Directional difference chain codes with quasi-lossless compression and run-length encoding

This paper considers a new contour-based representation of binary objects in raster images. Low processing and storage requirements of the decoder, satisfactory compression ratio and generality make this chain coding technique interesting for storing predefined graphical objects in embedded systems. Three improvements of the DDCC code were introduced. Extra Huffman codes are assigned to two frequent pairs of symbols, 135° directional differences in concave angles are omitted since they do not affect the outer object shape and, finally, longer line segments are run-length encoded. Comparison with six other chain coding techniques of similar implementation complexity confirms that the new technique represents an efficient alternative way to encode 8-connected contours.

► (45°, −45°) and (−45°, 45°) pairs deserve extra Huffman codes in the DDCC technique.
► Clockwise oriented polygon border pixels do not store directional changes of −135°.
► Run-length encoding is efficient for 12 or more consecutive 0° symbols in DDCC.
► New measure of chain code compression efficiency is independent of the input format.
► Comparison with six other chain coding techniques confirms the C_DDCC effectiveness.