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EP-4535792-B1 - VIDEO CODING METHOD ON BASIS OF SECONDARY TRANSFORM, AND DEVICE FOR SAME

EP4535792B1EP 4535792 B1EP4535792 B1EP 4535792B1EP-4535792-B1

Inventors

  • Koo, Moonmo
  • KIM, SEUNGHWAN
  • LIM, JAEHYUN

Dates

Publication Date
20260513
Application Date
20191219

Claims (4)

  1. An image decoding method performed by a decoding apparatus, the method comprising: obtaining (S910) a bitstream; deriving prediction samples based on an intra prediction mode applied to a target block; obtaining a two-dimensional array of transform coefficients based on the obtained bitstream; deriving (S920) a plurality of first transform coefficients from a top-left 4x4 region of the two-dimensional array of transform coefficients; deriving (S930) a plurality of second transform coefficients based on an inverse secondary transform of the plurality of first transform coefficients; deriving a two-dimensional array of values based on the plurality of second transform coefficients, wherein the plurality of second transform coefficients are mapped to a top-left 8x8 region of the two-dimensional array of values, excluding a bottom-right 4x4 region within the top-left 8x8 region based on a width of the target block being equal to or greater than 8 and a height of the target block being equal to or greater than 8, and wherein the plurality of second transform coefficients are mapped to a top-left 4x4 region of the two-dimensional array of values based on a size of the target block being 4xN or Nx4 (N≥4); deriving (S940) an array of residual samples based on an inverse primary transform of the two-dimensional array of values; and generating (S950) a reconstructed picture based on the array of residual samples and the prediction samples, wherein the deriving the plurality of second transform coefficients comprises: performing a matrix operation between a transform kernel matrix and the plurality of first transform coefficients, in which the plurality of first transform coefficients are arranged according to a forward diagonal scanning order of the top-left 4x4 region of the two-dimensional array of transform coefficients, wherein the matrix operation between the transform kernel matrix and the plurality of first transform coefficients of the top-left 4x4 region is (48 x 16 matrix) * (16 x 1 transform coefficient vector), wherein the intra prediction mode applied to the target block is one of 65 directional modes which are symmetric around intra prediction mode 34 in a top-left diagonal direction, wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a row-first direction based on the intra prediction mode being one of mode 2 to mode 34 in a left direction with respect to the intra prediction mode 34, and wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a column-first direction based on the intra prediction mode being one of mode 35 to mode 66 in a right direction with respect to the intra prediction mode 34.
  2. An image encoding method performed by an image encoding apparatus, the method comprising: deriving (S1110) prediction samples based on an intra prediction mode applied to a target block; deriving (S1120) an array of residual samples based on the prediction samples; deriving (S1130) a two-dimensional array of values based on a primary transform of the array of the residual samples; deriving a plurality of second transform coefficients from the two-dimensional array of values, wherein the plurality of second transform coefficients are derived from a top-left 8x8 region of the two-dimensional array of values, excluding a bottom-right 4x4 region within the top-left 8x8 region based on a width of the target block being equal to or greater than 8 and a height of the target block being equal to or greater than 8, and wherein the plurality of second transform coefficients are derived from a top-left 4x4 region of the two-dimensional array of values based on a size of the target block being 4xN or Nx4 (N≥4); deriving (S1140) a plurality of first transform coefficients based on a secondary transform of the plurality of second transform coefficients; deriving a two-dimensional array of transform coefficients based on the plurality of first transform coefficients by mapping the plurality of first transform coefficients to a top-left 4x4 region of the two-dimensional array of transform coefficients; and outputting (S1150) a bitstream that comprises information derived based on the two-dimensional array of transform coefficients, wherein the deriving the plurality of first transform coefficients comprises: performing a matrix operation between a transform kernel matrix and the plurality of second transform coefficients, in which the plurality of second transform coefficients are arranged for the matrix operation, wherein the matrix operation between the transform kernel matrix and the plurality of second transform coefficients of the top-left 4x4 region, the top-right 4x4 region and the bottom-left 4x4 region of the 8x8 region is (16 x 48 matrix) * (48 x 1 transform coefficient vector), wherein an intra prediction mode applied to the target block is one of 65 directional modes which are symmetric around intra prediction mode 34 in a top-left diagonal direction, wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a row-first direction based on the intra prediction mode being one of mode 2 to mode 34 in a left direction with respect to the intra prediction mode 34, and wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a column-first direction based on the intra prediction mode being one of mode 35 to mode 66 in a right direction with respect to the intra prediction mode 34.
  3. A non-transitory computer readable storage medium storing a bitstream generated by a method, the method comprising: deriving (S1110) prediction samples based on an intra prediction mode applied to a target block; deriving (S1120) an array of residual samples based on the prediction samples; deriving (S1130) a two-dimensional array of values based on a primary transform of the array of the residual samples; deriving a plurality of second transform coefficients from the two-dimensional array of values, wherein the plurality of second transform coefficients are derived from a top-left 8x8 region of the two-dimensional array of values, excluding a bottom-right 4x4 region within the top-left 8x8 region based on a width of the target block being equal to or greater than 8 and a height of the target block being equal to or greater than 8, and wherein the plurality of second transform coefficients are derived from a top-left 4x4 region of the two-dimensional array of values based on a size of the target block being 4xN or Nx4 (N≥4); deriving (S1140) a plurality of first transform coefficients based on a secondary transform of the plurality of second transform coefficients; deriving a two-dimensional array of transform coefficients based on the plurality of first transform coefficients by mapping the plurality of first transform coefficients to a top-left 4x4 region of the two-dimensional array of transform coefficients; and outputting (S1150) the bitstream that comprises information derived based on the two-dimensional array of transform coefficients, wherein the deriving the plurality of first transform coefficients comprises: performing a matrix operation between a transform kernel matrix and the plurality of second transform coefficients, in which the plurality of second transform coefficients are arranged for the matrix operation, wherein the matrix operation between the transform kernel matrix and the plurality of second transform coefficients of the top-left 4x4 region, the top-right 4x4 region and the bottom-left 4x4 region of the 8x8 region is (16 x 48 matrix) * (48 x 1 transform coefficient vector), wherein an intra prediction mode applied to the target block is one of 65 directional modes which are symmetric around intra prediction mode 34 in a top-left diagonal direction, wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a row-first direction based on the intra prediction mode being one of mode 2 to mode 34 in a left direction with respect to the intra prediction mode 34, and wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a column-first direction based on the intra prediction mode being one of mode 35 to mode 66 in a right direction with respect to the intra prediction mode 34.
  4. A transmission method of data for an image, the method comprising: obtaining a bitstream for the image, wherein the bitstream is generated based on deriving prediction samples based on an intra prediction mode applied to a target block, deriving an array of residual samples based on the prediction samples, deriving a two-dimensional array of values based on a primary transform of the array of the residual samples, deriving a plurality of second transform coefficients from the two-dimensional array of values, wherein the plurality of second transform coefficients are derived from a top-left 8x8 region of the two-dimensional array of values, excluding a bottom-right 4x4 region within the top-left 8x8 region based on a width of the target block being equal to or greater than 8 and a height of the target block being equal to or greater than 8, and wherein the plurality of second transform coefficients are derived from a top-left 4x4 region of the two-dimensional array of values based on a size of the target block being 4xN or Nx4 (N≥4), deriving a plurality of first transform coefficients based on a secondary transform of the plurality of second transform coefficients, deriving a two-dimensional array of transform coefficients based on the plurality of first transform coefficients by mapping the plurality of first transform coefficients to a top-left 4x4 region of the two-dimensional array of transform coefficients, and outputting the bitstream that comprises information derived based on the two-dimensional array of transform coefficients; and transmitting the data comprising the bitstream, wherein the deriving the plurality of first transform coefficients comprises: performing a matrix operation between a transform kernel matrix and the plurality of second transform coefficients, in which the plurality of second transform coefficients are arranged for the matrix operation, wherein the matrix operation between the transform kernel matrix and the plurality of second transform coefficients of the top-left 4x4 region, the top-right 4x4 region and the bottom-left 4x4 region of the 8x8 region is (16 x 48 matrix) * (48 x 1 transform coefficient vector), wherein an intra prediction mode applied to the target block is one of 65 directional modes which are symmetric around intra prediction mode 34 in a top-left diagonal direction, wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a row-first direction based on the intra prediction mode being one of mode 2 to mode 34 in a left direction with respect to the intra prediction mode 34, and wherein the plurality of second transform coefficients are two-dimensionally arranged in the two-dimensional array of values according to a column-first direction based on the intra prediction mode being one of mode 35 to mode 66 in a right direction with respect to the intra prediction mode 34.

Description

Technical Field The present disclosure relates generally to an image coding technology and, more particularly, to an image coding method based on a transform in an image coding system and an apparatus therefor. Related Art Nowadays, the demand for high-resolution and high-quality images/videos such as 4K, 8K or more ultra high definition (UHD) images/videos has been increasing in various fields. As the image/video data becomes higher resolution and higher quality, the transmitted information amount or bit amount increases as compared to the conventional image data. Therefore, when image data is transmitted using a medium such as a conventional wired/wireless broadband line or image/video data is stored using an existing storage medium, the transmission cost and the storage cost thereof are increased. Further, nowadays, the interest and demand for immersive media such as virtual reality (VR), artificial reality (AR) content or hologram, or the like is increasing, and broadcasting for images/videos having image features different from those of real images, such as a game image is increasing. Accordingly, there is a need for a highly efficient image/video compression technique for effectively compressing and transmitting or storing, and reproducing information of high resolution and high quality images/videos having various features as described above. Prior art is found in Koo M et al, "Description of SDR video coding technology proposal by LG Electronics", JVET-J0017-v2. SUMMARY The invention is set out in the independent claims. A technical aspect of the present disclosure is to provide a method and an apparatus for increasing image coding efficiency. Another technical aspect of the present disclosure is to provide a method and an apparatus for increasing transform efficiency. Still another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus which are based on a reduced secondary transform (RST). Yet another technical aspect of the present disclosure is to provide a method and an apparatus for increasing the efficiency of a secondary transform by changing the array of transform coefficients according to an intra prediction mode. Still another technical aspect of the present disclosure is to provide an image coding method and an image coding apparatus for increasing the efficiency of a secondary transform by optimizing the transformation kernel matrix applied to the secondary transform. According to the present disclosure, it is possible to increase overall image/video compression efficiency. According to the present disclosure, it is possible to increase the efficiency of a secondary transform by changing the array of transform coefficients according to an intra prediction mode. According to the present disclosure, it is possible to increase image coding efficiency by performing image coding based on a transform set. According to the present disclosure, it is possible to increase the efficiency of a secondary transform by optimizing the transformation kernel matrix applied to the secondary transform. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates an example of a video/image coding system to which the present disclosure is applicable.FIG. 2 is a diagram schematically illustrating a configuration of a video/image encoding apparatus to which the present disclosure is applicable.FIG. 3 is a diagram schematically illustrating a configuration of a video/image decoding apparatus to which the present disclosure is applicable.FIG. 4 schematically illustrates a multiple transform technique according to an embodiment of the present disclosure.FIG. 5 illustrates directional intra modes of 65 prediction directions.FIG. 6 is a diagram illustrating an RST according to an embodiment of the present disclosure.FIG. 7 is a diagram illustrating a transform coefficient scanning order according to an embodiment of the present disclosure.FIG. 8 is a flowchart illustrating an inverse RST process according to an embodiment of the present disclosure.FIG. 9 is a flowchart illustrating an operation of a video decoding apparatus according to an embodiment of the present disclosure.FIG. 10 is a control flowchart illustrating an inverse RST according to an embodiment of the present disclosure.FIG. 11 is a flowchart illustrating an operation of a video encoding apparatus according to an embodiment of the present disclosure.FIG. 12 is a control flowchart illustrating an RST according to an embodiment of the present disclosure.FIG. 13 illustrates the structure of a content streaming system to which the present disclosure is applied. DESCRIPTION OF EXEMPLARY EMBODIMENTS While the present disclosure may be susceptible to various modifications and include various embodiments, specific embodiments thereof have been shown in the drawings by way of example and will now be described in detail. However, this is not intended to limit the present disclosure to the specific