 200 can be a conventional central processing unit. Alternatively, the processor 202 can be another type of device, or multiple devices, capable of manipulating or processing information now existing or hereafter developed. For example, although the disclosed implementations can be practiced with one processor as shown (e.g., the processor 202), advantages in speed and efficiency can be achieved by using more than one processor.

[0055] A memory 204 in computing device 200 can be a read only memory (ROM) device or a random-access memory (RAM) device in an implementation. However, other suitable types of storage device can be used as the memory 204. The memory 204 can include code and data 206 that is accessed by the processor 202 using a bus 212. The memory 204 can further include an operating system 208 and application programs 210, the application programs 210 including at least one program that permits the processor 202 to perform the techniques described herein. For example, the application programs 210 can include applications 1 through N, which further include a video coding application that performs the techniques described herein. The computing device 200 can also include a secondary storage 214, which can, for example, be a memory card used with a mobile computing device. Because the video communication sessions may contain a significant amount of information, they can be stored in whole or in part in the secondary storage 214 and loaded into the memory 204 as needed for processing.

[0056] The computing device 200 can also include one or more output devices, such as a display 218. The display 218 may be, in one example, a touch sensitive display that combines a display with a touch sensitive element that is operable to sense touch inputs. The display 218 can be coupled to the processor 202 via the bus 212. Other output devices that permit a user to program or otherwise use the computing device 200 can be provided in addition to or as an alternative to the display 218. When the output device is or includes a display, the display can be implemented in various ways, including by a liquid crystal display (LCD), a cathode-ray tube (CRT) display, or a light emitting diode (LED) display, such as an organic LED (OLED) display.

[0057] The computing device 200 can also include or be in communication with an image-sensing device 220, for example, a camera, or any other image-sensing device 220 now existing or hereafter developed that can sense an image such as the image of a useroperating the computing device 200. The image-sensing device 220 can be positioned such that it is directed toward the user operating the computing device 200. In an example, the position and optical axis of the image-sensing device 220 can be configured such that the field of vision includes an area that is directly adjacent to the display 218 and from which the display 218 is visible.

[0058] The computing device 200 can also include or be in communication with a soundsensing device 222, for example, a microphone, or any other sound-sensing device now existing or hereafter developed that can sense sounds near the computing device 200. The sound-sensing device 222 can be positioned such that it is directed toward the user operating the computing device 200 and can be configured to receive sounds, for example, speech or other utterances, made by the user while the user operates the computing device 200.

[0059] Although FIG. 2 depicts the processor 202 and the memory 204 of the computing device 200 as being integrated into one unit, other configurations can be utilized. The operations of the processor 202 can be distributed across multiple machines (wherein individual machines can have one or more processors) that can be coupled directly or across a local area or other network. The memory 204 can be distributed across multiple machines such as a network-based memory or memory in multiple machines performing the operations of the computing device 200. Although depicted here as one bus, the bus 212 of the computing device 200 can be composed of multiple buses. Further, the secondary storage 214 can be directly coupled to the other components of the computing device 200 or can be accessed via a network and can comprise an integrated unit such as a memory card or multiple units such as multiple memory cards. The computing device 200 can thus be implemented in a wide variety of configurations.

[0060] FIG. 3 is a diagram of an example of a video stream 300 to be encoded and subsequently decoded. The video stream 300 includes a video sequence 302. At the next level, the video sequence 302 includes a number of adjacent frames 304. While three frames are depicted as the adjacent frames 304, the video sequence 302 can include any number of adjacent frames 304. The adjacent frames 304 can then be further subdivided into individual frames, for example, a frame 306. At the next level, the frame 306 can be divided into a series of planes or segments 308. The segments 308 can be subsets of frames that permit parallel processing, for example. The segments 308 can also be subsets of frames that can separate the video data into separate colors. For example, a frame 306 of color video data can include a luminance plane and two chrominance planes. The segments 308 may be sampled at different resolutions.

[0061] Whether or not the frame 306 is divided into segments 308, the frame 306 may be further subdivided into blocks 310, which can contain data corresponding to, for example, 16x16 pixels in the frame 306. The blocks 310 can also be arranged to include data from one or more segments 308 of pixel data. The blocks 310 can also be of any other suitable size such as 4x4 pixels, 8x8 pixels, 16x8 pixels, 8x16 pixels, 16x16 pixels, or larger. Unless otherwise noted, the terms block and macroblock are used interchangeably herein.

[0062] FIG. 4 is a block diagram of an encoder 400. The encoder 400 can be implemented, as described above, in the transmitting station 102, such as by providing a computer software program stored in memory, for example, the memory 204. The computer software program can include machine instructions that, when executed by a processor such as the processor 202, cause the transmitting station 102 to encode video data in the manner described in FIG. 4. The encoder 400 can also be implemented as specialized hardware included in, for example, the transmitting station 102. In one particularly desirable implementation, the encoder 400 is a hardware encoder.

[0063] The encoder 400 has the following stages to perform the various functions in a forward path (shown by the solid connection lines) to produce an encoded or compressed bitstream 420 using the video stream 300 as input: an intra / inter prediction stage 402, a transform stage 404, a quantization stage 406, and an entropy encoding stage 408. The encoder 400 may also include a reconstruction path (shown by the dotted connection lines) to reconstruct a frame for encoding of future blocks. In FIG. 4, the encoder 400 has the following stages to perform the various functions in the reconstruction path: a dequantization stage 410, an inverse transform stage 412, a reconstruction stage 414, and a loop filtering stage 416. Other structural variations of the encoder 400 can be used to encode the video stream 300.

[0064] When the video stream 300 is presented for encoding, respective adjacent frames 304, such as the frame 306, can be processed in units of blocks. At the intra / inter prediction stage 402, respective blocks can be encoded using intra-frame prediction (also called intraprediction) or inter-frame prediction (also called inter-prediction). In any case, a prediction block can be formed. In the case of intra-prediction, a prediction block may be formed from samples in the current frame that have been previously encoded and reconstructed. In the case of inter-prediction, a prediction block may be formed from samples in one or more previously constructed reference frames.

[0065] Next, the prediction block can be subtracted from the current block at the intra / inter prediction stage 402 to produce a residual block (also called a residual). Thetransform stage 404 transforms the residual into transform coefficients in, for example, the frequency domain using block-based transforms. The quantization stage 406 converts the transform coefficients into discrete quantum values, which are referred to as quantized transform coefficients, using a quantizer value or a quantization level. For example, the transform coefficients may be divided by the quantizer value and truncated.

[0066] The quantized transform coefficients are then entropy encoded by the entropy encoding stage 408. The entropy-encoded coefficients, together with other information used to decode the block (which may include, for example, syntax elements such as used to indicate the type of prediction used, transform type, motion vectors, a quantizer value, or the like), are then output to the compressed bitstream 420. The compressed bitstream 420 can be formatted using various techniques, such as variable length coding (VLC) or arithmetic coding. The compressed bitstream 420 can also be referred to as an encoded video stream or encoded video bitstream, and the terms will be used interchangeably herein.

[0067] The reconstruction path (shown by the dotted connection lines) can be used to ensure that the encoder 400 and a decoder 500 (described below with respect to FIG. 5) use the same reference frames to decode the compressed bitstream 420. The reconstruction path performs functions that are similar to functions that take place during the decoding process (described below with respect to FIG. 5), including dequantizing the quantized transform coefficients at the dequantization stage 410 and inverse transforming the dequantized transform coefficients at the inverse transform stage 412 to produce a derivative residual block (also called a derivative residual). At the reconstruction stage 414, the prediction block that was predicted at the intra / inter prediction stage 402 can be added to the derivative residual to create a reconstructed block. The loop filtering stage 416 can be applied to the reconstructed block to reduce distortion such as blocking artifacts.

[0068] Other variations of the encoder 400 can be used to encode the compressed bitstream 420. In some implementations, a non-transform based encoder can quantize the residual signal directly without the transform stage 404 for certain blocks or frames. In some implementations, an encoder can have the quantization stage 406 and the dequantization stage 410 combined in a common stage.

[0069] FIG. 5 is a block diagram of a decoder 500. The decoder 500 can be implemented in the receiving station 106, for example, by providing a computer software program stored in the memory 204. The computer software program can include machine instructions that, when executed by a processor such as the processor 202, cause the receiving station 106 to decode video data in the manner described in FIG. 5. The decoder 500 can also beimplemented in hardware included in, for example, the transmitting station 102 or the receiving station 106.

[0070] The decoder 500, similar to the reconstruction path of the encoder 400 discussed above, includes in one example the following stages to perform various functions to produce an output video stream 516 from the compressed bitstream 420: an entropy decoding stage 502, a dequantization stage 504, an inverse transform stage 506, an intra / inter prediction stage 508, a reconstruction stage 510, a loop filtering stage 512, and a deblocking filtering stage 514. Other structural variations of the decoder 500 can be used to decode the compressed bitstream 420.

[0071] When the compressed bitstream 420 is presented for decoding, the data elements within the compressed bitstream 420 can be decoded by the entropy decoding stage 502 to produce a set of quantized transform coefficients. The dequantization stage 504 dequantizes the quantized transform coefficients (e.g., by multiplying the quantized transform coefficients by the quantizer value), and the inverse transform stage 506 inverse transforms the dequantized transform coefficients to produce a derivative residual that can be identical to that created by the inverse transform stage 412 in the encoder 400. Using header information decoded from the compressed bitstream 420, the decoder 500 can use the intra / inter prediction stage 508 to create the same prediction block as was created in the encoder 400 (e.g., at the intra / inter prediction stage 402).

[0072] At the reconstruction stage 510, the prediction block can be added to the derivative residual to create a reconstructed block. The loop filtering stage 512 can be applied to the reconstructed block to reduce blocking artifacts. Other filtering can be applied to the reconstructed block. In this example, the deblocking filtering stage 514 is applied to the reconstructed block to reduce blocking distortion, and the result is output as the output video stream 516. The output video stream 516 can also be referred to as a decoded video stream, and the terms will be used interchangeably herein. Other variations of the decoder 500 can be used to decode the compressed bitstream 420. In some implementations, the decoder 500 can produce the output video stream 516 without the deblocking filtering stage 514.

[0073] FIG. 6 is a block diagram of a representation of a portion 600 of a frame, such as the frame 306 of FIG. 3. As shown, the portion 600 of the frame includes four 64^64 blocks 610, which may be referred to as superblocks, in two rows and two columns in a matrix or Cartesian plane. A superblock can have a larger or a smaller size. For example, a superblock can be 128x 128. A superblock can also be referred to as a coding tree block (CTB). WhileFIG. 6 is explained with respect to a superblock of size 64^64, the description is easily extendable to larger (e.g., 128x 128) or smaller superblock sizes.

[0074] In an example, a superblock can be a basic or maximum coding unit (CU). Each superblock can include four 32x32 blocks 620. Each 32x32 block 620 can include four 16x 16 blocks 630. Each 16x 16 block 630 can include four 8x8 blocks 640. Each 8x8 block 640 can include four 4x4 blocks 650. Each 4x4 block 650 can include 16 pixels, which can be represented in four rows and four columns in each respective block in the Cartesian plane or matrix. The pixels can include information representing an image captured in the frame, such as luminance information, color information, and location information. In an example, a block, such as a 16x l6-pixel block as shown, can include a luminance block 660, which can include luminance pixels 662; and two chrominance blocks 670 / 680, such as a U or Cb chrominance block 670, and a V or Cr chrominance block 680. The chrominance blocks 670 / 680 can include chrominance pixels 690. For example, the luminance block 660 can include 16x 16 luminance pixels 662, and each chrominance block 670 / 680 can include 8x8 chrominance pixels 690, as shown. Although one arrangement of blocks is shown, any arrangement can be used. Although FIG. 6 shows NxN blocks, in some implementations, NXM, where N M, blocks can be used. For example, 32x64 blocks, 64x32 blocks, 16x32 blocks, 32x 16 blocks, or any other size blocks can be used. In some implementations, Nx2N blocks, 2NxN blocks, or a combination thereof can be used.

[0075] In some implementations, video coding can include ordered block-level coding. Ordered block-level coding can include coding blocks of a frame in an order, such as rasterscan order, wherein blocks can be identified and processed starting with a block in the upper left corner of the frame, or a portion of the frame, and proceeding along rows from left to right and from the top row to the bottom row, identifying each block in turn for processing. For example, the superblock in the top row and left column of a frame can be the first block coded, and the superblock immediately to the right of the first block can be the second block coded. The second row from the top can be the second row coded, such that the superblock in the left column of the second row can be coded after the superblock in the rightmost column of the first row.

[0076] In an example, coding a block can include using quad-tree coding, which can include coding smaller block units with a block in raster-scan order. The 64x64 superblock shown in the bottom-left comer of the portion of the frame shown in FIG. 6, for example, can be coded using quad-tree coding in which the top-left 32x32 block can be coded, then the top-right 32x32 block can be coded, then the bottom-left 32x32 block can be coded, and thenthe bottom-right 32^32 block can be coded. Each 32x32 block can be coded using quad-tree coding in which the top-left 16x 16 block can be coded, then the top-right 16x 16 block can be coded, then the bottom-left 16x 16 block can be coded, and then the bottom-right 16x 16 block can be coded. Each 16x 16 block can be coded using quad-tree coding in which the top-left 8x8 block can be coded, then the top-right 8x8 block can be coded, then the bottom-left 8x8 block can be coded, and then the bottom-right 8x8 block can be coded. Each 8x8 block can be coded using quad-tree coding in which the top-left 4x4 block can be coded, then the topright 4x4 block can be coded, then the bottom-left 4x4 block can be coded, and then the bottom-right 4x4 block can be coded. In some implementations, 8x8 blocks can be omitted for a 16x 16 block, and the 16x 16 block can be coded using quad-tree coding in which the top-left 4x4 block can be coded, and then the other 4x4 blocks in the 16x 16 block can be coded in raster-scan order.

[0077] In an example, video coding can include compressing the information included in an original, or input, frame by omitting some of the information in the original frame from a corresponding encoded frame. For example, coding can include reducing spectral redundancy, reducing spatial redundancy, reducing temporal redundancy, or a combination thereof.

[0078] In an example, reducing spectral redundancy can include using a color model based on a luminance component (Y) and two chrominance components (U and V or Cb and Cr), which can be referred to as the YUV or YCbCr color model or color space. Using the YUV color model can include using a relatively large amount of information to represent the luminance component of a portion of a frame and using a relatively small amount of information to represent each corresponding chrominance component for the portion of the frame. For example, a portion of a frame can be represented by a high-resolution luminance component, which can include a 16x 16 block of pixels, and by two lower resolution chrominance components, each of which representing the portion of the frame as an 8x8 block of pixels. A pixel can indicate a value (e.g., a value in the range from 0 to 255) and can be stored or transmitted using, for example, eight bits. Although this disclosure is described with reference to the YUV color model, any color model can be used.

[0079] FIG. 7 is a flowchart of an example of a technique 700 for applying BAWP when decoding a current block. The technique 700 can be implemented, for example, as a software program that may be executed by computing devices such as transmitting station 102 or receiving station 106. The software program can include machine-readable instructions that may be stored in a memory such as the memory 204 or the secondary storage 214, and that,when executed by a processor, such as the processor 202, may cause the computing device to perform the technique 700. The technique 700 may be implemented in whole or in part in the intra / inter prediction stage 508 of the decoder 500 of FIG. 5. The technique 700 can be implemented using specialized hardware or firmware. Multiple processors, memories, or both, may be used.

[0080] The technique 700 can be used when decoding a current block of a current frame. As described with respect to FIG. 6, the current block can include a luminance block, which can include luminance pixels; and two chrominance blocks, such as a U or Cb chrominance block, and a V or Cr chrominance block. As mentioned, the disclosure is not limited to these color spaces and others are possible. Luminance Y pixels, chrominance U pixels, and chrominance U pixels may also be respectively referred to as the luma Y plane, chroma U plane, and chroma V plane.

[0081] In an example, B AWP can be applied to any block. In an example, BAWP can be applied only to blocks that are larger than or equal to a threshold luma size (e.g., 8^8) and coded in single inter prediction mode.

[0082] The technique 700 derives weight factor ay for the Y plane by using luma pixel values and reuses the weight factor ay for the chroma U and / or V planes. That is, and as further described herein, au = av = ay. A respective offset P (i.e., PY and Pu and / or Pv) are calculated for each of the color components by referring to the pixel values from the respective color component planes.

[0083] At 702, the technique 700 determines that BAWP is to be performed with respect to the luma Y component (i.e., the luma block of the current block) and a chroma component (i.e., a chroma block of the current block). The chroma component can be at least one of the chroma U component or the chroma V component of the current block.

[0084] The technique 700 can decode from a compressed bitstream, such as the compressed bitstream 420 of FIG. 5, one or more syntax elements (e.g., flags) indicating which of the color components BAWP is to be applied to.

[0085] The syntax elements may be decoded from a header of the current block or from a header of a group of blocks. As such, BAWP is to be applied according to the syntax elements to each of the blocks of the group of blocks. The group of blocks can be all of the blocks of the current frame. The group of blocks can be a tile of the current frame. As is known, a tile can be a rectangular region within the current frame that includes a group of blocks and can be independently decoded from other tiles of the current frame. The group of blocks can be a segment of the current frame. A segment is a group of blocks of the currentframe that may not be consecutive and that may not fit into a rectangular area. The group of blocks can be a superblock (e.g., a macroblock or a largest coding unit). A superblock can be a largest possible partition, which may be further partitioned in sub-blocks. A superblock can have a size of 64x64, 128x 128 luma pixels, or some other size.

[0086] As a general case, the syntax elements can include one or more of the syntax elements bawp_y, bawp_u, and bawp_v, which indicate, respectively, whether BAWP is to applied for the Y, U, and V components.

[0087] In a first example, whether flags for performing BAWP for the chroma components are signaled depends on whether BAWP is to be performed for the luma component. That is, if BAWP is not performed for the luma component, then BAWP is not performed for any of the chroma components. That is, BAWP may be minimally applied to the luma component. This first example is summarized in the pseudocode of Table I.

[0088] In a second example, a flag (bawp) indicates whether BAWP is to be applied to at least one of the Y, U, and V components. If BAWP is to be applied to at least one of the Y, U, and V components, then separate flags (bawp_y, bawp_u, and bawp_v) can indicate which of the components BAWP will be applied to. This second example is summarized in the pseudocode of Table II.

[0089] In a third example, which is a variation on the second implementation, a flag (bawp) indicates whether BAWP is to be applied to at least one of the Y, U, and V components. If BAWP is to be applied to at least one of the Y, U, and V components, then separate flags (bawp_y, bawp_u, and bawp_v) can indicate which of the components BAWP will be applied to. However, the bawp_v flag can be inferred to be set (=1) if thebawp_y and bawp_u flags are not set. This third example is summarized in the pseudocode of Table III.

[0090] In a fourth example, syntax elements bawp_y and bawp_uv, which indicate, respectively, whether BAWP is applied to luma Y and to both of the chroma U and V components, may be used. Whether the syntax element bawp_uv is signaled depends on whether BAWP is performed on luma component. This fourth example is summarized in the pseudocode of Table IV.

[0091] In yet another example, each of syntax elements bawp_y, bawp_u, and bawp_v may be separately encoded. That is, the three separate block-level (of group-of-block-level) flags can be separately and unconditionally signaled to specify whether BAWP is used for each of the Y, U, and V components. In yet another example, one block-level flag may be used to control whether BAWP is applied for all three of the Y, U, and V components. However, the Y, U, and V planes may exhibit different behaviors or characteristics with respect to illuminance, which may result in adding a large cost associated with the one component to the total rate-distortion cost, which may in turn skew the rate-distortion optimization process and worsen the compression performance.

[0092] The technique 700 is described based on a case that the BAWP is to be applied to the luma component (i.e., bawp_y = 1) and at least one of the chroma components U or V (i.e., bawp_u = 1 and / or bawp_v = 1). That is, at 702, the technique 700 determines that bawp_y = 1 and that bawp u = 1 and / or bawp v = 1.

[0093] At 704, a weight factor ay and an offset PY are obtained (e.g., calculated). The weight factor ay and the offset PY are obtained based on causal luma neighboring samples of the current block. The causal luma neighboring samples can be or include any reconstructed luma pixels peripheral to the current block. In an example, one line from top (above) and one column from left reconstructed samples of the current block and their corresponding luma samples in a reference frame can be used in the calculation of the weight factor ay and the offset PY. In an example, the integer pel motion vector (MV) of the current block is used in the calculation (e.g., derivation) of the weight factor ay and the offset PY. Causal neighboring samples are further described with respect to FIG. 8.

[0094] The weight factor ay and the offset PY can be derived (at both the encoder and the decoder) by minimizing the summation of square errors of equation (2). In equation (2), Re cY, neigh and Refy, neigh are, respectively, the reconstructed pixels of the causal luma neighboring samples and the corresponding reference luma samples in a reference frame.

[0095] The pseudocode of Table V can be used to derive the value of weight factor ay and the offset pY, where DIV LUT PREC BITS = 14, DIV LUT BITS = 8, and CONST = 5.Table V

[0096] At 706, an offset P (i.e., (3Chroma) is obtained for the chroma component based on the luma weight ay. In an example, a respective offset P is obtained for each of the chroma components for which BAWP is to be applied. Thus, the technique 706 may obtain an offset Pu for the chroma U component, an offsetfor the chroma V component, or both. The offset Pu and / or offsetvalues can be derived (similarly at both the encoder and the decoder) by minimizing the summation of square errors of equations (3) and (4) respectively.

[0097] In equation (3), RecU neighand RefUineighare, respectively, the reconstructed pixels of the causal chroma U neighboring samples and the corresponding reference chroma U samples in the reference frame; and, in equation (4), RecV neighand RefVineighare,respectively, the reconstructed pixels of the causal chroma V neighboring samples and the corresponding reference chroma V samples in the reference frame.

[0098] At 708, (final) prediction blocks are obtained for the luma Y component and the chroma component. The final prediction block corresponding to the luma block of the current block can be obtained using equation (1). Similarly, for the chroma component for which BAWP is determined to be applied, the (final) prediction block is also obtained using equation (1').

[0099] In equation (1 '), Predchroma orgdenotes a prediction block obtained for the chroma component according to conventional techniques and according to a prediction mode (which may be decoded from the compressed bitstream) associated with chroma block; and Predchroma bawpis the final prediction block for the chroma component.

[0100] As such, a final prediction block for the luma component is obtained based on the luma weight ay and the luma offset PY; and the final prediction block for the chroma component is obtained based on the luma weight ay and the offset P (i.e., / 3Chroma)- With respect to any chroma component to which BAWP is not be applied, then Predchroma orgof equation (1') is the final prediction block.

[0101] The prediction block(s) are used to obtain the current block. For example, respective residual blocks for each of the Y and U and / or V components may be decoded from the compressed bitstream and added to the respective (final) prediction blocks.

[0102] While FIG. 7 is described from a decoder perspective, at an encoder, such as the encoder 400 of FIG. 4, additional rate-distortion (RD) checks can be added for the coding blocks for which the BAWP mode is applicable. The motion information of BAWP off case is re-used for the BAWP mode and, therefore, no additional motion estimation process is introduced. In an example, the encoder may perform (e.g., conduct) a new motion search when BAWP is to be applied to a block. Performing the additional motion search may result in the identification of refined motion information (e.g., a refined motion vector) for BAWP at the cost of complexity increment at encoder side.

[0103] The encoder performs calculations as described with respect to the pseudocode of Table V (corresponding to equations (2)-(4)) and obtains the (final) prediction blocks according to equation (1) for each of the luma and chroma U and / or chroma Y blocks. Based on the RD analysis, the encoder encodes in a compressed bitstream, such as the bitstream 420 of FIG. 4, one or more syntax elements indicating whether BAWP is to be performed, withrespect to which color components, and how weight and the offset are to be calculated or reused.

[0104] FIG. 8 illustrates an example 800 of causal neighboring samples of a current block. The example 800 includes a current block 802 of a current frame (not shown). The current block includes top reconstructed neighboring blocks (e.g., blocks 804 and 806) and left reconstructed neighboring blocks (e.g., a block 816). While the example 800 shows two top (i.e., above) reconstructed neighboring blocks and one left reconstructed neighboring block, the disclosure is not so limited and other arrangements of reconstructed neighboring blocks are possible depending on an encoder determines to partition blocks of the current frame into sub-blocks.

[0105] The current block 802 is inter predicted based on an MV 812 and a reference block 810 of a reference frame (not shown). The MV 812 and reference frame can be decoded from a compressed bitstream. The current block 802 can be a luma or a chroma block. Thus, in the case that the current block 802 is a Y, U, or V block, then the reference block 810 is also a Y, U, or V block, respectively,

[0106] The causal neighboring samples (i.e., Recneighin equation (2)) is typically a subset of the pixels of the reconstructed neighboring blocks. In an example, the causal neighboring samples includes M number of rows of pixels of the top reconstructed neighboring blocks and N number of columns of the left reconstructed neighboring block. In an example, and to reduce computational complexity, M and N can be 1 (i.e., M=N=1). The causal neighboring samples are those pixels between a line 814 and to the right of a line 816.

[0107] The reference area (or set of pixels) in the reference frame corresponding to the causal neighboring samples is identified based on the MV 812 of the current block. Thus, as illustrated by MVs 818A and 818B (which can be equal to the MV 812), reference pixels 820 and 822 are identified. The collection of pixels of the reference area (i.e., the reference pixels 820 and 822) is denoted Refneighin equation (2).

[0108] In some situations, the MV 812 may be a fractional MV. That is, the MV 812 may represent a displacement that is less than one pixel, which means that the MV 812 can point to a location in the reference frame that is not aligned with the pixel grid (i.e., an integer pixel). In an example, and to reduce complexity, the MVs 818A and 818B can be obtained from the MV 812 by rounding the MV 812 to the nearest integer pixel location. As such, no interpolation filters need be applied to calculate the pixels in the reference area.

[0109] FIG. 9 is a flowchart of an example of a technique 900 for applying BAWP when decoding a current block. The technique 900 can be implemented, for example, as a software program that may be executed by computing devices such as transmitting station 102 or receiving station 106. The software program can include machine-readable instructions that may be stored in a memory such as the memory 204 or the secondary storage 214, and that, when executed by a processor, such as the processor 202, may cause the computing device to perform the technique 900. The technique 900 may be implemented in whole or in part in the intra / inter prediction stage 508 of the decoder 500 of FIG. 5. The technique 900 can be implemented using specialized hardware or firmware. Multiple processors, memories, or both, may be used.

[0110] At 902, is it determined that BAWP is to be performed with respect to at least a first color component and a second color component of a current block.[OHl] One or more syntax elements can be decoded from an compressed bitstream, such as the compressed bitstream 420 of FIG. 5, indicating whether a weight factor a is to be reused, whether an offset value P is to be reused, with respect to which color component s) (i.e., using which color component(s) pixel values of the current block) the weight factor a is to be obtained, and / or with respect to which color component(s) (i.e., using which color component s) pixel values of the current block) the offset value P is to be obtained. In an example, the one or more syntax elements may be an n-bit (where n > 2) syntax element that can be used to convey 2npossibilities. However, other ways of signaling are possible. The one or more syntax elements can be decoded from a header associated with the current block or from a header associated with a group of blocks.

[0112] In an example, the one or more syntax elements can indicate that weight factor avis to be derived from the chroma U plane pixel values and is to be reused on the V plane and that the offset values ftu andfor the chroma U and the chroma V plans, respectively, are then to be derived separately using the respective chroma U and chroma V pixel values of the current block. Said another way, avis derived from chroma U plane pixel values and reused on the V chroma plane; and ftuare then derived separately from the respective chroma U and chroma V pixel values.

[0113] In an example, the one or more syntax elements can indicate that one weight factor a is to be derived for the chroma U and chroma V planes by using pixel values from both the chroma U and the chroma V planes and that the offset values flu andfor the chroma U and the chroma V plans, respectively, are then to be derived separately using therespective chroma U and chroma V pixel values of the current block. Said another way, one single weight factor a is to be derived for the chroma U and the chroma V planes using pixel values from the chroma U and chroma V planes of the current block. puare then derived separately from the respective chroma U and chroma V pixel values. The offsets g can be derived using equations (3) and (4). In an example, the single weight factor a can be derived by minimizing the summation of square errors of equation (5).

[0114] As can be appreciated, equation (5), and other equations herein, can be expressed in other ways. For example, the minimization problem of equation (5) can be expressed as:

[0115] In an example, the one or more syntax elements can indicate that one weight factor a and one offset value are to be derived for the chroma U and chroma V planes by using pixel values from both the chroma U and the chroma V planes. Said another way, one single weight factor a and one single offset value are derived for the chroma U and the chroma V planes of the current block by using pixel values from the chroma U and the chroma V planes. In an example, the weight factor a and the offset value can be derived by minimizing the summation of square errors of equation (6):

[0116] As can be appreciated, equation (6) can be expressed in other ways. For example, the minimization problem of equation (6) can be expressed as:

[0117] In an example, the one or more syntax elements can indicate that one weight factor a and one offset value are to be derived for the luma Y, the chroma U, and the chroma V planes by using pixel values from the luma Y, the chroma U, and the chroma V planes. That is, one single a and one single are derived for the Y, U and V planes by using the pixel values from all of the three planes. In an example, the weight factor a and the offset value P can be derived by minimizing the summation of square errors of equation (7):

[0118] As can be appreciated, equation (7) can be expressed in other ways. For example, the minimization problem of equation (7) can be expressed as:

[0119] In an example, the one or more syntax elements can indicate that one weight factor a is to be derived for the luma Y, the chroma U, and chroma V planes by using pixel values from the luma Y, the chroma U, and the chroma V planes and that he offset values ftY, fi ,, for the chroma Y, the chroma U, and the chroma V plans, respectively, are then to be derived separately using the respective luma Y, chroma U, and chroma V pixel values of the current block. Said another way one single alpha for the Y, U, and V planes is derived by using the pixel values from all of the Y, U, and V planes, and that Y, U and V planes then a respective offset value is derived for each of the Y, U, and V planes based on the pixel values of the plane.

[0120] At 904, A weight a and a first offset Pi are obtained for the first color component. At 906, a second offset P2 is obtained for the second component. The second offset P2 can be obtained based on the weight a. At 908, a first prediction block is obtained for the first color component using BAWP based on the weight a and the first offset Pi. At 910, a second prediction block is obtained for the second color component using BAWP based on the weight a and the second offset P2.

[0121] In an example, the first color component can be the luma Y color component and the second color component is a chroma U (or V) component. As such, the weight a can be ay and can be obtained based on the pixel values of the luma Y plane of the current block as described herein. The weight ay can be reused with / for the second color component - the chroma U (or V) component. An offset Pu (or Pv) can be obtained using the pixel values of the chroma U (or V) plane.

[0122] In an example, the first color component can be the chroma U component and the second color component can be the chroma V component. The weights and offsets can be as described with respect to equation (5). As such, the technique 900 obtains a single weight a value and separate fig (e.g., the first offset Pi) and(e.g., the second offset P2) values.

[0123] In an example, the first color component can be a chroma U component and the second color component can be the chroma V component. The weights and offsets can be as described with respect to equation (6). As such, the technique 900 obtains a single weight avalue and a single offset P value. That is, the first offset Pi and the second offset P2 can be the same value. As such, at 906, obtaining the second offset P2 for the second component can mean setting the second offset P2 to the first offset Pi or using the first offset Pi for the second offset P2.

[0124] In an example, the weight a and the first offset Pi can be obtained using the pixel values from luma Y, the chroma U, and the chroma V planes, as described with respect to equation (6). As such, at 906, obtaining the second offset P2 for the second component can mean setting the second offset P2 to the first offset Pi or using the first offset Pi for the second offset P2.

[0125] In an example, the first color component can be the luma Y color component, and the second color component can include the chroma U component and the chroma V component. The weight a can be obtained using the pixel values from the luma Y, the chroma U, and the chroma V planes; the first offset Pi can be PY and can be obtained based on luma Y pixel values. The first offset P2 can comprise a first chroma offset Pu and a second chroma offset Pv. Each of the offsets PY, PU, and Pv can be obtained respective pixels of the corresponding plane of the current block.

[0126] The pseudocode of Table V can be adapted to the different ways described with respect to FIG. 9 for obtaining weights and offsets.

[0127] In some implementations, the chroma B AWP can be exclusively applied to blocks that are larger than or equal to 8x8 in size and are coded using single inter prediction mode. This selective application ensures that the BAWP is effectively utilized for blocks where it can provide significant benefits without unnecessary computational overhead for smaller blocks.

[0128] In some implementations, the decisions for the U plane and V plane are made together and are only evaluated when the BAWP flag for the Y plane (bawp_y) is true. If the bawp_y flag is determined to be false for a particular block, the bawp_uv flag is automatically set to false. However, if the bawp_y flag is true, the bawp_uv flag is then read to decide whether BAWP is to be applied to the Chroma planes.

[0129] In some implementations, for the derivation of block-level weighted prediction parameters for the U and V planes, av and ?Y for the Y plane are calculated and then av is reused for the U and V planes (i.e., au = av = <ZY). Subsequently, ?u and ?v can be independently calculated by computing the means of the neighboring chroma reconstructed samples and the chroma reference samples.

[0130] In some implementations, an encoder, such as the encoder 400 of FIG. 4 determines whether BAWP is applied and, if so, to which planes. The encoder performs such a determination based on rate-distortion analysis. As is known, a rate-distortion value refers to a ratio that balances an amount of distortion (e.g., a loss in video quality) with rate (e.g., a number of bits) for coding a block or other video component. As such, the scheme that minimizes the rate-distortion value to encode the video block is selected. The encoder may perform rate-distortion analyses corresponding to the following combination of flag values: 1) bawp y = bawp uv = 0; 2) bawp y = 1 and bawp uv = 0; and 3) bawp y = bawp uv = 1.

[0131] For simplicity of explanation, the techniques 700 and 900 of FIGS. 7 and 9, respectively, are each depicted and described as a respective series of steps or operations. However, the steps or operations in accordance with this disclosure can occur in various orders and / or concurrently. Additionally, other steps or operations not presented and described herein may be used. Furthermore, not all illustrated steps or operations may be required to implement a technique in accordance with the disclosed subject matter.

[0132] The aspects of encoding and decoding described above illustrate some examples of encoding and decoding techniques. However, it is to be understood that encoding and decoding, as those terms are used in the claims, could mean compression, decompression, transformation, or any other processing or change of data.

[0133] The word “example” is used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as “example” is not necessarily to be construed as being preferred or advantageous over other aspects or designs. Rather, use of the word “example” is intended to present concepts in a concrete fashion. As used in this application, the term “or” is intended to mean an inclusive “or” rather than an exclusive “or.” That is, unless specified otherwise or clearly indicated otherwise by the context, the statement “X includes A or B” is intended to mean any of the natural inclusive permutations thereof. That is, if X includes A; X includes B; or X includes both A and B, then “X includes A or B” is satisfied under any of the foregoing instances. In addition, the articles “a” and “an” as used in this application and the appended claims should generally be construed to mean “one or more,” unless specified otherwise or clearly indicated by the context to be directed to a singular form. Moreover, use of the term “an implementation” or the term “one implementation” throughout this disclosure is not intended to mean the same embodiment or implementation unless described as such.

[0134] Implementations of the transmitting station 102 and / or the receiving station 106 (and the algorithms, methods, instructions, etc., stored thereon and / or executed thereby, including by the encoder 400 and the decoder 500) can be realized in hardware, software, or any combination thereof. The hardware can include, for example, computers, intellectual property (IP) cores, application-specific integrated circuits (ASICs), programmable logic arrays, optical processors, programmable logic controllers, microcode, microcontrollers, servers, microprocessors, digital signal processors, or any other suitable circuit. In the claims, the term “processor” should be understood as encompassing any of the foregoing hardware, either singly or in combination. The terms “signal” and “data” are used interchangeably. Further, portions of the transmitting station 102 and the receiving station 106 do not necessarily have to be implemented in the same manner.

[0135] Further, in one aspect, for example, the transmitting station 102 or the receiving station 106 can be implemented using a general-purpose computer or general-purpose processor with a computer program that, when executed, carries out any of the respective methods, algorithms, and / or instructions described herein. In addition, or alternatively, for example, a special purpose computer / processor can be utilized which can contain other hardware for carrying out any of the methods, algorithms, or instructions described herein.

[0136] The transmitting station 102 and the receiving station 106 can, for example, be implemented on computers in a video conferencing system. Alternatively, the transmitting station 102 can be implemented on a server, and the receiving station 106 can be implemented on a device separate from the server, such as a handheld communications device. In this instance, the transmitting station 102, using an encoder 400, can encode content into an encoded video signal and transmit the encoded video signal to the communications device. In turn, the communications device can then decode the encoded video signal using a decoder 500. Alternatively, the communications device can decode content stored locally on the communications device, for example, content that was not transmitted by the transmitting station 102. Other suitable transmitting and receiving implementation schemes are available. For example, the receiving station 106 can be a generally stationary personal computer rather than a portable communications device, and / or a device including an encoder 400 may also include a decoder 500.

[0137] Further, all or a portion of implementations of the present disclosure can take the form of a computer program product accessible from, for example, a computer-usable or computer-readable medium. A computer-usable or computer-readable medium can be any device that can, for example, tangibly contain, store, communicate, or transport the programfor use by or in connection with any processor. The medium can be, for example, an electronic, magnetic, optical, electromagnetic, or semiconductor device. Other suitable mediums are also available.

[0138] The above-described embodiments, implementations, and aspects have been described to facilitate easy understanding of this disclosure and do not limit this disclosure. On the contrary, this disclosure is intended to cover various modifications and equivalent arrangements included within the scope of the appended claims, which scope is to be accorded the broadest interpretation as is permitted under the law to encompass all such modifications and equivalent arrangements.

Claims

What is claimed is:

1. A method, comprising: determining that block-level adaptive weighted prediction (BAWP) is to be performed with respect to a luma component of a current block and a chroma component of the current block; obtaining a luma weight ay and a luma offset PY for the luma component; obtaining an offset P for the chroma component using the luma weight ay; and obtaining final prediction blocks for the luma component and the chroma component based on the luma weight ay, the luma offset PY, and the offset p.

2. The method of claim 1, wherein obtaining the final prediction blocks for the luma component and the chroma component based on the luma weight ay, the luma offset PY, and the offset P comprises: obtaining a first final prediction block for the luma component based on the luma weight ay and the luma offset PY; and obtaining a second final prediction block for the chroma component based on the luma weight ay and the offset p.

3. The method of any one of claims 1 to 2, wherein the chroma component is at least one of a chroma U component or chroma V component of the current block.

4. The method of any one of claims 1 to 3, wherein obtaining the luma weight ay comprises: obtaining the luma weight ay and the luma offset PY by minimizing a summation of squared errors between reconstructed luma pixels and reference luma pixels.

5. The method of any one of claims 1 to 4, wherein obtaining the offset P for the chroma component using the luma weight ay comprises: obtaining the offset P for the chroma component by minimizing a summation of squared errors between reconstructed chroma pixels and reference chroma pixels.

6. The method of any one of claims 1 to 5, further comprising: setting a chroma weight for the chroma component to the luma weight ay.

7. The method of any one of claims 1 to 6, further comprising: decoding, from a compressed bitstream, a first flag indicating that BAWP is to be performed with respect to the luma component; and decoding, from the compressed bitstream, a second flag indicating that BAWP is to be performed with respect to the luma component.

8. The method of any one of claims 1 to 7, wherein an encoder performed ratedistortion checks to determine that BAWP is to be performed with respect to the luma component and the chroma component.

9. A method, comprising: determining that a block-level adaptive weighted prediction (BAWP) is to be performed with respect to a first color component and a second color component of a current block; obtaining a weight a and a first offset Pi for the first color component; obtaining a second offset P2 for the second color component; obtaining a first final prediction block of the first color component using BAWP based on the weight a and the first offset Pi; and obtaining a second final prediction block of the second color component using BAWP based on the weight a and the second offset P2.

10. The method of claim 9, wherein the first color component is a luma Y color component, and the second color component is at least one of a chroma U or V component, wherein the weight a is obtained based on pixel values of a luma Y plane of the current block, wherein the second final prediction block is obtained based on the weight a, and wherein the second offset P2 is obtained using pixel values of a color plane corresponding the second color component.

11. The method of any one of claims 9 to 10, wherein the first color component is a chroma U component and the second color component is a chroma V component.

12. The method of claim 11, wherein obtaining the second offset P2 for the second color component comprises: setting the second offset P2 to the first offset Pi.

13. The method of any one of claims 9 to 12, wherein the first color component is a luma Y component and the second color component includes a chroma U component and a chroma V component, and wherein the weight a and the first offset Pi are obtained using respective pixel values from a luma Y plane, a chroma U plane, and a chroma V plane of the current block.

14. The method of claim 13, wherein the second offset P2 is set to the first offset Pi-15. The method of any one of claims 9 to 14, wherein the weight a is obtained by minimizing a summation of squared errors between reconstructed pixels and reference pixels for the first color component.

16. The method of any one of claims 9 to 15, further comprising: decoding, from a compressed bitstream, a first flag indicating that BAWP is to be performed with respect to the first color component; and decoding, from the compressed bitstream, a second flag indicating that BAWP is to be performed with respect to the second color component.

17. The method of any one of claims 9 to 16, wherein the first final prediction block is obtained by applying the weight a and the first offset Pi to an intermediate prediction block for the first color component.

18. The method of any one of claims 9 to 17, wherein the second final prediction block is obtained by applying the weight a and the second offset P2 to an intermediate prediction block for the second color component.

19. A device, comprising: a processor that is configured to perform the method of any one of claims 1 to 18.

20. A device, comprising: a memory; and a processor, the processor configured to execute instructions stored in the memory to perform the method of any one of claims 1 to 18.

21. A non-transitory computer-readable storage medium, comprising executable instructions that, when executed by a processor, facilitate performance of operations, comprising operations that perform the method of any one of claims 1 to 18.

22. A non-transitory computer-readable storage medium having stored thereon an encoded bitstream, wherein the encoded bitstream is configured for decoding by the method of any one of claims 1 to 18.

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