A Novel Distortion Model and Lagrangian Multiplier for Depth Maps Coding

In three-dimensional videos (3-DV) coding systems, depth maps are not used for viewing but for rendering virtual views. Therefore, the traditional rate distortion criterion (including distortion criterion, and Lagrangian multiplier) is not suitable for depth map coding. In order to design an effective rate distortion criterion for depth maps, the relationship between the distortion of synthesized virtual view and the coding error of depth maps is analyzed in detail. Through the analysis, a polynomial model revealing the relationship between the coding error of depth maps and the distortion of synthesized virtual view is derived. Model parameters are estimated by utilizing camera parameters and features of the texture video corresponding to the depth map. Based on the model, a virtual view-based Lagrangian multiplier for depth map coding is also proposed. Experimental results demonstrated the accuracy of the model. The squared correlation coefficients between the actual distortion of virtual view and the estimated distortion are all larger than 0.98 for all tested sequences. When incorporating the proposed model and Lagrangian multiplier into the mode decision procedure of joint model version 18.5 (JM18.5) of H.264/AVC, a maximum 0.470 dB BD PSNR and an average 0.251 dB BD PSNR can be achieved.