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 images, bur the blocking effects peculiar to the scheme appear more clearly 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 measuring the above blocking effects among several types of image degradation by means of the techniques of nonlinear signal processing for spectral information (cepstral techniques), in order to compare the amount of blocking effects for the different coding images. First a two-component 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 procedure to compute the cepstral information for two-dimensional image signals taking the horizontal and vertical directions into account, and introduce a cepstral mean square error (CMSE) as a new measure to estimate the amount of blocking effects. The computer simulation results fur some test images using different coding schemes show that thr amount of blocking effects in each image can be easily measured and estimated be this method even when the blocking effects appear slightly.