Adaptive Vector Quantization In Transform Domain With Variable Block Size

Abstract

A novel method for adaptive vector quantization has been proposed to address the problem of edge degradation in image coding. This technique utilizes variable block size, in our example, 4x4 and 2x2. The basic idea is to partition the image into two parts: non-active and active. For the non-active area, a large block size is used, whereas for the active area a small block size is employed. The quality of the reconstructed images is improved using this algorithm because the bits saved in the non-active areas are allocated to the active areas where the edges may exist. To decrease the complexity of the encoder and decoder, one codebook is used for both active and non-active areas. First, both non-active blocks (large block size) and active blocks (small block size) undergo a two-dimensional cosine transform. The same number of coefficients are retained in both cases; for the large size blocks this could tend to be the lower order coefficients, whereas for the small size blocks, some of the higher order coefficients are retained. A single codebook is then generated. The experimental results show that good quality of reconstructed images by this algorithm is obtained at bit rates as low as 0.8 bits/pixel.