Lossless index coding for indexed colour images

Abstract

This paper presents a simple and efficient index coding method to reduce the storage cost for indexed colour images. The method exploits the high degree of similarity among neighbouring indices by using a sorted palette. The indices that were compressed by the colour image quantisation are classified into three categories. Every category employs a different encoding rule to process the indices. To compress the indices of the second category, two optional approaches are provided. Experimental results show that the proposed method can significantly cut down the number of bit rates without incurring extra image degradation.

Keywords:

• colour image compression
• colour image quantisation
• palette design
• relatively addressing
• Huffman code

This research was supported by Providence University, Taichung, Taiwan under contract no. PU 97-B21 and the National Science Council, Taipei, Taiwan under contract no. NSC 98-2221-E-126-008.