Three States QRLE (Quantized Run Length Encoding) Based JPEG Image Compression Method

Abstract

We present in this work, an improved JPEG-based image compression method. The proposedmethod appeals a so-called QRLE (Quantized Run Length Encoding) technique where the couple of values(‘zero’ followed by its run number) is replaced just by one value. In this work, we substitute the Huffmanencoding process by the QRLE method. The key idea of the QRLE method is to guarantee that the MSB bit ofthe binary representation of the non-null values is ‘0’ while that of the ‘zero’ run number is ‘1’; this is done byadding the value 2N-1 to that number where N is its binary representation length. However, given that the zerorun numbers could exceed (27-1≡127) value, provided that the RGB colored images are 8 bits long, the MSB is,necessarily, ‘1’. Even worse, the zero run number can be greater than 255 which implies occupying more thanone octet. To solve that; the basic idea is to treat the zero run numbers of the AC zig-zag coefficients, accordingto 3 pre-defined ranges as follows: [1..127], [128..255], and [256..maximum. For the first range, ‘128’ value isadded to the zero run numbers; while for the second one, the zero run numbers are unchanged but preceded by‘0’ value. Finally, for the third range, the zero run numbers are kept unchanged while preceded by the number ofoctets of their binary representation. In terms of obtained results, comparing the proposed method with theclassical JPEG, the reconstitution values remain the same for both technics. On the other hands, the compressionratio is considerably improved rising from 1:16.35 to 1:22.62 being provided an RGB image with 3 times atypical quantization matrix (for a quality of 50% as specified in the original JPEG Standard) while the PSNR isaround 26.215both algorithms.