Patent ID: 8259813

Claim:
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)″.