Efficient DCT domain implementation of picture masking and compositing

An efficient method for implementing picture masking and compositing in the DCT domain is presented. The method is based on representing the masking function in terms of the DCT basis functions and computing the masking as a weighted sum of the results of masking by the DCT basis functions. In the DCT domain, masking by the DCT basis functions has very simple and efficient implementation. Because of the energy compaction property of the DCT, the weight of many of the basis functions is very small and can be dropped from the weighted sum without introducing noticeable artifacts. This leads to very efficient implementations for the masking and compositing images in the DCT domain, typically requiring less than 3 multiplications per pixel