Low complexity image filter
There is provided a method for encoding or decoding an image. The method comprises obtaining a first luma sample value, L1, associated with the image. The method comprises obtaining a second luma sample value, L2, associated with the image. The method further comprises obtaining a first luma delta value, ΔL1, wherein ΔL1=L2−L1. The method comprises obtaining a first product, P1, using ΔL1 and a first coefficient value, C1, wherein P1=(C1)(ΔL1). The method comprises calculating a first residual correction value, ΔI1 using P1 and a set of other products. The method comprises filtering an unfiltered chroma value, R C , associated with the image using the first residual correction value, ΔI1, thereby producing a filtered chroma value R F C associated with the image.
1. A method for encoding or decoding an image, the method comprising:
obtaining a first luma sample value, L1, associated with the image;
obtaining a second luma sample value, L2, associated with the image;
obtaining a first luma delta value, ΔL1, wherein ΔL1=L2−L1;
obtaining a first coefficient value, C1, from a set of predefined integers (Z sub ), wherein Z sub comprises:
a first subset of integers (Z two ), wherein each integer in Z two is a power of two or −1 times a power of two or zero; and
a second subset of integers (Z ext ) comprising a first integer that is equal to α2 n +β2 p , where α=±1, β=±1, n is an integer greater than or equal to 0, p is an integer greater than or equal to 0, and p≠n, and further wherein Z ext does not include any positive integer that is not equal to a sum of two different powers of two;
obtaining a first product, P1, using ΔL1 and C1, wherein P1=(C1)(ΔL1);
calculating a first residual correction value, ΔI1 using P1 and a set of other products; and
filtering an unfiltered chroma value, R C , associated with the image using the first residual correction value, ΔI1, thereby producing a filtered chroma value R C F associated with the image.
2. The method of claim 1 , wherein filtering the unfiltered chroma value to produce the filtered chroma value consists of calculating: R C F =ΔI1+R C .
3. The method of claim 1 , wherein
the set of other products comprises a second product, P2,
P 2=( C 2)(Δ L 2),
C2 is a second coefficient value,
ΔL2 is a second luma delta value that is equal to L3−L1, and
L3 is a third luma sample value associated with the image.
4. The method of claim 1 , wherein
L1 has a first position within a two-dimensional block of luma sample values associated with the image, wherein the coordinates of the first position are x1,y1,
L2 has a second position within the two-dimensional block of luma sample values, wherein the coordinates of the second position are x2,y2,
the absolute value of (x1-x2) is less than or equal to 4, and
the absolute value of (y1-y2) is less than or equal to 4.
5. The method of claim 4 , wherein
the absolute value of (x1-x2) is less than or equal to 1, and
the absolute value of (y1-y2) is less than or equal to 2.
6. The method of claim 1 , wherein
R C has a position within a two-dimensional block of chroma sample values associated with the image, where the coordinates of the position are xc,yc,
L1 has a first position within a two-dimensional block of luma sample values associated with the image, wherein the coordinates of the first position are x1,y1,
L2 has a second position within the two-dimensional block of luma sample values, wherein the coordinates of the second position are x2,y2, and
the second position is obtained from the position of R C within the two-dimensional block of chroma sample values.
7. The method of claim 6 , wherein
x 2=( Wc )( xc ),
y 2=( Hc )( yc ),
Wc is a first predetermined coefficient that is based on the format of the image, and
Hc is a second predetermined coefficient that is based on the format of the image.
8. The method of claim 7 , wherein
when the format of the image is 4:2:0, Wc=Hc=2;
when the format of the image is 4:2:2, Wc=2 and Hc=1; and
when the format of the image is 4:4:4, Wc=Hc=1.
9. A non-transitory computer readable medium storing a computer program comprising instructions which when executed by processing circuitry causes the processing circuitry to perform the method of claim 1 .
10. An apparatus, the apparatus comprising:
processing circuitry; and
a memory, said memory containing instructions executable by said processing circuitry, wherein said apparatus is operative to perform a method comprising:
obtaining a first luma sample value, L1, associated with the image;
obtaining a second luma sample value, L2, associated with the image;
obtaining a first luma delta value, ΔL1, wherein ΔL1=L2−L1;
obtaining a first coefficient value, C1, from a set of predefined integers (Z sub ), wherein Z sub comprises:
a first subset of integers (Z two ), wherein each integer in Z two is a power of two or −1 times a power of two or zero; and
a second subset of integers (Z ext ) comprising a first integer that is equal to α2 n +β2 p , where α=±1, β=±1, n is an integer greater than or equal to 0, p is an integer greater than or equal to 0, and p≠n, and further wherein Z ext does not include any positive integer that is not equal to a sum of two different powers of two;
obtaining a first product, P1, using ΔL1 and C1, wherein P1=(C1)(ΔL1);
calculating a first residual correction value, ΔI1, using P1 and a set of other products; and
filtering an unfiltered chroma value, R C , associated with the image using the first residual correction value, ΔI1 thereby producing a filtered chroma value R C F associated with the image.
11. The apparatus of claim 10 , wherein filtering the unfiltered chroma value to produce the filtered chroma value consists of calculating: R C F =ΔI1+R C .
12. The apparatus of claim 10 , wherein
the set of other products comprises a second product, P2,
P 2=( C 2)(Δ L 2),
C2 is a second coefficient value,
ΔL2 is a second luma delta value that is equal to L3−L1, and
L3 is a third luma sample value associated with the image.
13. The apparatus of claim 10 , wherein
L1 has a first position within a two-dimensional block of luma sample values associated with the image, wherein the coordinates of the first position are x1,y1,
L2 has a second position within the two-dimensional block of luma sample values, wherein the coordinates of the second position are x2,y2,
the absolute value of (x1-x2) is less than or equal to 4, and
the absolute value of (y1-y2) is less than or equal to 4.
14. The apparatus of claim 13 , wherein
the absolute value of (x1-x2) is less than or equal to 1, and
the absolute value of (y1-y2) is less than or equal to 2.
15. The apparatus of claim 10 , wherein
R C has a position within a two-dimensional block of chroma sample values associated with the image, where the coordinates of the position are xc,yc,
L1 has a first position within a two-dimensional block of luma sample values associated with the image, wherein the coordinates of the first position are x1,y1,
L2 has a second position within the two-dimensional block of luma sample values, wherein the coordinates of the second position are x2,y2, and
the second position is obtained from the position of R C within the two-dimensional block of chroma sample values.
16. The apparatus of claim 15 , wherein
x 2=( Wc )( xc ),
y 2=( Hc )( yc ),
Wc is a first predetermined coefficient that is based on the format of the image, and
Hc is a second predetermined coefficient that is based on the format of the image.
17. The apparatus of claim 15 , wherein
when the format of the image is 4:2:0, Wc=Hc=2;
when the format of the image is 4:2:2, Wc=2 and Hc=1; and
when the format of the image is 4:4:4, Wc=Hc=1.
18. The method of claim 1 , wherein
every positive integer within Z ext can be expressed in the form of either 3×2 m or 5×2 m , where m is an integer greater than or equal to 0, and
every negative integer within Z ext can be expressed in the form of either −3×2 m or −5×2 m .
19. The method of claim 1 , wherein every integer in Z sub is greater than −x and less than x.
20. The method of claim 19 , wherein x=129.