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

Abstract

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 x 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 bitmap of each non-uniform block. The two parameters iota and theta of a line edge with the equation of x cos theta + gamma sin theta = iota 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 theta, and a 2-bit or 3-bit index for iota for a non-uniform block. An average compression ratio of 22.49 or 33.32 can be obtained for 4 x 4 or 5 x 5 image blocks, respectively. Experimental results show the feasibility and efficiency of the proposed approach for color image compression. (C) 1998 Elsevier Science B.V, All rights reserved.