A variational model for image reconstruction is introduced and analyzed in function space. Specific to the model is the data fidelity, which is realized via a basis transformation with respect to a Riesz basis followed by interval constraints. This setting in particular covers the task of reconstructing images constrained to data obtained from JPEG or JPEG 2000 compressed files. As image prior, the total generalized variation (TGV) functional of arbitrary order is employed. The present paper, the first of two works that deal with both analytical and numerical aspects of the model, provides a comprehensive analysis in function space and defines concrete instances for particular applications. A new, noncoercive existence result and optimality conditions, including a characterization of the subdifferential of the TGV functional, are obtained in the general setting.

/pdf/a-tgv-based-framework-for-variational-image-decompression-4di64rlhhf.pdf

A TGV-Based Framework for Variational Image Decompression, Zooming, and Reconstruction. Part I: Analytics ∗

The popularity of 3D video is increasing daily due to the availability of low-cost 3D televisions and high-speed Internet access. However, currently the contents of 3D video can be distributed illegally without any protection. For views generated using a depth-image-based rendering technique, not only the left and right views can be distributed as 3D content, but also the center, left, or right views individually as 2D content. As digital video watermarking is a possible way of protecting these views from unauthorized distribution, in this paper, we propose a digital watermarking method for depth-image-based rendered 3D video. In this method, the watermark is embedded in both of the chrominance channels of a YUV representation of the center view using the dual-tree complex wavelet transform. Then, the left and right views are generated from the watermarked center view and depth map using a depth-image based rendering technique. Finally, the watermark can be extracted from the center, left, and right views in a blind fashion without using the original unwatermarked center, left, or right views. This watermark is robust to geometric distortions, such as upscaling, rotation and cropping, downscaling to an arbitrary resolution, and the most common video distortions, including lossy compression and additive noise. Due to the approximate shift invariance characteristic of the dual-tree complex wavelet transform, the technique is robust against distortions in the left and right views generated using depth-image based rendering. The proposed method can also survive baseline distance adjustment and both 2D and 3D camcording.

Robust DT CWT-Based DIBR 3D Video Watermarking Using Chrominance Embedding

Robust DT-CWT watermarking for DIBR 3D images and videos = DIBR 3D 이미지 및 비디오에 대한 DT-CWT 기반의 워터마킹

View synthesis with depth-image-based rendering (DIBR) has attracted great interest in that it can provide a virtual image at any arbitrary viewpoint in 3-D video and free-viewpoint TV. An inherent problem in the DIBR view synthesis is occurrence of holes in a synthesized image, which is also known as disocclusion problem. The disoccluded regions need to be handled properly in order to generate a synthesized view of good quality. This paper provides a fundamental examination of hole generation mechanism in the DIBR oriented view synthesis process. A necessary and sufficient condition of hole generation is first shown, and the corresponding hole location and length is obtained analytically. Furthermore, in view that the conventional hole filling algorithms may fail to fill up a hole correctly when lacking (adequate) visible background information, we propose utilizing the occluded (invisible) information to identify and locate the relevant background pixels around a hole. We then make use of the visible and invisible background information together to perform hole filling. Experimental results validate our hole generation model demonstrating agreement to our analytical results, while our proposed hole filling approach shows superior performance in terms of visual quality of synthesized views.

Depth Image Based View Synthesis: New Insights and Perspectives on Hole Generation and Filling

The depth image based rendering (DIBR) plays a key role in 3D video synthesis, by which other virtual views can be generated from a 2D video and its depth map. However, in the synthesis process, the background occluded by the foreground objects might be exposed in the new view, resulting in some holes in the synthetized video. In this paper, a hole filling approach based on background reconstruction is proposed, in which the temporal correlation information in both the 2D video and its corresponding depth map are exploited to construct a background video. To construct a clean background video, the foreground objects are detected and removed. Also motion compensation is applied to make the background reconstruction model suitable for moving camera scenario. Each frame is projected to the current plane where a modified Gaussian mixture model is performed. The constructed background video is used to eliminate the holes in the synthetized video. Our experimental results have indicated that the proposed approach has better quality of the synthetized 3D video compared with the other methods.

/pdf/a-hole-filling-approach-based-on-background-reconstruction-jlzgrgta53.pdf

A Hole Filling Approach Based on Background Reconstruction for View Synthesis in 3D Video

Depth image-based rendering (DIBR) is a process that uses one 2-D color image and its associated depth map to render virtual view 3-D images. One of the main problems in DIBR is how to reduce holes that occur on the generated virtual view images. In general, preprocessing the whole depth image by smoothing filter before image warping can reduce the hole occurrence. However, smoothing the whole depth image not only produces some geometric distortions on the generated virtual directional images, but also increases computation time. This paper proposes an adaptive edge-oriented smoothing process to solve the above problem, in which the adaptive smoothing filter for the depth map is determined by the characteristics of the hole region with or without vertical lines in the color image. The adaptive smoothing filter contains two types: the asymmetric smoothing filter is used to reduce the geometric distortions by smoothing the hole regions with vertical lines that belong to the background; and the horizontal smoothing filter is used to reduce hole occurrence and computation time by smoothing the hole regions without vertical lines. The experiment results show that the proposed method turns out to be a good tradeoff between time saving, hole reduction rate, and virtual view quality.

Nongeometric Distortion Smoothing Approach for Depth Map Preprocessing

A depth image based rendering (DIBR) is the process which uses one 2D color image and its associated depth image to render virtual view images. A problem in DIBR is how to reduce the number of holes occurring on the generated virtual view images. To reduce the holes occurrence, the depth image is pre-processed by smoothing filter before image warping. However, smoothing the whole depth image may introduce some geometric distortions on the generated virtual images and increase the computational time. In this paper, an adaptive edge-oriented smoothing process is proposed to solve the problem. The proposed method adopts an edge dependent depth filter to predict the holes region and then the horizontal smoothing filter is first employed on the predicted holes regions. If hole regions are with vertical edges, the depth image is further pre-processed by asymmetric smoothing filter. The experimental results show that the proposed method can reduce the geometric distortions on the virtual view and preserve the depth quality.

Adaptive edge-oriented depth image smoothing approach for depth image based rendering

For multimedia transmission over noisy channels, the error robustness of JPEG2000 evidently outperforms that of JPEG. Since JPEG2000 is based on the discrete wavelet transform (DWT), traditional error concealment algorithms for still images in the discrete cosine transform (DCT) domain are not suitable for JPEG2000. In JPEG2000, decoding is processed bitplane by bitplane. Any data loss occurring in the bitstream will affect the consequent bitplanes and their wavelet coefficients. To solve this problem, the JPEG2000 VM7.2 program replaces the missing wavelet coefficients by zeros. However, the replacement may affect lots of significant nonzero coefficients such that some high frequency components are lost. In this paper, we present a novel error concealment algorithm for image transmission in the bitplane base. The proposed algorithm recovers the damaged bitplane data according to the cross subband and undamaged bitplane information. The recovered wavelet coefficients are similar with error-free data. The objective results show that the proposed algorithm has 3/spl sim/8dB improvement than those without the error resilient mechanism. From a subjective viewpoint, the proposed algorithm can achieve much smoother edges on the reconstructed image using our concealment algorithm.

Bit-plane error recovery via cross subband for image transmission in JPEG2000

Digital image transmission is widely used in consumer products, e.g., digital camera and cellular phone, etc. The newly defined JPEG 2000 delivers image with lower bit rate in the Internet and wireless communications. However, JPEG 2000 decoding is processed bitplane by bitplane. Any data loss in bitstream affects the consequent bitplanes and even possible destroy the whole picture. We propose a new algorithm to recover the damaged bitplanes data according to the interested directional sets (IDS) of in-subband. The proposed algorithm is quite simple, but is very efficient in concealing the loss data of any subband in streaming real-time video data in the Internet and wireless communications. The simulation results show that the proposed algorithm has 1.5-3dB improvements than previously presented error resilient mechanism. In a subjective view, the proposed concealment algorithm can achieve much smoother edges on the reconstructed images.

https://video.ee.ntu.edu.tw/publication/paper/[C][2003][ICCE][Pei-Jun.Lee][1].pdf

Error concealment algorithm using interested direction for JPEG 2000 image transmission

In this paper, a new error concealment algorithm for the new coding standard H.264 is presented. The algorithm consists of a block size determination step to determine the size type of the lost block and a motion vector recovery step to find the lost motion vector from multiple reference frames. The main feature of this algorithm are as follows. In the block size determination step, we propose a criterion to determine the size type of the lost block from the current frame. In the motion vector recovery step, the optimal motion vector for the lost block chosen from multiple previous reference frames with the minimum value of the side match distortion. The proposed algorithm not only can determine the most correct mode for the lost block, but also can save much more computation time for motion vector recovery. Experimental results show that the proposed algorithm achieves 0.4/spl sim/7 dB improvement over the conventional VM method.

A new error concealment algorithm for H.264 video transmission

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