Method, apparatus, decoder, encoder, program and bitstream generating method for cross-component linear modeling for intra prediction - Patents.com

Abstract

To provide an apparatus and method for encoding and decoding by applying a cross-component linear model.SOLUTION: A method for intra-predicting a chroma sample of a block by applying a cross-component linear model includes: obtaining reconstructed luma samples; determining maximum and minimum luma sample values based on the reconstructed luma samples; obtaining a difference between the maximum and minimum luma sample values; fetching a value from a lookup table (LUT) by using a set of bits as an index, the set of bits following a position of the most-significant bit; obtaining linear model parameters based on the fetched value; and calculating a predicted chroma sample value by using the obtained linear model parameters.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] [CROSS REFERENCE TO RELATED APPLICATIONS] This application claims the benefit of U.S. Provisional Application No. 62 / 786,563, entitled "METHOD AND APPARATUS FOR CROSS-COMPONENT LINEAR MODELING FOR INTRA PREDICTION," filed December 31, 2018, which is incorporated herein by reference. FIELD OF THE DISCLOSURE Embodiments of the present disclosure relate generally to the field of image processing, and more specifically to intra prediction using cross-component linear modeling. [Background technology]

[0002] Video coding (video encoding and video decoding) is used in a wide range of digital video applications, such as broadcast digital TV, video transmission over the Internet and mobile networks, real-time conversation applications such as video chat, video conferencing, DVDs and Blu-ray Discs, video content acquisition and editing systems, and camcorders for security applications.

[0003] The amount of video data required to show even a relatively short video can be substantial, which can create difficulties when the data is streamed or otherwise communicated over a communication network with limited bandwidth capacity. Thus, video data is generally compressed before being communicated over modern telecommunications networks. The size of the video can also be an issue when the video is stored on a storage device, since memory resources may be limited. Video compression devices often use software and / or hardware at the source to code the video data before transmission or storage, thereby reducing the amount of data required to represent a digital video image. The compressed data is then received at the destination by a video decompression device that decodes the video data. With limited network resources and an ever-increasing demand for higher video quality, improved compression and decompression techniques that improve compression ratios with little to no sacrifice in image quality are desirable. Summary of the Invention

[0004] Embodiments of the present application provide apparatus and methods for encoding and decoding as set forth in the independent claims.

[0005] These and other objects are achieved by the subject matter of the independent claims. Further implementations become apparent from the dependent claims, the description and the figures.

[0006] According to a first aspect, the present invention relates to a method for intra-predicting chroma samples of a block by applying a cross-component linear model. The method includes the steps of obtaining a reconstructed luma sample, determining a maximum luma sample value and a minimum luma sample value based on the reconstructed luma sample, obtaining a difference between the maximum luma sample value and the minimum luma sample value, and determining a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value. The method also includes the steps of fetching a value from a look-up table (LUT) by using a bit set as an index, the bit set following the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value, obtaining a linear model parameter α and a linear model parameter β based on the fetched value, and calculating a predicted chroma sample value by using the obtained linear model parameter α and the linear model parameter β.

[0007] According to a first aspect of the invention, the index of the LUT is calculated in an elegant manner that extracts some bits in the binary representation, resulting in an efficient fetching of values ​​from the LUT.

[0008] In such a possible implementation of the method according to the first aspect, the method obtains the linear model parameters α and β by multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples.

[0009] Because of the increased efficiency in fetching values ​​from the LUT, the size of the multipliers to obtain the linear model parameters α and β is minimized.

[0010] In such a possible implementation of the method according to the first aspect, the LUT includes at least two adjacent values ​​stored in the LUT, which correspond to different stages of the obtained difference, the value of this stage increasing or constant with the difference value. The index of the LUT is calculated in an elegant manner that extracts some bits in the binary representation, and accordingly the size of the entry in the LUT corresponding to the index is minimized. As a result, the size of the LUT is minimized.

[0011] An apparatus for intra-predicting chroma samples of a block by applying a cross-component linear model is provided according to a second aspect of the present invention. The apparatus according to the second aspect of the present invention includes an acquisition unit, a determination unit, and a calculation unit. The acquisition unit is configured to acquire a reconstructed luma sample. The determination unit is configured to determine a maximum luma sample value and a minimum luma sample value based on the reconstructed luma sample. The acquisition unit is further configured to acquire a difference between the maximum luma sample value and the minimum luma sample value. The determination unit is further configured to determine a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value. The calculation unit is configured to fetch a value from a look-up table (LUT) by using a set of bits following a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value as an index, obtain linear model parameters α and β based on the fetched value, and calculate a predicted chroma sample value by using the obtained linear model parameters α and β.

[0012] According to a second aspect of the invention, the device calculates the index of the LUT in an elegant manner that extracts some bits in the binary representation, resulting in more efficient fetching of values ​​from the LUT.

[0013] According to a third aspect, the invention relates to an apparatus for decoding a video stream, comprising a processor and a memory, the memory storing instructions causing the processor to carry out the method according to the first aspect or any possible embodiment of the first aspect.

[0014] According to a fourth aspect, the invention relates to an apparatus for encoding a video stream, comprising a processor and a memory storing instructions for causing the processor to carry out a method according to the first aspect or any possible embodiment thereof.

[0015] According to a fifth aspect, a computer-readable storage medium is proposed having stored thereon instructions which, when executed, cause one or more processors to be configured to code video data, the instructions causing the one or more processors to perform a method according to the first aspect or any possible embodiment of the first aspect.

[0016] According to a sixth aspect, the present invention relates to a computer program comprising a program code for performing the method according to the first aspect or any possible embodiment of the first aspect, when the computer program is executed on a computer.

[0017] The details of one or more embodiments are set forth in the accompanying drawings and the description below. Other features, objects and advantages will become apparent from the description, drawings, and claims. [Brief description of the drawings]

[0018] Embodiments of the invention are described in more detail below with reference to the accompanying figures and drawings. [Figure 1A] 1 is a block diagram illustrating an example of a video coding system configured to implement embodiments of the present invention. [Figure 1B] 2 is a block diagram illustrating another example of a video coding system configured to implement embodiments of the present invention. [Diagram 2]FIG. 2 is a block diagram illustrating an example of a video encoder configured to implement embodiments of the present invention. [Diagram 3] 2 is a block diagram illustrating an exemplary structure of a video decoder configured to implement embodiments of the present invention. [Figure 4] 1 is a block diagram showing an example of an encoding device or a decoding device. [Diagram 5] FIG. 2 is a block diagram showing another example of an encoding device or a decoding device. [Figure 6] 1 is a diagram illustrating the concept of a cross-component linear model for chrominance intra prediction. [Figure 7] 1 illustrates a simplified method for linear model parameter derivation. [Figure 8] 13 is a diagram showing the occurrence probability distribution of a difference between a maximum value and a minimum value of a reference luma sample. [Figure 9] 4 is a flow chart illustrating an exemplary lookup table generation process according to an embodiment of the present invention. [Figure 10] 1 includes a flowchart illustrating an exemplary lookup table index derivation embodiment. [Figure 11] 11 is a flowchart illustrating an example intra prediction of chroma samples of a block by applying a cross-component linear model. [Figure 12] FIG. 2 is a block diagram illustrating an example structure of an apparatus for intra-prediction of chroma samples of a block by applying a cross-component linear model. [Figure 13] 31 is a block diagram showing an exemplary structure of a content supply system 3100 for implementing a content distribution service. [Figure 14] 1 is a block diagram showing the structure of an example of a terminal device.In the following, unless expressly specified otherwise, identical reference signs refer to identical or at least functionally equivalent features. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] In the following description, reference is made to the accompanying drawings which form a part of this disclosure and which show, by way of illustration, certain aspects of embodiments of the invention or in which embodiments of the invention may be used. It is understood that embodiments of the invention may be used in other ways and may include structural or logical changes not shown in the drawings. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.

[0020] For example, it is understood that disclosure related to a described method may also apply to a corresponding device or system configured to perform the method, and vice versa. For example, when one or more specific method steps are described, the corresponding device may include one or more units, e.g., functional units, for performing the described one or more method steps (e.g., one unit performing one or more steps, or multiple units each performing one or more of the multiple steps), even when such one or more units are not explicitly described or shown in the figure. On the other hand, for example, when a particular apparatus is described based on one or more units, e.g., functional units, the corresponding method may include one step for performing the function of one or more units (e.g., one step performing the function of one or more units, or multiple steps each performing one or more functions of the multiple units), even when such one or more steps are not explicitly described or shown in the figure. Furthermore, it is understood that features of various exemplary embodiments and / or aspects described herein may be combined with each other, unless specifically stated otherwise.

[0021] Video coding typically refers to the processing of a series of images forming a video or a video sequence. Instead of the term "image", the terms "frame" or "image" may be used as synonyms in the field of video coding. Video coding (or coding in general) includes two parts: video encoding and video decoding. Video encoding is performed at the source side and typically involves processing the original video image (e.g., by compression) to reduce the amount of data required to represent the video image (for more efficient storage and / or transmission). Video decoding is performed at the destination side and typically involves the reverse process compared to the encoder to reconstruct the video image. The embodiments referring to "coding" of a video image (or images in general) shall be understood to relate to "encoding" or "decoding" of the video image or the respective video sequence. The combination of the encoding and decoding parts is also referred to as a codec (coding and decoding).

[0022] In the case of lossless video coding, the original video image can be reconstructed (assuming there is no transmission loss or other data loss during storage or transmission). That is, the reconstructed video image has the same quality as the original video image. In the case of lossy video coding, further compression is performed, for example by quantization, to reduce the amount of data representing the video image that cannot be completely reconstructed at the decoder. That is, the quality of the reconstructed video image is low or poor compared to the quality of the original video image.

[0023] Some video coding standards belong to the group of "lossy hybrid video codecs" (i.e., they combine spatial and temporal prediction in the sample domain with 2D transform coding to apply quantization in the transform domain). Each image of a video sequence is typically partitioned into a set of non-overlapping blocks, and coding is typically performed at the block level. In other words, at the encoder, the video is typically processed, i.e., encoded, at the block (video block) level, for example, by generating a predictive block using spatial (intra-image) prediction and / or temporal (inter-image) prediction, subtracting the predictive block from a current block (currently being processed / to be processed in the future) to obtain a residual block, transforming the residual block, and quantizing the residual block in the transform domain to reduce the amount of data to be transmitted (compression), while at the decoder, the reverse processing compared to the encoder is applied to the encoded or compressed block in order to reconstruct the current block for representation. Furthermore, the encoder repeats the decoder's processing loop so that both will generate the same predictions (e.g., intra-prediction and inter-prediction) and / or reconstructions for processing, i.e., coding, subsequent blocks.

[0024] In the following embodiment of a video coding system 10, a video encoder 20 and a video decoder 30 are described with reference to FIGS. 1-3.

[0025] 1A is a schematic block diagram illustrating an example coding system 10 that may utilize techniques of the present application, such as video coding system 10 (or, for short, coding system 10). A video encoder 20 (or, for short, encoder 20) and a video decoder 30 (or, for short, decoder 30) of video coding system 10 represent examples of devices that may be configured to perform techniques in accordance with various examples described herein.

[0026] As shown in FIG. 1A, coding system 10 includes a source device 12 configured to provide encoded image data 21 to, for example, a destination device 14 for decoding the encoded image data 21.

[0027] The source device 12 comprises an encoder 20 and may additionally, i.e. optionally, comprise an image source 16 , a pre-processor (or pre-processing unit) 18 , for example an image pre-processor 18 , and a communication interface or unit 22 .

[0028] Image source 16 may comprise or be any kind of imaging device, e.g., a camera for capturing real-world images, and / or any kind of image generating device, e.g., a computer graphics processor for generating computer-animated images, or any kind of other device for acquiring and / or providing real-world images, computer-generated images (e.g., screen content, virtual reality (VR) images), and / or any combination thereof (e.g., augmented reality (AR) images). Image source may be any kind of memory or storage that stores any of the above mentioned images.

[0029] In distinction to the pre-processor 18 and the processing performed by the pre-processing unit 18 , the image or image data 17 may also be referred to as raw image or raw image data 17 .

[0030] The pre-processor 18 is configured to receive the (raw) image data 17 and perform pre-processing on the image data 17 to obtain a pre-processed image 19 or pre-processed image data 19. The pre-processing performed by the pre-processor 18 may include, for example, cropping, color format conversion (e.g., from RGB to YCbCr), color correction or noise removal. It can be understood that the pre-processing unit 18 may be an optional component.

[0031] Video encoder 20 is configured to receive preprocessed image data 19 and provide encoded image data 21 (described in further detail below, e.g., based on FIG. 2). Communications interface 22 of source device 12 may be configured to receive encoded image data 21 and transmit encoded image data 21 (or any further processed version thereof) via communications channel 13 to another device, e.g., destination device 14 or any other device, for storage or direct reconstruction.

[0032] The destination device 14 comprises a decoder 30 (e.g., a video decoder 30), and may additionally, i.e. optionally, comprise a communications interface or unit 28, a post-processor 32 (or post-processing unit 32), and a display device 34.

[0033] The communications interface 28 of the destination device 14 is configured to receive the encoded image data 21 (or any further processed version thereof), for example directly from the source device 12 or from any other source, for example a storage device, for example a storage device for encoded image data, and to provide the encoded image data 21 to a decoder 30.

[0034] The communication interface 22 and the communication interface 28 may be configured to transmit or receive the encoded image data 21 or the encoded data 13 via a direct communication link between the source device 12 and the destination device 14, e.g., a direct wired or wireless connection, or via any type of network, e.g., a wired or wireless network or any combination thereof, or any type of private and public network or any combination thereof.

[0035] The communications interface 22 may be configured, for example, to package the encoded image data 21 into an appropriate format, e.g., packets, and / or process the encoded image data using any type of transmission encoding or processing for transmission over a communications link or network.

[0036] Communications interface 28, which forms a counterpart of communications interface 22, may be configured, for example, to receive transmitted data and process the transmitted data using any type of corresponding transmission decoding or processing and / or depackaging to obtain encoded image data 21.

[0037] Both communication interface 22 and communication interface 28 may be configured as unidirectional communication interfaces, as indicated by the arrows for communication channel 13 pointing from source device 12 to destination device 14 in FIG. 1A , or as bidirectional communication interfaces, e.g., configured to send and receive messages, e.g., set up connections, and confirm and exchange communications links and / or any other information related to data transmission, e.g., transmission of encoded image data.

[0038] The decoder 30 is configured to receive the encoded image data 21 and provide decoded image data 31 or a decoded image 31 (further details are described below, e.g., based on FIG. 3 or FIG. 5).

[0039] The post-processor 32 of the destination device 14 is configured to post-process the decoded image data 31 (also called reconstructed image data), e.g. the decoded image 31, to obtain post-processed image data 33, e.g. the post-processed image 33. The post-processing performed by the post-processing unit 32 may include, e.g. color format conversion (e.g. from YCbCr to RGB), color correction, cropping or resampling, or any other processing, e.g. for the purpose of preparing the decoded image data 31 for display by, e.g., a display device 34.

[0040] A display device 34 of destination device 14 is configured to receive the post-processed image data 33 for displaying the image, e.g., to a user or viewer. Display device 34 may be or comprise any type of display for presenting the reconstructed image, e.g., an integrated or external display or monitor. The display may comprise, for example, a liquid crystal display (LCD), an organic light emitting diode (OLED) display, a plasma display, a projector, a micro LED display, liquid crystal on silicon (LCoS), a digital light processor (DLP), or any type of other display.

[0041] 1A illustrates source device 12 and destination device 14 as separate devices, an embodiment of the devices may also include both or both of their functionality, i.e., source device 12 or corresponding functionality and destination device 14 or corresponding functionality. In such an embodiment, source device 12 or corresponding functionality and destination device 14 or corresponding functionality may be implemented using the same hardware and / or software or by separate hardware and / or software or any combination thereof.

[0042] As will be clear to a person skilled in the art based on the description, the presence and (exact) division of functions of different units or functions within source device 12 and / or destination device 14 as shown in FIG. 1A may vary depending on the actual device and application.

[0043] The encoder 20 (e.g., video encoder 20) or the decoder 30 (e.g., video decoder 30) or both the encoder 20 and the decoder 30 may be implemented via processing circuitry as shown in FIG. 1B, such as one or more microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), discrete logic, hardware, dedicated to video coding, or any combination thereof. The encoder 20 may be implemented via processing circuitry 46 to embody various modules discussed in connection with the encoder 20 of FIG. 2 and / or any other encoder system or encoder subsystem described herein. The decoder 30 may be implemented via processing circuitry 46 to embody various modules discussed in connection with the decoder 30 of FIG. 3 and / or any other decoder system or decoder subsystem described herein. The processing circuitry may be configured to perform various operations as discussed later. 5, where these techniques are implemented in part in software, the device may store instructions for the software on a suitable non-transitory computer-readable storage medium and may execute the instructions in hardware using one or more processors to perform the techniques of this disclosure. Either video encoder 20 and video decoder 30 may be integrated as part of a combined encoder / decoder (codec) in a single device, for example, as shown in FIG. 1B.

[0044] The source device 12 and the destination device 14 may comprise any of a wide range of devices, including any type of handheld or stationary device, such as a notebook or laptop computer, a mobile phone, a smartphone, a tablet or tablet computer, a camera, a desktop computer, a set-top box, a television, a display device, a digital media player, a video game console, a video streaming device (such as a content service server or a content distribution server), a broadcast receiver or transmitter device, and the like, and may use no operating system or any type of operating system. In some cases, the source device 12 and the destination device 14 may be equipped for wireless communication. Thus, the source device 12 and the destination device 14 may be wireless communication devices.

[0045] In some cases, the video coding system 10 shown in FIG. 1A is merely an example, and the techniques of the present application may be applied to video coding settings (e.g., video encoding or video decoding) that do not necessarily include any data communication between an encoding device and a decoding device. In other examples, data may be retrieved from local memory, streamed over a network, etc. A video encoding device may encode and store data in memory, and / or a video decoding device may retrieve and decode data from memory. In some examples, encoding and decoding are performed by devices that do not communicate with each other, but simply encode data to memory and / or retrieve and decode data from memory.

[0046] For ease of explanation, embodiments of the present invention are described herein with reference to reference software of High-Efficiency Video Coding (HEVC) or Versatile Video Coding (VVC), which are next-generation video coding standards developed by the Joint Collaboration Team on Video Coding (JCT-VC) of the ITU-T Video Coding Experts Group (VCEG) and the ISO / IEC Motion Picture Experts Group (MPEG). Those skilled in the art will appreciate that embodiments of the present invention are not limited to HEVC or VVC. [Encoder and encoding method]

[0047] FIG. 2 shows a schematic block diagram of an exemplary video encoder 20 configured to implement the techniques of the present application. In the example of FIG. 2, the video encoder 20 includes an input 201 (or an input interface 201), a residual calculation unit 204, a transform processing unit 206, a quantization unit 208, an inverse quantization unit 210, an inverse transform processing unit 212, a reconstruction unit 214, a loop filter unit 220, a decoded picture buffer (DPB) 230, a mode selection unit 260, an entropy encoding unit 270, and an output 272 (or an output interface 272). The mode selection unit 260 may include an inter prediction unit 244, an intra prediction unit 254, and a partitioning unit 262. The inter prediction unit 244 may include a motion estimation unit and a motion compensation unit (not shown). The video encoder 20 as shown in FIG. 2 may also be referred to as a hybrid video encoder, or a video encoder with a hybrid video codec.

[0048] The residual calculation unit 204, the transform processing unit 206, the quantization unit 208, and the mode selection unit 260 may be referred to as forming a forward signal path of the encoder 20, while the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the buffer 216, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244, and the intra prediction unit 254 may be referred to as forming a backward signal path of the video encoder 20. The backward signal path of the video encoder 20 corresponds to the signal path of the decoder (see the video decoder 30 in FIG. 3). The inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244, and the intra prediction unit 254 may also be referred to as forming a "built-in decoder" of the video encoder 20. [Images and Image Segmentation (Images and Blocks)]

[0049] The encoder 20 may be configured to receive, for example via an input 201, an image 17 (or image data 17), e.g., a image of a sequence of images forming a video or a video sequence. The received image or image data may be a preprocessed image 19 (or preprocessed image data 19). For simplicity, the following description refers to the image 17. The image 17 may also be referred to as a current image or a picture to be coded (particularly in video coding, to distinguish the current image from other images, e.g., previously encoded and / or decoded images of the same video sequence, i.e., a video sequence that also includes the current image).

[0050] A (digital) image is or can be considered as a two-dimensional array or matrix of samples with intensity values. The samples in the array can also be called pixels (short for picture element) or pels. The number of samples in the horizontal and vertical directions (or axes) of the array or image determines the size and / or resolution of the image. For color representation, typically three color components are used; that is, an image can be represented as or contain three sample arrays. In an RGB format or RGB color space, an image contains corresponding red, green and blue sample arrays. However, in video coding, each pixel is typically represented in a luminance and chrominance format or color space, e.g. YCbCr, which contains a luminance component denoted by Y (sometimes L is used instead) and two chrominance components denoted by Cb and Cr. The luminance (or luma for short) component Y represents the brightness or intensity of a gray level (e.g., as in a grayscale image), while the two chrominance (or chroma for short) components Cb and Cr represent the chromaticity or color information components. Thus, an image in YCbCr format includes a luminance sample array of luminance sample values ​​(Y) and two chrominance sample arrays of chrominance values ​​(Cb and Cr). An image in RGB format may be converted or transformed to YCbCr format, or vice versa, a process also known as color conversion or color transformation. If an image is monochrome, the image may include only a luminance sample array. Thus, an image may be, for example, an array of luma samples in monochrome format, or an array of luma samples and two corresponding arrays of chroma samples in 4:2:0, 4:2:2 and 4:4:4 color formats.

[0051] An embodiment of the video encoder 20 may include an image partitioning unit (not shown in FIG. 2) configured to partition an image 17 into multiple (typically non-overlapping) image blocks 203. These blocks may also be referred to as root blocks, macroblocks (H.264 / AVC) or coding tree blocks (CTBs) or coding tree units (CTUs) (H.265 / HEVC and VVC). The image partitioning unit may be configured to partition each image into corresponding blocks using the same block size for all images of a video sequence and a corresponding grid that defines the block size, or to vary the block size among images or subsets or groups of images.

[0052] In a further embodiment, the video encoder may be configured to directly receive a block 203 of the image 17, e.g., one, some or all of the blocks forming the image 17. The image block 203 may also be referred to as a current image block or an image block to be coded.

[0053] Similar to the image 17, the image block 203 is also or may be considered as a two-dimensional array or matrix of samples having smaller dimensions than the image 17 but with intensity values ​​(sample values). In other words, the block 203 may include, for example, one sample array (e.g., a luma array in the case of a monochrome image 17, or a luma array or a chroma array in the case of a color image), or three sample arrays (e.g., one luma array and two chroma arrays in the case of a color image 17), or any other number and / or type of arrays depending on the color format applied. The number of samples in the horizontal and vertical directions (or axes) of the block 203 determines the size of the block 203. Thus, the block may be, for example, an M×N (M columns×N rows) array of samples or an M×N array of transform coefficients.

[0054] An embodiment of the video encoder 20 as shown in FIG. 2 may be configured to encode the image 17 block-by-block, eg, encoding and prediction are performed for each block 203. [Residual calculation]

[0055] The residual calculation unit 204 may be configured to calculate the residual block 205 (also referred to as residual 205) based on the image block 203 and the prediction block 265 (further details about the prediction block 265 are provided later), for example, by subtracting sample values ​​of the prediction block 265 sample-by-sample (pixel-by-pixel) from sample values ​​of the image block 203 to obtain the residual block 205 in the sample domain. [conversion]

[0056] The transform processing unit 206 may be configured to apply a transform, such as a discrete cosine transform (DCT) or a discrete sine transform (DST), to the sample values ​​of the residual block 205 to obtain transform coefficients 207 in a transform domain. The transform coefficients 207 may also be referred to as transform residual coefficients and represent the residual block 205 in the transform domain.

[0057] The transform processing unit 206 may be configured to apply an integer approximation of a DCT / DST, such as the transform specified for H.265 / HEVC. Compared to an orthogonal DCT transform, such an integer approximation is typically scaled by a certain factor. To preserve the norm of the residual block processed by the forward transform and the inverse transform, an additional scaling factor is applied as part of the transform process. The scaling factor is typically chosen based on certain constraints, such as a scaling factor that is a power of two for shift operations, a bit depth of the transform coefficients, a trade-off between accuracy and implementation cost, etc. For example, a certain scaling factor may be specified for the inverse transform, e.g., by the inverse transform processing unit 212 (and a corresponding inverse transform, e.g., by the inverse transform processing unit 312 in the video decoder 30), and a corresponding scaling factor for the forward transform, e.g., by the transform processing unit 206 in the encoder 20, may be specified accordingly.

[0058] An embodiment of video encoder 20 (respectively, transform processing unit 206) may be configured to output transform parameters, such as the type of transform or transforms, e.g., directly or after being encoded or compressed via entropy encoding unit 270, so that, for example, video decoder 30 may receive and use the transform parameters for decoding. [Quantization]

[0059] The quantization unit 208 may be configured to quantize the transform coefficients 207, for example by applying scalar quantization or vector quantization, to obtain quantized coefficients 209. The quantized coefficients 209 may also be referred to as quantized transform coefficients 209 or quantized residual coefficients 209.

[0060] The quantization process may reduce the bit depth associated with some or all of the transform coefficients 207. For example, an n-bit transform coefficient may be rounded down to an m-bit transform coefficient during quantization, where n is greater than m. The degree of quantization may be modified by adjusting a quantization parameter (QP). For example, in the case of scalar quantization, different scaling may be applied to achieve finer or coarser quantization. A smaller quantization step size corresponds to a finer quantization, while a larger quantization step size corresponds to a coarser quantization. The applicable quantization step sizes may be indicated by a quantization parameter (QP). The quantization parameter may, for example, be an index of a predefined set of applicable quantization step sizes. For example, a small quantization parameter may correspond to a finer quantization (small quantization step size) and a large quantization parameter may correspond to a coarser quantization (large quantization step size), or vice versa. Quantization may include division by a quantization step size, and corresponding and / or inverse dequantization, e.g., by the inverse quantization unit 210, may include multiplication by the quantization step size. Some standard embodiments, e.g., HEVC, may be configured to use a quantization parameter to determine the quantization step size. In general, the quantization step size may be calculated based on the quantization parameter using a fixed-point approximation of an equation that includes a division. To restore the norm of the residual block, an additional scaling factor may be introduced in the quantization and dequantization, which may be modified due to the scaling used in the fixed-point approximation of the equation for the quantization step size and the quantization parameter. In one exemplary implementation, the scaling of the inverse transform and dequantization may be combined. Alternatively, customized quantization tables may be used and signaled, e.g., in the bitstream, from the encoder to the decoder. Quantization is a lossy operation, and the larger the quantization step size, the greater the loss.

[0061] An embodiment of video encoder 20 (respectively, quantization unit 208) may be configured to output a quantization parameter (QP), e.g., directly or after being encoded via entropy encoding unit 270. As a result, for example, video decoder 30 may receive and apply the quantization parameter for decoding. [Dequantization]

[0062] Inverse quantization unit 210 is configured to apply the inverse quantization of quantization unit 208 to the quantized coefficients, e.g., by applying the inverse of the quantization scheme applied by quantization unit 208 based on or using the same quantization step size as quantization unit 208, to obtain dequantized coefficients 211. The dequantized coefficients 211, which may also be referred to as dequantized residual coefficients 211, correspond to the transform coefficients 207, although they are typically not identical to the transform coefficients due to losses due to quantization. [Inverse Transformation]

[0063] The inverse transform processing unit 212 is configured to apply an inverse transform of the transform applied by the transform processing unit 206, such as an inverse discrete cosine transform (DCT) or an inverse discrete sine transform (DST) or other inverse transform, to obtain a reconstructed residual block 213 (or corresponding dequantized coefficients 213) in the sample domain. The reconstructed residual block 213 may also be referred to as a transform block 213. [Rebuild]

[0064] The reconstruction unit 214 (e.g., an adder or summator 214) is configured to add the transform block 213 (i.e., the reconstructed residual block 213) to the prediction block 265, for example by adding the sample values ​​of the reconstructed residual block 213 and the sample values ​​of the prediction block 265 sample by sample, to obtain a reconstructed block 215 in the sample domain. [filtering]

[0065] The loop filter unit 220 (or "loop filter" 220 for short) is configured to filter the reconstructed block 215 to obtain a filtered block 221, or in general, to filter the reconstructed samples to obtain filtered samples. The loop filter unit is configured to, for example, smooth pixel transitions or otherwise improve video quality. The loop filter unit 220 may include one or more loop filters, such as a deblocking filter, a sample adaptive offset (SAO) filter, or one or more other filters, such as a bilateral filter, an adaptive loop filter (ALF), a sharpening filter, a smoothing filter, or a collaborative filter, or any combination thereof. The loop filter unit 220 is illustrated in FIG. 2 as being an in-loop filter, but in other configurations may be implemented as a post-loop filter. The filtered block 221 may also be referred to as a filtered reconstructed block 221.

[0066] Embodiments of video encoder 20 (respectively, loop filter unit 220) may be configured to output loop filter parameters (such as sample adaptive offset information), e.g., directly or after being encoded via entropy encoding unit 270. As a result, for example, decoder 30 may receive and apply the same loop filter parameters or respective loop filters for decoding. [Decoded image buffer]

[0067] The decoded picture buffer (DPB) 230 may be a memory that stores reference pictures or generally reference image data for encoding video data by the video encoder 20. The DPB 230 may be formed by any of a variety of memory devices, such as dynamic random access memory (DRAM), including synchronous DRAM (SDRAM), magnetoresistive RAM (MRAM), resistive RAM (RRAM), or other types of memory devices. The decoded picture buffer (DPB) 230 may be configured to store one or more filtered blocks 221. The decoded picture buffer 230 may further be configured to store other previously filtered blocks, e.g. previously reconstructed filtered blocks 221, of the same current picture or a different picture, e.g. a previously reconstructed picture, and may provide a complete, previously reconstructed, i.e. decoded picture (corresponding reference blocks and reference samples) and / or a partially reconstructed current picture (corresponding reference blocks and reference samples), e.g. for inter prediction. The decoded picture buffer (DPB) 230 may also be configured to store one or more unfiltered reconstructed blocks 215 or, in general, unfiltered reconstructed samples, for example if the reconstructed blocks 215 have not been filtered by the loop filter unit 220, or any other further processed version of the reconstructed blocks or samples. Mode Selection (Segmentation and Prediction)

[0068] The mode selection unit 260 comprises a partitioning unit 262, an inter prediction unit 244 and an intra prediction unit 254, and is configured to receive or obtain original image data, e.g., original block 203 (current block 203 of current image 17), and reconstructed image data, e.g., filtered and / or unfiltered reconstructed samples or blocks of the same (current) image and / or from one or more previously decoded images, e.g., from a decoded image buffer 230 or other buffers (e.g., line buffers, not shown). The reconstructed image data is used as reference image data for prediction, e.g., inter prediction or intra prediction, to obtain a prediction block 265 or a predictor 265.

[0069] The mode selection unit 260 may be configured to determine or select a partitioning for the current block prediction mode (not including partitioning) and a prediction mode (e.g., an intra prediction mode or an inter prediction mode) and generate a corresponding prediction block 265 used for calculation of the residual block 205 and reconstruction of the reconstructed block 215.

[0070] An embodiment of the mode selection unit 260 may be configured to select a partitioning and prediction mode (e.g., from those supported by or available for the mode selection unit 260) that provides the best match, or in other words, the smallest residual (smallest residual means better compression rate for transmission or storage) or the smallest signaling overhead (smallest signaling overhead means better compression rate for transmission or storage), or both are considered or a balance of both is taken into account. The mode selection unit 260 may be configured to determine the partitioning and prediction mode based on rate-distortion optimization (RDO), i.e., to select the prediction mode that provides the smallest rate-distortion. Terms such as "best", "minimum", "optimum", etc. in this context do not necessarily refer to an overall "best", "minimum", "optimum", etc., but may also refer to the achievement of a termination or selection criterion, such as a value exceeding or falling below a threshold value, or other constraints that potentially lead to a "suboptimal selection" but reduce complexity and processing time.

[0071] In other words, the partitioning unit 262 may be configured to partition the block 203 into smaller block partitions or sub-blocks (reforming the block) using, for example, a quad-tree partitioning (QT), a binary partitioning (BT) or a triple-tree partitioning (TT) or any combination thereof iteratively, and to perform, for example, prediction on each of the block partitions or sub-blocks. The mode selection includes the selection of a tree structure of the partitioned block 203, and a prediction mode is applied to each of the block partitions or sub-blocks.

[0072] The partitioning (eg, by partitioning unit 262) and prediction (eg, by inter prediction unit 244 and intra prediction unit 254) processes performed by the exemplary video encoder 20 are described in more detail below. [Partitioning]

[0073] The partitioning unit 262 may partition (or split) the current block 203 into smaller partitions, e.g., smaller blocks of square or rectangular size. These smaller blocks (which may also be referred to as sub-blocks) may be further partitioned into even smaller partitions. This is also referred to as tree partitioning or hierarchical tree partitioning. A root block, e.g., root tree level 0 (hierarchical level 0, depth 0), may be partitioned recursively, e.g., into two or more blocks of nodes at the next lower tree level, e.g., tree level 1 (hierarchical level 1, depth 1). These blocks may be partitioned again into two or more blocks at the next lower level, e.g., tree level 2 (hierarchical level 2, depth 2), etc., until the partitioning is terminated, e.g., due to a termination criterion being met, e.g., a maximum tree depth or a minimum block size being reached. Blocks that are not further partitioned are also referred to as leaf blocks or leaf nodes of the tree. A tree that uses partitioning into two partitions is called a binary tree (BT), a tree that uses partitioning into three partitions is called a ternary tree (TT), and a tree that uses partitioning into four partitions is called a quad tree (QT).

[0074] As mentioned before, the term "block" as used herein may be a portion of an image, in particular a square or rectangular portion. For example, with reference to HEVC and VVC, a block may be or correspond to a coding tree unit (CTU), coding unit (CU), prediction unit (PU) or transform unit (TU) and / or a corresponding block, such as a coding tree block (CTB), coding block (CB), transform block (TB) or prediction block (PB).

[0075] For example, the coding tree unit (CTU) may be or comprise a CTB of luma samples and two corresponding CTBs of chroma samples of an image having three sample arrays, or a CTB of samples of a monochrome image or of an image coded with three separate color planes and syntax structures used to code the samples. Correspondingly, the coding tree block (CTB) may be an N×N block of samples of a certain value N, such that the division of the components into CTBs is a partitioning. The coding unit (CU) may be or comprise a coding block of luma samples and two corresponding coding blocks of chroma samples of an image having three sample arrays, or a coding block of samples of a monochrome image or of an image coded with three separate color planes and syntax structures used to code the samples. Correspondingly, the coding block (CB) may be an M×N block of samples of certain values ​​M and N, such that the division of the CTB into coding blocks is a partitioning.

[0076] In some embodiments, for example according to HEVC, coding tree units (CTUs) may be divided into CUs by using a quad-tree structure represented as a coding tree. The decision of whether to code an image area with inter-image (temporal) prediction or intra-image (spatial) prediction is made at the CU level. Each CU may be further divided into one, two or four PUs according to the partition type of the PU. Inside one PU, the same prediction process is applied, and related information is sent to the decoder on a PU basis. After obtaining the residual block by applying the prediction process based on the partition type of the PU, the CU may be partitioned into transform units (TUs) according to another quad-tree structure similar to the coding tree of the CU.

[0077] For example, in an embodiment according to the latest video coding standard currently under development, called Versatile Video Coding (VVC), quad-tree and binary-tree (QTBT) partitioning is used to partition the coding block. In the QTBT block structure, the CU may have either a square or rectangular shape. For example, the coding tree unit (CTU) is first partitioned by a quad-tree structure. The quad-tree leaf node is further partitioned by a binary tree or a ternary (or triple) tree structure. The partitioning tree leaf node is called the coding unit (CU), and its segmentation is used for prediction and transformation processing without any further partitioning. This means that the CU, PU and TU have the same block size in the QTBT coding block structure. In parallel, it has also been proposed to use multiple partitioning, for example, triple-tree partitioning, with the QTBT block structure.

[0078] In one example, mode selection unit 260 of video encoder 20 may be configured to perform any combination of the partitioning techniques described herein.

[0079] As described above, video encoder 20 is configured to determine or select a best or optimal prediction mode from a (predetermined) set of prediction modes, which may include, for example, intra-prediction modes and / or inter-prediction modes. [Intra prediction]

[0080] The set of intra prediction modes may include 35 different intra prediction modes, e.g., non-directional modes such as DC (or average) mode and planar mode, or directional modes defined, e.g., in HEVC, and may include 67 different intra prediction modes, e.g., non-directional modes such as DC (or average) mode and planar mode, or directional modes defined, e.g., for VVC.

[0081] The intra prediction unit 254 is configured to generate an intra prediction block 265 according to an intra prediction mode from a set of intra prediction modes using reconstructed samples of neighboring blocks of the same current image.

[0082] Intra prediction unit 254 (or generally, mode selection unit 260) may further be configured to output intra prediction parameters (or generally, information indicating the selected intra prediction mode for the block) to entropy encoding unit 270 in the form of syntax element 266 for inclusion in encoded image data 21. As a result, for example, video decoder 30 may receive and use the prediction parameters for decoding. [Inter prediction]

[0083] The set of inter prediction modes (or possible inter prediction modes) depends on the available reference images (i.e., previous, at least partially decoded images, e.g., stored in DPB 230) and other inter prediction parameters, e.g., whether the entire reference image or only a part of it, e.g., a search window area around the area of ​​the current block of the reference image, is used to search for the best matching reference block, and / or, e.g., whether pixel interpolation, e.g., half / semi-pel and / or quarter-pel interpolation, is applied. In addition to the above prediction modes, skip mode and / or direct mode may be applied.

[0084] The inter prediction unit 244 may include a motion estimation (ME) unit and a motion compensation (MC) unit (both not shown in FIG. 2). The motion estimation unit may be configured to receive or obtain the image block 203 (the current image block 203 of the current image 17) and the decoded image 231, or at least one or more previously reconstructed blocks, such as reconstructed blocks of one or more other / different previously decoded images 231, for motion estimation. For example, a video sequence may include the current image and the previously decoded image 231, or in other words, the current image and the previously decoded image 231 may be part of or form a series of images forming a video sequence.

[0085] The encoder 20 may be configured to, for example, select a reference block from multiple reference blocks of the same or different images of multiple other images, and provide the reference image (or reference image index) and / or an offset (spatial offset) between the position (x coordinate, y coordinate) of the reference block and the position of the current block as an inter-prediction parameter to the motion estimation unit. This offset is also called a motion vector (MV).

[0086] The motion compensation unit is configured to obtain, e.g., receive, inter prediction parameters, and perform inter prediction based on or using the inter prediction parameters to obtain an inter prediction block 265. The motion compensation performed by the motion compensation unit may involve fetching or generating a prediction block based on a motion / block vector determined by motion estimation, and possibly performing interpolation with sub-pixel accuracy. Interpolation filtering may generate additional pixel samples from known pixel samples. Thus, the number of candidate prediction blocks that may be used to code the image block is potentially increased. Upon receiving a motion vector for the PU of the current image block, the motion compensation unit may locate the prediction block to which the motion vector points in one of the reference image lists.

[0087] The motion compensation unit may also generate block and video slice related syntax elements used by video decoder 30 in decoding the image blocks of the video slices. [Entropy coding]

[0088] The entropy encoding unit 270 is configured to, for example, apply an entropy encoding algorithm or scheme (e.g., a variable length coding (VLC) scheme, a context-adaptive VLC scheme (CAVLC), an arithmetic coding scheme, binarization, context-adaptive binary arithmetic coding (CABAC), syntax-based context-adaptive binary arithmetic coding (SBAC), probability interval partitioning entropy (PIPE) coding, or another entropy encoding method or technique) or bypass (no compression) to the quantized coefficients 209, the inter-prediction parameters, the intra-prediction parameters, the loop filter parameters, and / or other syntax elements to obtain encoded image data 21, which may be output via an output 272, for example, in the form of an encoded bitstream 21. As a result, for example, the video decoder 30 may receive and use the parameters for decoding. The encoded bitstream 21 may be transmitted to the video decoder 30 or stored in a memory for later transmission or retrieval by the video decoder 30.

[0089] Other structural variations of the video encoder 20 may be used to encode the video stream. For example, a non-transform-based encoder 20 may directly quantize the residual signal without a transform processing unit 206 for a particular block or frame. In another implementation, the encoder 20 may have the quantization unit 208 and the inverse quantization unit 210 combined into a single unit. [Decoder and Decoding Method]

[0090] 3 illustrates an example of a video decoder 30 configured to implement the techniques of the present application. The video decoder 30 is configured to receive encoded image data 21 (e.g., encoded bitstream 21), e.g., as encoded by encoder 20, to obtain a decoded image 331. The encoded image data or bitstream includes information for decoding the encoded image data, e.g., data representing image blocks of encoded video slices and associated syntax elements.

[0091] In the example of Figure 3, the decoder 30 includes an entropy decoding unit 304, an inverse quantization unit 310, an inverse transform processing unit 312, a reconstruction unit 314 (e.g., summer 314), a loop filter 320, a decoded picture buffer (DPB) 330, an inter prediction unit 344, and an intra prediction unit 354. The inter prediction unit 344 may be or may include a motion compensation unit. The video decoder 30 may, in some examples, perform a decoding path that is generally the reverse of the encoding path described in connection with the video encoder 20 of Figure 2.

[0092] As described in connection with the encoder 20, the inverse quantization unit 210, the inverse transform processing unit 212, the reconstruction unit 214, the loop filter 220, the decoded picture buffer (DPB) 230, the inter prediction unit 244, and the intra prediction unit 254 are also referred to as forming a “built-in decoder” of the video encoder 20. Thus, the inverse quantization unit 310 may be functionally identical to the inverse quantization unit 210, the inverse transform processing unit 312 may be functionally identical to the inverse transform processing unit 212, the reconstruction unit 314 may be functionally identical to the reconstruction unit 214, the loop filter 320 may be functionally identical to the loop filter 220, and the decoded picture buffer 330 may be functionally identical to the decoded picture buffer 230. Thus, the descriptions provided for the respective units and functions of the video encoder 20 apply correspondingly to the respective units and functions of the video decoder 30. [Entropy Decoding]

[0093] The entropy decoding unit 304 is configured to analyze the bitstream 21 (or generally, the encoded image data 21) and, for example, perform entropy decoding on the encoded image data 21 to obtain, for example, quantized coefficients 309 and / or decoded coding parameters (not shown in FIG. 3), for example, any or all of inter prediction parameters (e.g., reference image index and motion vectors), intra prediction parameters (e.g., intra prediction modes or intra prediction indexes), transform parameters, quantization parameters, loop filter parameters, and / or other syntax elements. The entropy decoding unit 304 may be configured to apply a decoding algorithm or a decoding scheme corresponding to an encoding scheme such as described in connection with the entropy encoding unit 270 of the encoder 20. The entropy decoding unit 304 may further be configured to provide the inter prediction parameters, intra prediction parameters, and / or other syntax elements to the mode selection unit 360 and other parameters to other units of the decoder 30. The video decoder 30 may receive the syntax elements at a video slice level and / or a video block level. [Dequantization]

[0094] Inverse quantization unit 310 may be configured to receive a quantization parameter (QP) (or generally, information related to inverse quantization) and quantized coefficients (e.g., by parsing and / or decoding, e.g., by entropy decoding unit 304) from encoded image data 21 and apply inverse quantization to the decoded quantized coefficients 309 based on the quantization parameter to obtain dequantized coefficients 311, which may also be referred to as transform coefficients 311. The inverse quantization process may include use of the quantization parameter determined by video encoder 20 for each video block in a video slice to determine the degree of quantization, and thus the degree of inverse quantization to be applied. [Inverse Transformation]

[0095] The inverse transform processing unit 312 may be configured to receive the dequantized coefficients 311, also referred to as transform coefficients 311, and apply a transform to the dequantized coefficients 311 to obtain a reconstructed residual block 313 in the sample domain. The reconstructed residual block 313 may also be referred to as a transform block 313. This transform may be an inverse transform, e.g., an inverse DCT, an inverse DST, an inverse integer transform, or a conceptually similar inverse transform process. The inverse transform processing unit 312 may further be configured to receive transform parameters or corresponding information from the encoded image data 21 (e.g., by analysis and / or decoding, e.g., by the entropy decoding unit 304) to determine the transform to be applied to the dequantized coefficients 311. [Rebuild]

[0096] The reconstruction unit 314 (e.g., an adder or summator 314) may be configured to add the reconstructed residual block 313 to the prediction block 365, for example, by adding sample values ​​of the reconstructed residual block 313 and sample values ​​of the prediction block 365 to obtain a reconstructed block 315 in the sample domain. [filtering]

[0097] A loop filter unit 320 (either in the coding loop or after the coding loop) is configured to filter the reconstructed block 315 to obtain a filtered block 321, e.g., to smooth pixel transitions or otherwise improve video quality. The loop filter unit 320 may include one or more loop filters, such as a deblocking filter, a sample adaptive offset (SAO) filter, or one or more other filters, such as, e.g., a bilateral filter, an adaptive loop filter (ALF), a sharpening filter, a smoothing filter, or a collaborative filter, or any combination thereof. Although the loop filter unit 320 is shown in FIG. 3 as being an in-loop filter, in other configurations it may be implemented as a post-loop filter. [Decoded image buffer]

[0098] The decoded video block 321 of the image is then stored in a decoded image buffer 330 which stores the decoded image 331 as a reference image for subsequent motion compensation of other images and / or for output or display, respectively.

[0099] The decoder 30 is arranged to output a decoded image 311, for example via an output 312, for presentation or viewing to a user. [prediction]

[0100] The inter prediction unit 344 may be identical to the inter prediction unit 244 (in particular the motion compensation unit), and the intra prediction unit 354 may be functionally identical to the intra prediction unit 254 and performs the partitioning or partitioning decision and prediction based on partitioning parameters and / or prediction parameters or respective information received (e.g. by parsing and / or decoding, e.g. by the entropy decoding unit 304) from the encoded image data 21. The mode selection unit 360 may be configured to perform prediction (intra prediction or inter prediction) on a block-by-block basis based on the reconstructed image, block or respective samples (filtered or unfiltered) to obtain a prediction block 365.

[0101] If the video slice is coded as an intra-coded (I) slice, the intra prediction unit 354 of the mode selection unit 360 is configured to generate a prediction block 365 for an image block of the current video slice based on the signaled intra prediction mode and data from a previously decoded block of the current image. If the video image is coded as an inter-coded (i.e., B or P) slice, the inter prediction unit 344 (e.g., a motion compensation unit) of the mode selection unit 360 is configured to generate a prediction block 365 for a video block of the current video slice based on the motion vector and other syntax elements received from the entropy decoding unit 304. For inter prediction, the prediction block may be generated from one of the reference images included in one of the reference image lists. The video decoder 30 may construct the reference frame lists, List 0 and List 1, based on the reference images stored in the DPB 330 using a default construction technique.

[0102] Mode selection unit 360 is configured to determine prediction information for the video blocks of the current video slice by analyzing the motion vectors and other syntax elements, and uses the prediction information to generate predictive blocks for the current video block being decoded. For example, mode selection unit 360 uses some of the received syntax elements to determine a prediction mode (e.g., intra prediction or inter prediction) to be used to code the video blocks of the video slice, an inter-prediction slice type (e.g., a B slice, a P slice, or a GPB slice), construction information regarding one or more of the reference image lists for the slice, a motion vector for each of the inter-encoded video blocks of the slice, an inter-prediction status for each of the inter-coded video blocks of the slice, and other information for decoding the video blocks in the current video slice.

[0103] Other variations of the video decoder 30 may be used to decode the encoded image data 21. For example, the decoder 30 may generate an output video stream without a loop filtering unit 320. For example, the non-transform-based decoder 30 may directly inverse quantize the residual signal without an inverse transform processing unit 312 for a particular block or frame. In another implementation, the video decoder 30 may have the inverse quantization unit 310 and the inverse transform processing unit 312 combined into a single unit.

[0104] It should be understood that in the encoder 20 and the decoder 30, the processing result of the current stage may be further processed and then output to the next stage. For example, after the interpolation filtering, the motion vector derivation or the loop filtering, further operations such as Clip or Shift may be performed on the processing result of the interpolation filtering, the motion vector derivation or the loop filtering.

[0105] It should be noted that further operations may be applied to the derived motion vector of the current block (including but not limited to control point motion vectors in affine mode, sub-block motion vectors in affine mode, planar mode, ATMVP mode, and temporal motion vectors, etc.). For example, the value of the motion vector is restricted to a predefined range according to its representation bit number. If the representation bit of the motion vector is bitDepth, its range is -2^(bitDepth-1) to 2^(bitDepth-1)-1. "^" means exponentiation. For example, if bitDepth is set equal to 16, its range is -32768 to 32767, and if bitDepth is set equal to 18, its range is -131072 to 131071. For example, the value of the derived motion vector (e.g., MVs of four 4x4 sub-blocks in one 8x8 block) is restricted such that the maximum difference between the integer parts of the four 4x4 sub-block MVs is N pixels or less, such as 1 pixel or less. Here, we provide two methods to constrain the motion vector according to bitDepth.

[0106] Method 1: Remove the overflow MSB (most significant bit) by the following operation:

number

number

number

number

[0107] For example, if the value of mvx is -32769, then after applying equations (1) and (2), the resulting value is 32767. In computer systems, decimal numbers are stored as two's complement. The two's complement of -32769 is 1, 0111, 1111, 1111, 1111 (17 bits), then the MSB is discarded so the resulting two's complement is 0111, 1111, 1111, 1111 (decimal number is 32767), which is the same as the output by applying equations (1) and (2).

number

number

number

number

[0108] Method 2: Remove the overflow MSB by clipping the value.

number

number

number

[0109] 4 is a schematic diagram of a video coding device 400 according to an embodiment of the present disclosure. The video coding device 400 is suitable for implementing the embodiments of the present disclosure described herein. In an embodiment, the video coding device 400 may be a decoder, such as the video decoder 30 of FIG. 1A, or an encoder, such as the video encoder 20 of FIG. 1A.

[0110] Video coding device 400 comprises an ingress port 410 (or input port 410) and a receiver unit (Rx) 420 for receiving data, a processor, logic unit or central processing unit (CPU) 430 for processing data, a transmitter unit (Tx) 440 and an egress port 450 (or output port 450) for transmitting data, and a memory 460 for storing data. Video coding device 400 may also comprise optical / electrical (OE) and electrical / optical (EO) components coupled to the ingress port 410, the receiver unit 420, the transmitter unit 440, and the egress port 450 for egress or ingress of optical or electrical signals.

[0111] The processor 430 is implemented by hardware and software. The processor 430 may be implemented as one or more CPU chips, cores (e.g., as a multi-core processor), FPGA, ASIC, and DSP. The processor 430 communicates with the ingress port 410, the receiver unit 420, the transmitter unit 440, the egress port 450, and the memory 460. The processor 430 has a coding module 470. The coding module 470 implements the disclosed embodiments described above. For example, the coding module 470 implements, processes, prepares, or provides various coding operations. Thus, the inclusion of the coding module 470 provides a substantial improvement in the functionality of the video coding device 400, resulting in the transformation of the video coding device 400 to different states. Alternatively, the coding module 470 is implemented as instructions stored in the memory 460 and executed by the processor 430.

[0112] Memory 460 may comprise one or more disks, tape drives, and solid state drives, and may be used as an overflow data storage device for storing programs when such programs are selected for execution, and for storing instructions and data read during execution of the programs. Memory 460 may be, for example, volatile and / or non-volatile, and may be read only memory (ROM), random access memory (RAM), ternary content addressable memory (TCAM), and / or static random access memory (SRAM).

[0113] FIG. 5 is a simplified block diagram of an apparatus 500 that may be used as either or both of the source device 12 and the destination device 14 of FIG. 1A according to an example embodiment.

[0114] The processor 502 in the device 500 may be a central processing unit. Alternatively, the processor 502 may be any other type of device or devices, now existing or later developed, that can manipulate or process information. Although the disclosed implementations may be practiced with a single processor as shown, such as the processor 502, speed and efficiency advantages may be realized with more than one processor.

[0115] In implementation, the memory 504 in the apparatus 500 may be a read-only memory (ROM) device or a random access memory (RAM) device. Any other suitable type of storage device may be used as the memory 504. The memory 504 may include code and data 506 that is accessed by the processor 502 using a bus 512. The memory 504 may further include an operating system 508 and application programs 510, which include at least one program that enables the processor 502 to perform the methods described herein. For example, the application programs 510 may include applications 1 through N, which further include a video coding application that performs the methods described herein.

[0116] The apparatus 500 may also include one or more output devices, such as a display 518. The display 518, in one example, may be a touch-sensitive display that combines a display with a touch-sensitive element operable to detect touch input. The display 518 may be coupled to the processor 502 via the bus 512.

[0117] Although shown here as a single bus, the bus 512 of the device 500 may be comprised of multiple buses. Additionally, the secondary storage 514 may be directly coupled to other components of the device 500 or may be accessed over a network and may comprise a single integrated unit such as a memory card or multiple units such as multiple memory cards. Thus, the device 500 may be implemented in a wide variety of configurations. Intra prediction of chroma samples may be performed using samples of the reconstructed luma block.

[0118] During the development of HEVC, Cross-Component Linear Model (CCLM) chroma intra prediction [J. Kim, S.-W. Park, J.-Y. Park, and B.-M. Jeon, Intra Chroma Prediction Using Inter Channel Correlation, document JCTVC-B021, Jul. 2010] was proposed. CCLM uses linear correlation between chroma and luma samples at corresponding positions in a coding block. When a chroma block is coded using CCLM, a linear model is derived from the reconstructed adjacent luma and chroma samples by linear regression. The chroma samples in the current block can then be predicted by the reconstructed luma samples in the current block using the derived linear model (see Figure 6).

number

number

number

[0119] If the encoded or decoded image has a format that specifies different numbers of samples for the luma and chroma components (e.g., 4:2:0 YCbCr format), the luma samples are downsampled before modeling and prediction.

[0120] The method has been adopted for use in VTM 2.0. Specifically, the parameter derivation is performed as follows.

number

number

[0121] [G. Laroche, J. Taquet, C. Gisquet, P. Onno (Canon), "CE3: Cross-component linear model simplification (Test 5.1)", Input document to 12 th At the JVET Meeting in Macao, China, Oct. 2018, a different method was proposed to derive α and β (see Figure 7). In particular, the linear model parameters α and β are obtained according to the following equations:

number

number

number

number

[0122] It has also been proposed to implement the division operation using multiplication by numbers stored in a look-up table (LUT) specified in Table 1. This substitution is possible by using the following method.

number

[0123] Table 1 provides the matching of LUT index ranges (given in the first row of the table) with lists of values ​​stored in the LUT, each of which corresponds to an index range.

number

number

[0124] Using the LUT defined in Table 1 (or equivalently calculated using the above formula), the calculation of α is performed as follows:

number

[0125] The shift parameter S can be decomposed into several parts, namely:

number

number

number

number

[0126] In this case, the linear model coefficients α have a fractional value, fixed-point integer representation, and the precision of α is used in obtaining the values ​​of the chroma prediction samples.

number

number

[0127] The size of the LUT is of great importance in the hardware implementation of an encoder or decoder. The most straightforward way to solve this problem is to periodically subsample the LUT by keeping only the elements of the initial LUT that are specified, i.e., every Nth element (where N is the subsampling ratio) in Table 1.

[0128] After normal subsampling with a power-of-two subsampling ratio of N, the fetches from the LUT are made different, i.e.

number

number

[0129] For natural images,

number

number

[0130] Therefore, keeping only every Nth element of the initial LUT is far from optimal, since it corresponds to an equal probability distribution of that argument not being true.

[0131] By taking this distribution into account, it is possible to achieve a better trade-off between the size of the LUT and the accuracy of the calculation than regular subsampling can provide.

[0132] Specifically, if two adjacent LUT entries

number

[0133] One computationally efficient solution is

number

number

[0134] Specific embodiments are shown in FIGS. 9 and 10. FIG. 9 shows a flowchart of LUT value calculation, and FIG. 10 shows

Number

[0135] By using the steps shown in FIG. 9, it is possible to obtain the values stored in the LUT for further use in CCLM modeling. In FIG. 9, the "ctr" variable is

Number

[0136] As shown in FIG. 9, the flowchart shows an exemplary look-up table generation process according to an embodiment of the present invention. In step 902, the video coding device starts the look-up table generation process. The video coding device may be a decoder such as the video decoder 30 in FIGS. 1A, 1B, and 3, or an encoder such as the video encoder 20 in FIGS. 1A, 1B, and 2, or the video coding device 400 in FIG. 4, or the device 500 in FIG. 5.

[0137] In step 904, set ctr = 1 and lut_shift = 1. In step 906, it is determined whether the index lut_shift < lut_shiftmax. If lut_shift < lut_shiftmax, the step is calculated in step 908 as 1 << max(0, lut_shift) and col = 0; otherwise, the generation process ends in step 922. In step 910, the start offset is provided by the step "ctr = ctr+(step >> 1)". Thereafter, it is determined in step 912 whether col < colmax. If col < colmax, in step 914, LUT[ctr] = (1 << S) / ctr, where one row of the LUT is generated by the pre-calculated LUT values defined from step 912 to step 918; otherwise, in step 920, set the index lut_shift = lut_shift + 1. In step 916, the value of ctr corresponding to the start point of each sub-range is set as ctrl + step. In step 918, the generation process moves to the next column, and then this process returns to step 912.

[0138] An exemplary LUT generated using the flowchart shown in FIG. 9 is given in Table 2. The rows of this table correspond to sub-ranges having the "lut_shift" index. This table is obtained using "lut_shift" equal to 6 and "col" equal to 3, and thus 48 entries are brought about in the LUT. The values of ctr corresponding to the start points of each sub-range (zero "col" values) are 0, 8, 17, 35, 71, 143, 287. max ", and "col" equal to 3 max ", and thus 48 entries are brought about in the LUT. The values of ctr corresponding to the start points of each sub-range (zero "col" values) are 0, 8, 17, 35, 71, 143, 287.

[0139] These values are not always powers of two because the subsampling within each subrange is performed relative to the center of the subrange. The corresponding start offset is provided by the "ctr=ctr+(step>>1)" step shown in FIG. 9. The value of "step" for "lut_shift" values not greater than 0 is set to be equal to 1. Table 2 Exemplary LUT Generated Using the Flowchart Shown in FIG. 9 [Table 2]

[0140] In FIG. 10(A), to determine the position of the corresponding entry in the LUT shown in Table 2, the binary representation 1001 of the input value (e.g., the difference [Number] ) is being processed. The most significant non-zero bit of the input value is shown as 1002. The "msb" value is determined by the position of this bit. In fact, the msb value is log2() of the input value 1001. Subtracting 1 from "msb" gives the "lut_shift" value for selecting the row in Table 2. Otherwise, the step is calculated as "1<<lut_shift".

[0141] The selection of the column is performed by putting the "col max " bit next to 1002. The value of "col" in Table 2 is obtained as follows. The value of "high_bits" is obtained by selecting the "col max +1" bits following the most significant bit 1020, col is set to be equal to the value stored in "high_bits" decremented by 1.

[0142] If the alignment step "ctr=ctr+(step>>1)" is not performed in FIG. 9, the derivation of the "lut_shift" value is the same, and the derivation of the "col" value is even simpler (FIG. 10B). The value of "col" is the "col max The index is obtained by selecting the "col" bits. This index derivation method corresponds to Table 3. The "ctr" values ​​(Figure 9) corresponding to the start of each subrange (zero "col" value) are 0, 8, 16, 32, 64, 128, 256. Table 3: Another exemplary LUT generated using the flowchart shown in FIG. 9 when "ctr=ctr+(step>>1)" is skipped [Table 3]

[0143] When deriving the value of "col", the msb is max ". In this case, the value of "col" is the "col" of the input difference 1001. max " is set equal to the least significant bit.

[0144] In a practical implementation, the LUT index is one-dimensional. The LUTs shown in Tables 2 and 3 are

number

[0145] Both the LUTs shown in Table 2 and Table 3 store values ​​with very different magnitudes. Therefore, it is reasonable to have a similar number of bits for all values ​​stored in the LUT. The value being fetched from the LUT may be further left-shifted according to the value of lut_shift. The only exception from this rule is the first four values, which have a different precision than the last four values ​​in the row. However, this problem may be solved by an additional LUT that stores this additional shift for the first four values. In this embodiment, the multiplier values ​​are restored from the values ​​fetched from the LUT as follows:

number

number

[0146] It can be seen that the last rows of Table 4 are very similar to each other. Therefore, it is possible to reduce the size of the LUT by storing only one row for some settings of the subrange. In a particular embodiment, if the value of lut_shift is greater than a certain threshold, the value of lut_shift is set equal to this threshold, and the value of δ is reduced by the difference between the initial value "lut_shift" and the threshold.

[0147] 11 is a flowchart illustrating an example of intra prediction of chroma samples of a block by applying a cross-component linear model. At stage 1102, a video coding device obtains reconstructed luma samples. The video coding device may be a decoder such as the video decoder 30 of FIG. 1A, FIG. 1B, FIG. 3, or an encoder such as the video encoder 20 of FIG. 1A, FIG. 1B, FIG. 2, or the video coding device 400 of FIG. 4, or the device 500 of FIG. 5.

[0148] At stage 1104, the video coding device determines the location of the maximum reconstructed sample value and the minimum reconstructed sample value within the reconstructed luma sample, for example, the reconstructed luma sample is an adjacent reconstructed luma sample that corresponds to a chroma sample.

[0149] At stage 1106, the video coding device obtains a difference value between the maximum and minimum values ​​of the reconstructed luma samples.

[0150] At stage 1108, the video coding device calculates an index into the LUT to fetch a multiplier value that corresponds to the difference value of the maximum and minimum values ​​of the reconstructed luma samples.

[0151] For example, the video coding device determines a location of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value, and fetches the value using a set of bits following the location of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value as an index into the LUT. The location of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value may be obtained as the logarithm of 2 of the difference. The video coding device determines a set of bits following the location of the most significant bit of the difference. As a possible result, the set of bits includes four bits.

[0152] The LUT may be generated with or without an alignment step. The LUT may include at least two adjacent values ​​stored in the LUT corresponding to different steps of the difference obtained, the step values ​​increasing or constant with the difference value.

[0153] As disclosed in the exemplary Tables 1 to 4, the LUT may include sub-ranges of values. The step of the difference value of the maximum and minimum values ​​of the reconstructed luma samples is constant within a sub-range, and the step of different sub-ranges is different. As an example, the step of the difference value of the maximum and minimum values ​​of the reconstructed luma samples increases with increasing sub-index. For example, the step of the difference value of the maximum and minimum values ​​of the reconstructed luma samples may be a power of two of the sub-index.

[0154] The LUT includes at least three values, a first value, a second value, and a third value. Of the three values, the first value and the second value are two adjacent values, and the second value and the third value are two adjacent values. A step (i.e., precision or difference) between the first value and the second value may be equal to or different from a step between the second value and the third value. If the first value is indexed by a first set of bits and the second value is indexed by a second set of bits, then when the value of the first set of bits is greater than the value of the second set of bits, the first value is less than the second value, or when the value of the first set of bits is less than the value of the second set of bits, the first value is greater than the second value.

[0155] The LUT is divided into sub-ranges. The position of the most significant non-zero bit of the difference between the maximum and minimum values ​​of the reconstructed luma samples is used to determine the sub-index. As an example, the size of the sub-range is set to 8 and the number of sub-ranges is 6. As another example, different adjacent sub-ranges have different value increments for the same step.

[0156] The LUT may include a non-linear index. Two adjacent LUT entries correspond to different stages of L(B)-L(A). L(B) represents the maximum value of the reconstructed luma sample, and L(A) represents the minimum value of the reconstructed luma sample. The stage value of this entry may increase with the index of this entry.

[0157] If the LUT uses several most significant bits of L(B)-L(A), the position of the most significant bit of L(B)-L(A) defines the precision (i.e., the step between two adjacent entries of the LUT) based on the position of the most significant bit. A larger value of the position of the most significant bit may correspond to a lower precision and a larger step value.

[0158] At step 1110, the video coding device obtains the linear model parameters α and β by multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples.

[0159] At step 1112, the video coding device calculates predicted chroma sample values ​​using the obtained linear model parameters α and β.

[0160] FIG. 12 is a block diagram illustrating an example structure of an apparatus 1200 for intra prediction of chroma samples of a block by applying a cross-component linear model. The apparatus 1200 is configured to perform the above method, an acquisition unit 1210 configured to acquire reconstructed luma samples; a determining unit 1220 configured to determine a maximum luma sample value and a minimum luma sample value based on the reconstructed luma samples; may include The obtaining unit 1210 is further configured to obtain a difference between a maximum luma sample value and a minimum luma sample value; The determining unit 1220 is further configured to determine a position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value. For example, the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value is the logarithm of the difference by 2. As an implementation, the most significant bit is the first non-zero bit.

[0161] The apparatus 1200 further includes a calculation unit 1230 configured to fetch a value from a look-up table (LUT) by using a bit set following a most significant bit position of a difference between a maximum luma sample value and a minimum luma sample value as an index, obtain linear model parameters α and β based on the fetched value, and calculate a predicted chroma sample value by using the obtained linear model parameters α and β. For example, the bit set includes four bits.

[0162] The computation unit may obtain the linear model parameters α and β based on the fetched values ​​and the difference between the maximum and minimum values ​​of the reconstructed chroma samples, for example, by multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples to obtain the linear model parameters α and β.

[0163] Advantages of the embodiments of the present invention 1. The index of the LUT is calculated in an elegant way that extracts some bits in the binary representation, resulting in more efficient fetching of values ​​from the LUT. 2. The size of the multipliers to obtain the linear model parameters α and β is minimized due to the increased efficiency of fetching values ​​from the LUT. 3. The size of the LUT is minimized. The curve of the division function (f(x)=1 / x, known as a hyperbola) in an embodiment of the present invention was approximated in the following manner. 1) The size of the LUT table may be 16. i. (Minimum number of entries for approximating a 1 / x curve with derivatives varying from 0 to infinity) 2) The elements of the LUT have a nonlinear dependence on the entry index. i. (To approximate the 1 / x curve) 3) The multipliers (elements of the LUT) are 3-bit unsigned integers (0…7). i. (Minimum accuracy for approximating 1 / x curves with derivatives varying from 0 to infinity)

[0164] The following is a description of the application of the encoding and decoding methods as illustrated in the above mentioned embodiments and the systems using them.

[0165] 13 is a block diagram showing a content supply system 3100 for implementing a content distribution service. The content supply system 3100 includes an imaging device 3102, a terminal device 3106, and optionally includes a display 3126. The imaging device 3102 communicates with the terminal device 3106 via a communication link 3104. The communication link may include the communication channel 13 described above. The communication link 3104 includes, but is not limited to, WiFi, Ethernet, cable, wireless (3G / 4G / 5G), or USB, or any type of combination thereof, etc.

[0166] The imaging device 3102 may generate data and encode the data by the encoding method as shown in the above embodiment. Alternatively, the imaging device 3102 may distribute the data to a streaming server (not shown in the figure), which encodes the data and transmits the encoded data to the terminal device 3106. The imaging device 3102 includes, but is not limited to, a camera, a smartphone or pad, a computer or laptop, a video conferencing system, a PDA, an in-vehicle device, or any combination thereof. For example, the imaging device 3102 may include a source device 12 as described above. If the data includes video, the video encoder 20 included in the imaging device 3102 may actually perform the video encoding process. If the data includes audio (i.e., voice), the audio encoder included in the imaging device 3102 may actually perform the audio encoding process. In some practical scenarios, the imaging device 3102 distributes the encoded video data and audio data by multiplexing them together. In other practical scenarios, for example in a video conferencing system, the encoded audio data and the encoded video data are not multiplexed, and the imaging device 3102 delivers the encoded audio data and the encoded video data to the terminal device 3106 separately.

[0167] In the content supply system 3100, the terminal device 310 receives and reproduces the encoded data. The terminal device 3106 may be a device with data receiving and recovery capabilities, such as a smartphone or pad 3108, a computer or laptop 3110, a network video recorder (NVR) / digital video recorder (DVR) 3112, a TV 3114, a set-top box (STB) 3116, a video conferencing system 3118, a video surveillance system 3120, a personal digital assistant (PDA) 3122, an in-vehicle device 3124, or any combination thereof, etc. that can decode the encoded data mentioned above. For example, the terminal device 3106 may include a destination device 14 as described above. If the encoded data includes video, the video decoder 30 included in the terminal device prioritizes the execution of video decoding. If the encoded data includes audio, the audio decoder included in the terminal device prioritizes the execution of audio decoding process.

[0168] For a terminal device having a display, such as a smartphone or pad 3108, a computer or laptop 3110, a network video recorder (NVR) / digital video recorder (DVR) 3112, a TV 3114, a personal digital assistant (PDA) 3122 or an in-vehicle device 3124, the terminal device can provide the decoded data to its display. For a terminal device not equipped with a display, such as a STB 3116, a video conferencing system 3118 or a video surveillance system 3120, an external display 3126 is contacted internally to receive and show the decoded data.

[0169] If each device in the system performs encoding or decoding, an image encoding device or an image decoding device may be used, as shown in the above mentioned embodiments.

[0170] 14 is a diagram illustrating an example structure of a terminal device 3106. After the terminal device 3106 receives a stream from the imaging device 3102, the protocol processing unit 3202 analyzes the transmission protocol of the stream. The protocol includes, but is not limited to, Real Time Streaming Protocol (RTSP), HyperText Transfer Protocol (HTTP), HTTP Live Streaming Protocol (HLS), MPEG-DASH, Real Time Transport Protocol (RTP), Real Time Messaging Protocol (RTMP), or any kind of combination thereof, etc.

[0171] After the protocol processing unit 3202 processes the stream, a stream file is generated. The file is output to the demultiplexing unit 3204. The demultiplexing unit 3204 can separate the multiplexed data into encoded audio data and encoded video data. As described above, in some practical scenarios, for example in a video conferencing system, the encoded audio data and the encoded video data are not multiplexed. In this situation, the encoded data is sent to the video decoder 3206 and the audio decoder 3208 without passing through the demultiplexing unit 3204.

[0172] Through the demultiplexing process, a video elementary stream (ES), an audio ES, and optionally subtitles are generated. The video decoder 3206, including the video decoder 30 as described in the above-mentioned embodiment, decodes the video ES by the decoding method as shown in the above-mentioned embodiment to generate video frames, and supplies this data to the synchronization unit 3212. The audio decoder 3208 decodes the audio ES to generate audio frames, and supplies this data to the synchronization unit 3212. Alternatively, the video frames may be stored in a buffer (not shown in FIG. 14) before supplying them to the synchronization unit 3212. Similarly, the audio frames may be stored in a buffer (not shown in FIG. 14) before supplying them to the synchronization unit 3212.

[0173] The synchronization unit 3212 synchronizes the video and audio frames and provides the video / audio to a video / audio display 3214. For example, the synchronization unit 3212 synchronizes the presentation of video and audio information. The information may be coded in a syntax with timestamps for the presentation of the coded audio and visual data and timestamps for the delivery of the data stream itself.

[0174] If the stream contains subtitles, the subtitle decoder 3210 decodes the subtitles, synchronizes it with the video and audio frames, and provides the video / audio / subtitles to the video / audio / subtitle display 3216.

[0175] The present invention is not limited to the above-mentioned system, and any of the image encoding devices or image decoding devices in the above-mentioned embodiments may be incorporated into other systems, for example, automobile systems.

[0176] Although the embodiments of the present invention have been described primarily based on video coding, it should be noted that the embodiments of the coding system 10, the encoder 20 and the decoder 30 (and accordingly the system 10), as well as other embodiments described herein, may be configured for still image processing or coding, i.e., processing or coding of an individual image independent of any previous or successive images as in video coding. In general, when image processing coding is limited to a single image 17, only the inter prediction units 244 (encoder) and 344 (decoder) may not be available. All other functions (also referred to as tools or techniques) of the video encoder 20 and the video decoder 30 may be equally used for still image processing, e.g., residual calculation 204 / 304, transform 206, quantization 208, inverse quantization 210 / 310, (inverse) transform 212 / 312, partitioning 262 / 362, intra prediction 254 / 354, and / or loop filtering 220, 320, as well as entropy coding 270 and entropy decoding 304.

[0177] The embodiments of, e.g., the encoder 20 and the decoder 30, and the functions described herein with reference to, e.g., the encoder 20 and the decoder 30, may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on a computer-readable medium and transmitted as one or more instructions or codes over a communication medium and executed by a hardware-based processing unit. The computer-readable medium may include a computer-readable storage medium corresponding to a tangible medium, such as a data storage medium, or a communication medium including any medium that facilitates the transfer of a computer program from one place to another, e.g., according to a communication protocol. Thus, the computer-readable medium may generally correspond to (1) a non-transitory tangible computer-readable storage medium, or (2) a communication medium, such as a signal or carrier wave. The data storage medium may be any available medium that can be accessed by one or more computers or one or more processors to obtain instructions, code and / or data structures for implementation of the techniques described in this disclosure. The computer program product may include a computer-readable medium.

[0178] By way of example and not limitation, such computer-readable storage media may include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, flash memory, or any other medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if instructions are transmitted from a website, server or other remote source using coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio waves and microwaves, the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio waves and microwaves are included in the definition of media. However, it should be understood that computer-readable storage media and data storage media do not include connections, carrier waves, signals or other transitory media, but instead cover non-transitory tangible storage media. Disk and disc as used herein include compact discs (CDs), laser discs, optical discs, digital versatile discs (DVDs), floppy disks and Blu-ray discs, where disks typically reproduce data magnetically, while discs reproduce data optically with a laser. Combinations of the above should also be included within the scope of computer readable media.

[0179] The instructions may be executed by one or more processors, such as one or more digital signal processors (DSPs), general-purpose microprocessors, application specific integrated circuits (ASICs), field programmable logic arrays (FPGAs), or other equivalent integrated or discrete logic circuits. Thus, the term "processor" as used herein may refer to any of the foregoing structures, or any other structure suitable for implementing the techniques described herein. In addition, in some aspects, the functions described herein may be provided within dedicated hardware and / or software modules configured for encoding and decoding, or may be incorporated into a combined codec. Also, these techniques may be fully implemented in one or more circuits or logic elements.

[0180] The techniques of the present disclosure may be implemented in a wide variety of devices or apparatuses, including wireless handsets, integrated circuits (ICs) or IC sets (e.g., chipsets). Various components, modules or units are described in this disclosure to highlight functional aspects of devices configured to perform the disclosed techniques, but do not necessarily require realization by different hardware units. Rather, as described above, the various units may be combined into a codec hardware unit, along with suitable software and / or firmware, or may be provided by a collection of interoperable hardware units including one or more processors as described above. [Other possible items] (Item 1) 1. A method for intra predicting chroma samples of a block by applying a cross-component linear model, comprising the steps of: obtaining a reconstructed luma sample; determining a maximum luma sample value and a minimum luma sample value based on the reconstructed luma samples; obtaining a difference between the maximum luma sample value and the minimum luma sample value; determining a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; fetching a value from a look-up table (LUT) by using a set of bits as an index, the set of bits following the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; obtaining a linear model parameter α and a linear model parameter β based on the fetched values; calculating a predicted chroma sample value by using the obtained linear model parameters α and β; A method comprising: (Item 2) 2. The method of claim 1, wherein the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value is obtained as the logarithm of 2 of the difference. (Item 3) 3. The method of claim 1 or 2, wherein determining the set of bits following the position of the most significant bit of the difference results in the set of bits including four bits. (Item 4) 4. The method of any one of items 1 to 3, wherein the most significant bit is the first non-zero bit. (Item 5) obtaining the linear model parameters α and β based on differences between the fetched values ​​and maximum and minimum values ​​of reconstructed chroma samples; 5. The method according to any one of items 1 to 4, comprising: (Item 6) multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples to obtain the linear model parameters α and β. The method of item 5, comprising: (Item 7) the LUT includes at least three values: a first value, a second value, and a third value; Among the three values, the first value and the second value are two adjacent values, and the second value and the third value are two adjacent values. 7. The method according to any one of items 1 to 6. (Item 8) 8. The method according to claim 7, wherein the step between the first value and the second value is equal to the step between the second value and the third value. (Item 9) 8. The method according to claim 7, wherein the step between the first value and the second value is different from the step between the second value and the third value. (Item 10) the first value is indexed by a first set of bits and the second value is indexed by a second set of bits; if the value of the first set of bits is greater than the value of the second set of bits, the first value is less than the second value, or if the value of the first set of bits is less than the value of the second set of bits, then the first value is greater than the second value; The method according to items 7 to 9. (Item 11) 11. The method according to any one of items 1 to 10, wherein the LUT comprises a plurality of sub-ranges of values, and any two adjacent value steps are constant within one sub-range. (Item 12) 1. An apparatus for intra-predicting chroma samples of a block by applying a cross-component linear model, the apparatus being an encoder or a decoder, the apparatus comprising: an acquisition unit configured to acquire a reconstructed luma sample, the acquisition unit being further configured to acquire a difference between a maximum luma sample value and a minimum luma sample value; a determination unit configured to determine the maximum luma sample value and the minimum luma sample value based on the reconstructed luma sample, the determination unit further configured to determine a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; a calculation unit configured to fetch a value from a look-up table (LUT) by using a set of bits following the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value as an index, obtain a linear model parameter α and a linear model parameter β based on the fetched value, and calculate a predicted chroma sample value by using the obtained linear model parameter α and the linear model parameter β. An apparatus comprising: (Item 13) Item 13. The apparatus of item 12, wherein the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value is the logarithm of two of the difference. (Item 14) 14. The apparatus of claim 12 or 13, wherein the set of bits includes four bits. (Item 15) 15. The apparatus of any one of items 12 to 14, wherein the most significant bit is the first non-zero bit. (Item 16) 16. The apparatus of any one of items 12 to 15, wherein the calculation unit is configured to obtain the linear model parameters α and β based on differences between the fetched values ​​and maximum and minimum values ​​of reconstructed chroma samples. (Item 17) the calculation unit is configured to obtain the linear model parameters α and β by multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples. Item 17. The device according to item 16. (Item 18) 12. An encoder comprising a processing circuit for carrying out the method according to any one of items 1 to 11. (Item 19) 12. A decoder comprising processing circuitry for carrying out the method according to any one of items 1 to 11. (Item 20) 12. A computer program product comprising a program code for performing the method according to any one of items 1 to 11. (Item 21) A decoder comprising: one or more processors; a non-transitory computer-readable storage medium coupled to said processor and storing programming for execution by said processor, said programming, when executed by said processor, configuring said decoder to perform a method according to any one of items 1 to 11; A decoder comprising: (Item 22) 1. An encoder comprising: one or more processors; a non-transitory computer-readable storage medium coupled to the processor and storing programming for execution by the processor, the programming, when executed by the processor, configuring the encoder to perform a method according to any one of items 1 to 11; An encoder comprising: (Item 23) A non-transitory recording medium comprising a predictively encoded bitstream to be decoded by an apparatus, said bitstream being generated according to any one of items 1 to 11.

Claims

1. 1. A method for intra predicting chroma samples of a block by applying a cross-component linear model, comprising the steps of: obtaining a reconstructed luma sample; determining a maximum luma sample value and a minimum luma sample value based on the reconstructed luma samples; obtaining a difference between the maximum luma sample value and the minimum luma sample value; determining a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; fetching a value from a look-up table (LUT) by using a set of bits as an index, the set of bits following the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; Obtaining a linear model parameter α and a linear model parameter β based on the fetched value, wherein a division operation is performed between the fetched value and a shift parameter S when obtaining the parameter α. ０ and a multiplication with a right shift by , said parameter β being obtained based on said parameter α; Calculating a predicted chroma sample value by using the obtained linear model parameters α and β, and calculating a shift parameter S １ a further right shift by is performed based on the multiplication of the linear model parameter α and the luma sample value; A method comprising:

2. The method of claim 1 , wherein the position of the most significant bit of the difference between the maximum and minimum luma sample values ​​is obtained as the logarithm of two of the difference.

3. 3. The method of claim 1, wherein determining the set of bits following the position of the most significant bit of the difference results in the set of bits comprising four bits.

4. The method of claim 1 , wherein the most significant bit is the first non-zero bit.

5. obtaining the linear model parameters α and β based on differences between the fetched values ​​and maximum and minimum values ​​of reconstructed chroma samples; The method according to claim 1 , comprising:

6. multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples to obtain the linear model parameters α and β. The method of claim 5 comprising:

7. the LUT includes at least three values: a first value, a second value, and a third value; Among the three values, the first value and the second value are included in two adjacent entries of the LUT, and the second value and the third value are included in two adjacent entries of the LUT.

7. The method according to any one of claims 1 to 6.

8. The method of claim 7 , wherein the difference between the first value and the second value is equal to the difference between the second value and the third value.

9. The method of claim 7 , wherein the difference between the first value and the second value is different from the difference between the second value and the third value.

10. the first value is indexed by a first set of bits and the second value is indexed by a second set of bits; if the value of the first set of bits is greater than the value of the second set of bits, the first value is less than the second value; or if the value of the first set of bits is less than the value of the second set of bits, the first value is greater than the second value; 10. The method according to any one of claims 7 to 9.

11. 11. The method of claim 1, wherein the LUT comprises a plurality of sub-ranges of values, and any two adjacent value steps are constant within a sub-range.

12. 1. An apparatus for intra-predicting chroma samples of a block by applying a cross-component linear model, the apparatus being an encoder or a decoder, the apparatus comprising: an acquisition unit configured to acquire a reconstructed luma sample, the acquisition unit being further configured to acquire a difference between a maximum luma sample value and a minimum luma sample value; a determination unit configured to determine the maximum luma sample value and the minimum luma sample value based on the reconstructed luma sample, the determination unit further configured to determine a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; a calculation unit configured to fetch a value from a look-up table (LUT) by using a set of bits following the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value as an index, obtain a linear model parameter α and a linear model parameter β based on the fetched value, and calculate a predicted chroma sample value by using the obtained linear model parameter α and the linear model parameter β; Equipped with When obtaining the parameter α, a division operation is performed by multiplying the fetched value by a shift parameter S ０ and multiplication with a right shift by , the parameter β being obtained based on the parameter α; When calculating the predicted chroma sample values, a shift parameter S １ a further right shift by is performed based on the multiplication of the linear model parameter α and the luma sample value.

13. The apparatus of claim 12 , wherein the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value is the logarithm of two of the difference.

14. 14. Apparatus according to claim 12 or 13, wherein the set of bits comprises four bits.

15. 15. The apparatus of claim 12, wherein the most significant bit is the first non-zero bit.

16. 16. The apparatus of claim 12, wherein the calculation unit is configured to obtain the linear model parameters α and β based on differences between the fetched values ​​and maximum and minimum values ​​of reconstructed chroma samples.

17. the calculation unit is configured to obtain the linear model parameters α and β by multiplying the fetched values ​​by the difference between the maximum and minimum values ​​of the reconstructed chroma samples.

17. The apparatus of claim 16.

18. 18. Apparatus according to any one of claims 12 to 17, wherein the LUT comprises a number of sub-ranges of values, and any two adjacent value steps are constant within a sub-range.

19. An encoder comprising processing circuitry for carrying out the method according to any one of claims 1 to 11.

20. A decoder comprising processing circuitry for carrying out the method according to any one of claims 1 to 11.

21. A computer program comprising a program code for carrying out the method according to any one of claims 1 to 11.

22. A decoder comprising: one or more processors; a non-transitory computer-readable storage medium coupled to the processor and storing programming for execution by the processor, the programming, when executed by the processor, configuring the decoder to perform the method of any one of claims 1 to 11; A decoder comprising:

23. 1. An encoder comprising: one or more processors; a non-transitory computer-readable storage medium coupled to the processor and storing programming for execution by the processor, the programming, when executed by the processor, configuring the encoder to perform the method of any one of claims 1 to 11; An encoder comprising:

24. 1. A method for generating a bitstream using intra prediction of chroma samples of a block by applying a cross-component linear model, comprising: obtaining a reconstructed luma sample; determining a maximum luma sample value and a minimum luma sample value based on the reconstructed luma samples; obtaining a difference between the maximum luma sample value and the minimum luma sample value; determining a position of a most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; fetching a value from a look-up table (LUT) by using a set of bits as an index, the set of bits following the position of the most significant bit of the difference between the maximum luma sample value and the minimum luma sample value; Obtaining a linear model parameter α and a linear model parameter β based on the fetched value, wherein a division operation is performed between the fetched value and a shift parameter S when obtaining the parameter α. ０ and a multiplication with a right shift by , said parameter β being obtained based on said parameter α; Calculating a predicted chroma sample value by using the obtained linear model parameters α and β, and calculating a shift parameter S １ a further right shift by is performed based on the multiplication of the linear model parameter α and the luma sample value; A method for generating a bitstream comprising:

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