Freeman chain code with digits of unequal cost

Abstract

Chain codes are the most size-efficient lossless compression methods for representing rasterised binary objects and contours. Satisfactory compression ratio, low processing cost and low storage requirements of the decoder make chain code technique interesting for storage and transmission of predefined graphical objects in embedded environments. Each element in the chain is encoded to show the relative angle difference between two adjacent pixels along the boundary of an object. The cost of binary bits representing the codes are considered to be equal. Yet, more efficient encoding is possible by considering and applying technique that treats the binary bits differently considering its requirement of storage space, energy consumption, speed of execution and etc. This paper considers cost of binary digits as unequal and proposes a new representation of the eight-direction Freeman chain code based on a variation of Huffman coding technique, which considers cost of bits as unequal. The evaluation and comparison of the cost efficiency between classical Freeman chain code and the new representation of the chain code is provided. Our experiments yield that the proposed representation of Freeman Chain code reduces overall storage/transmission cost of encoded objects considerably with compared to classical Freeman chain code.