Synthesized disparity vectors for 3D video coding

In 3D video coding, some dependent-view coding tools may utilize derived disparity vectors (DV) to locate inter-view correspondences, such as the Backward block-based View Synthesis Prediction (BVSP) and Depth-based Motion Vector Prediction (DMVP) in ATM. A typical way to derive a DV for a target block, as performed in ATM, is to convert reconstructed depth values associated with the block to a DV. However, this approach only works in depth-first coding order (DFCO) and becomes inapplicable when the dependent-view texture is coded prior to the depth, i.e., in texture-first coding order (TFCO). In this paper, a sparse DV field is synthesized from the depth map of a coded reference view to provide the DVs required by dependent-view coding tools in TFCO. The synthesized sparse DV field is accurate to support disparity-aided coding tools in different coding orders, while only introducing 2% decoding time increase. With the proposed method, BVSP and DMVP can be applied in both TFCO and DFCO, which mitigates the large coding performance gap (around 20% BD rate) between TFCO and DFCO of ATM.