Methods for signaling virtual boundaries and wrap-around motion compensation

Abstract

To provide methods for picture processing.SOLUTION: The methods can include: receiving a bitstream comprising a set of pictures; determining, according to the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures; in response to the virtual boundary being signaled at the sequence level, determining a position of the virtual boundary for the set of pictures, the position being bounded by a range signaled in the received bitstream; and disabling in-loop filtering operations across the virtual boundary.SELECTED DRAWING: Figure 7A

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This disclosure claims priority to U.S. Provisional Patent Application No. 62 / 954,828, filed December 30, 2019, the entire contents of which are incorporated herein by reference.

[0002] Technical Field FIELD OF THE DISCLOSURE

[0002] This disclosure relates generally to video processing, and more particularly to methods for signaling virtual boundaries and wraparound motion compensation. [Background technology]

[0003] background

[0003] A video is a set of static pictures (or "frames") that capture visual information. To reduce storage memory and transmission bandwidth, a video can be compressed before storage or transmission and decompressed before display. The compression process is usually referred to as encoding, and the decompression process is usually referred to as decoding. There are various video coding formats that use standardized video coding techniques, most commonly based on prediction, transform, quantization, entropy coding, and in-loop filtering. Standardization organizations have developed video coding standards that specify specific video coding formats, such as the High Efficiency Video Coding (HEVC / H.265) standard, the Versatile Video Coding (VVC / H.266) standard, and the AVS standard. As more and more advanced video coding techniques are adopted into video standards, the coding efficiency of new video coding standards becomes higher. Summary of the Invention [Means for solving the problem]

[0004] This disclosure provides a method for picture processing, which may include receiving a bitstream including a set of pictures, determining, according to the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures, determining, in response to the virtual boundary being signaled at the sequence level, a position of the virtual boundary for the set of pictures, the position being constrained by a range signaled in the received bitstream, and disabling in-loop filtering operations that cross the virtual boundary.

[0005]

[0005] Embodiments of the present disclosure further provide an apparatus for picture processing, which may include a memory that stores a set of instructions and one or more processors, the one or more processors being configured to execute the set of instructions to cause the apparatus to receive a bitstream including a set of pictures, determine, in accordance with the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures, in response to the virtual boundary being signaled at the sequence level, determine a position of the virtual boundary for the set of pictures, the position being bounded by a range signaled in the received bitstream, and disable in-loop filtering operations that cross the virtual boundary.

[0006]

[0006] An embodiment of the present disclosure further provides a non-transitory computer-readable medium storing a set of instructions, the set of instructions being executable by at least one processor of a computer to cause the computer to perform a picture processing method, the method including receiving a bitstream including a set of pictures; determining, according to the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures; determining, in response to the virtual boundary being signaled at the sequence level, a position of the virtual boundary for the set of pictures, the position being limited by the range signaled in the received bitstream; and disabling in-loop filtering operations that cross the virtual boundary.

[0007] BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Embodiments and various aspects of the present disclosure are illustrated in the following detailed description and the accompanying drawings, in which the various features shown are not drawn to scale. [Brief explanation of the drawings]

[0008] [Figure 1] 8 illustrates the structure of an exemplary video sequence according to some embodiments of the present disclosure. [Figure 2A]

[0009] 1 shows a schematic diagram of an example encoding process for a hybrid video encoding system, in accordance with some embodiments of the present disclosure. [Figure 2B]

[0010] 1 shows a schematic diagram of another example encoding process of a hybrid video encoding system, in accordance with some embodiments of the present disclosure. [Figure 3A]

[0011] 1 shows a schematic diagram of an example decoding process of a hybrid video coding system, in accordance with some embodiments of the present disclosure. [Figure 3B]

[0012] 1 shows a schematic diagram of another example decoding process of a hybrid video coding system, in accordance with some embodiments of the present disclosure. [Figure 4]

[0013] 1 shows a block diagram of an exemplary device for encoding or decoding video in accordance with some embodiments of the present disclosure. [Figure 5]

[0014] 1 illustrates an example sequence parameter set (SPS) syntax for signaling virtual boundaries, according to some embodiments of the present disclosure. [Figure 6]

[0015] 1 illustrates an example picture header (PH) syntax for signaling virtual boundaries, according to some embodiments of the present disclosure. [Figure 7A]

[0016] 1 illustrates an example horizontal wraparound motion compensation for equirectangular projection (ERP) in accordance with some embodiments of the present disclosure. [Figure 7B]

[0017] 1 illustrates an example horizontal wraparound motion compensation for padded ERP (PERP), according to some embodiments of the present disclosure. [Figure 8]

[0018] 1 illustrates an example syntax for wraparound motion compensation, according to some embodiments of the present disclosure. [Figure 9]

[0019] 1 illustrates an example SPS syntax for signaling maximum picture width and height values, according to some embodiments of the present disclosure. [Figure 10]

[0020] 1 illustrates an example syntax for signaling wraparound motion compensation in accordance with some embodiments of the present disclosure. [Figure 11]

[0021] 1 illustrates an example SPS syntax for signaling virtual boundaries, according to some embodiments of the present disclosure. [Figure 12]

[0022] 10 illustrates another example SPS syntax for signaling virtual boundaries, consistent with some embodiments of the present disclosure. [Figure 13]

[0023] 1 illustrates an example SPS syntax for signaling wraparound motion compensation, according to some embodiments of the present disclosure. [Figure 14]

[0024] 10 illustrates another example SPS syntax for signaling wraparound motion compensation, according to some embodiments of the present disclosure. [Figure 15]

[0025] 1 illustrates an exemplary method for picture processing, according to some embodiments of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0009] Detailed Description

[0026] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which like reference numerals in different drawings represent the same or similar elements unless otherwise indicated. The implementations set forth in the following description of exemplary embodiments do not represent all implementations in accordance with the present disclosure. Rather, they are merely examples of apparatus and methods in accordance with aspects related to the present disclosure as recited in the appended claims. Particular aspects of the present disclosure are described in more detail below. In the event of a conflict with terms and / or definitions incorporated by reference, the terms and definitions provided herein shall control.

[0010]

[0027] As mentioned above, video is a time-sequential arrangement of frames for storing visual information. A video capture device (e.g., a camera) can be used to capture and store these pictures in time sequence, and a video playback device (e.g., a television, a computer, a smartphone, a tablet computer, a video player, or any end-user terminal with a display capability) can be used to display such pictures in time sequence. In addition, in some applications, the video capture device can transmit the captured video in real time to a video playback device (e.g., a computer with a monitor) for supervision, conferencing, live broadcasting, etc.

[0011]

[0028] To reduce the storage space and transmission bandwidth required by such applications, video can be compressed before storage and transmission and decompressed before display. Compression and decompression can be performed by software executed by a processor (e.g., a processor in a general-purpose computer) or by specialized hardware. A module for compression is commonly referred to as an “encoder,” and a module for decompression is commonly referred to as a “decoder.” Collectively, the encoder and decoder may be referred to as a “codec.” The encoder and decoder can be implemented as any of a variety of suitable hardware, software, or combinations thereof. For example, hardware implementations of the encoder and decoder may include circuitry such as one or more microprocessors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), discrete logic, or any combination thereof. Software implementations of the encoder and decoder may include program code, computer-executable instructions, firmware, or any suitable computer-implemented algorithm or process fixed in a computer-readable medium. In some applications, a codec can decompress video from a first encoding standard and recompress the decompressed video using a second encoding standard, in which case the codec may be referred to as a "transcoder."

[0012]

[0029] A video coding process can identify and retain useful information that can be used to reconstruct a picture and ignore information that is not important for reconstruction. If the ignored, unimportant information cannot be perfectly reconstructed, such a coding process may be called "lossy." Otherwise, it may be called "lossless." Most coding processes are lossy; this is a tradeoff to reduce the required storage space and transmission bandwidth.

[0013]

[0030] Useful information about the picture being coded (called the "current picture") includes changes relative to a reference picture (e.g., a previously coded and reconstructed picture). Such changes can include changes in pixel position, brightness, or color, of which position changes are the most important. Changes in the position of a group of pixels representing an object can reflect the movement of the object between the reference picture and the current picture.

[0014]

[0031] A picture that is coded without reference to another picture (i.e., it is its own reference picture) is called an "I-picture." A picture that is coded using a previous picture as a reference picture is called a "P-picture." A picture that is coded using both a previous picture and a future picture as a reference picture (i.e., the references are "bidirectional") is called a "B-picture."

[0015]

[0032] To achieve the same subjective quality as HEVC / H.265 using half the bandwidth, JVET is developing a technology that goes beyond HEVC using the Joint Search Model (JEM) reference software. Because the coding technology was incorporated into JEM, JEM achieved substantially higher coding performance than HEVC.

[0016]

[0033] The VVC standard continues to include more coding techniques that result in better compression performance. VVC is based on the same hybrid video coding system used in modern video compression standards such as HEVC, H.264 / AVC, MPEG2, and H.263. In applications such as 360-degree video, the layout of a particular projection format typically has multiple surfaces. For example, MPEG-I Part 2: Omnidirectional Media Format (OMAF) standardizes a cube-map-based projection format named CMP, which has six surfaces. For projection formats with multiple surfaces, discontinuities occur between two or more adjacent surfaces in a frame-packed picture, regardless of the type of compact frame packing configuration used. If in-loop filtering operations are performed across these discontinuities, surface seam artifacts may become visible in the rendered reconstructed image. To mitigate surface seam artifacts, in-loop filtering operations across discontinuities in a frame-packed picture must be disabled. Virtual boundaries can be configured as a coding tool for 360-degree video to disable in-loop filtering across the virtual boundaries and prevent artifacts.

[0017]

[0034] 1 illustrates the structure of an exemplary video sequence 100 according to some embodiments of the present disclosure. The video sequence 100 may be live video or captured and archived video. The video 100 may be real video, computer-generated video (e.g., computer game video), or a combination thereof (e.g., real video with augmented reality effects). The video sequence 100 may be input from a video capture device (e.g., a camera), a video archive containing previously captured video (e.g., video files stored in a storage device), or a video supply interface (e.g., a video broadcast transceiver) for receiving video from a video content provider.

[0018]

[0035] As shown in FIG. 1, video sequence 100 may include a series of pictures arranged temporally along a timeline, including pictures 102, 104, 106, and 108. Pictures 102-106 are consecutive, with additional pictures between pictures 106 and 108. In FIG. 1, picture 102 is an I-picture, and its reference picture is picture 102 itself. Picture 104 is a P-picture, and its reference picture is picture 102, as indicated by the arrow. Picture 106 is a B-picture, and its reference pictures are pictures 104 and 108, as indicated by the arrows. In some embodiments, the reference picture of a picture (e.g., picture 104) need not immediately precede or follow that picture. For example, the reference picture of picture 104 may be the picture before picture 102. It should be noted that the reference pictures of pictures 102-106 are merely examples, and this disclosure does not limit the reference picture embodiments to the examples shown in FIG.

[0019]

[0036] Typically, video codecs do not encode or decode an entire picture at once due to the computational complexity of such a task. Rather, they may divide a picture into elementary segments and encode or decode the picture segment-by-segment. Such elementary segments are referred to as basic processing units ("BPUs") in this disclosure. For example, structure 110 in FIG. 1 illustrates an example structure for a picture (e.g., any of pictures 102-108) of video sequence 100. In structure 110, the picture is divided into 4x4 basic processing units, the boundaries of which are shown as dashed lines. In some embodiments, the basic processing units may be referred to as "macroblocks" in some video coding standards (e.g., MPEG family, H.261, H.263, or H.264 / AVC) or as "coding tree units" ("CTUs") in some other video coding standards (e.g., H.265 / HEVC or H.266 / VVC). The basic processing units can have any arbitrary shape and size of variable size or pixels in a picture, such as 128x128, 64x64, 32x32, 16x16, 4x8, 16x32, etc. The size and shape of the basic processing unit can be selected based on a balance between coding efficiency and the level of detail to be maintained in the basic processing unit for the picture.

[0020]

[0037] A basic processing unit may be a logical unit that can include groups of different types of video data stored in computer memory (e.g., in a video frame buffer). For example, a basic processing unit for a color picture may include a luma component (Y) that represents colorless luminance information, one or more chroma components (e.g., Cb and Cr) that represent color information, and related syntax elements, where the luma and chroma components may have the same size of the basic processing unit. The luma and chroma components may be referred to as "coding tree blocks" ("CTBs") in some video coding standards (e.g., H.265 / HEVC or H.266 / VVC). Any operation performed on a basic processing unit may be performed repeatedly on each of its luma and chroma components.

[0021]

[0038] Video coding has multiple computational stages, examples of which are shown in detail in Figures 2A-2B and 3A-3B. At each stage, the size of the basic processing unit may still become too large for processing and therefore may be further divided into segments referred to as "basic processing subunits" in this disclosure. In some embodiments, the basic processing subunits may be referred to as "blocks" in some video coding standards (e.g., MPEG family, H.261, H.263, or H.264 / AVC) or as "coding units" ("CUs") in some other video coding standards (e.g., H.265 / HEVC or H.266 / VVC). The basic processing subunits may have the same or smaller size than the basic processing units. Similar to the basic processing units, the basic processing subunits are also logical units that can contain groups of different types of video data (e.g., Y, Cb, Cr, and related syntax elements) stored in computer memory (e.g., in a video frame buffer). Any operation performed on a basic processing sub-unit may be repeatedly performed on each of its luma and chroma components. Note that such division may be performed to further levels as needed for processing. Also note that different stages may use different schemes to divide the basic processing units.

[0022]

[0039] For example, in the mode decision stage (an example of which is shown in detail in FIG. 2B ), the encoder can decide what prediction mode (e.g., intra-picture prediction or inter-picture prediction) to use for a basic processing unit, but the basic processing unit may be too large to make such a decision. The encoder can divide the basic processing unit into multiple basic processing sub-units (e.g., CUs, as in the case of H.265 / HEVC or H.266 / VVC) and decide the type of prediction for each individual basic processing sub-unit.

[0023]

[0040] As another example, in the prediction stage (an example of which is shown in detail in FIGS. 2A-2B), the encoder may perform prediction operations at the level of basic processing sub-units (e.g., CUs). However, in some cases, the basic processing sub-units may still be too large to process. The encoder may further divide the basic processing sub-units into smaller segments (e.g., referred to as "prediction blocks" or "PBs" in H.265 / HEVC or H.266 / VVC), at which level the prediction operations may be performed.

[0024]

[0041] As another example, in the transform stage (an example of which is shown in detail in FIGS. 2A-2B), the encoder may perform transform operations for residual basic processing sub-units (e.g., CUs). However, in some cases, the basic processing sub-units may still be too large to process. The encoder may further divide the basic processing sub-units into smaller segments (e.g., referred to as "transform blocks" or "TBs" in H.265 / HEVC or H.266 / VVC), at which levels the transform operations may be performed. Note that the division scheme of the same basic processing sub-unit may be different in the prediction stage and the transform stage. For example, in H.265 / HEVC or H.266 / VVC, the prediction blocks and transform blocks of the same CU may have different sizes and numbers.

[0025]

[0042] 1, the basic processing units 112 are further divided into 3x3 basic processing sub-units, the boundaries of which are shown as dotted lines. Different basic processing units of the same picture may be divided into basic processing sub-units in different ways.

[0026]

[0043] In some implementations, to provide parallel processing and error resilience capabilities to video encoding and decoding, a picture can be divided into regions for processing, so that the encoding or decoding process does not rely on information about a picture region from any other region of the picture. In other words, each region of a picture can be processed independently. This allows a codec to process different regions of a picture in parallel, thereby increasing coding efficiency. Also, when data for a region is corrupted during processing or lost during network transmission, the codec can correctly encode or decode other regions of the same picture without relying on the corrupted or lost data, thereby providing error resilience. Some video coding standards allow a picture to be divided into different types of regions. For example, H.265 / HEVC and H.266 / VVC provide two types of regions: "slices" and "tiles." It should also be noted that different pictures in video sequence 100 may have different partitioning schemes for dividing the picture into regions.

[0027]

[0044] For example, in Figure 1, structure 110 is divided into three regions 114, 116, and 118, the boundaries of which are shown as solid lines within structure 110. Region 114 includes four basic processing units. Regions 116 and 118 each include six basic processing units. It should be noted that the basic processing units, basic processing subunits, and regions of structure 110 in Figure 1 are merely examples, and the present disclosure does not limit the embodiments thereof.

[0028]

[0045] FIG. 2A shows a schematic diagram of an exemplary encoding process 200A according to an embodiment of the present disclosure. For example, encoding process 200A may be performed by an encoder. As shown in FIG. 2A, the encoder may encode a video sequence 202 into a video bitstream 228 according to process 200A. Similar to video sequence 100 in FIG. 1, video sequence 202 may include a set of pictures (referred to as "original pictures") arranged in a temporal order. Similar to structure 110 in FIG. 1, each original picture of video sequence 202 may be divided into basic processing units, basic processing sub-units, or regions for processing by the encoder. In some embodiments, the encoder may perform process 200A at the level of basic processing units for each original picture of video sequence 202. For example, the encoder may perform process 200A in an iterative manner, in which case the encoder may encode a basic processing unit in one iteration of process 200A. In some embodiments, the encoder may perform process 200A in parallel for a region (eg, regions 114-118) of each original picture of video sequence 202.

[0029]

[0046] 2A , an encoder may provide a fundamental processing unit (referred to as an “original BPU”) of an original picture of a video sequence 202 to a prediction stage 204 to generate prediction data 206 and a predicted BPU 208. The encoder may subtract the predicted BPU 208 from the original BPU to generate a residual BPU 210. The encoder may provide the residual BPU 210 to a transform stage 212 and a quantization stage 214 to generate quantized transform coefficients 216. The encoder may provide the prediction data 206 and the quantized transform coefficients 216 to a binary coding stage 226 to generate a video bitstream 228. Components 202, 204, 206, 208, 210, 212, 214, 216, 226, and 228 may be referred to as a “forward path.” During process 200A, after quantization stage 214, the encoder may provide quantized transform coefficients 216 to inverse quantization stage 218 and inverse transform stage 220 to generate reconstructed residual BPU 222. The encoder may add reconstructed residual BPU 222 to prediction BPU 208 to generate prediction reference 224, which is used in prediction stage 204 for the next iteration of process 200A. Components 218, 220, 222, and 224 of process 200A may be referred to as a "reconstruction path." The reconstruction path may be used to ensure that both the encoder and decoder use the same reference data for prediction.

[0030]

[0047] The encoder may perform process 200A iteratively to encode each original BPU of the original picture (in the forward path) and generate (in the reconstruction path) a prediction reference 224 for encoding the next original BPU of the original picture. After encoding all original BPUs of the original picture, the encoder may proceed to encode the next picture in video sequence 202.

[0031]

[0048] Referring to process 200A, an encoder may receive a video sequence 202 generated by a video capture device (e.g., a camera). As used herein, the term "receive" may refer to receiving, inputting, acquiring, obtaining, getting, reading, accessing, or any act by any method for inputting data.

[0032]

[0049] In the prediction step 204, in the current iteration, the encoder may receive the original BPU and a prediction reference 224, perform a prediction operation, and generate predicted data 206 and a predicted BPU 208. The prediction reference 224 may be generated from a reconstruction path of a previous iteration of the process 200A. The purpose of the prediction step 204 is to reduce information redundancy by extracting predicted data 206, which can be used to reconstruct the original BPU as a predicted BPU 208 from the predicted data 206 and the prediction reference 224.

[0033]

[0050] Ideally, predicted BPU 208 would be identical to the original BPU. However, due to non-ideal prediction and reconstruction operations, predicted BPU 208 generally differs slightly from the original BPU. To record such differences, after generating predicted BPU 208, the encoder can subtract it from the original BPU to generate residual BPU 210. For example, the encoder can subtract pixel values (e.g., grayscale or RGB values) of predicted BPU 208 from corresponding pixel values of the original BPU. Each pixel of residual BPU 210 can have a residual value that is the result of such a subtraction between the corresponding pixel of the original BPU and predicted BPU 208. Compared to the original BPU, predicted data 206 and residual BPU 210 can have fewer bits, which can be used to reconstruct the original BPU without significant quality degradation. Therefore, the original BPU is compressed.

[0034]

[0051] To further compress the residual BPU 210, in the transform stage 212, the encoder can reduce spatial redundancy in the residual BPU 210 by decomposing it into a set of two-dimensional "basis patterns," each associated with a "transform coefficient." The basis patterns can have the same size (e.g., the size of the residual BPU 210). Each basis pattern can represent a change frequency (e.g., a frequency of luminance change) component of the residual BPU 210. None of the basis patterns can be reconstructed from any combination (e.g., a linear combination) of any other basis patterns. In other words, the decomposition can decompose the changes in the residual BPU 210 into the frequency domain. Such a decomposition is similar to a discrete Fourier transform of a function, where the basis patterns are similar to the basis functions (e.g., trigonometric functions) of the discrete Fourier transform, and the transform coefficients are similar to the coefficients associated with the basis functions.

[0035]

[0052] Different transform algorithms can use different basis patterns. For example, various transform algorithms can be used in transform stage 212, such as a discrete cosine transform, a discrete sine transform, or the like. The transform in transform stage 212 is invertible. That is, the encoder can recover residual BPU 210 by inverting the transform (referred to as an "inverse transform"). For example, to recover pixels of residual BPU 210, the inverse transform can multiply the values of corresponding pixels in the basis pattern by their associated coefficients and add the products to generate a weighted sum. For video coding standards, both the encoder and decoder can use the same transform algorithm (and therefore the same basis pattern). Therefore, the encoder can record only the transform coefficients, and the decoder can reconstruct residual BPU 210 from the transform coefficients without receiving the basis pattern from the encoder. Compared to residual BPU 210, the transform coefficients can have fewer bits, but they can be used to reconstruct residual BPU 210 without significant quality degradation. Therefore, the residual BPU 210 is further compressed.

[0036]

[0053] The encoder can further compress the transform coefficients in the quantization stage 214. In the transform process, different basis patterns can represent different change frequencies (e.g., luminance change frequencies). Because the human eye is generally better at perceiving low-frequency changes, the encoder can ignore high-frequency change information without significant quality degradation during decoding. For example, in the quantization stage 214, the encoder can generate quantized transform coefficients 216 by dividing each transform coefficient by an integer value (referred to as a "quantization parameter") and rounding the quotient to its nearest integer. After such an operation, some transform coefficients of high-frequency basis patterns can be converted to zero, and transform coefficients of low-frequency basis patterns can be converted to smaller integers. The encoder can ignore zero-valued quantized transform coefficients 216, thereby further compressing the transform coefficients. The quantization process can also be inverted, in which case the quantized transform coefficients 216 can be reconstructed into transform coefficients in an inverse operation of quantization (referred to as "dequantization").

[0037]

[0054] Because the encoder ignores the remainder of such a division in a rounding operation, quantization stage 214 may be lossy. Typically, quantization stage 214 may contribute the greatest information loss in process 200A. The greater the information loss, the fewer bits the quantized transform coefficients 216 may require. To achieve different levels of information loss, the encoder may use different values of the quantization parameter or any other parameter of the quantization process.

[0038]

[0055] In the binary encoding stage 226, the encoder may encode the prediction data 206 and the quantized transform coefficients 216 using a binary encoding technique, such as, for example, entropy coding, variable length coding, arithmetic coding, Huffman coding, context-adaptive binary arithmetic coding, or any other lossless or lossy compression algorithm. In some embodiments, in addition to the prediction data 206 and the quantized transform coefficients 216, the encoder may encode other information in the binary encoding stage 226, such as, for example, a prediction mode used in the prediction stage 204, parameters of the prediction operation, the type of transform in the transform stage 212, parameters of the quantization process (e.g., quantization parameters), encoder control parameters (e.g., bitrate control parameters), or the like. The encoder may generate a video bitstream 228 using the output data of the binary encoding stage 226. In some embodiments, the video bitstream 228 may be further packetized for network transmission.

[0039]

[0056] Referring to the reconstruction path of process 200A, in an inverse quantization stage 218, the encoder may perform inverse quantization on the quantized transform coefficients 216 to generate reconstructed transform coefficients. In an inverse transform stage 220, the encoder may generate a reconstructed residual BPU 222 based on the reconstructed transform coefficients. The encoder may add the reconstructed residual BPU 222 to a prediction BPU 208 to generate a prediction reference 224 to be used in the next iteration of process 200A.

[0040]

[0057] It should be noted that other variations of process 200A may be used to encode video sequence 202. In some embodiments, the stages of process 200A may be performed in a different order by the encoder. In some embodiments, one or more stages of process 200A may be combined into a single stage. In some embodiments, a single stage of process 200A may be split into multiple stages. For example, transform stage 212 and quantization stage 214 may be combined into a single stage. In some embodiments, process 200A may include additional stages. In some embodiments, process 200A may omit one or more stages in FIG. 2A.

[0041]

[0058] 2B shows a schematic diagram of another exemplary encoding process 200B according to an embodiment of the present disclosure. Process 200B may be modified from process 200A. For example, process 200B may be used by an encoder compliant with a hybrid video coding standard (e.g., the H.26x series). Compared to process 200A, the forward path of process 200B additionally includes a mode decision stage 230 and divides the prediction stage 204 into a spatial prediction stage 2042 and a temporal prediction stage 2044. The reconstruction path of process 200B additionally includes a loop filter stage 232 and a buffer 234.

[0042]

[0059] Generally, prediction techniques can be categorized into two types: spatial prediction and temporal prediction. Spatial prediction (e.g., intra-picture prediction or "intra-prediction") can use pixels from one or more already-encoded neighboring BPUs within the same picture to predict the current BPU. That is, the prediction reference 224 in spatial prediction can include neighboring BPUs. Spatial prediction can reduce the inherent spatial redundancy of a picture. Temporal prediction (e.g., inter-picture prediction or "inter-prediction") can use regions from one or more already-encoded pictures to predict the current BPU. That is, the prediction reference 224 in temporal prediction can include an encoded picture. Temporal prediction can reduce the inherent temporal redundancy of a picture.

[0043]

[0060] Referring to process 200B, within the forward path, the encoder performs prediction operations in a spatial prediction stage 2042 and a temporal prediction stage 2044. For example, in the spatial prediction stage 2042, the encoder may perform intra prediction. For an original BPU of a picture being encoded, the prediction reference 224 may include one or more neighboring BPUs within the same picture that are coded (in the forward path) and reconstructed (in the reconstruction path). The encoder may generate the predicted BPU 208 by extrapolating the neighboring BPUs. Extrapolation techniques may include, for example, linear extrapolation or interpolation, polynomial extrapolation or interpolation, or the like. In some embodiments, the encoder may perform extrapolation at the pixel level, such as by extrapolating, for each pixel of the predicted BPU 208, the value of the corresponding pixel. The neighboring BPUs used for extrapolation can be located relative to the original BPU from various directions, such as vertically (e.g., above the original BPU), horizontally (e.g., to the left of the original BPU), diagonally (e.g., below-left, below-right, above-left, or above-right of the original BPU), or any direction defined in the video coding standard used. For intra prediction, the prediction data 206 may include, for example, the locations (e.g., coordinates) of the neighboring BPUs used, the sizes of the neighboring BPUs used, parameters of the extrapolation, the orientations of the neighboring BPUs used relative to the original BPU, or the like.

[0044]

[0061] As another example, in the temporal prediction stage 2044, the encoder may perform inter-prediction. For the original BPU of the current picture, the prediction reference 224 may include one or more pictures (referred to as "reference pictures") that have been coded (in the forward path) and reconstructed (in the reconstruction path). In some embodiments, the reference pictures may be coded and reconstructed for each BPU. For example, the encoder may add the reconstructed residual BPU 222 to the predicted BPU 208 to generate a reconstructed BPU. When all the reconstructed BPUs of the same picture have been generated, the encoder may generate the reconstructed picture as the reference picture. The encoder may perform a "motion estimation" operation to search for a matching region within a range (referred to as a "search window") of the reference picture. The location of the search window in the reference picture may be determined based on the location of the original BPU of the current picture. For example, the search window may be centered in the reference picture at a location having the same coordinates as the original BPU in the current picture and may extend outward for a predetermined distance. When the encoder identifies a region similar to the original BPU within the search window (e.g., by using a pixel-recursive algorithm, a block-matching algorithm, or the like), the encoder can determine such a region as a matching region. The matching region can have different dimensions than the original BPU (e.g., smaller than, equal to, larger than, or a different shape than the original BPU). Because the reference picture and the current picture are temporally separated in a timeline (e.g., as shown in FIG. 1), the matching region can be considered to "move" to the location of the original BPU over time. The encoder can record the direction and distance of such movement as a "motion vector." When multiple reference pictures are used (e.g., like picture 106 in FIG. 1), the encoder can search for the matching region for each reference picture and determine its associated motion vector. In some embodiments, the encoder can assign weights to the pixel values of the matching region in each matching reference picture.

[0045]

[0062] Motion estimation can be used to identify various types of motion, such as, for example, translation, rotation, zooming, or the like. For inter prediction, prediction data 206 can include, for example, the location (e.g., coordinates) of the matching region, a motion vector associated with the matching region, the number of reference pictures, weights associated with the reference pictures, or the like.

[0046]

[0063] To generate the predicted BPU 208, the encoder may perform a "motion compensation" operation. Motion compensation may be used to reconstruct the predicted BPU 208 based on the prediction data 206 (e.g., a motion vector) and the prediction reference 224. For example, the encoder may shift the matching region of a reference picture according to the motion vector, in which case the encoder may predict the original BPU of the current picture. When multiple reference pictures are used (e.g., as in picture 106 in FIG. 1), the encoder may shift the matching region of the reference picture according to each motion vector and average the pixel values of the matching region. In some embodiments, if the encoder weights the pixel values of the matching region of each matching reference picture, the encoder may add a weighted sum of the pixel values to the shifted matching region.

[0047]

[0064] In some embodiments, inter-prediction can be unidirectional or bidirectional. Unidirectional inter-prediction can use one or more reference pictures in the same temporal direction relative to the current picture. For example, picture 104 in FIG. 1 is a unidirectional inter-predicted picture in which a reference picture (i.e., picture 102) precedes picture 104. Bidirectional inter-prediction can use one or more reference pictures in both temporal directions relative to the current picture. For example, picture 106 in FIG. 1 is a bidirectional inter-predicted picture in which reference pictures (i.e., pictures 104 and 108) are in both temporal directions relative to picture 104.

[0048]

[0065] Still referring to the forward path of process 200B, after spatial prediction 2042 and temporal prediction step 2044, in mode decision step 230, the encoder may select a prediction mode (e.g., one of intra prediction or inter prediction) for the current iteration of process 200B. For example, the encoder may perform a rate-distortion optimization technique. In this technique, the encoder may select a prediction mode to minimize the value of a cost function that depends on the bitrate of the candidate prediction mode and the distortion of the reconstructed reference picture under the candidate prediction mode. Depending on the selected prediction mode, the encoder may generate a corresponding predicted BPU 208 and predicted data 206.

[0049]

[0066] Within the reconstruction path of process 200B, if an intra-prediction mode is selected within the forward path, after generating the prediction reference 224 (e.g., the current BPU coded and reconstructed in the current picture), the encoder can directly provide the prediction reference 224 to the spatial prediction stage 2042 for later use (e.g., for extrapolation of the next BPU of the current picture). If an inter-prediction mode is selected within the forward path, after generating the prediction reference 224 (e.g., the current picture coded and reconstructed in all BPUs), the encoder can provide the prediction reference 224 to the loop filter stage 232, where the encoder can apply a loop filter to the prediction reference 224 to reduce or eliminate distortions (e.g., blocking artifacts) introduced by the inter prediction. The encoder can apply various loop filter techniques within the loop filter stage 232, such as deblocking, sample adaptive offset, adaptive loop filter, or the like. The loop-filtered reference picture may be stored in a buffer 234 (or "decoded picture buffer") for later use (e.g., to be used as an inter-prediction reference picture for a future picture in the video sequence 202). The encoder may store one or more reference pictures in the buffer 234 for use in the temporal prediction stage 2044. In some embodiments, the encoder may encode loop filter parameters (e.g., loop filter strength) along with the quantized transform coefficients 216, the prediction data 206, and other information in the binary encoding stage 226.

[0050]

[0067] FIG. 3A shows a schematic diagram of an exemplary decoding process 300A according to an embodiment of the present disclosure. Process 300A may be a decompression process corresponding to compression process 200A in FIG. 2A. In some embodiments, process 300A may be similar to the reconstruction path of process 200A. A decoder may follow process 300A to decode video bitstream 228 into video stream 304. Video stream 304 may be similar to video sequence 202. However, due to information loss in the compression and decompression processes (e.g., quantization stage 214 in FIGS. 2A-2B), video stream 304 is generally not identical to video sequence 202. Similar to processes 200A and 200B in FIGS. 2A-2B, a decoder may perform process 300A at the level of a basic processing unit (BPU) for each picture encoded in video bitstream 228. For example, the decoder may perform process 300A in an iterative manner, in which case the decoder may decode a basic processing unit in one iteration of process 300A. In some embodiments, the decoder may perform process 300A in parallel for regions (e.g., regions 114-118) of each picture encoded in video bitstream 228.

[0051]

[0068] In FIG. 3A , a decoder may provide a portion of a video bitstream 228 associated with a basic processing unit (referred to as a “coding BPU”) of a coded picture to a binary decoding stage 302. In the binary decoding stage 302, the decoder may decode the portion into prediction data 206 and quantized transform coefficients 216. The decoder may provide the quantized transform coefficients 216 to an inverse quantization stage 218 and an inverse transform stage 220 to generate a reconstructed residual BPU 222. The decoder may provide the prediction data 206 to a prediction stage 204 to generate a prediction BPU 208. The decoder may add the reconstructed residual BPU 222 to the prediction BPU 208 to generate a prediction reference 224. In some embodiments, the prediction reference 224 may be stored in a buffer (e.g., a decoded picture buffer in computer memory). The decoder may provide the prediction reference 224 to the prediction stage 204 for performing a prediction operation in a next iteration of the process 300A.

[0052]

[0069] The decoder may perform process 300A iteratively to decode each coded BPU of a coded picture and generate a prediction reference 224 for encoding the next coded BPU of the coded picture. After decoding all coded BPUs of a coded picture, the decoder may output the picture to video stream 304 for display and proceed to decode the next coded picture in video bitstream 228.

[0053]

[0070] In binary decoding stage 302, the decoder may perform the inverse operation of the binary coding technique used by the encoder (e.g., entropy coding, variable length coding, arithmetic coding, Huffman coding, context-adaptive binary arithmetic coding, or any other lossless compression algorithm). In some embodiments, in addition to prediction data 206 and quantized transform coefficients 216, the decoder may decode other information in binary decoding stage 302, such as, for example, a prediction mode, parameters of the prediction operation, type of transform, parameters of the quantization process (e.g., quantization parameters), encoder control parameters (e.g., bitrate control parameters), or the like. In some embodiments, if video bitstream 228 is transmitted in the form of packets over a network, the decoder may depacketize video bitstream 228 before providing it to binary decoding stage 302.

[0054]

[0071] 3B shows a schematic diagram of another exemplary decoding process 300B according to an embodiment of the present disclosure. Process 300B may be modified from process 300A. For example, process 300B may be used by a decoder compliant with a hybrid video coding standard (e.g., the H.26x series). Compared to process 300A, process 300B additionally divides prediction stage 204 into spatial prediction stage 2042 and temporal prediction stage 2044, and additionally includes loop filter stage 232 and buffer 234.

[0055]

[0072] In process 300B, prediction data 206 decoded by the decoder from binary decoding stage 302 for a coding basic processing unit (referred to as the “current BPU”) of a coding picture being decoded (referred to as the “current picture”) may include various types of data, depending on what prediction mode was used by the encoder to encode the current BPU. For example, if intra-prediction was used by the encoder to encode the current BPU, prediction data 206 may include a prediction mode indicator (e.g., a flag value) indicating intra-prediction, parameters of the intra-prediction operation, or the like. Parameters of the intra-prediction operation may include, for example, the location (e.g., coordinates) of one or more neighboring BPUs used as references, the size of the neighboring BPUs, parameters of extrapolation, the orientation of the neighboring BPUs relative to the original BPU, or the like. As another example, if inter-prediction was used by the encoder to encode the current BPU, prediction data 206 may include a prediction mode indicator (e.g., a flag value) indicating inter-prediction, parameters of the inter-prediction operation, or the like. Parameters for the inter prediction operation may include, for example, the number of reference pictures associated with the current BPU, weights associated with each of the reference pictures, locations (e.g., coordinates) of one or more matching regions within each reference picture, one or more motion vectors associated with each of the matching regions, or the like.

[0056]

[0073] Based on the prediction mode indicator, the decoder may determine whether to perform spatial prediction (e.g., intra prediction) in spatial prediction step 2042 or temporal prediction (e.g., inter prediction) in temporal prediction step 2044. Details of performing such spatial or temporal prediction are described in FIG. 2B and will not be repeated below. After performing such spatial or temporal prediction, the decoder may generate a predicted BPU 208. The decoder may add the predicted BPU 208 and the reconstructed residual BPU 222 to generate a prediction reference 224, as described in FIG. 3A.

[0057]

[0074] In process 300B, the decoder may provide the prediction reference 224 to the spatial prediction stage 2042 or the temporal prediction stage 2044 to perform the prediction operation in the next iteration of process 300B. For example, if the current BPU is decoded using intra prediction in the spatial prediction stage 2042, after generating the prediction reference 224 (e.g., the decoded current BPU), the decoder may provide the prediction reference 224 directly to the spatial prediction stage 2042 for later use (e.g., for extrapolation of the next BPU of the current picture). If the current BPU is decoded using inter prediction in the temporal prediction stage 2044, after generating the prediction reference 224 (e.g., the reference picture from which all BPUs are decoded), the encoder may provide the prediction reference 224 to the loop filter stage 232 to reduce or eliminate distortion (e.g., blocking artifacts). The decoder may apply a loop filter to the prediction reference 224 in the manner as described in FIG. 2B. The loop-filtered reference picture may be stored in a buffer 234 (e.g., a decoded picture buffer in computer memory) for later use (e.g., to be used as an inter-prediction reference picture for a future coded picture of the video bitstream 228). The decoder may store one or more reference pictures in the buffer 234 for use in the temporal prediction stage 2044. In some embodiments, when the prediction mode indicator of the prediction data 206 indicates that inter-prediction was used to encode the current BPU, the prediction data may further include parameters of the loop filter (e.g., loop filter strength).

[0058]

[0075] FIG. 4 is a block diagram of an exemplary device 400 for encoding or decoding video in accordance with an embodiment of the present disclosure. As shown in FIG. 4, device 400 may include a processor 402. When processor 402 executes instructions described herein, device 400 can become a specialized machine for video encoding or decoding. Processor 402 can be any type of circuitry capable of manipulating or processing information. For example, processor 402 can include any number and combination of a central processing unit (or "CPU"), a graphics processing unit (or "GPU"), a neural processing unit ("NPU"), a microcontroller unit ("MCU"), an optical processor, a programmable logic controller, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a programmable logic array (PLA), a programmable array logic (PAL), a generic array logic (GAL), a complex programmable logic device (CPLD), a field programmable gate array (FPGA), a system-on-chip (SoC), an application-specific integrated circuit (ASIC), or the like. In some embodiments, processor 402 may be a set of processors grouped as a single logical entity. For example, as shown in FIG. 4, processor 402 may include multiple processors, including processor 402a, processor 402b, and processor 402n.

[0059]

[0076] The device 400 may also include a memory 404 configured to store data (e.g., a set of instructions, computer code, intermediate data, or the like). For example, as shown in FIG. 4, the stored data may include program instructions (e.g., program instructions for performing steps in processes 200A, 200B, 300A, or 300B) and data for processing (e.g., video sequence 202, video bitstream 228, or video stream 304). The processor 402 may access the program instructions and data for processing (e.g., via bus 410), execute the program instructions, and perform operations or manipulations on the data for processing. The memory 404 may include a high-speed random-access storage device or a non-volatile storage device. In some embodiments, the memory 404 may include any number or combination of random-access memory (RAM), read-only memory (ROM), optical disks, magnetic disks, hard drives, solid-state drives, flash drives, security digital (SD) cards, memory sticks, compact flash (CF) cards, or the like. Memory 404 may also be a group of memories (not shown in FIG. 4) grouped as a single logical entity.

[0060]

[0077] Bus 410 may be a communication device that transfers data between components internal to device 400, such as an internal bus (e.g., a CPU-memory bus), an external bus (e.g., a Universal Serial Bus port, a Peripheral Component Interconnect Express port), or the like.

[0061]

[0078] For ease of explanation and without ambiguity, the processor 402 and other data processing circuitry will be collectively referred to in this disclosure as "data processing circuitry." The data processing circuitry may be implemented entirely in hardware or as a combination of software, hardware, or firmware. In addition, the data processing circuitry may be a single, stand-alone module or may be fully or partially combined with any other component of the device 400.

[0062]

[0079] Device 400 may further include a network interface 406 for providing wired or wireless communication with a network (e.g., the Internet, an intranet, a local area network, a mobile communication network, or the like). In some embodiments, network interface 406 may include any number and combination of a network interface controller (NIC), a radio frequency (RF) module, a transponder, a transceiver, a modem, a router, a gateway, a wired network adapter, a wireless network adapter, a Bluetooth® adapter, an infrared adapter, a near field communication ("NFC") adapter, a cellular network chip, or the like.

[0063]

[0080] In some embodiments, apparatus 400 may optionally further include a peripheral interface 408 for providing connection to one or more peripheral devices. As shown in Figure 4A, the peripheral devices may include, but are not limited to, a cursor control device (e.g., a mouse, a touchpad, or a touchscreen), a keyboard, a display (e.g., a cathode ray tube display, a liquid crystal display, or a light emitting diode display), a video input device (e.g., a camera, or an input interface coupled to a video archive), or the like.

[0064]

[0081] It should be noted that a video codec (e.g., a codec performing process 200A, 200B, 300A, or 300B) may be implemented as any combination of software or hardware modules within device 400. For example, some or all of the stages of process 200A, 200B, 300A, or 300B may be implemented as one or more software modules of device 400, such as program instructions that may be loaded into memory 404. As another example, some or all of the stages of process 200A, 200B, 300A, or 300B may be implemented as one or more hardware modules of device 400, such as specialized data processing circuitry (e.g., FPGA, ASIC, NPU, or the like).

[0065]

[0082] According to the disclosed embodiments, several coding tools can be used to encode 360-degree video or progressive decoding refresh (GDR). Virtual boundaries are one of these coding tools. In applications such as 360-degree video, the layout of a particular projection format typically has multiple surfaces. For example, MPEG-I Part 2: Omnidirectional Media Format (OMAF) standardizes a cube-map-based projection format named CMP, which has six surfaces. For projection formats that include multiple surfaces, regardless of the type of compact frame packing configuration used, discontinuities occur between two or more adjacent surfaces in a frame-packed picture. If in-loop filtering operations are performed across these discontinuities, surface seam artifacts may become visible in the rendered reconstructed image. To mitigate the surface seam artifacts, in-loop filtering operations across the discontinuities in the frame-packed picture must be disabled. Therefore, according to the disclosed embodiments, a concept called virtual boundaries can be used, in which loop filtering operations are disabled across the discontinuities. An encoder can set discontinuity boundaries as virtual boundaries, thereby not applying loop filters across the discontinuity boundaries. The location of the virtual boundary is signaled in the bitstream, and the encoder can change the location of the virtual boundary according to the current projection format.

[0066]

[0083] In addition to 360-degree video, virtual boundaries can also be used in gradual decoding refresh (GDR), which is primarily used in ultra-low latency applications. In ultra-low latency applications, inserting intra-coded pictures as random access point pictures can cause unacceptable transmission latency due to the large size of intra-coded pictures. To reduce latency, GDR is adopted, in which pictures are gradually refreshed by inserting intra-coded regions within B / P pictures. To prevent error propagation, pixels within a refreshed region in a picture cannot reference those within unrefreshed regions of the current picture or reference picture. Therefore, loop filtering cannot be applied across the boundary between the refreshed and unrefreshed regions. With the above virtual boundary scheme, an encoder can set the boundary between the refreshed and unrefreshed regions as a virtual boundary, and in this case, loop filtering operations cannot be applied across the boundary.

[0067]

[0084] According to some embodiments, virtual boundaries can be signaled in a sequence parameter set (SPS) or a picture header (PH). A picture header carries information about a particular picture and includes information common to all slices belonging to the same picture. A PH may include information related to virtual boundaries. One PH is configured per picture. A sequence parameter set includes syntax elements related to a coded layer video sequence (CLVS). An SPS contains sequence-level information shared by all pictures in the entire coded layer video sequence (CLVS) and can provide an overall picture of what a bitstream contains and how the information in the bitstream can be used. In an SPS, a virtual boundary present flag "sps_virtual_boundaries_present_flag" is signaled first. If the flag is true, the number of virtual boundaries and the location of each virtual boundary are signaled for the picture that references the SPS. If "sps_virtual_boundaries_present_flag" is false, another virtual boundary present flag "ph_virtual_boundaries_present_flag" may be signaled within the PH. Similarly, if "ph_virtual_boundaries_present_flag" is true, the number of virtual boundaries and the location of each virtual boundary may be signaled for the picture associated with the PH.

[0068]

[0085] The SPS syntax for virtual boundaries is shown in Table 1 of Figure 5. The semantics of the SPS syntax in Figure 5 are as follows:

[0069]

[0086] "sps_virtual_boundaries_present_flag" equal to 1 specifies that virtual boundary information is signaled in the SPS. "sps_virtual_boundaries_present_flag" equal to 0 specifies that virtual boundary information is not signaled in the SPS. If one or more virtual boundaries are signaled in the SPS, in-loop filtering operations across the virtual boundaries in pictures that reference the SPS are disabled. In-loop filtering operations include deblocking filters, sample adaptive offset filters, and adaptive loop filter operations.

[0070]

[0087] "sps_num_ver_virtual_boundaries" specifies the number of "sps_virtual_boundaries_pos_x[i]" syntax elements in the SPS. If "sps_num_ver_virtual_boundaries" is absent, its value is inferred to be equal to 0.

[0071]

[0088] "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_x[i]" is in the range of 1 to Ceil(pic_width_in_luma_samples÷8)-1.

[0072]

[0089] "sps_num_hor_virtual_boundaries" specifies the number of "sps_virtual_boundaries_pos_y[i]" syntax elements in the SPS. If "sps_num_hor_virtual_boundaries" is absent, its value is inferred to be equal to 0.

[0073]

[0090] "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_in_luma_samples÷8)-1.

[0074]

[0091] The PH syntax for virtual boundaries is shown in Table 2 of Figure 6. The semantics of the PH syntax in Figure 6 are as follows:

[0075]

[0092] "ph_num_ver_virtual_boundaries" specifies the number of "ph_virtual_boundaries_pos_x[i]" syntax elements in PH. If "ph_num_ver_virtual_boundaries" is absent, its value is inferred to be equal to 0.

[0076]

[0093] The parameter VirtualBoundariesNumVer is derived as follows: VirtualBoundariesNumVer=sps_virtual_boundaries_present_flag? sps_num_ver_virtual_boundaries:ph_num_ver_virtual_boundaries

[0077]

[0094] "ph_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma samples divided by 8. The value of "ph_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_in_luma_samples÷8)-1.

[0078]

[0095] The position of the vertical virtual boundary "VirtualBoundariesPosX[i]" in luma samples is derived as follows: VirtualBoundariesPosX[i]=(sps_virtual_boundaries_present_flag? sps_virtual_boundaries_pos_x[i]:ph_virtual_boundaries_pos_x[i])*8

[0079]

[0096] The distance between any two vertical virtual boundaries can be greater than or equal to CtbSizeY luma samples.

[0080]

[0097] "ph_num_hor_virtual_boundaries" specifies the number of "ph_virtual_boundaries_pos_y[i]" syntax elements in PH. If "ph_num_hor_virtual_boundaries" is absent, its value is inferred to be equal to 0.

[0081]

[0098] The parameter VirtualBoundariesNumHor is derived as follows: VirtualBoundariesNumHor=sps_virtual_boundaries_present_flag? sps_num_hor_virtual_boundaries:ph_num_hor_virtual_boundaries

[0082]

[0099] "ph_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "ph_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_in_luma_samples÷8)-1.

[0083]

[0100] The position of the horizontal virtual boundary "VirtualBoundariesPosY[i]" in luma samples is derived as follows: VirtualBoundariesPosY[i]=(sps_virtual_boundaries_present_flag? sps_virtual_boundaries_pos_y[i]:ph_virtual_boundaries_pos_y[i])*8

[0084]

[0101] The distance between any two horizontal virtual boundaries can be greater than or equal to CtbSizeY luma samples.

[0085]

[0102] Wraparound motion compensation is another 360-degree video coding tool. In traditional motion compensation, when a motion vector references a sample beyond the picture boundary of a reference picture, repetition padding is applied to derive the value of the out-of-boundary sample by copying from the nearest neighbor on the corresponding picture boundary. For 360-degree video, this repetition padding method is not suitable and can cause visual artifacts called "seam artifacts" in the reconstructed viewport video. Because 360-degree video is captured on a sphere and does not inherently have "boundaries," reference samples outside the boundary of the reference picture in the projection region can always be obtained from neighboring samples in the spherical region. Deriving corresponding neighboring samples in the spherical region can be difficult in common projection formats, due to the inclusion of 2D-to-3D and 3D-to-2D coordinate transformations and sample interpolation for fractional sample positions. This problem is very simple for the left and right boundaries of equirectangular projection (ERP) or padded ERP (PERP) formats, since the spherical neighborhood outside the left picture boundary can be derived from samples inside the right picture boundary, and vice versa. Given the widespread use of, and relative ease of implementation of, the ERP or PERP projection formats, horizontal wraparound motion compensation can be used to improve the visual quality of 360-degree video encoded in the ERP projection format.

[0086]

[0103] Figure 7A illustrates the horizontal wraparound motion compensation process. If a portion of a reference block is outside the left (or right) boundary of a reference picture within the projection region, instead of repeated padding, the "out-of-bounds" portion is taken from the corresponding spherical neighborhood located within the reference picture toward the right (or left) boundary within the projection region. Repeated padding is used only for the top and bottom picture boundaries. As shown in Figure 7B, horizontal wraparound motion compensation can be combined with non-normative padding methods often used in 360-degree video coding. This can be achieved by signaling a high-level syntax element to indicate the wraparound offset, which should be set to the width of the ERP picture before padding. This syntax is used to adjust the position of the horizontal wraparound accordingly. This syntax is not affected by the specific padding amount on the left and right picture boundaries, and therefore naturally supports asymmetric padding of ERP pictures (where left and right padding are different). Horizontal wraparound motion compensation provides more meaningful information for motion compensation when the reference samples are outside the left and right boundaries of the reference picture. This tool improves compression performance not only in terms of rate-distortion performance, but also in terms of reducing seam artifacts and improving subjective quality of the reconstructed 360-degree video. Horizontal wraparound motion compensation can also be used for other single-plane projection formats with constant sampling density in the horizontal direction, such as adjusted equal-area projection.

[0087]

[0104] According to some embodiments, wrap-around motion compensation is signaled within an SPS. First, an enable flag is signaled. If the enable flag is true, the wrap-around offset is signaled. The SPS syntax is shown in Figure 8, and the corresponding semantics are given below.

[0088]

[0105] "sps_ref_wraparound_enabled_flag" equal to 1 specifies that horizontal wraparound motion compensation is applied within inter prediction. "sps_ref_wraparound_enabled_flag" equal to 0 specifies that horizontal wraparound motion compensation is not applied. If the value of (CtbSizeY / MinCbSizeY+1) is greater than (pic_width_in_luma_samples / MinCbSizeY-1) and "pic_width_in_luma_samples" is the value of "pic_width_in_luma_samples" in any picture parameter set (PPS) that references an SPS, the value of "sps_ref_wraparound_enabled_flag" is equal to 0.

[0089]

[0106] "sps_ref_wraparound_offset_minus1" plus 1 specifies the offset used to calculate the horizontal wraparound position in MinCbSizeY luma samples. The value of "ref_wraparound_offset_minus1" is in the range (CtbSizeY / MinCbSizeY)+1 to (pic_width_in_luma_samples / MinCbSizeY)-1, and "pic_width_in_luma_samples" is the value of "pic_width_in_luma_samples" in any PPS that references the SPS.

[0090]

[0107] CtbSizeY is the luma size of the coding tree block (CTB), MinCbSizeY is the minimum size of the luma coding block, and "pic_width_in_luma_samples" is the picture width in luma samples.

[0091]

[0108] According to some embodiments, the maximum width and height of all pictures in a picture sequence are signaled in an SPS, and then the picture width and height for the current picture are signaled in each PPS. The syntax for signaling the maximum picture width and height is shown in Table 4 of Figure 9, and the syntax for signaling the picture width and height is shown in Table 5 of Figure 10. The semantics corresponding to Figures 9 and 10 are given below.

[0092]

[0109] A "ref_pic_resampling_enabled_flag" equal to 1 specifies that reference picture resampling can be applied when decoding a coded picture in a coding layer video sequence (CLVS) that references an SPS. A ref_pic_resampling_enabled_flag equal to 0 specifies that reference picture resampling is not applied when decoding a picture in a CLVS that references an SPS. For example, a decoding program may decode each of the frames. If the decoding program determines that the resolution of the current frame is different from the resolution of the reference picture, the decoding program may perform appropriate resampling on the reference picture and use the generated resampled reference picture as the reference picture for the current frame. That is, reference picture resampling is necessary if the spatial resolution of a picture is allowed to change within a video sequence. The appropriate resampling of the reference picture may be downsampling or upsampling of the reference picture.

[0093]

[0110] "pic_width_max_in_luma_samples" specifies the maximum width in luma samples of each decoded picture that references an SPS. "pic_width_max_in_luma_samples" does not have to be equal to 0 and can be an integer multiple of Max(8,MinCbSizeY).

[0094]

[0111] "pic_height_max_in_luma_samples" specifies the maximum height in luma samples of each decoded picture that references an SPS. "pic_height_max_in_luma_samples" does not have to be equal to 0 and can be an integer multiple of Max(8,MinCbSizeY).

[0095]

[0112] "pic_width_in_luma_samples" specifies the width in luma samples of each decoded picture that references the PPS. "pic_width_in_luma_samples" does not have to be equal to 0. Rather, "pic_width_in_luma_samples" may be an integer multiple of Max(8,MinCbSizeY) and may be less than or equal to "pic_width_max_in_luma_samples".

[0096]

[0113] If "subpics_present_flag" is equal to 1 or "ref_pic_resampling_enabled_flag" is equal to 0, the value of "pic_width_in_luma_samples" is equal to "pic_width_max_in_luma_samples".

[0097]

[0114] "pic_height_in_luma_samples" specifies the height in luma samples of each decoded picture referencing the PPS. "pic_height_in_luma_samples" does not have to be equal to 0. Rather, "pic_height_in_luma_samples" may be an integer multiple of Max(8,MinCbSizeY) and may be less than or equal to "pic_height_max_in_luma_samples".

[0098]

[0115] If "subpics_present_flag" is equal to 1 or "ref_pic_resampling_enabled_flag" is equal to 0, the value of "pic_height_in_luma_samples" is equal to "pic_height_max_in_luma_samples".

[0099]

[0116] The SPS signaling of the virtual boundaries described above may cause some ambiguity. Specifically, the ranges of "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]" signaled within an SPS are 0 to Ceil(pic_width_in_luma_samples÷8)-1 and 0 to Ceil(pic_height_in_luma_samples÷8)-1, respectively. However, as explained above, "pic_width_in_luma_samples" and "pic_height_in_luma_samples" are signaled within a PPS, and they may vary from PPS to PPS. Since there can be multiple PPSs referencing the same SPS, it is not clear whether "pic_width_in_luma_samples" and "pic_height_in_luma_samples" should be set as upper bounds on "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]".

[0100]

[0117] Furthermore, the SPS signaling of the wraparound motion compensation described above may have some problems. Specifically, "sps_ref_wraparound_enabled_flag" and "sps_ref_wraparound_offset_minus1" are syntax elements signaled within the SPS, but there is a conformance constraint for "sps_ref_wraparound_enabled_flag" that depends on "pic_width_in_luma_samples" signaled on the PPS. The range of "sps_ref_wraparound_offset_minus1" also depends on "pic_width_in_luma_samples" signaled on the PPS. These dependencies cause some problems. First, restricting the value of an SPS syntax element by a syntax element in all of the associated PPSs is not an efficient method because the SPS is at a higher level than the PPS. Furthermore, it is usually understood that a high-level syntax should not refer to a low-level syntax. Second, in the current design, "sps_ref_wraparound_enabled_flag" can be true only if the widths of all pictures in the sequence that reference the SPS satisfy the constraint. Therefore, even if only one frame in the entire sequence does not satisfy the constraint, wraparound motion compensation cannot be used. Therefore, the benefit of wraparound motion compensation for the entire sequence is lost because of only one frame.

[0101]

[0118] The present disclosure provides methods for solving the above problems associated with signaling virtual boundaries or wraparound motion compensation. Some exemplary embodiments according to the disclosed methods are described in detail below.

[0102]

[0119] In some example embodiments, to solve the above problems related to signaling virtual boundaries, the values of "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]" are upper bounded to the minimum width and height of a picture in the sequence. Thus, for each picture, the positions of the virtual boundaries ("sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]") signaled in the SPS do not cross picture boundaries.

[0103]

[0120] The semantics according to these embodiments are described below.

[0104]

[0121] "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_in_luma_samples÷8)-1, and "pic_width_in_luma_samples" is the value of "pic_width_in_luma_samples" in any PPS that references the SPS.

[0105]

[0122] "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_in_luma_samples÷8)-1, and "pic_height_in_luma_samples" is the value of "pic_width_in_luma_samples" in any PPS that references the SPS.

[0106]

[0123] In some example embodiments, to solve the above problems related to signaling virtual boundaries, the values of "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]" are capped to the maximum width and height of a picture in the sequence, "pic_width_max_in_luma_samples" and "pic_height_max_in_luma_samples", respectively. For each picture, if the position of the virtual boundary signaled in the SPS ("sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]") exceeds the picture boundary, the virtual boundary is clipped or discarded within the boundary.

[0107]

[0124] The semantics according to these embodiments are described below.

[0108]

[0125] "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_max_in_luma_samples÷8)-1.

[0109]

[0126] "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_max_in_luma_samples÷8)-1.

[0110]

[0127] As an example, for each picture, the positions of the virtual boundaries signaled in the SPS are clipped within the current picture boundary. In this example, the derived virtual boundary positions VirtualBoundariesPosX[i] and VirtualBoundariesPosY[i] and the numbers of virtual boundaries VirtualBoundariesNumVer and VirtualBoundariesNumHor are derived as follows: VirtualBoundariesNumVer=sps_virtual_boundaries_present_flag? sps_num_ver_virtual_boundaries:ph_num_ver_virtual_boundaries VirtualBoundariesPosX[i]=(sps_virtual_boundaries_present_flag? min(Ceil(pic_width_in_luma_samples÷8)-1,sps_virtual_boundaries_pos_x[i]):ph_virtual_boundaries_pos_x[i])*8 VirtualBoundariesNumHor=sps_virtual_boundaries_present_flag? sps_num_hor_virtual_boundaries:ph_num_hor_virtual_boundaries VirtualBoundariesPosY[i]=(sps_virtual_boundaries_present_flag? min(Ceil(pic_width_in_luma_samples÷8)-1,sps_virtual_boundaries_pos_y[i]):ph_virtual_boundaries_pos_y[i])*8

[0111]

[0128] The distance between any two vertical virtual boundaries can be 0 or greater than or equal to CtbSizeY luma samples.

[0112]

[0129] The distance between any two horizontal virtual boundaries can be 0 or greater than or equal to CtbSizeY luma samples.

[0113]

[0130] As another example, for each picture, if the position of the virtual boundary signaled in the SPS exceeds the current picture boundary, the virtual boundary is not used in the current picture. The derived virtual boundary positions VirtualBoundariesPosX[i] and VirtualBoundariesPosY[i] and the numbers of virtual boundaries VirtualBoundariesNumVer and VirtualBoundariesNumHor are derived as follows: VirtualBoundariesNumVer=sps_virtual_boundaries_present_flag? sps_num_ver_virtual_boundaries:ph_num_ver_virtual_boundaries VirtualBoundariesPosXInPic[i]=(sps_virtual_boundaries_present_flag? sps_virtual_boundaries_pos_x[i]:ph_virtual_boundaries_pos_x[i])*8,(i=0..VirtualBoundariesNumVer) VirtualBoundariesNumHor=sps_virtual_boundaries_present_flag? sps_num_hor_virtual_boundaries:ph_num_hor_virtual_boundaries VirtualBoundariesPosYInPic[i]=(sps_virtual_boundaries_present_flag? sps_virtual_boundaries_pos_y[i]:ph_virtual_boundaries_pos_y[i])*8,(i=0..VirtualBoundariesNumHor) for(i=0,j=0;i <VirtualBoundariesNumVer;i++){ if(VirtualBoundariesPosXInPic[i]<=Ceil(pic_width_in_luma_samples÷8)-1){ VirtualBoundariesPosX[j++]=VirtualBoundariesPosXInPic[i] } } VirtualBoundariesNumVer=j for(i=0,j=0;i <VirtualBoundariesNumHor;i++){ if(VirtualBoundariesPosYInPic[i]<=Ceil(pic_height_in_luma_samples÷8)-1){ VirtualBoundariesPosY[j++]=VirtualBoundariesPosYInPic[i] } } VirtualBoundariesNumHor=j

[0114]

[0131] Instead, the positions of the derived virtual boundaries "VirtualBoundariesPosX[i]", "VirtualBoundariesPosY[i]" and the numbers of virtual boundaries VirtualBoundariesNumVer and VirtualBoundariesNumHor are derived as follows: for(i=0,j=0;i <sps_num_ver_virtual_boundaries;i++){ if(sps_virtual_boundaries_pos_x[i]<=Ceil(pic_width_in_luma_samples÷8)-1){ VirtualBoundariesPosX[j++]=sps_virtual_boundaries_pos_x[i] } } VirtualBoundariesNumVer=j for(i=0,j=0;i<sps_num_hor_virtual_boundaries;i++){ if(sps_virtual_boundaries_pos_y[i]<=Ceil(pic_height_in_luma_samples÷8)-1){ VirtualBoundariesPosY[j++]=sps_virtual_boundaries_pos_y[i] } } VirtualBoundariesNumHor=j VirtualBoundariesNumVer=sps_virtual_boundaries_present_flag? VirtualBoundariesNumVer:ph_num_ver_virtual_boundaries VirtualBoundariesPosX[i]=(sps_virtual_boundaries_present_flag? VirtualBoundariesPosX[i]:ph_virtual_boundaries_pos_x[i])*8,(i=0..VirtualBoundariesNumVer) VirtualBoundariesNumHor=sps_virtual_boundaries_present_flag? VirtualBoundariesNumHor:ph_num_hor_virtual_boundaries VirtualBoundariesPosY[i]=(sps_virtual_boundaries_present_flag? VirtualBoundariesPosY[i]:ph_virtual_boundaries_pos_y[i])*8,(i=0..VirtualBoundariesNumHor)

[0115]

[0132] In some example embodiments, to solve the above problems related to signaling virtual boundaries, the values of "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]" are upper bounded to the maximum width and height of a picture in the sequence, "pic_width_max_in_luma_samples" and "pic_height_max_in_luma_samples", respectively. For each picture, the positions of the virtual boundaries ("sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]") signaled in the SPS are scaled according to the ratio between the maximum picture width and height signaled in the SPS and the width and height of the current picture signaled in the PPS.

[0116]

[0133] The semantics according to these embodiments are described below.

[0117]

[0134] "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_max_in_luma_samples÷8)-1.

[0118]

[0135] "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_max_in_luma_samples÷8)-1.

[0119]

[0136] To derive the position of the virtual boundary for each picture, the scaling ratio is first calculated, and then the position of the virtual boundary signaled in the SPS is scaled as follows: VBScaleX=((pic_width_max_in_luma_samples<<14)+(pic_width_in_luma_samples>>1)) / pic_width_in_luma_samples VBScaleY=((pic_height_max_in_luma_samples<<14)+(pic_height_in_luma_samples>>1)) / pic_height_in_luma_samples SPSVirtualBoundariesPosX[i]=(sps_virtual_boundaries_pos_x[i]×VBScaleX+(1<<13))>>14 SPSVirtualBoundariesPosY[i]=(sps_virtual_boundaries_pos_y[i]×VBScaleY+(1<<13))>>14

[0120]

[0137] For example, "SPSVirtualBoundariesPosX[i]" and "SPSVirtualBoundariesPosY[i]" can be further rounded to an 8-pixel grid as follows: SPSVirtualBoundariesPosX[i]=((SPSVirtualBoundariesPosX[i]+4)>>3)<<3 SPSVirtualBoundariesPosY[i]=((SPSVirtualBoundariesPosY[i]+4)>>3)<<3

[0121]

[0138] Finally, the positions of the virtual boundaries "VirtualBoundariesPosX[i]" and "VirtualBoundariesPosY[i]" and the numbers of virtual boundaries "VirtualBoundariesNumVer" and "VirtualBoundariesNumHor" are derived as follows: VirtualBoundariesNumVer=sps_virtual_boundaries_present_flag? sps_num_ver_virtual_boundaries:ph_num_ver_virtual_boundaries VirtualBoundariesPosX[i]=(sps_virtual_boundaries_present_flag? SPSVirtualBoundariesPosX[i]:ph_virtual_boundaries_pos_x[i])*8,(i=0..VirtualBoundariesNumVer) VirtualBoundariesNumHor=sps_virtual_boundaries_present_flag? sps_num_hor_virtual_boundaries:ph_num_hor_virtual_boundaries VirtualBoundariesPosY[i]=(sps_virtual_boundaries_present_flag? SPSVirtualBoundariesPosY[i]:ph_virtual_boundaries_pos_y[i])*8,(i=0..VirtualBoundariesNumHor)

[0122]

[0139] In some exemplary embodiments, to solve the above problems related to signaling virtual boundaries, signaling of virtual boundaries at the sequence level and changing picture widths and heights are used mutually exclusive. For example, if a virtual boundary is signaled in an SPS, the width and height of a picture cannot be changed in a sequence. If the width and height of a picture are changed in a sequence, the virtual boundary cannot be signaled in an SPS.

[0123]

[0140] In an embodiment of the present invention, the upper limit of the values of "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]" is changed to "pic_width_max_in_luma_samples" and "pic_width_max_in_luma_samples", which are the maximum width and height of a picture in the sequence, respectively.

[0124]

[0141] The semantics of "sps_virtual_boundaries_pos_x[i]" and "sps_virtual_boundaries_pos_y[i]" according to an embodiment of the present invention are as follows:

[0125]

[0142] "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_max_in_luma_samples÷8)-1.

[0126]

[0143] "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_max_in_luma_samples÷8)-1.

[0127]

[0144] As an example, bitstream conformance requirements for "pic_width_in_luma_samples" and "pic_height_in_luma_samples" can be imposed as follows:

[0128]

[0145] The value of "pic_width_in_luma_samples" is equal to "pic_width_max_in_luma_samples" if (1) "subpics_present_flag" is equal to 1, or (2) "ref_pic_resampling_enabled_flag" is equal to 0, or (3) "sps_virtual_boundaries_present_flag" is equal to 1. Subject to the third condition of this constraint (i.e., "sps_virtual_boundaries_present_flag" is equal to 1), if the virtual boundaries are within the SPS, then each picture in the sequence has the same width equal to the maximum width of any picture in the sequence.

[0129]

[0146] The value of "pic_height_in_luma_samples" is equal to "pic_height_max_in_luma_samples" if (1) "subpics_present_flag" is equal to 1, or (2) "ref_pic_resampling_enabled_flag" is equal to 0, or (3) "sps_virtual_boundaries_present_flag" is equal to 1. Subject to the third condition of this constraint (i.e., "sps_virtual_boundaries_present_flag" is equal to 1), if the virtual boundaries are within the SPS, then each picture in the sequence has the same height equal to the maximum height of any picture in the sequence.

[0130]

[0147] As another example, bitstream conformance requirements for "pic_width_in_luma_samples" and "pic_height_in_luma_samples" can be imposed as follows:

[0131]

[0148] The value of "pic_width_in_luma_samples" is equal to "pic_width_max_in_luma_samples" if (1) "subpics_present_flag" is equal to 1, or (2) "ref_pic_resampling_enabled_flag" is equal to 0, or (3) "sps_num_ver_vritual_boundaries" is not equal to 0. Subject to the third condition of this constraint (i.e., "sps_num_ver_vritual_boundaries" is not equal to 0), if the number of vertical virtual boundaries is greater than 0 (i.e., there is at least one vertical virtual boundary), then each picture in the sequence has the same width, equal to the maximum width of any picture in the sequence.

[0132]

[0149] The value of "pic_height_in_luma_samples" is equal to "pic_height_max_in_luma_samples" if (1) "subpics_present_flag" is equal to 1, or (2) "ref_pic_resampling_enabled_flag" is equal to 0, or (3) "sps_num_hor_vritual_boundaries" is not equal to 0. Subject to the third condition of this constraint (i.e., "sps_num_hor_vritual_boundaries" is not equal to 0), if the number of vertical virtual boundaries is greater than 0 (i.e., there is at least one vertical virtual boundary), then each picture in the sequence has the same width, equal to the maximum width of any picture in the sequence.

[0133]

[0150] As another example, a bitstream conformance requirement for "sps_virtual_boundaries_present_flag" can be imposed as follows: It is a bitstream conformance requirement that "sps_virtual_boundaries_present_flag" is 0 if "ref_pic_resampling_enabled_flag" is 1. According to this constraint, if reference picture resampling is enabled, the virtual boundary should not be within the SPS. The rationale for this constraint is as follows: Reference picture resampling is used when the current picture has a different resolution than the reference picture. If the resolution of pictures is allowed to change within a sequence, different pictures may have different resolutions, so the position of the virtual boundary can also change from picture to picture. Therefore, the position of the virtual boundary can be signaled at the picture level (e.g., in the PPS). Signaling of the virtual boundary at the sequence level (i.e., signaled within the SPS) is not appropriate.

[0134]

[0151] As another example, "sps_virtual_boundaries_present_flag" is conditionally signaled based on "ref_pic_resampling_enabled_flag." For example, "ref_pic_resampling_enabled_flag" equal to 0 specifies that reference picture resampling is not applied when decoding pictures in a CLVS that reference an SPS, and "sps_virtual_boundaries_present_flag" is signaled based on "!ref_pic_resampling_enabled_flag" having a value of 1. This syntax is shown in Figure 11, with changes to the syntax in Table 1 (Figure 5) in italics. The associated semantics are described as follows:

[0135]

[0152] "sps_virtual_boundaries_present_flag" equal to 1 specifies that virtual boundary information is signaled in the SPS. "sps_virtual_boundaries_present_flag" equal to 0 specifies that virtual boundary information is not signaled in the SPS. If one or more virtual boundaries are signaled in the SPS, in-loop filtering operations that cross the virtual boundaries in pictures that reference the SPS are disabled. If "sps_virtual_boundaries_present_flag" is absent, its value is inferred to be 0. In-loop filtering operations include a deblocking filter, a sample adaptive offset filter, and an adaptive loop filter operation.

[0136]

[0153] As another example, "ref_pic_resampling_enabled_flag" is conditionally signaled based on "sps_virtual_boundaries_present_flag." This syntax is shown in Figure 12, with changes to the syntax in Table 1 (Figure 5) indicated using italics and strikethrough. The associated semantics are described below.

[0137]

[0154] "ref_pic_resampling_enabled_flag" equal to 1 specifies that reference picture resampling can be applied when decoding coded pictures in CLVS that reference an SPS. "ref_pic_resampling_enabled_flag" equal to 0 specifies that reference picture resampling is not applied when decoding pictures in CLVS that reference an SPS. If "ref_pic_resampling_enabled_flag" is absent, its value is inferred to be 0.

[0138]

[0155] Furthermore, to solve the above problems related to signaling wraparound motion compensation, the "sps_ref_wraparound_enabled_flag" can be true only if the widths of all pictures in the sequence that reference the SPS satisfy the constraint, and the following embodiments are provided by this disclosure:

[0139]

[0156] In some embodiments, the constraints on the wraparound motion compensation enable flag and the wraparound offset are modified to depend on the maximum picture width signaled in the SPS. At the picture level, a picture width check is introduced. Wraparound can be applied only to pictures with a width that meets the condition. For pictures whose width does not meet the condition, wraparound is turned off even if 'sps_ref_wraparound_enabled_flag' is true. By doing so, there is no need to restrict 'sps_ref_wraparound_enabled_flag' and 'sps_ref_wraparound_offset_minus1' signaled in the SPS using the picture width signaled in the PPS. The syntax remains unchanged, and the semantics of 'sps_ref_wraparound_enabled_flag' and 'sps_ref_wraparound_offset_minus1' are as follows:

[0140]

[0157] "sps_ref_wraparound_enabled_flag" equal to 1 specifies that horizontal wraparound motion compensation may be applied within inter prediction. sps_ref_wraparound_enabled_flag equal to 0 specifies that horizontal wraparound motion compensation is not applied. If the value of (CtbSizeY / MinCbSizeY+1) is greater than (pic_width_max_in_luma_samples / MinCbSizeY-1), the value of sps_ref_wraparound_enabled_flag shall be equal to 0.

[0141]

[0158] "sps_ref_wraparound_offset_minus1" plus 1 specifies the maximum offset used to calculate the horizontal wraparound position in MinCbSizeY luma samples. The value of sps_ref_wraparound_offset_minus1 shall be in the range (CtbSizeY / MinCbSizeY)+1 to (pic_width_max_in_luma_samples / MinCbSizeY)-1.

[0142]

[0159] pic_width_max_in_luma_samples is the maximum width in luma samples of each decoded picture that references an SPS, as per VVC Draft 7. CtbSizeY and MinCbSizeY are as specified in VVC Draft 7.

[0143]

[0160] For each picture in the sequence, the variable "PicRefWraparoundEnableFlag" is defined as follows:

[0144]

[0161] PicRefWraparoundEnableFlag=sps_ref_wraparound_enabled_flag&&sps_ref_wraparound_offset_minus1<=(pic_width_in_luma_samples / MinCbSizeY-1))

[0145]

[0162] where "pic_width_in_luma_samples" is the picture width referring to the PPS where "pic_width_in_luma_samples" is signaled, as per VVC Draft 7. CtbSizeY and MinCbSizeY are as defined in VVC Draft 7.

[0146]

[0163] The variable "PicRefWraparoundEnableFlag" is used to determine whether wraparound MC can be enabled for the current picture.

[0147]

[0164] In an alternative method, for each picture in the sequence, two variables "PicRefWraparoundEnableFlag" and "PicRefWraparoundOffset" are defined as follows:

[0148]

[0165] PicRefWraparoundEnableFlag=sps_ref_wraparound_enabled_flag&&((ctbSizeY / MinCbSizeY+1)<=(pic_width_in_luma_samples / MinCbSizeY-1))

[0149]

[0166] PicRefWraparoundOffset=min(sps_ref_wraparound_ofset_minus+1,(pic_width_in_luma_samples / MinCbSizeY))

[0150]

[0167] where "pic_width_in_luma_samples" is the picture width referring to the PPS where "pic_width_in_luma_samples" is signaled, as per VVC Draft 7. CtbSizeY and MinCbSizeY are as defined in VVC Draft 7.

[0151]

[0168] The variable "PicRefWraparoundEnableFlag" is used to determine whether wraparound MC can be enabled for the current picture. If wraparound MC can be enabled, the offset "PicRefWraparoundOffset" can be used in the motion compensation process.

[0152]

[0169] Some embodiments provide for mutually exclusive use of wraparound motion compensation and sequence-level virtual boundary signaling and picture width modification: When wraparound motion compensation is enabled, picture width cannot be modified within a sequence; if picture width is modified within a sequence, wraparound motion compensation is disabled.

[0153]

[0170] As an example, the semantics of "sps_ref_wraparound_enabled_flag" and "sps_ref_wraparound_offset_minus1" according to an embodiment of the present invention are described as follows:

[0154]

[0171] "sps_ref_wraparound_enabled_flag" equal to 1 specifies that horizontal wraparound motion compensation is applied in inter prediction. "sps_ref_wraparound_enabled_flag" equal to 0 specifies that horizontal wraparound motion compensation is not applied. The value of sps_ref_wraparound_enabled_flag may be equal to 0 if the value of (CtbSizeY / MinCbSizeY+1) is greater than (pic_width_max_in_luma_samples / MinCbSizeY-1).

[0155]

[0172] "sps_ref_wraparound_offset_minus1" plus 1 specifies the offset used to calculate the horizontal wraparound position in MinCbSizeY luma samples. The value of "ref_wraparound_offset_minus1" can be in the range of (CtbSizeY / MinCbSizeY)+1 to (pic_width_max_in_luma_samples / MinCbSizeY)-1.

[0156]

[0173] Bitstream conformance requirements for "pic_width_in_luma_samples" and "pic_height_in_luma_samples" can be imposed as follows:

[0157]

[0174] If "subpics_present_flag" is equal to 1, or "ref_pic_resampling_enabled_flag" is equal to 0, or "sps_ref_wraparound_enabled_flag" is equal to 1, then the value of "pic_width_in_luma_samples" is equal to "pic_width_max_in_luma_samples".

[0158]

[0175] As another example, a bitstream conformance requirement for "sps_ref_wraparound_enabled_flag" can be imposed. The semantics of "sps_ref_wraparound_enabled_flag" and "sps_ref_wraparound_offset_minus1" according to an embodiment of the present invention are described as follows:

[0159]

[0176] "sps_ref_wraparound_enabled_flag" equal to 1 specifies that horizontal wraparound motion compensation is applied in inter prediction. "sps_ref_wraparound_enabled_flag" equal to 0 specifies that horizontal wraparound motion compensation is not applied. If the value of (CtbSizeY / MinCbSizeY+1) is greater than (pic_width_max_in_luma_samples / MinCbSizeY-1), the value of sps_ref_wraparound_enabled_flag is equal to 0.

[0160]

[0177] If ref_pic_resampling_enabled_flag is 1, the value of "sps_ref_wraparound_enabled_flag" may be 0. ref_pic_resampling_enabled_flag specifies whether reference resampling is enabled. Reference resampling is used to resample a reference picture when the resolution of the reference picture is different from the resolution of the current picture. Therefore, at the picture level (e.g., PPS, PH), wraparound motion compensation is not used to predict the current picture if the resolution of the reference picture is different from that of the current picture.

[0161]

[0178] "sps_ref_wraparound_offset_minus1" plus 1 specifies the offset used to calculate the horizontal wraparound position in MinCbSizeY luma samples. The value of "ref_wraparound_offset_minus1" is in the range (CtbSizeY / MinCbSizeY)+1 to (pic_width_max_in_luma_samples / MinCbSizeY)-1.

[0162]

[0179] As another example, "sps_ref_wraparound_enabled_flag" is conditionally signaled based on "ref_pic_resampling_enabled_flag". This syntax is shown in Figure 13, with changes to the syntax in Table 3 (Figure 8) shown in italics. The associated semantics are described as follows:

[0163]

[0180] "sps_ref_wraparound_enabled_flag" equal to 1 specifies that horizontal wraparound motion compensation is applied in inter prediction. "sps_ref_wraparound_enabled_flag" equal to 0 specifies that horizontal wraparound motion compensation is not applied. If the value of (CtbSizeY / MinCbSizeY+1) is greater than (pic_width_max_in_luma_samples / MinCbSizeY-1), the value of "sps_ref_wraparound_enabled_flag" is equal to 0. If "sps_ref_wraparound_enabled_flag" is absent, its value is inferred to be 0.

[0164]

[0181] "sps_ref_wraparound_offset_minus1" plus 1 specifies the offset used to calculate the horizontal wraparound position in MinCbSizeY luma samples. The value of ref_wraparound_offset_minus1 is in the range (CtbSizeY / MinCbSizeY)+1~(pic_width_max_in_luma_samples / MinCbSizeY)-1.

[0165]

[0182] As an example, "ref_pic_resampling_enabled_flag" is conditionally signaled based on "sps_ref_wraparound_enabled_flag." This syntax is shown as Table 9 in Figure 14, with changes to the syntax in Table 3 (Figure 8) indicated using italics and strikethrough. The associated semantics are as follows:

[0166]

[0183] "ref_pic_resampling_enabled_flag" equal to 1 specifies that reference picture resampling can be applied when decoding coded pictures in CLVS that reference an SPS. ref_pic_resampling_enabled_flag equal to 0 specifies that reference picture resampling is not applied when decoding pictures in CLVS that reference an SPS. If ref_pic_resampling_enabled_flag is absent, its value is inferred to be 0.

[0167]

[0184] 15 shows a flowchart of an example method 1500 according to some embodiments of the present disclosure. In some embodiments, method 1500 may be performed by one or more software or hardware components of an encoder, an apparatus (e.g., apparatus 400 of FIG. 4). For example, a processor (e.g., processor 402 of FIG. 4) may perform method 1500. In some embodiments, method 1500 may be implemented by a computer program product embodied in a computer-readable medium that includes computer-executable instructions, such as program code, executed by a computer (e.g., apparatus 400 of FIG. 4).

[0168]

[0185] A virtual boundary can be set as one of the coding tools for 360-degree video or gradual decoding refresh (GDR) coding so that in-loop filtering can be disabled to prevent errors and artifacts. This is exemplified in the manner shown in FIG. 15.

[0169]

[0186] In step 1501, a bitstream including a sequence of pictures is received. The sequence of pictures may be a set of pictures. As described, a basic processing unit of a color picture may include a luma component (Y) representing colorless luminance information, one or more chroma components (e.g., Cb and Cr) representing color information, and related syntax elements, where the luma and chroma components may have the same size of the basic processing unit. The luma and chroma components may be referred to as "coding tree blocks" ("CTBs") in some video coding standards (e.g., H.265 / HEVC or H.266 / VVC). Any operation performed on a basic processing unit may be repeatedly performed on each of its luma and chroma components.

[0170]

[0187] In step 1503, it is determined according to the received stream whether virtual boundaries are signaled at the sequence level (i.e., in the SPS). If virtual boundaries are signaled at the sequence level, the number of virtual boundaries and the position of each virtual boundary are signaled for the picture that references the SPS.

[0171]

[0188] Virtual boundaries can be signaled in the Sequence Parameter Set (SPS) or the Picture Header (PH). In the SPS, the virtual boundary present flag "sps_virtual_boundaries_present_flag" is signaled first. If the flag is true, the number of virtual boundaries and the position of each virtual boundary are signaled for the picture that references the SPS.

[0172]

[0189] In step 1505, optionally, in response to virtual boundaries not being signaled at the sequence level for the set of pictures, it is determined whether virtual boundaries are signaled at the picture level (e.g., PPS or PH) for pictures in the set of pictures according to the received stream. For example, if "sps_virtual_boundaries_present_flag" is false, another virtual boundary presence flag "ph_virtual_boundaries_present_flag" may be signaled in the PH. Similarly, if "ph_virtual_boundaries_present_flag" is true, the number of virtual boundaries and the position of each virtual boundary may be signaled for pictures associated with the PH. Step 1505 is optional, and in some embodiments, the method may include step 1505 in response to virtual boundaries not being signaled at the sequence level. In some embodiments, in response to virtual boundaries not being signaled at the sequence level, the method may terminate without performing step 1505. In response to the virtual boundary being signaled at the picture level, the method proceeds to step 1507 for determining the location of the virtual boundary.

[0173]

[0190] In some embodiments, it may be determined whether any condition indicating that a virtual boundary is not signaled at the sequence level is met. As described above in the example, the value of "sps_virtual_boundaries_present_flag" in Table 1 of FIG. 5 may be determined, with a value of 1 indicating that a virtual boundary is signaled at the sequence level. However, there are other conditions that indicate that a virtual boundary is not applied at the sequence level. The first condition indicating that a virtual boundary at the sequence level is not signaled is that reference resampling is enabled. The second condition is that resolution changes of pictures within the set of pictures are allowed. If either of these two conditions is met, a virtual boundary is not signaled at the sequence level. If neither of these two conditions is met, and if the value of "sps_virtual_boundaries_present_flag" is determined to be 1, as in this example, it is determined that a virtual boundary is signaled at the sequence level for the set of pictures. The method proceeds to step 1507, which determines the location of the virtual boundary.

[0174]

[0191] In some embodiments, it is determined whether reference resampling is enabled for a sequence of pictures according to the received bitstream, and in response to reference resampling being enabled for a sequence of pictures, no virtual boundary is signaled at the sequence level.

[0175]

[0192] The decoding program can decode each of the frames. If the decoding program determines that the resolution of the current frame is different from the resolution of the reference picture, the decoding program can perform appropriate resampling on the reference picture and use the generated resampled reference block as a reference block for decoding blocks in the current frame. Reference picture resampling is necessary if the spatial resolution of a picture is allowed to change within a video sequence. When resampling is enabled, resolution changes may or may not be allowed. When a picture's resolution is allowed to change, resampling is necessary, and therefore resampling is enabled. The appropriate resampling of the reference picture may be downsampling or upsampling of the reference picture. For example, as shown in FIG. 9, a "ref_pic_resampling_enabled_flag" equal to 1 specifies that reference picture resampling can be applied when decoding coded pictures in a CLVS that reference an SPS. A "ref_pic_resampling_enabled_flag" equal to 0 specifies that reference picture resampling is not applied when decoding pictures in a CLVS that reference an SPS.

[0176]

[0193] For example, "sps_virtual_boundaries_present_flag" in Table 1 of FIG. 5 may be conditionally signaled based on "ref_pic_resampling_enabled_flag." The value of "ref_pic_resampling_enabled_flag" can be determined. "ref_pic_resampling_enabled_flag" equal to 0 specifies that reference picture resampling is not applied when decoding pictures in the CLVS that reference an SPS. If "ref_pic_resampling_enabled_flag" is 1, then "sps_virtual_boundaries_present_flag" is 0.

[0177]

[0194] In some embodiments, determining whether a change in resolution of a picture in a sequence of pictures is allowed, and in response to the change in resolution being allowed, determining that the virtual boundary is not signaled at the sequence level.

[0178]

[0195] Reference picture resampling is used when the current picture has a different resolution from the reference picture. If the resolution of a picture is allowed to change within a sequence, different pictures may have different resolutions, so the position of the virtual boundary may also change for each picture. Therefore, while the position of the virtual boundary can be signaled at the picture level (e.g., PPS and PH), signaling the virtual boundary at the sequence level (i.e., signaled in the SPS) is not appropriate. Therefore, if changing the resolution of a picture is allowed, it is determined that the virtual boundary is not signaled at the sequence level. At the same time, if resampling is allowed but changing the resolution of a picture is not allowed, no constraints are imposed on the signaling of the virtual boundary.

[0179]

[0196] In some embodiments, in response to reference resampling being enabled for the sequence of pictures, it is determined that wraparound motion compensation is disabled for the sequence of pictures.

[0180]

[0197] For example, the value of "ref_pic_resampling_enabled_flag" in FIG. 13 is 1, "sps_ref_wraparound_enabled_flag" is 0, and it is determined that horizontal wraparound motion compensation is not applied. "ref_pic_resampling_enabled_flag" specifies whether reference resampling is enabled. Reference resampling is used to resample a reference picture when the resolution of the reference picture is different from the resolution of the current picture. At the picture level (e.g., PPS), in this example, if the resolution of the reference picture is different from that of the current picture, wraparound motion compensation is not used to predict the current picture. If it is determined that the value of "ref_pic_resampling_enabled_flag" is 0, "sps_ref_wraparound_enabled_flag" is 1, and horizontal wraparound motion compensation is applied.

[0181]

[0198] In some embodiments, in response to allowing a change in resolution of a picture within the sequence of pictures, it is determined that wraparound motion compensation is disabled for the sequence of pictures.

[0182]

[0199] In step 1507, in response to the virtual boundaries being signaled at the sequence level, positions of the virtual boundaries of the sequence are determined. The positions are constrained by ranges based on the widths and heights of the pictures in the sequence. The virtual boundaries may include vertical and horizontal boundaries. The positions of the virtual boundaries may include vertical boundary position points and horizontal boundary position points. For example, as shown in Table 1 of FIG. 5, "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8, while "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8.

[0183]

[0200] In some embodiments, the vertical extent of this position is less than or equal to the maximum width allowed for each picture in the sequence, and the horizontal extent is less than or equal to the maximum height allowed for each picture in the set. The maximum width and height are signaled in the received stream. An example of semantics is as follows:

[0184]

[0201] "sps_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_max_in_luma_samples÷8)-1.

[0185]

[0202] "sps_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "sps_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_max_in_luma_samples÷8)-1.

[0186]

[0203] If virtual boundaries are in the SPS, i.e. "sps_virtual_boundaries_present_flag" is equal to 1, then each picture in the sequence has the same width equal to the widest width of any picture in the sequence.

[0187]

[0204] In some embodiments, the location of a virtual boundary for a picture in a set of pictures may be determined in response to a virtual boundary being signaled at the picture level for that picture. One or more boundaries may be signaled for one or more pictures in the set. For example, as shown in the semantics of the PH syntax in Figure 6, "ph_num_ver_virtual_boundaries" specifies the number of "ph_virtual_boundaries_pos_x[i]" syntax elements in the PH. If "ph_num_ver_virtual_boundaries" is absent, its value is inferred to be equal to 0.

[0188]

[0205] "ph_virtual_boundaries_pos_x[i]" specifies the position of the ith vertical virtual boundary in luma samples divided by 8. The value of "ph_virtual_boundaries_pos_x[i]" is in the range 1 to Ceil(pic_width_in_luma_samples÷8)-1.

[0189]

[0206] "ph_virtual_boundaries_pos_y[i]" specifies the position of the ith horizontal virtual boundary in luma sample units divided by 8. The value of "ph_virtual_boundaries_pos_y[i]" is in the range 1 to Ceil(pic_height_in_luma_samples÷8)-1.

[0190]

[0207] As mentioned above, in applications such as 360-degree video, the layout of a particular projection format typically has multiple surfaces. For example, MPEG-I Part 2: Omnidirectional Media Format (OMAF) standardizes a cube-map-based projection format named CMP, which has six surfaces. For projection formats with multiple surfaces, discontinuities occur between two or more adjacent surfaces in a frame-packed picture, regardless of the type of compact frame packing configuration used. If in-loop filtering operations are performed across these discontinuities, surface seam artifacts may become visible in the rendered reconstructed image. To mitigate surface seam artifacts, in-loop filtering operations across discontinuities in a frame-packed picture must be disabled. A virtual boundary, across which loop filtering operations are disabled, can be used. An encoder can set the discontinuity boundary as a virtual boundary, thereby not applying loop filters across the discontinuity boundary. In addition to 360-degree video, virtual boundaries can also be used for gradual decoding refresh (GDR), which is primarily used in ultra-low latency applications. In ultra-low latency applications, inserting an intra-coded picture as a random access point picture may cause unacceptable transmission latency due to the large size of the intra-coded picture. To reduce latency, GDR is adopted, in which pictures are gradually refreshed by inserting intra-coded regions within B / P pictures. To prevent error propagation, pixels in a refreshed region within a picture cannot reference those in an unrefreshed region of the current picture or a reference picture. Therefore, loop filtering cannot be applied across the boundary between the refreshed region and the unrefreshed region. With the above virtual boundary scheme, the encoder can set the boundary between the refreshed region and the unrefreshed region as a virtual boundary, and therefore loop filtering operations cannot be applied across the boundary.

[0191]

[0208] Step 1509 disables in-loop filtering operations (e.g., look filter stage 232 in FIG. 3A) that cross a virtual boundary of a picture. If one or more virtual boundaries are signaled in the SPS, in-loop filtering operations that cross the virtual boundary in a picture that references the SPS may be disabled. In-loop filtering operations include a deblocking filter, a sample adaptive offset filter, and an adaptive loop filter operation.

[0192]

[0209] According to some embodiments of the present disclosure, another exemplary method 1600 is provided. The method may be performed by one or more software or hardware components of an encoder, an apparatus (e.g., apparatus 400 of FIG. 4). For example, a processor (e.g., processor 402 of FIG. 4) may perform method 1600. In some embodiments, method 1600 may be implemented by a computer program product embodied in a computer-readable medium that includes computer-executable instructions, such as program code, executed by a computer (e.g., apparatus 400 of FIG. 4). The method may include the following steps:

[0193]

[0210] In step 1601, a bitstream including a sequence of pictures is received. The sequence of pictures may be a set of pictures. As described, a basic processing unit of a color picture may include a luma component (Y) representing colorless luminance information, one or more chroma components (e.g., Cb and Cr) representing color information, and related syntax elements, where the luma and chroma components may have the same size of the basic processing unit. The luma and chroma components may be referred to as "coding tree blocks" ("CTBs") in some video coding standards (e.g., H.265 / HEVC or H.266 / VVC). Any operation performed on a basic processing unit may be repeatedly performed on each of its luma and chroma components.

[0194]

[0211] Step 1603 determines whether reference resampling is enabled for the sequence of pictures according to the received bitstream.

[0195]

[0212] Step 1605 determines that wraparound motion compensation is disabled for the sequence of pictures in response to reference resampling being enabled for the sequence of pictures.

[0196]

[0213] For example, the value of "ref_pic_resampling_enabled_flag" in FIG. 13 is 1, "sps_ref_wraparound_enabled_flag" is 0, and it is determined that horizontal wraparound motion compensation is not applied. "ref_pic_resampling_enabled_flag" specifies whether reference resampling is enabled. Reference resampling is used to resample a reference picture when the resolution of the reference picture is different from the resolution of the current picture. At the picture level (e.g., PPS), in this example, if the resolution of the reference picture is different from that of the current picture, wraparound motion compensation is not used to predict the current picture. If it is determined that the value of "ref_pic_resampling_enabled_flag" is 0, "sps_ref_wraparound_enabled_flag" is 1, and horizontal wraparound motion compensation is applied.

[0197]

[0214] Therefore, step 1703, which is an alternative to step 1603, determines whether the resolution of a reference picture of the sequence of pictures is different from the resolution of the current picture of the sequence of pictures.

[0198]

[0215] Step 1705, which is an alternative to step 1605, determines that wraparound motion compensation is disabled for the current picture in response to the resolution of a reference picture of the sequence of pictures being different from the resolution of the current picture of the sequence of pictures.

[0199]

[0216] In some embodiments, a non-transitory computer-readable storage medium containing instructions is also provided, which can be executed by a device (such as the encoders and decoders of the present disclosure) to perform the above-described methods. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, a hard disk, a solid-state drive, a magnetic tape or any other magnetic data storage medium, a CD-ROM, any other optical data storage medium, any physical medium with a pattern of holes, RAM, PROM and EPROM, FLASH-EPROM or any other flash memory, NVRAM, cache, registers, any other memory chip or cartridge, and networked versions thereof. A device can include one or more processors (CPUs), input / output interfaces, network interfaces, and / or memory.

[0200]

[0217] The disclosed embodiments can be further described using the following clauses: 1. receiving a set of pictures; Determining the width and height of the pictures in the set; and determining a position of a virtual boundary for the set of pictures based on said width and height; A method comprising: 2. Determining the minimum of the determined width and height of the picture and determining a position of a virtual boundary for the set of pictures based on the width and height further comprises: determining a position of a virtual boundary for the set of pictures based on said minimum value; 2. The method of clause 1, further comprising: 3. Determining the maximum value of the determined width and height of the picture and determining a position of a virtual boundary for the set of pictures based on the width and height further comprises: determining a position of a virtual boundary for the set of pictures based on said maximum value; 2. The method of clause 1, further comprising: 4. Determining whether the width of the first picture in the set satisfies a given condition; and Disabling horizontal wraparound motion compensation for the first picture in response to determining that the width of the first picture satisfies a given condition. 2. The method of clause 1, further comprising: 5. Disabling in-loop filtering operations that cross the virtual boundary of a set of pictures 2. The method of clause 1, further comprising: 6. Determining whether resampling has been performed on the first picture in the set; and disabling at least one of virtual boundary or wraparound motion compensation signaling for the first picture in response to determining that resampling for the first picture has not occurred. 2. The method of clause 1, further comprising: 7. The method of clause 1, wherein the location of the virtual boundary is signaled in at least one of a sequence parameter set (SPS) or a picture header (PH). 8. A memory for storing a set of instructions; and one or more processors, wherein the one or more processors receiving a set of pictures; Determining the width and height of the pictures in the set; and determining a position of a virtual boundary for the set of pictures based on said width and height; 10. An apparatus configured to execute a set of instructions to cause the apparatus to perform the following: 9. One or more processors may: Determining the minimum of the determined width and height of the picture and determining a position of a virtual boundary for a set of pictures based on the width and height, the virtual boundary position being determined based on the width and height of the set of pictures ... determining a position of a virtual boundary for the set of pictures based on said minimum value; 10. The device described in clause 8, further comprising: 10. One or more processors may: Determining the maximum of the determined width and height of the picture and determining a position of a virtual boundary for a set of pictures based on the width and height, the virtual boundary position being determined based on the width and height of the set of pictures ... determining a position of a virtual boundary for the set of pictures based on said maximum value; 10. The device described in clause 8, further comprising: 11. One or more processors may: determining whether the width of the first picture in the set satisfies a given condition; and Disabling horizontal wraparound motion compensation for the first picture in response to determining that the width of the first picture satisfies a given condition. 9. The apparatus of clause 8, configured to execute a set of instructions to cause the apparatus to further: 12. One or more processors may: Disabling in-loop filtering operations across virtual boundaries of a set of pictures 9. The apparatus of clause 8, configured to execute a set of instructions to cause the apparatus to further: 13. One or more processors may: determining whether resampling has been performed on a first picture in the set; and disabling at least one of virtual boundary or wraparound motion compensation signaling for the first picture in response to determining that resampling for the first picture has not occurred. 9. The apparatus of clause 8, configured to execute a set of instructions to cause the apparatus to further: 14. The device of clause 8, wherein the location of the virtual boundary is signaled in at least one of a sequence parameter set (SPS) or a picture header (PH). 15. A non-transitory computer-readable medium storing a set of instructions, the set of instructions executable by at least one processor of a computer to cause the computer to perform a video processing method, the method comprising: receiving a set of pictures; Determining the width and height of the pictures in the set; and determining a position of a virtual boundary for the set of pictures based on said width and height; 1. A non-transitory computer-readable medium comprising: 16. A set of instructions is Determining the minimum of the determined width and height of the picture and determining a position of a virtual boundary for the set of pictures based on the width and height comprises: determining a position of a virtual boundary for the set of pictures based on said minimum value; 16. The non-transitory computer-readable medium of clause 15, further comprising: 17. A set of instructions is Determining the maximum of the determined width and height of the picture and determining a position of a virtual boundary for the set of pictures based on the width and height comprises: determining a position of a virtual boundary for the set of pictures based on said maximum value; 16. The non-transitory computer-readable medium of clause 15, further comprising: 18. A set of instructions is determining whether the width of the first picture in the set satisfies a given condition; and Disabling horizontal wraparound motion compensation for the first picture in response to determining that the width of the first picture satisfies a given condition. 16. The non-transitory computer-readable medium of claim 15, executable by a computer to further cause the computer to perform 19. A set of instructions is Disabling in-loop filtering operations across virtual boundaries of a set of pictures 16. The non-transitory computer-readable medium of claim 15, executable by a computer to further cause the computer to perform 20. A set of instructions is determining whether resampling has been performed on a first picture in the set; and disabling at least one of virtual boundary or wraparound motion compensation signaling for the first picture in response to determining that resampling for the first picture has not occurred. 16. The non-transitory computer-readable medium of claim 15, executable by a computer to further cause the computer to perform 21. The non-transitory computer-readable medium of clause 15, wherein the location of the virtual boundary is signaled in at least one of a sequence parameter set (SPS) or a picture header (PH).

[0201]

[0218] It should be noted that relational terms herein, such as "first" and "second," are used merely to distinguish one entity or operation from another, and do not require or imply any actual relationship or order between those entities or operations. Furthermore, the words "comprise," "have," "contain," and "include," and other similar forms, are intended to be equivalent in meaning and open-ended in that the element or elements following any of these words are not meant to be an exclusive listing of such elements or elements, or to be limited to only the listed element or elements.

[0202]

[0219] As used herein, unless specifically stated otherwise, the term "or" includes all possible combinations unless impracticable. For example, if it is stated that a database can include A or B, then the database can include A or B, or A and B, unless specifically stated otherwise or impracticable. As a second example, if it is stated that a database can include A, B, or C, then the database can include A, B, or C, or A and B, A and C, or B and C, or A and B and C, unless specifically stated otherwise or impracticable.

[0203]

[0220] It is understood that the above-described embodiments can be implemented by hardware, or software (program code), or a combination of hardware and software. If implemented by software, it can be stored in the above-described computer-readable medium. The software, when executed by a processor, can perform the methods of the present disclosure. The computational units and other functional units described in the present disclosure can be implemented by hardware, or software, or a combination of hardware and software. Those skilled in the art will also understand that multiple of the above-described modules / units can be combined into one module / unit, and that each of the above-described modules / units can be further divided into multiple sub-modules / sub-units.

[0204]

[0221] In the foregoing specification, embodiments have been described with reference to numerous specific details that may vary from implementation to implementation. Certain adaptations and modifications of the above-described embodiments may be made. Other embodiments may be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered exemplary only, with the true scope and spirit of the invention being indicated by the appended claims. It is also intended that the sequences of steps depicted in the figures are for illustrative purposes only and are not intended to be limited to any particular sequence of steps. As such, one skilled in the art will recognize that these steps may be performed in different orders while implementing the same method.

[0205]

[0222] Illustrative embodiments have been disclosed in the drawings and herein. However, many variations and modifications to these embodiments may be made. Thus, although specific terminology is employed, it is used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. 1. A method for picture processing, comprising: receiving a bitstream including a set of pictures; determining, according to the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures; determining a location of the virtual boundary with respect to the set of pictures in response to the virtual boundary being signaled at the sequence level, the location being constrained by a range signaled in the received bitstream; and Disabling in-loop filtering operations that cross the virtual boundary. A method comprising:

2. the range to which the position is limited includes at least one of a vertical range or a horizontal range; the vertical extent is less than or equal to a maximum width allowed for the set of pictures, the maximum width being signaled in the received stream; and The method of claim 1 , wherein the horizontal extent is less than or equal to a maximum height allowed for the set of pictures, the maximum height being signaled in the received bitstream.

3. Determining whether the virtual boundary is signaled at the sequence level according to the received bitstream comprises: determining whether reference resampling is enabled for the set of pictures according to the received bitstream; and determining, in response to the reference resampling being enabled for the set of pictures, that the virtual boundary is not signaled at the sequence level; The method of claim 1 , comprising:

4. determining, in response to the reference resampling being enabled for the set of pictures, that wraparound motion compensation is disabled for the set of pictures; The method of claim 3 further comprising:

5. Determining whether the virtual boundary is signaled at the sequence level according to the received bitstream includes: determining whether a change in resolution of a first picture in the set of pictures is allowed according to the received bitstream; and determining that the virtual boundary is not signaled at the sequence level in response to the resolution change of the first picture being allowed; The method of claim 1 , comprising:

6. determining, in response to the resolution change of the first picture being allowed, that wraparound motion compensation is disabled for the set of pictures; The method of claim 5 further comprising:

7. 1. An apparatus for picture processing, comprising: a memory for storing a set of instructions; one or more processors, wherein the one or more processors: receiving a bitstream including a set of pictures; determining, according to the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures; determining a location of the virtual boundary with respect to the set of pictures in response to the virtual boundary being signaled at the sequence level, the location being constrained by a range signaled in the received bitstream; and Disabling in-loop filtering operations that cross the virtual boundary. an apparatus configured to execute the set of instructions to cause the apparatus to perform

8. the range to which the position is limited includes at least one of a vertical range or a horizontal range; the vertical extent is less than or equal to a maximum width allowed for the set of pictures, the maximum width being signaled in the received stream; and The apparatus of claim 7 , wherein the horizontal extent is less than or equal to a maximum height allowed for the set of pictures, the maximum height being signaled in the received bitstream.

9. Determining whether the virtual boundary is signaled at the sequence level according to the received bitstream includes: determining whether reference resampling is enabled for the set of pictures according to the received bitstream; and determining, in response to the reference resampling being enabled for the set of pictures, that the virtual boundary is not signaled at the sequence level; 8. The device of claim 7, comprising:

10. the one or more processors: determining, in response to the reference resampling being enabled for the set of pictures, that wraparound motion compensation is disabled for the set of pictures; 10. The device of claim 9, configured to execute the set of instructions to further cause the device to:

11. Determining whether the virtual boundary is signaled at the sequence level according to the received bitstream includes: determining whether a change in resolution of a first picture in the set of pictures is allowed according to the received bitstream; and determining that the virtual boundary is not signaled at the sequence level in response to the resolution change of the first picture being allowed; 8. The device of claim 7, comprising:

12. the one or more processors: determining, in response to the resolution change of the first picture being allowed, that wraparound motion compensation is disabled for the set of pictures; 12. The device of claim 11, configured to execute the set of instructions to further cause the device to:

13. the one or more processors: in response to the virtual boundary not being signaled at the sequence level, determining whether the virtual boundary is signaled at the picture level for one or more pictures in the set; and determining a location of the virtual boundary for the one or more pictures in the set in response to the virtual boundary being signaled at the picture level for the one or more pictures in the set; 8. The device of claim 7, configured to execute the set of instructions to further cause the device to:

14. 1. A non-transitory computer-readable medium storing a set of instructions, the set of instructions executable by at least one processor of a computer to cause the computer to perform a picture processing method, the method comprising: receiving a bitstream including a set of pictures; determining, according to the received bitstream, whether a virtual boundary is signaled at a sequence level for the set of pictures; determining a location of the virtual boundary with respect to the set of pictures in response to the virtual boundary being signaled at the sequence level, the location being constrained by a range signaled in the received bitstream; and Disabling in-loop filtering operations that cross the virtual boundary.

1. A non-transitory computer-readable medium comprising:

15. the range to which the position is limited includes at least one of a vertical range or a horizontal range; the vertical extent is less than or equal to a maximum width allowed for the set of pictures, the maximum width being signaled in the received stream; and 15. The non-transitory computer-readable medium of claim 14, wherein the horizontal extent is less than or equal to a maximum height allowed for the set of pictures, the maximum height being signaled in the received bitstream.

16. Determining whether the virtual boundary is signaled at the sequence level according to the received bitstream includes: determining whether reference resampling is enabled for the set of pictures according to the received bitstream; and determining, in response to the reference resampling being enabled for the set of pictures, that the virtual boundary is not signaled at the sequence level; 15. The non-transitory computer-readable medium of claim 14, comprising:

17. The set of instructions determining, in response to the reference resampling being enabled for the set of pictures, that wraparound motion compensation is disabled for the set of pictures; 20. The non-transitory computer-readable medium of claim 16, executable by the computer to further cause the computer to:

18. Determining whether the virtual boundary is signaled at the sequence level according to the received bitstream includes: determining whether a change in resolution of a first picture in the set of pictures is allowed according to the received bitstream; and determining that the virtual boundary is not signaled at the sequence level in response to the resolution change of the first picture being allowed; 15. The non-transitory computer-readable medium of claim 14, further comprising:

19. The set of instructions determining, in response to the resolution change of the first picture being allowed, that wraparound motion compensation is disabled for the set of pictures; 20. The non-transitory computer-readable medium of claim 18, executable by the computer to further cause the computer to:

20. The set of instructions in response to the virtual boundary not being signaled at the sequence level, determining whether the virtual boundary is signaled at the picture level for one or more pictures in the set; and determining a location of the virtual boundary for the one or more pictures in the set in response to the virtual boundary being signaled at the picture level for the one or more pictures in the set; 15. The non-transitory computer-readable medium of claim 14, executable by the computer to further cause the computer to:

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