Data compression and decompression for map images using an indexed color system Optimized Run-length and Huffman coding techniques

Abstract

The thesis introduces an efficient data compression technique that utilizes the characteristics of topographic map images. Each pixel’s color value is converted from a standard RGB code to index numbers. This is called an Indexed Color System. Optimized Run-Length Coding (ORLC) is developed from basic Run-Length Coding to eliminate spatial redundancy by grouping the adjacent pixels that have identical indexes into single code. This data is then developed from fixed length codes and saved in variable length codes with Huffman Coding. It has been proven by experiments that image size is smaller than with Winzip 29 – 44% while maintaining an acceptable printed image quality from both offset and digital printing process.