Block Distortion in Orthogonal Transform Coding--Analysis, Minimization, and Distortion Measure

Psychophysical considerations show that the block-shaped distortion peculiar to orthogonal transform coding (OTC) is ten times more objectionable than random noise distortion. Minimizing the blockshaped distortion is considered here by analyzing the process of generation of coding errors, and the required characteristics of the orthogonal transform function (OTF) are clarified. Computer simulations substantiate its validity. Graphical illustration and measures of the block-shaped distortion are proposed and substantiated. With the aid of these measures, one can evaluate the performance of OTC or a new OTF, if proposed, without conducting visual assessment tests.