Approximation and Compression of Piecewise Smooth Images Using a Wavelet/Wedgelet Geometric Model
Baraniuk, Richard G.
image geometry; wedgelets; wavelets; image compression; piecewise smooth images; nonlinear approximation
Inherent to photograph-like images are two types of structures: large smooth regions and geometrically smooth edge contours separating those regions. Over the past years, efficient representations and algorithms have been developed that take advantage of each of these types of structure independently: quadtree models for 2D wavelets are well-suited for uniformly smooth images (CÂ² everywhere), while quadtree-organized <i>wedgelet</i> approximations are appropriate for purely geometrical images (containing nothing but CÂ² contours). This paper shows how to <i>combine</i> the wavelet and wedgelet representations in order to take advantage of both types of structure simultaneously. We show that the asymptotic approximation and rate-distortion performance of a wavelet-wedgelet representation on piecewise smooth images mirrors the performance of both wavelets (for uniformly smooth images) and wedgelets (for purely geometrical images). We also discuss an efficient algorithm for fitting the wavelet-wedgelet representation to an image; the convenient quadtree structure of the combined representation enables new algorithms such as the recent WSFQ geometric image coder.