Patent ID: 7218794

Claim:
A method of processing video signals representing video image frames comprising pixels, to detect the existence and the positions of a block grid in each frame resulting from block-based transform coding, wherein the video signal value is a function f of pixel positions in each frame, comprising the steps of: (i) computing a horizontal second derivative f h ″ and a vertical second derivative f v ″, for the function f at multiple pixel positions in a frame; (ii) determining the zero-crossings of the second derivatives and generating horizontal and vertical second derivative zero-crossing masks; (iii) computing a horizontal integral projection of the horizontal zero-crossing mask to generate a horizontal projected one dimensional signal, and computing a vertical integral projection of the vertical zero-crossing mask to generate a vertical projected one dimensional signal; (iv) generating a local maximum mask for each of the two projected one dimensional signals; and (v) determining the grid block boundary position by computing the locations of the local maximum masks in the frame.