The Basics of Chain Coding
A line drawing is an image of line or curve segments that may be connected or disconnected. Several applications require the storage of line drawings in computer graphics, image processing, pattern recognition and even Automated Cartography in Geographic Information Systems where contours of maps have to be stored.
Freeman et al. proposed several methods called Chain Coding to represent line drawings that help efficient transmission and storage of such data. For this purpose it is required to quantize and encode the 2D figure. A uniform mesh is superimposed on the line drawing. We assume that the distance between two consecutive mesh nodes is T. A line drawing is quantized or approximated using curve points. Curve points are chosen to represent points on the line drawing by specifying mesh nodes that are close to the curve in terms of the different quantization schemes, giving different representations for each scheme. Three such quantization methods are described below.