Methods for encoding and decoding pictures and associated apparatus
A method for decoding a picture, a method for encoding a picture, an encoder, and a decoder are provided. The method for encoding a picture includes (i) determining a width and a height of a coding block in the picture; (ii) if the width and the height are equal to N, where N is a positive integer power of 2, determining a matrix-based intra prediction (MIP) size identifier indicating that an MIP prediction size equal to N; (iii) deriving a group of reference samples of the coding block; and (iv) deriving an MIP prediction of the coding block based on the group of reference samples and an MIP matrix corresponding to the MIP size identifier.
1. A method for decoding a picture, comprising:
parsing a bitstream to determine a width, a height and a prediction mode of a coding block;
when the prediction mode indicates a matrix-based intra prediction (MIP) mode is used in decoding the coding block, if the width and the height are equal to N, determining an MIP size identifier indicating that an MIP prediction size equal to N, wherein N is a positive integer power of 2;
deriving a group of reference samples of the coding block; and
deriving an MIP prediction of the coding block based on the group of reference samples and an MIP matrix corresponding to the MIP size identifier by:
deriving the MIP prediction of the coding block based on following equations:
oW =(1«( sW− 1))− fO *(Σ i=0 inSize-1 p[i ]) and
predMip[ x][y ]=(((Σ i=0 inSize-1 mWeight[ i][y *predSize+ x]*p[i ])+ oW )» sW )+pTemp[0], for x from 0 to “predSize−1”, for y from 0 to “predSize−1”,
wherein “sW” represents a shifting number parameter, “fO” represents a shifting offset parameter, “oW” represents a parameter based on the shifting offset parameter and the shifting number parameter, “inSize” represents a variable indicating the number of input samples used in deriving the MIP prediction, “p [i]” represents an input sample, “predMip[x][y]” represents the MIP prediction, “mWeight [i][j]” represents an MIP weighting matrix, “predSize” represents a size of the MIP prediction, “pTemp [0]” represents the 0-th value in a reference sample buffer, symbol “<<” represents a binary left shifting operator, and symbol “>>” represents a binary right shifting operator;
determining the shifting number parameter and the shifting offset parameter; and
deriving the MIP prediction of the coding block based on the group of reference samples, the shifting number parameter, the shifting offset parameter, and the MIP matrix according to the MIP size identifier, wherein different MIP size identifiers correspond to the same shifting number parameter, and different MIP size identifiers correspond to the same shifting offset parameter and the shifting offset parameter is a constant equal to 32.
2. The method of claim 1 , further comprising:
downsampling the group of reference samples of the coding block to obtain the reference sample buffer, wherein the reference sample buffer contains the downsampled group of reference samples of the coding block; and
determining the input samples according to reference samples in the reference sample buffer, the MIP size identifier, and a bitdepth of luminance component.
3. The method of claim 2 , wherein determining the input samples according to reference samples in the reference sample buffer, the MIP size identifier, and the bitdepth of luminance component comprises:
deriving the input samples based on following conditions:
if the MIP size identifier is equal to 2, p[x]=pTemp[x+1]-pTemp [0];
if the MIP size identifier is less than 2,
{
p
[
0
]
=
(
1
<<
(
BitDepth
-
1
)
)
-
pTemp
[
0
]
p
[
x
]
=
pTemp
[
x
]
-
pTemp
[
0
]
for
x
=
1
,
…
,
inSize
-
1
′
wherein “p[x]” represents the input sample, “pTemp[x]” represents the x-th value in the reference sample buffer, and “BitDepth” represents the bitdepth of luminance component.
4. The method of claim 3 , wherein
the MIP size identifier is set as 0 on condition that the width and the height of the coding block are equal to 4;
the MIP size identifier is set as 1 on condition that the width x height is equal to N×4, 4×N, or 8×8; or
the MIP size identifier is set as 2 on condition that the width and the height of the coding block are not equal to 4 and the width x height is not equal to N×4, 4×N, or 8×8.
5. The method of claim 1 , further comprising deriving the group of reference samples of the coding block based on neighboring samples, wherein the neighboring samples include above-neighboring samples and/or left-neighboring samples.
6. The method of claim 1 , further comprising setting a prediction of the coding block equal to the MIP prediction of the coding block.
7. A method for encoding a picture, comprising:
determining a width and a height of a coding block in the picture;
if the width and the height are equal to N, wherein N is a positive integer power of 2, determining a matrix-based intra prediction (MIP) size identifier indicating that an MIP prediction size equal to N;
deriving a group of reference samples of the coding block; and
deriving an MIP prediction of the coding block based on the group of reference samples and an MIP matrix according to the MIP size identifier by:
deriving the MIP prediction of the coding block based on following equations:
oW =(1«( sW− 1))− fO *(Σ i=0 inSize-1 p[i ]) and
predMip[ x][y ]=(((Σ i=0 inSize-1 mWeight[ i][y *predSize+ x]*p[i ])+ oW )» sW )+pTemp[0], for x from 0 to “predSize−1”, for y from 0 to “predSize−1”,
wherein “sW” represents a shifting number parameter, “fO” represents a shifting offset parameter, “oW” represents a parameter based on the shifting offset parameter and the shifting number parameter, “inSize” represents a variable indicating the number of input samples used in deriving the MIP prediction, “p [i]” represents an input sample, “predMip[x] [y]” represents the MIP prediction, “mWeight[i] [j]” represents an MIP weighting matrix, “predSize” represents a size of the MIP prediction, “pTemp[0]” represents the 0-th value in a reference sample buffer, symbol “<<” represents a binary left shifting operator, and symbol “>>” represents a binary right shifting operator;
determining the shifting number parameter and the shifting offset parameter; and
deriving the MIP prediction of the coding block based on the group of reference samples, the shifting number parameter, the shifting offset parameter, and the MIP matrix according to the MIP size identifier, wherein different MIP size identifiers correspond to the same shifting number parameter, and different MIP size identifiers correspond to the same shifting offset parameter and the shifting offset parameter is a constant equal to 32.
8. The method of claim 7 , further comprising:
downsampling the group of reference samples of the coding block to obtain the reference sample buffer, wherein the reference sample buffer contains the downsampled group of reference samples of the coding block; and
determining the input samples according to reference samples in the reference sample buffer, the MIP size identifier, and a bitdepth of luminance component.
9. The method of claim 8 , wherein determining the input samples according to reference samples in the reference sample buffer, the MIP size identifier, and the bitdepth of luminance component comprises:
deriving the input samples based on following conditions:
if the MIP size identifier is equal to 2, p[x]=pTemp[x+1]-pTemp [0];
if the MIP size identifier is less than 2,
{
p
[
0
]
=
(
1
<<
(
BitDepth
-
1
)
)
-
pTemp
[
0
]
p
[
x
]
=
pTemp
[
x
]
-
pTemp
[
0
]
for
x
=
1
,
…
,
inSize
-
1
′
wherein “p[x]” represents the input sample, “pTemp[x]” represents the x-th value in the reference sample buffer, and “BitDepth” represents the bitdepth of luminance component.
10. The method of claim 9 , wherein
the MIP size identifier is set as 0 on condition that the width and the height of the coding block are equal to 4;
the MIP size identifier is set as 1 on condition that the width x height is equal to N×4, 4×N, or 8×8; or
the MIP size identifier is set as 2 on condition that the width and the height of the coding block are not equal to 4 and the width x height is not equal to N×4, 4×N, or 8×8.
11. The method of claim 7 , further comprising deriving the group of reference samples of the coding block based on neighboring samples, wherein the neighboring samples include above-neighboring samples and/or left-neighboring samples.
12. The method of claim 7 , further comprising setting a prediction of the coding block equal to the MIP prediction of the coding block.
13. A decoder for decoding a picture, comprising:
a processor; and
a memory storing one or more computer programs which, when executed by the processor, cause the processor to:
parse a bitstream to determine a width, a height and a prediction mode of a coding block; and
when the prediction mode indicates a matrix-based intra prediction (MIP) mode is used in decoding the coding block, determine an MIP size identifier indicating that an MIP prediction size equal to N, if the width and the height are equal to N, wherein N is a positive integer power of 2, and wherein the processor is configured to derive a group of reference samples of the coding block, and wherein the processor is configured to derive an MIP prediction of the coding block based on the group of reference samples and an MIP matrix corresponding to the MIP size identifier by:
deriving the MIP prediction of the coding block based on following equations:
oW =(1«( sW− 1))− fO *(Σ i=0 inSize-1 p[i ]) and
predMip[ x][y ]=(((Σ i=0 inSize-1 mWeight[ i][y *predSize+ x]*p[i ])+ oW )» sW )+pTemp[0], for x from 0 to “predSize−1”, for y from 0 to “predSize−1”,
wherein “sW” represents a shifting number parameter, “fO” represents a shifting offset parameter, “oW” represents a parameter based on the shifting offset parameter and the shifting number parameter, “inSize” represents a variable indicating the number of input samples used in deriving the MIP prediction, “p[i]” represents an input sample, “predMip[x] [y]” represents the MIP prediction, “mWeight[i][j]” represents an MIP weighting matrix, “predSize” represents a size of the MIP prediction, “pTemp[0]” represents the 0-th value in a reference sample buffer, symbol “<<” represents a binary left shifting operator, and symbol “>>” represents a binary right shifting operator;
determining the shifting number parameter and the shifting offset parameter; and
deriving the MIP prediction of the coding block based on the group of reference samples, the shifting number parameter, the shifting offset parameter, and the MIP matrix according to the MIP size identifier, wherein different MIP size identifiers correspond to the same shifting number parameter, and different MIP size identifiers correspond to the same shifting offset parameter and the shifting offset parameter is a constant equal to 32.
14. The decoder of claim 13 , wherein when executed by the processor, the one or more computer programs further cause the processor to:
downsample the group of reference samples of the coding block to obtain the reference sample buffer, wherein the reference sample buffer contains the downsampled group of reference samples of the coding block; and
determine the input samples according to reference samples in the reference sample buffer, the MIP size identifier, and a bitdepth of luminance component.
15. The decoder of claim 14 , wherein the one or more computer programs causing the processor to determine the input samples according to reference samples in the reference sample buffer, the MIP size identifier, and the bitdepth of luminance component, causes the processor to:
derive the input samples based on following conditions:
if the MIP size identifier is equal to 2, p[x]=pTemp[x+1]-pTemp[0];
if the MIP size identifier is less than 2,
{
p
[
0
]
=
(
1
<<
(
BitDepth
-
1
)
)
-
pTem
p
[
0
]
p
[
x
]
=
pTemp
[
x
]
-
pTemp
[
0
]
for
x
=
1
,
…
,
inSize
-
1
′
wherein “p[x]” represents the input sample, “pTemp[x]” represents the x-th value in the reference sample buffer, and “BitDepth” represents the bitdepth of luminance component.
16. The decoder of claim 15 , wherein
the MIP size identifier is set as 0 on condition that the width and the height of the coding block are equal to 4;
the MIP size identifier is set as 1 on condition that the width x height is equal to N×4, 4×N, or 8×8; or
the MIP size identifier is set as 2 on condition that the width and the height of the coding block are not equal to 4 and the width x height is not equal to N×4, 4×N, or 8×8.
17. The decoder of claim 13 , wherein when executed by the processor, the one or more computer programs further cause the processor to:
derive the group of reference samples of the coding block based on neighboring samples,
wherein the neighboring samples include above-neighboring samples and/or left-neighboring samples.
18. The decoder of claim 13 , wherein when executed by the processor, the one or more computer programs further cause the processor to:
set a prediction of the coding block equal to the MIP prediction of the coding block.