Planar intra-prediction using position dependent prediction combination
The present disclosure provides methods and devices of intra predicting a block of a picture. The method comprises for a sample of the block: obtaining a predicted sample value from one or more reference sample values by performing intra-prediction using a DC intra-prediction mode; multiplying the predicted sample value by a sample weighting factor to produce a weighted predicted sample value; adding an additional value to the weighted predicted sample value to produce a non-normalized predicted sample value; and normalizing the non-normalized predicted sample value by an arithmetic right shift; wherein the sample weighting factor is ((2<<p)−wL−wT), wherein p is a parameter of the sample weighting factor, wL is a horizontal weighting factor, and wT is a vertical weighting factor.
1. A coding device, comprising:
one or more processors; and
a non-transitory computer-readable medium in communication with the one or more processors to store program code, which when executed by the one or more processors, causes the coding device to:
for a sample of a block of a picture:
acquire one or more reference sample values from neighboring blocks of the block;
obtain a predicted sample value of the block from the one or more reference sample values by performing intra prediction using a PLANAR intra prediction mode;
multiply the predicted sample value by a sample weighting factor to produce a weighted predicted sample value; and
obtain a modified predicted sample value by performing an arithmetic right shift on a sum of an additional value and the weighted predicted sample value;
wherein the sample weighting factor is ((2<<p)−wL−wT) or (64−wL−wT),
wherein
p is a parameter of the sample weighting factor,
wL is a horizontal weighting factor, and
wT is a vertical weighting factor.
2. The coding device of claim 1 , wherein the program code, when executed by the one or more processors, further causes the coding device to:
calculate the additional value using the PLANAR intra prediction mode.
3. The coding device of claim 1 , wherein the additional value is a sum of one or more summands that include a summand depending on at least one of the one or more reference sample values.
4. The coding device of claim 3 , wherein the summand is wL×R −1,y +wT×R x,−1 , R x,−1 and R −1,y representing values of nearest reference samples located above and to the left of a predicted sample, respectively.
5. The coding device of claim 1 , wherein the horizontal weighting factor wL or the vertical weighting factor wT is a power of two.
6. The coding device of claim 1 , wherein
the horizontal weighting factor wL=(2<<(p−1)) >>((x<<1) >>nScale), wherein x is a horizontal coordinate of the sample of the block,
the vertical weighting factor wT=(2<<(p−1)) >>((y<<1) >>nScale), wherein y is a vertical coordinate of the sample of the block, and
nScale is a scale parameter.
7. The coding device of claim 6 , wherein the program code, when executed by the one or more processors, further causes the coding device to:
derive the scale parameter nScale from a size of the block.
8. The coding device of claim 7 , wherein the scale parameter nScale is ((Log2(nTbW)+Log2 (nTbH)−2) >>2), and wherein nTW is a width of the block and nTbH is a height of the block.
9. The coding device of claim 1 , wherein
obtaining the modified predicted sample value comprises:
( wL×R −1,y +wT×R x,−1 +(64− wL−wT )× P ( x,y ) +32)>>6
wherein
P (x, y) represents the predicted sample value,
(64−wL−wT) represents the sample weighting factor,
(64−wL−wT)×P(x, y) represents the weighted predicted sample value,
wL×R −1,y , +wt×R x,−1 represents the additional value,
>>represents the arithmetic right shift,
R x,−1 , R −1,y represent values of nearest reference samples located above and to the left of a predicted sample, respectively.
10. A coding method, comprising:
for a sample of a block of a picture:
acquiring one or more reference sample values from neighboring blocks of the block;
obtaining a predicted sample value of the block from the one or more reference sample values by performing intra prediction using a PLANAR intra prediction mode;
multiplying the predicted sample value by a sample weighting factor to produce a weighted predicted sample value; and
obtaining a modified predicted sample value by performing an arithmetic right shift on a sum of an additional value and the weighted predicted sample value;
wherein the sample weighting factor is ((2<<p)−wL−wT) or (64−wL−wT), wherein
p is a parameter of the sample weighting factor,
wL is a horizontal weighting factor, and
wT is a vertical weighting factor.
11. The coding method of claim 10 , further comprising:
calculating the additional value using the PLANAR intra prediction mode.
12. The coding method of claim 10 , wherein the additional value is a sum of one or more summands that include a summand depending on at least one of the one or more reference sample values.
13. The coding method of claim 12 , wherein the summand is wL×R −1,y +wT×R x,−1 , R x,−1 and R −1,y representing values of nearest reference samples located above and to the left of a predicted sample, respectively.
14. The coding method of claim 10 , wherein the horizontal weighting factor wL or the vertical weighting factor wT is a power of two.
15. The coding method of claim 10 , wherein
the horizontal weighting factor wL=(2<<(p−1)) >>((x<<1) >>nScale), wherein x
is a horizontal coordinate of the sample of the block,
the vertical weighting factor wT=(2<<(p−1)) >>((<<1) >>nScale), wherein y is
a vertical coordinate of the sample of the block, and
nScale is a scale parameter.
16. The coding method of claim 15 , further comprising:
deriving the scale parameter nScale from a size of the block.
17. The coding method of claim 10 , wherein
obtaining the modified predicted sample value comprises:
( wL×R −1,y +wT×R x,−1 +(64− wL−wT )× P ( x,y ) +32)>>6
wherein
P (x, y) represents the predicted sample value,
(64−wL−wT) represents the sample weighting factor,
(64−wL−wT)×P(x, y) represents the weighted predicted sample value,
wL×R −1,y , +wT×R x,−1 represents the additional value,
>>represents the arithmetic right shift,
R x,−1 , R −1,y represent values of nearest reference samples located above and to the left of a predicted sample, respectively.
18. The coding method of claim 10 , further comprising:
determining whether to perform position-dependent prediction combination (PDPC) based on a value of a flag;
wherein performing the PDPC comprises:
multiplying the predicted sample value by the sample weighting factor to produce the weighted predicted sample value, and
normalizing the sum of the additional value and the weighted predicted sample value by the arithmetic right shift to obtain the modified predicted sample value.