Progressive contour coding in the wavelet domain

This paper presents a new wavelet-based image contour coding technique, suitable for representing either shapes or generic contour maps. Starting from a contour map (e.g. a segmentation map or the result of a contour extraction operator), this is first converted in a one-dimensional signal. Coordinate jumps among different contour extremities are converted, if under a suitable threshold, into signal discontinuities which can be compactly represented in the wavelet domain. Otherwise, the exceeding discontinuities are coded as side information. This side information is minimized by an optimized contour segment sequencing. The obtained 1D signal is decomposed and coded in the wavelet domain by using a 1D version of an improved implementation of the SPIHT algorithm. This technique can efficiently code every kind of 2D contour map, from one to many unconnected contour segments. It guarantees a fully embedded progressive coding, state-of-art coding performance, good approximation capabilities for both open and closed contours, and visually graceful degradation at low bit-rates.