A NEW METHOD OF MEASURING THE BLOCKING EFFECTS OF IMAGES BASED ON CEPSTRAL INFORMATION

The transform coding scheme is often used for data compression of imag es, bur the blocking effects peculiar to the scheme appear more clearl y in reproduced images as a coding rate (bits/pixel) decreases. These effects can sometimes be viewed as a periodical square-grid overlaying the images. In this paper, we propose a new method for selectively me asuring the above blocking effects among several types of image degrad ation by means of the techniques of nonlinear signal processing for sp ectral information (cepstral techniques), in order to compare the amou nt of blocking effects for the different coding images. First a two-co mponent model which consists of DC and AC images, is discussed from a viewpoint of subimage-by-subimage coding, and some basic properties of cepstral information for the model are investigated. Then we show a p rocedure to compute the cepstral information for two-dimensional image signals taking the horizontal and vertical directions into account, a nd introduce a cepstral mean square error (CMSE) as a new measure to e stimate the amount of blocking effects. The computer simulation result s fur some test images using different coding schemes show that thr am ount of blocking effects in each image can be easily measured and esti mated be this method even when the blocking effects appear slightly.