Shape coding using polar coordinates and the discrete cosine transform

This paper discusses a new technique for shape coding for mobile video communication using polar coordinates and the DCT. First the Cartesian x and y shape coordinate functions are transformed to the domain of polar coordinates yielding an r and a φ function. Then these functions are transformed using a DCT. Using Cartesian coordinates means describing the shape in terms of straight lines and blocks, while for using polar coordinates this is in terms of circles and curves. Because of this more natural representation, compression can be more efficient and degradation due to errors or low bit rates will be more graceful. Using a spectral decomposition enables bit-rate and distortion control, error-resilience and layered coding while degrading the shape as a whole without specific local artifacts or errors. Bit allocation is possible using standard techniques and the computational load is low. A first implementation shows promising results around 1 to 2 bits per shape point, allowing an error of 2 to 1 pixels respectively