An improved normal-mesh-based image coder

The normal-mesh-based image coder of Jansen, Baraniuk, and Lavu (JBL) is studied. First, the JBL coder is introduced, and several of its shortcomings are identified. Then, to address these shortcomings, three modifications to this coder are proposed, namely, the use of a data-dependent base mesh, an integer representation for normal/vertical offsets, and a different scan-conversion scheme based on bicubic interpolation. Experimental results show that these proposed changes lead to improved coding performance in terms of both objective and subjective image-quality measures. In particular, the use of a data-dependent base mesh helps to locate horizons more quickly and preserve image edges better. The number of bits required to encode the normal/vertical offsets is reduced by representing this information with integers (as opposed to real numbers). Lastly, bicubic interpolation is found to yield higher-quality image reconstructions, while still maintaining sharp edges.