Enhanced intra-prediction coding using planar representations
The present invention provides low complexity planar mode coding in which a first prediction value is calculated using linear interpolation between a value of respective horizontal boundary pixels and a value of one of vertical boundary pixels, and a second prediction value is calculated using linear interpolation between a value of respective vertical boundary pixels and a value of one of the horizontal boundary pixels. The first and second prediction values are then averaged to derive a respective prediction pixel value in a prediction block. A residual between the prediction block and a target block is signaled to a decoder.
1. A video encoding method for predicting pixel values of target pixels in a target block under a planar mode, the method comprising computer executable steps executed by a processor of a video encoder to implement:
(a) calculating a first prediction value of a target pixel in the target block using linear interpolation between a pixel value of a horizontal boundary pixel horizontally co-located with the target pixel, the horizontal boundary pixel being from among a plurality of horizontal boundary pixels located on an upper side of the target block, and a pixel value of one vertical boundary pixel from among a plurality of vertical boundary pixels located on a left side of the target block, wherein the first prediction value consists only of a first value derived solely from the linear interpolation between the pixel value of the horizontal boundary pixel horizontally co-located with the target pixel and the pixel value of said one vertical boundary pixel;
(b) calculating a second prediction value of the target pixel using linear interpolation between a pixel value of a vertical boundary pixel vertically co-located with the target pixel, the vertical boundary pixel being from among a plurality of the vertical boundary pixels and a pixel value of one horizontal boundary pixel from among a plurality of the horizontal boundary pixels, wherein the second prediction value consists only of a second value derived solely from the linear interpolation between the pixel value of the vertical boundary pixel vertically co-located with the target pixel and the pixel value of said one horizontal boundary pixel;
(c) averaging the first and second prediction values of the target pixel to derive a prediction pixel value in a prediction block, wherein the prediction pixel value consists only of an average of the first and second prediction values; and
(d) repeating steps (a)-(c) on a reset of the target pixels in the target block.
2. The method according to claim 1 , further comprising signaling a residual between the prediction block and the target block.
3. The method according to claim 2 , further comprising:
switching from a primary set of transform kernel H N (i, j) to a secondary set of transform kernel G N (i, j); and
transforming the residual, using the secondary set of transform kernel G N (i, j).
4. The method according to claim 3 , wherein the secondary set of transform kernel G N (i, j) is defined by one of the following equations:
G
N
(
i
,
j
)
=
k
i
×
sin
(
(
2
i
-
1
)
j
π
2
N
+
1
)
;
(
a
)
G
N
(
i
,
j
)
=
k
i
×
sin
(
(
2
i
-
1
)
(
2
j
-
1
)
π
4
N
)
;
and
(
b
)
G
N
(
i
,
j
)
=
k
i
×
cos
(
(
i
-
1
)
(
2
j
-
1
)
π
2
N
)
.
(
c
)
5. The method according to claim 3 , wherein the secondary set of transform kernel G N (i, j) for size N×N is defined by the primary set of transform kernel H M (i, j) for size M×M, where M>N.
6. The method according to claim 5 , wherein the secondary set of transform kernel G N (i, j) is defined by G N (i, j)=k i ×H 2N (2i, N+1−j), if transform kernels of size 2N×2N(H 2N ) are supported, or G N (i, j)=H N (i, j) otherwise.
7. A video decoding method for predicting pixel values of target pixels in a target block under a planar mode, the method comprising computer executable steps executed by a processor of a video decoder to implement:
(a) calculating a first prediction value of a target pixel in the target block using linear interpolation between a pixel value of a horizontal boundary pixel horizontally co-located with the target pixel, the horizontal boundary pixel being from among a plurality of horizontal boundary pixels located on an upper side of the target block, and a pixel value of one vertical boundary pixel from among a plurality of vertical boundary pixels located on a left side of the target block, wherein the first prediction value consists only of a first value derived solely from the linear interpolation between the pixel value of the horizontal boundary pixel horizontally co-located with the target pixel and the pixel value of said one vertical boundary pixel;
(b) calculating a second prediction value of the target pixel using linear interpolation between a pixel value of a vertical boundary pixel vertically co-located with the target pixel, the vertical boundary pixel being from among a plurality of the vertical boundary pixels and a pixel value of one horizontal boundary pixel from among a plurality of the horizontal boundary pixels, wherein the second prediction value consists only of a second value derived solely from the linear interpolation between the pixel value of the vertical boundary pixel vertically co-located with the target pixel and the pixel value of said one horizontal boundary pixel;
(c) averaging the first and second prediction values of the target pixel to derive a prediction pixel value in a prediction block, wherein the prediction pixel value consists only of an average of the first and second prediction values; and
(d) repeating steps (a)-(c) on a rest of the target pixels in the target block.
8. The method according to claim 7 , further comprising:
decoding a residual signaled from an encoder which was generated under the planar mode at an encoder; and
adding the decoded residual to the prediction block to reconstruct image data.
9. A video encoder that predicts pixel values of target pixels in a target block under a planar mode, comprising a processor of a computer system and a memory that stores programs executable by the processor to:
(a) calculate a first prediction value of a target pixel in the target block using linear interpolation between a pixel value of a horizontal boundary pixel horizontally co-located with the target pixel, the horizontal boundary pixel being from among a plurality of horizontal boundary pixels located on an upper side of the target block, and a pixel value of one vertical boundary pixel from among a plurality of vertical boundary pixels located on a left side of the target block, wherein the first prediction value consists only of a first value derived solely from the linear interpolation between the pixel value of the horizontal boundary pixel horizontally co-located with the target pixel and the pixel value of said one vertical boundary pixel;
(b) calculate a second prediction value of the target pixel using linear interpolation between a pixel value of a vertical boundary pixel vertically co-located with the target pixel. The vertical boundary pixel being from among a plurality of the vertical boundary pixels and a pixel value of one horizontal boundary pixel from among a plurality of the horizontal boundary pixels, wherein the second prediction value consists only of a second value derived solely from the linear interpolation between the pixel value of the vertical boundary pixel vertically co-located with the target pixel and the pixel value of said one horizontal boundary pixel;
(c) average the first and second prediction values of the target pixel to derive a prediction pixel value in a prediction block, wherein the prediction pixel value consists only of an average of the first and second prediction values; and
(d) repeating steps (a)-(c) on a rest of the target pixels in the target block.
10. The video encoder according to claim 9 , wherein the processor signals a residual between the prediction block and the target block.
11. The video encoder according to claim 10 , wherein the processor:
switch from a primary set of transform kernel H N (i, j) to a secondary set of transform kernel G N (i, j); and
transform the residual, using the secondary set of transform kernel G N (i, j).
12. The video encoder according to claim 11 , wherein the secondary set of transform kernel G N (i, j) is defined by one of the following equations:
G
N
(
i
,
j
)
=
k
i
×
sin
(
(
2
i
-
1
)
j
π
2
N
+
1
)
;
(
a
)
G
N
(
i
,
j
)
=
k
i
×
sin
(
(
2
i
-
1
)
(
2
j
-
1
)
π
4
N
)
;
and
(
b
)
G
N
(
i
,
j
)
=
k
i
×
cos
(
(
i
-
1
)
(
2
j
-
1
)
π
2
N
)
.
(
c
)
13. The video encoder according to claim 11 , wherein the secondary set of transform kernel G N (i, j) for size N×N is defined by the primary set of transform kernel H M (i, j) for size MxM, where M>N.
14. The video encoder according to claim 13 , wherein the secondary set of transform kernel G N (i, j) is defined by G N (i, j)=k i ×H F 2N (2i, N+1−j), if transform kernels of size 2N×2N(H F 2N ) are supported, or G N (i, j)=H F N (i, j) otherwise.
15. A video decoder that predicts pixel values of target pixels in a target block under a planar mode, comprising a processor of a computer system and a memory that stores programs executable by the processor to:
(a) calculate a first prediction value of a target pixel in the target block using linear interpolation between a pixel value of a horizontal boundary pixel horizontally co-located with the target pixel, the horizontal boundary pixel being from among a plurality of horizontal boundary pixels located on an upper side of the target block, and a pixel value of one vertical boundary pixel from among a plurality of vertical boundary pixels located on a left side of the target block, wherein the first prediction value consists only of a first value derived solely from the linear interpolation between the pixel value of the horizontal boundary pixel horizontally co-located with the target pixel and the pixel value of said one vertical boundary pixel;
(b) calculate a second prediction value of the target pixel using linear interpolation between a pixel value of a vertical boundary pixel vertically co-located with the target pixel, the vertical boundary pixel being from among a plurality of the vertical boundary pixels and a pixel value of one horizontal boundary pixel from among a plurality of the horizontal boundary pixels, wherein the second prediction value consists only of a second value derived solely from the linear interpolation between the pixel value of the vertical boundary pixel vertically co-located with the target pixel and the pixel value of said one horizontal boundary pixel,
(c) average the first and second prediction values of the target pixel to derive a prediction pixel value in a prediction block, wherein the prediction pixel value consists only of an average of the first and second prediction values; and
(d) repeating steps (a)-(c) on a rest of the target pixels in the target block.
16. The video decoder according to claim 15 , wherein the processor further:
decodes a residual signaled from an encoder; and
adds the decoded residual to the prediction block.