HYBRID DIFFERENTIAL PULSE CODE MODULATION IN WAVELET DOMAIN AND LOSSLESS METHODS FOR IMAGE COMPRESSION

Abstract

Abstract:Digital images are widely used in computer applications. Uncompressed digitalimages require considerable storage capacity and transmission bandwidth. Efficient imagecompression solutions are becoming more critical with the recent growth of data intensiveand multimedia-based web application.In this paper, Hybrid Differential Pulse Code Modulation (DPCM) in waveletdomain and lossless methods (Huffman and Run length code) for image compression isinvestigated. The image signal is composed into four scales (approximate, horizontal,vertical and diagonal coefficients). The energy level of approximate is different from that ofdetail information; therefore, the approximate is quantized alone and horizontal and verticalare quantized alone by using the differential pulse code modulation (DPCM). In allsimulations the diagonal coefficients are discarded. Two types of coding are used, Huffmancode and run length coding (RLC) techniques. The results show that truncate horizontaland vertical coefficients using hard threshold gives best performance than soft thresholdwith gain about 3 dB to get the same compression ratio (CR). The wavelet based imagecompression using Huffman code gives CR about 77% compared with RLC that gives CRabout 71% with suitable peak signal to noise ratio (PSNR).Key words: image compression, discrete wavelet transforms (DWT), differential pulsecode modulation (DPCM), Huffman code and run length code (RLC)