Variable Width Admissible Control Point Band for Vertex Based Operational-Rate-Distortion Optimal Shape Coding Algorithms

Existing vertex-based operational-rate-distortion (ORD) optimal shape coding algorithms use a fixed width admissible control point band (FCB) around the shape boundary as the search space for possible control points. The width of the band however, is fixed and arbitrarily chosen independent of the admissible distortion and shape contour, so it fails to fully exploit the admissible control point band to reduce the bit-rate. This paper proposes a variable width admissible control point band (VCB) where the width associated to each boundary point is dynamically determined from the admissible peak distortion and shape information. In addition, the paper uses an accurate distortion measurement method to overcome a key limitation of existing distortion and tolerance band based methods. Experimental results reveal that both the qualitative and quantitative performance of the existing ORD algorithms are improved by seamlessly integrating the VCB and accurate distortion measuring approach.