Algorithm for fractional multiple image enlargement based on all phase DCT

Abstract

Image enlargement technique is widely used in image processing and video format transforming. This paper proposes an algorithm for fractional multiple image enlargement based on All Phase Discrete Cosine Transform (APDCT) interpolation. The All Phase Digital Filter (APDF) is a new type of linear phase filter. For a data vector with a length of N obtained by blocking a signal, there are N different phase data blocks that include the same sampling point. Through taking the mean of the N values as the filtering output, the APDF can eliminate different meanings of the orthogonal transform filtering values of those data vectors and thereby the block effect. According to this idea, this paper deduces the formula of two-dimension APDCT filter. As a good integration of Discrete Cosine Transform (DCT) and all phase idea, a family of separable interpolation kernel, which is constructed by cosine function, is put forward. Look-up method is then discussed for real time image enlargement. The objective and subjective experiments show that better image quality is obtained by using interpolation kernel proposed than using 6*6 cubic interpolation kernel.