KEYWORDS: Wavelets, Motion estimation, Video coding, Wavelet transforms, Video, 3D image processing, Motion analysis, Multilayers, 3D imaging standards, 3D video streaming
This paper proposes an advanced motion-threading technique to improve the coding efficiency of the 3D wave-let coding. We extend the original motion-threading technique to the lifting wavelet structure. This extension solves the artificial motion thread truncation problem in long support temporal wavelet filtering, and enables the accuracy of motion alignment to be fractional-pixel with guaranteed perfect reconstruction. Furthermore, the mismatch problem in the motion-threading caused by occlusion or scene-change is considered. In general, the temporal wavelet decomposition consists of multiple layers. Unlike the original motion-threading scheme, in the proposed scheme each layer owns one set of motion vectors so as to achieve both high coding efficiency and temporal scalability. To reduce the motion cost, direct mode is used to exploit the motion vector correlation. An R-D optimized technique is introduced to estimate motion vectors and select proper prediction modes for each macroblock. The proposed advanced motion-threading scheme can outperform the original motion-threading scheme up to 1.5~5.0 dB. The experimental results also demonstrate that the 3D wavelet coding scheme can be competitive with the start-of-the-art JVT video standard on coding efficiency.
The concentric mosaics offer a quick solution to the construction and navigation of a virtual environment. To reduce the vast data amount of the concentric mosaics, a compression scheme based on 3D wavelet transform has been proposed in a previous paper. In this work, we investigate the efficient implementation of the renderer. It is preferable not to expand the compressed bitstream as a whole, so that the memory consumption of the renderer can be reduced. Instead, only the data necessary to render the current view are accessed and decoded. The progressive inverse wavelet synthesis (PIWS) algorithm is proposed to provide the random data access and to reduce the calculation for the data access requests to a minimum. A mixed cache is used in PIWS, where the entropy decoded wavelet coefficient, intermediate result of lifting and fully synthesized pixel are all stored at the same memory unit because of the in- place calculation property of the lifting implementation. PIWS operates with a finite state machine, where each memory unit is attached with a state to indicate what type of content is currently stored. The computational saving achieved by PIWS is demonstrated with extensive experiment results.
As a new scene representation scheme, the concentric mosaic offers a quick way to capture and model a realistic 3D environment. This is achieved by shooting a lot of photos of the scene. Novel views can be rendered by patching vertical slits of the captured shots. The data amount in the concentric mosaic is huge. In this work, we compress the concentric mosaic image array with a 3D wavelet scheme. The proposed scheme first aligns the mosaic images, and then applies a 3D wavelet transform on the aligned mosaic image array. After that, the wavelet coefficients in each subband are split into cubes, where each of the cubes is encoded independently with an embedded block coder. Various cube bitstreams are then assembled to form the final compressed bitstream. Experimental result shows that the proposed 3D wavelet coder achieves a good compression performance.
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