Color image compression using quantization, thresholding, and edge detection techniques all based on the moment-preserving principle

A new approach to color image compression with high compression ratios and good quality of reconstructed images using quantization, thresholding, and edge detection all based on the moment-preserving principle is proposed. An input image with 24 bits per pixel is quantized into 8 bits per pixel using a new color quantization method based on the moment-preserving principle. The quantized image is then divided into n=n non-overlapping square blocks. Two representative colors for each block are computed by moment-preserving thresholding. A bit-map is then generated, consisting of 0s and 1s indicating whether the block pixels are assigned to the first color or the second according to the Euclidean distance measure. A moment-based edge detector is performed further on the bit-map of each non-uniform block. The two parameters l and u of a line edge with the equation of x cos uqy sin us l are obtained. The image is finally coded with a codebook of a 256-color palette; a 1-bit indicator for each block which specifies whether the block is uniform or not; an 8-bit color index for a uniform block, or two 8-bit color indices, a 3-bit index for u , and a 2-bit or 3-bit index for l for a non-uniform block. An average compression ratio of 22.49 or 33.32 can be obtained for 4=4 or 5=5 image blocks, respectively. Experimental results show the feasibility and efficiency of the proposed approach for color image compression. q 1998 Elsevier Science B.V. All rights reserved.