Method and apparatus for video coding using intra prediction based on reference sample line derivation
A method and apparatus for video coding utilize intra prediction based on reference sample line derivation. The video coding method and the apparatus derive reference sample lines of the current block by using various derivation schemes. The video coding method and the apparatus perform intra prediction of the current block by using the derived reference sample lines.
1 . A method performed by a video decoding device for intra-predicting a current block, the method comprising:
decoding, from a bitstream, an intra-prediction mode of the current block, and a derivation mode index of the current block, the derivation mode index indicating a reference sample line-derivation mode that is one of a fixed-location reference sample-line mode, a variable-location reference sample-line mode, or a reference sample line list-referencing mode;
determining the reference sample line-derivation mode according to the derivation mode index;
deriving reference sample lines of the current block according to the reference sample line-derivation mode, the reference sample lines including a left reference sample line and a top reference sample line; and
generating a prediction block of the current block according to the intra-prediction mode by using reference samples in the reference sample lines,
wherein when the reference sample line-derivation mode is the reference sample line list-referencing mode:
decoding, from the bitstream, a reference index indicative of one of reference sample lines included in a reference sample line list, and
wherein deriving the reference sample lines includes:
deriving, by using the reference index, the left reference sample line and the top reference sample line from the reference sample line list.
2 . The method of claim 1 , wherein the derivation mode index is encoded when satisfying a first condition, by the video encoding device to indicate the variable-location reference sample-line mode or the reference sample line list-referencing mode,
wherein the first condition is equivalent to when at least a preset number of prediction units among reconstructed prediction units including neighboring pixels of the current block and at preset locations, has been reconstructed by inter prediction.
3 . The method of claim 1 , wherein deriving the reference sample lines includes:
when the reference sample line-derivation mode is the fixed-location reference sample-line mode, deriving, as the reference sample lines, pixel lines adjacent to left and top boundaries of the current block, respectively.
4 . The method of claim 1 , further comprising:
when the reference sample line-derivation mode is the variable-location reference sample-line mode, decoding, from the bitstream, a derivation method index of a left reference sample line and a derivation method index of a top reference sample line, the derivation method index of the left reference sample line and the derivation method index of the top reference sample line each indicating utilization of a first derivation method, a second derivation method, or a third derivation method.
5 . The method of claim 4 , wherein deriving the reference sample lines includes:
deriving samples in a range of (xL, yL+α) to (xL, yL+puH×2−1) as the left reference sample line, when the first derivation method is utilized and (xL, yL) are coordinates of a pixel, which shares a common y-axis coordinate with a top-left pixel of the current block, among left neighboring samples of a processing unit containing the current block,
wherein the α is a preset integer and the puH is a height of the current block.
6 . The method of claim 5 , wherein the processing unit is generated by partitioning a coding tree unit (CTU), and the processing unit includes at least one or more coding units.
7 . The method of claim 4 , wherein deriving the reference sample lines includes:
deriving samples in a range of (xL, yL+α) to (xL, yL+puH×2−1) as the left reference sample line, when the second derivation method is utilized and (xL, yL) are coordinates of a pixel, which shares a common y-axis coordinate with a top-left (0, 0) pixel of the current block, among left neighboring samples of a prediction unit containing an (−1, 0) pixel,
wherein the α is a preset integer and the puH is a height of the current block.
8 . The method of claim 4 , wherein deriving the reference sample lines includes:
deriving samples in a range of (xL, yL+α) to (xL, yL+puH×2−1) as the left reference sample line, when the third derivation method is utilized and (xL, yL) are coordinates of an arbitrary pixel, which is present at a left side of the current block, among a region decoded before the current block within a processing unit,
wherein the α is a preset integer and the puH is a height of the current block.
9 . The method of claim 4 , wherein deriving the reference sample lines includes:
when the reference sample lines derived according to the first derivation method, the second derivation method, or the third derivation method are included in a plurality of prediction units, performing filtering for removing a blocking artifact on pixels adjacent to boundaries between the plurality of prediction units.
10 . The method of claim 1 , wherein deriving the reference sample lines includes:
updating the reference sample line list by adding a top boundary sample line or a left boundary sample line of a reconstructed prediction unit to the reference sample line list.
11 . A method performed by a video encoding device for intra-predicting a current block, the method comprising:
determining an intra-prediction mode of the current block;
determining a reference sample line-derivation mode of the current block, wherein the reference sample line-derivation mode is selected from at least one of: a fixed-location reference sample-line mode, a variable-location reference sample-line mode, or a reference sample line list-referencing mode;
determining reference sample lines of the current block according to the reference sample line-derivation mode, the reference sample lines including a left reference sample line and a top reference sample line; and
generating a prediction block of the current block according to the intra-prediction mode by using reference samples in the reference sample lines; and
encoding a derivation mode index indicating the reference sample line-derivation mode,
wherein, when the reference sample line-derivation mode is the reference sample line list-referencing mode, the method further comprises encoding a reference index indicating the reference sample lines of the current block in a reference sample line list.
12 . The method of claim 11 , wherein the derivation mode index indicates, under a first condition when satisfied, the variable-location reference sample-line mode or the reference sample line list-referencing mode,
wherein the first condition is equivalent to when at least a preset number of prediction units among reconstructed prediction units including neighboring pixels of the current block and at preset locations, has been reconstructed by inter prediction.
13 . A non-transitory computer-readable recording medium storing a bitstream generated by a video encoding method, the video encoding method comprising:
determining an intra-prediction mode of the current block;
determining a reference sample line-derivation mode of the current block, wherein the reference sample line-derivation mode is selected from at least one of: a fixed-location reference sample-line mode, a variable-location reference sample-line mode, or a reference sample line list-referencing mode;
determining reference sample lines of the current block according to the reference sample line-derivation mode, the reference sample lines including a left reference sample line and a top reference sample line; and
generating a prediction block of the current block according to the intra-prediction mode by using reference samples in the reference sample lines; and
encoding a derivation mode index indicating the reference sample line-derivation mode,
wherein, when the reference sample line-derivation mode is the reference sample line list-referencing mode, the method further comprises encoding a reference index indicating the reference sample lines of the current block in a reference sample line list.