No-Reference Depth Assessment Based on Edge Misalignment Errors for T + D Images

The quality of depth is crucial in all depth-based applications. Unfortunately, the error-free ground truth is often unattainable for depth. Therefore, no-reference quality assessment is very much desired. This paper presents a novel depth quality assessment scheme that is completely different from conventional approaches. In particular, this scheme focuses on depth edge misalignment errors in texture-plus-depth (T+D) images and develops a robust method to detect them. Based on the detected misalignments, a no-reference metric is calculated to evaluate the quality of depth maps. In the proposed scheme, misalignments are detected by matching texture and depth edges through three constraints: 1) spatial similarity; 2) edge orientation similarity; and 3) segment length similarity. Furthermore, the matching is performed on edge segments instead of individual pixels, which enables robust edge matching. Experimental results demonstrate that the proposed scheme can detect misalignment errors accurately. The proposed no-reference depth quality metric is highly consistent with the full-reference metric, and is also well-correlated with the quality of synthesized virtual views. Moreover, the proposed scheme can also use the detected edge misalignments to facilitate depth enhancement in various practical texture-plus-depth-based applications.