Patent ID: 6327304
Filing Date: 2001-12-04
Classification: H04N

Abstract:
A method of operating a digital computer, a data structure corresponding to an image having a plurality of pixels arranged in two dimensions, said method comprising the steps of:(a) selecting the data from said structure corresponding to adjacent lines of pixels of said image;(b) calculating the vertical differentials between said adjacent lines of pixels using a computer, each vertical being the difference between the value of a first pixel and second pixel, said first pixel being a pixel in a first line of said adjacent lines, and said second pixel being a pixel in a second line of said adjacent lines, said second pixel being the pixel in said second line closest to said first pixel;(c) calculating a set of deltas from said vertical differentials using a computer, each of said deltas representing the difference between the value of a vertical differential and the value of a second, adjacent vertical differential; and,(d) selecting a quantized delta from a set of predetermined quantized deltas to represent each of said deltas being in one of a plurality of ranges, the quantized delta selected being closest to the value of the respective calculated delta,wherein said plurality of ranges comprising negative ranges and positive ranges, said negative ranges being NR.sub.1, NR.sub.2 . . . NR.sub.y wherein y is an integer, and said positive ranges being PR.sub.1, PR.sub.2, . . . PR.sub.y, each of said negative ranges being a series of negative numbers, and each of said positive ranges being a series of positive numbers, said set of predetermined quantized deltas comprising negative quantized deltas and positive quantized deltas, said negative-quantized deltas being NQD.sub.1, NQD.sub.2, . . . NQD.sub.y and said positive quantized deltas being PQD.sub.1, PQD.sub.2, . . . PQD.sub.y, said quantized deltas being used to represent said deltas such that a negative quantized delta NQD.sub.x is used to represent any of the deltas in a negative range NR.sub.x, and a positive quantized delta PQD.sub.x is used to represent any of the deltas in a positive range PR.sub.x, wherein x is an integer between 1 and said y, and wherein said set of predetermined quantized deltas is asymmetric such that the absolute value of at least one NQD.sub.x is different from the absolute value of PQD.sub.x.