Abstract
Fractal image coding is a novel technique for image compression and has been successfully developed to automatically convert a still image into a set of affine transformation coefficients. To save the bit rate for storing affine transformation information, a scheme of flexible segmentation of range blocks is essential. In the past years, several low bit rate schemes of fractal image coding were proposed in which they all employ the quadtree segmentation technique. In this thesis, a low bit rate region-based fractal image compression algorithm s proposed, several techniques are included as follows. First, we improve the performance of quadtree segmentation by adaptive threshold. Then, a merging scheme is employed to the resulting quadtree segmentation that combines several similar blocks into a small number of regions. We also provide a quadtree-based segmented chain code to efficiently record the contours of the regions. In the coding process, we consider both the bit rate and the quality (in PSNR) simultaneously to reconstruct the image. The experimental results show that the proposed scheme has the lowest bit rate among the existing schemes at the same level of quality. Typically, the bit rate is 0.089 bits/pixel at PSNR 29.0 dB for the 512x512 grey-level image "Lena".