Patent ID: 6067118
Filing Date: 2000-05-23
Classification: H04N

Abstract:
A method of reducing distortion in a video signal by coding a video frame utilizing a quantization matrix specifically determined for the video frame, the quantization step sizes for a block of DCT coefficients being dependent on the quantization matrix, the method comprising the steps of:(a) determining the degree to which the video signal is spread about an average value of the DCT coefficients;(b) determining the target weighted distortion for all DCT frequency bands in the video frame through the determination of a reference weighted distortion;(c) determining the individual weights in a quantization matrix in each of the DCT frequency bands such that the weighted distortion across all the frequency bands is minimized by carrying out the further steps of determining a normalized distortion function f(B.sub.k,l), where ##EQU18## determining the average quantizer scale-value Q for the video frame; and determining each weight W.sub.k,l for each DCT frequency band from the relationship: ##EQU19## and (d) coding the video frame taking into account the determined weights in the quantization matrix, wherein .alpha. is the perceptual-weighting factor, .beta. is the quantization step normalized by the spread of the corresponding DCT coefficient, and .lambda. is the average value of the DCT coefficients.