Abstract
This paper proposes an efficient reversible compression technique that utilizes the characteristics of topographic map images, which normally consist of limited number of colors. Firstly, each pixel's color value is converted from a standard RGB code to an index number. This is called an Indexed Color System. Secondly, optimized Run-Length Coding (ORLC) is developed from basic Run-Length Coding to eliminate spatial redundancy by grouping the adjacent pixels that have identical indices into a single code. These data are finally developed from the fixed length codes and saved in the variable codes with Huffman coding. It has been proven by the experiments that the data size is smaller than with Winzip compression technique 29—44%: while the process time depends on the scanned image resolution and the efficiency of CPU and RAM.
