Restoration of low frequency coefficients

The DC coefficient restoration scheme is a technique which can be used to increase the compression ability of transform image coding by not transmitting the DC coefficients but instead estimating them from the transmitted AC component. Tse and Cham (see Fifth International Conference on Image Processing and Its Application, p.569-73, 1995) proposed an improved version of the technique which allows an image to be restored with no or small visual degradation by transmitting a small portion of the DC coefficients. We show that the same technique can be used to restore not only the DC coefficients but also a portion of AC coefficients. As a result, a higher compression ratio can be obtained.