Packed-TS transform [for image compression]

Abstract

Summary form only given. As a reversible integer wavelet transform, the TS transform gains much attention in both lossless and lossy compression. It is a good approximation to the (2, 6) wavelet, which is one of the best biorthogonal wavelets for image compression, and it can be implemented by only using integer addition/subtraction and shift. Most gray-scale images are in 8-bit form; the TS transform coefficients of them can be represented by 16-bit words, while in most modern computers, 32-bit arithmetic and 16-bit arithmetic have the same speed. We propose a method to speed up the TS transform for image compression. The new algorithm is called the packed-TS transform. The proposed method packs two adjacent pixels in one double-word; therefore, it can make use of the 32-bit computational capability of modern computers to accomplish two additions/subtractions in one instruction cycle. The packed-TS transform is also a reversible transform. In the packed-TS transform, the two adjacent pixels or coefficients are stored in the high-word and the low-word of a double-word, respectively. Then the decomposition/reconstruction is performed on this double-word. We compare the performance of the original TS transform and the proposed packed-TS transform on five images: Girl, Lena, Peppers, Couple and Man, respectively . The experiment shows that the packed-TS transform is faster than the original TS transform by about 30 percent, with a comparable performance in the quality of the reconstructed images.