Mmetric++: An improved quality metric to judge the lossless compression of 3D meshes

During the past decade, 3D meshes have been widely used to represent immersive content The Moving Picture Experts Group (MPEG) is working on a new standard called Video-based Dynamic Mesh Coding (V-DMC) for compressing dynamic meshes. Due to market demand, lossless compression represents an important test condition for this standard. The quality metric denoted mmetric currently used by the standard to verify the lossless character of a proposed codec evaluates the geometry and attributes coordinates differences. However, 3D meshes are also characterized by their connectivity, which is a parameter completely overlooked by the current metric, leading to wrong decisions when evaluating the lossless character of a 3D mesh codec. In this paper, we propose an improved quality metric to correctly judge whether a mesh has been losslessly encoded or not. The proposed method employs the configurations of the triangle fan (TF) defined in Triangle Fan-based compression (TFAN) to traverse the original mesh and the decoded one in order to compare their connectivity. Experimental results on the V-DMC test sequences demonstrate that the proposed method can effectively determine the differences existing in the connectivity. The proposed metric has been recently adopted and will be integrated soon into the new version of the mmetric tool set.