Adaptive depth truncation filter for MVC based compressed depth image

• Boundary artifacts of the synthesized views are minimized by sharpening the depth map edges that are blurred by subsampling process or transform coding of 3DV-ATM.
• Sharp depth edge pixels are adaptively detected with horizontal and vertical gradients.
• Depth image is divided into non-overlapped blocks for edge block detection. To increase the accuracy of depth map refining, each edge block is adaptively repositioned and then expanded in order to locate the edge regions at the center of the block.
• A modified block truncation technique is used to recover the sharp edges within the edge blocks.

In multiview video plus depth (MVD) format, virtual views are generated from decoded texture videos with corresponding decoded depth images through depth image based rendering (DIBR). 3DV-ATM is a reference model for the H.264/AVC based multiview video coding (MVC) and aims at achieving high coding efficiency for 3D video in MVD format. Depth images are first downsampled then coded by 3DV-ATM. However, sharp object boundary characteristic of depth images does not well match with the transform coding based nature of H.264/AVC in 3DV-ATM. Depth boundaries are often blurred with ringing artifacts in the decoded depth images that result in noticeable artifacts in synthesized virtual views. This paper presents a low complexity adaptive depth truncation filter to recover the sharp object boundaries of the depth images using adaptive block repositioning and expansion for increasing the depth values refinement accuracy. This new approach is very efficient and can avoid false depth boundary refinement when block boundaries lie around the depth edge regions and ensure sufficient information within the processing block for depth layers classification. Experimental results demonstrate that the sharp depth edges can be recovered using the proposed filter and boundary artifacts in the synthesized views can be removed. The proposed method can provide improvement up to 3.25 dB in the depth map enhancement and bitrate reduction of 3.06% in the synthesized views.