A fast encoding method without search for fractal image compression

Abstract

A fast coding algorithm for images using vector quantization (VQ) and pixelwise fractal approximation is proposed. The low frequency component of an input image is approximated and its residual is used to calculate the scaling factor of the fractal transform. The scaling factor is compressed by transform VQ (TVQ). In the proposed method, to encode a digital image by an iterated function system (IFS), we use the pixel-based IFS (PIFS) rather than the block-based IFS: the scaling factor is computed for each pixel. In the proposed method, the scaling factor of each pixel is calculated with the constraint of contraction mapping and it is transformed by wavelets and quantized by VQ. For approximation of an original image, the variable block-size segmentation using quadtrees is employed. Because the proposed method calculates the scaling factor using the PIFS, the encoding time is faster than the conventional algorithm using block-based IFS with search.