I. Introduction
With the widespread development of video communication, many efficient image compression methods have been developed and standardized. Especially, high quality image communication with low bit-rate is widely used for video conferencing, videophone, etc. Block-based discrete cosine transform (BDCT) is the most widely used technique for the compression of both still and moving images [1]. Most of image and video coding standards, such as JPEG and MPEG, are based on BDCT. One of the most noticeable artifacts caused by coding algorism is an artificial discontinuity across the block boundaries called “blocking artifact”, due to the independent quantization of the transform coefficients. Peak signal to noise ratio (PSNR) and mean square error (MSE) are popular image quality evaluation criterions, but they are ineffective measurements for blocking artifacts that are structural disturbance [2]. It is therefore essential to develop metrics that have good consistency to the visual perception.