Wavelet image compression using sub-block DCT

A wavelet image compression method using sub-block DCT is presented. The presented method is a hybrid type of DWT and DCT. The sub-block DCT is employed to the DWT-details. DWT-details have usually zero mean and small variance and hence the sub-block DCT method is very efficient. The size of sub-block for DCT is 8×8 pixel for level 1 DWT-details and 4×4 pixel for level 2 DWT-details. The simulation examples show that the presented method gives a better picture quality that of the usual JPEG method.