Method and system for improving color sharpness in video and images

1. A method in a decoding process for determining full-resolution chroma pixel information (Cx) corresponding to a spatial fraction of a still-image or a video-frame represented by full-resolution luma pixel information (Y) and decimated chroma pixel information (Cxd) decimated by a decimation process, comprising:

receiving the full-resolution luma pixel information at video or image processing apparatus;

decimating, at the video or image processing apparatus, the full-resolution luma pixel information (Y) by said decimation process resulting in a decimated spatial luma fraction (Yd);

determining, with the video or image processing apparatus, if the decimated chroma pixel information (Cxd) at least approximately can be expressed by {(Yd+shift1)*scale−shift2}, wherein the spatial fraction corresponds to a square block of pixels, and the shift1 is −Yd center , where Yd center is a center pixel value of Yd, the shift2 is −Cxd center , where Cxd center is a center pixel value of Cxd, and the scale is (Cxd+shift2)/(Yd+shift1);

storing, in an electronic memory of the video or image processing apparatus, values of scale, shift1, and shift2 that result in a minimum deviation between {(Yd+shift1)*scale−shift2} and Cxd; and calculating, with the video or image processing apparatus, {(Y+shift1)*scale−shift2} as a first candidate (Cx 1 ) for the full-resolution chroma pixel information (Cx)″.

2. The method according to claim 1 , further comprising:

calculating a quality parameter (Q) by comparing {(Yd+shift1)*scale−shift2} with Cxd;

interpolating Cxd, by an interpolation process corresponding to the decimation process, resulting in a second candidate (Cx 2 ) for the full-resolution chroma pixel information (Cx); and

combining the first and the second candidates according to the quality parameter to create the full-resolution chroma pixel information (Cx).

3. The method according to claim 2 , wherein

the quality parameter is a floating number from 0 to 1, wherein 0 appears when there is no match between {(Yd+shift1)*scale−shift2} and Cxd, and 1 appears when there is an optimal match between {(Yd+shift1)*scale−shift2} and Cxd.

4. The method according to claim 2 , wherein the step of combing the first and the second candidates according to the quality parameter includes creating the full-resolution chroma pixel information (Cx) as a linear mix between the first and second candidates according to an expression Cx=Q*Cx 1 +(1−Q)*Cx 2 .

5. The method according to claim 1 , wherein

the full resolution chroma pixel information includes blue chroma difference information.

6. The method according to claim 1 , wherein the full resolution chroma pixel information includes red chroma difference information.

7. An apparatus configured to implement a decoding process for determining full-resolution chroma pixel information (Cx) corresponding to a spatial fraction of a still-image or a video-frame represented by full-resolution luma pixel information (Y) and decimated chroma pixel information (Cxd) decimated by a decimation process, comprising:

a decimator that decimates the full-resolution luma pixel information (Y) by said decimation process resulting in a decimated spatial luma fraction (Yd); a processor configured to determine if the decimated chroma pixel information (Cxd) at least approximately can be expressed by {(Yd+shift1)*scale−shift2}, wherein the spatial fraction corresponds to a square block of pixels, and the shift1 is −Yd center , where Yd center is a center pixel value of Yd, the shift2 is −Cxd center , where Cxd center is a center pixel value of Cxd, and the scale is (Cxd+shift2)/(Yd+shift1); and

a memory that stores values of scale, shift1, and shift2 that result in a minimum deviation between {(Yd+shift1)*scale−shift2} and Cxd,

wherein the processor is configure to calculate {(Y+shift1)*scale−shift2} as a first candidate (Cx 1 ) for the full-resolution chroma pixel information (Cx).

8. The apparatus according to claim 7 , wherein the processor is further configured to

calculate a quality parameter (Q) by comparing {(Yd+shift1)*scale−shift2} with Cxd,

interpolate Cxd, by an interpolation process corresponding to the decimation process, resulting in a second candidate (Cx 2 ) for the full-resolution chroma pixel information (Cx), and

to combine the first and the second candidates according to the quality parameter to create the full-resolution chroma pixel information (Cx).

9. The apparatus according to claim 7 , wherein

the quality parameter is a floating number from 0 to 1, wherein 0 appears when there is no match between {(Yd+shift1)*scale−shift2} and Cxd, and 1 appears when there is an optimal match between {(Yd+shift1)*scale−shift2} and Cxd.

10. The apparatus according to claim 7 , wherein the processor is further configured to create the full-resolution chroma pixel information (Cx) as a linear mix between the first and second candidates according to an expression Cx=Q*Cx 1 +(1−Q)*Cx 2 .

11. The apparatus according to claim 7 , wherein

the full resolution chroma pixel information includes blue chroma difference information.

12. The apparatus according to claim 7 , wherein the full resolution chroma pixel information includes red chroma difference information.

13. A non-transitory computer readable storage medium encoded with instructions, which when executed by a computer cause the computer to implement a method in a decoding process for determining full-resolution chroma pixel information (Cx) corresponding to a spatial fraction of a still-image or a video-frame represented by full-resolution luma pixel information (Y) and decimated chroma pixel information (Cxd) decimated by a decimation process, the method comprising:

decimating the full-resolution luma pixel information (Y) by said decimation process resulting in a decimated spatial luma fraction (Yd);

determining if the decimated chroma pixel information (Cxd) at least approximately can be expressed by {(Yd+shift1)*scale−shift2}, wherein the spatial fraction corresponds to a square block of pixels, and the shift1 is −Yd center , where Yd center is a center pixel value of Yd, the shift2 is −Cxd center , where Cxd center is a center pixel value of Cxd, and the scale is (Cxd+shift2)/(Yd+shift 1);

storing values of scale, shift1, and shift2 that result in a minimum deviation between {(Yd+shift1)*scale−shift2} and Cxd; and

calculating {(Y+shift1)*scale−shift2} as a first candidate (Cx 1 ) for the full-resolution chroma pixel information (Cx).

14. The non-transitory computer readable storage medium of claim 13 , wherein the method further comprises:

calculating a quality parameter (Q) by comparing {(Yd+shift1)*scale−shift2} with Cxd;

interpolating Cxd, by an interpolation process corresponding to the decimation process, resulting in a second candidate (Cx 2 ) for the full-resolution chroma pixel information (Cx); and

combining the first and the second candidates according to the quality parameter to create the full-resolution chroma pixel information (Cx).

15. The non-transitory computer readable storage medium of claim 14 , wherein the quality parameter is a floating number from 0 to 1, wherein 0 appears when there is no match between {(Yd+shift1)*scale−shift2} and Cxd, and 1 appears when there is a match between {(Yd+shift1)*scale−shift2} and Cxd.

16. The non-transitory computer readable storage medium of claim 14 , wherein the step of combing the first and the second candidates according to the quality parameter includes creating the full-resolution chroma pixel information (Cx) as a linear mix between the first and second candidates according to an expression Cx=Q*Cx 1 +(1−Q)*Cx 2 .