Reflection-type integral imaging scheme for displaying three-dimensional images

A reflection-type integral imaging scheme for displaying three-dimensional images is proposed. By use of a concave mirror array instead of a lens array, three-dimensional images are integrated in the form of a reflection type, and the experimental results are demonstrated. This scheme can readily be applied to a large integral imaging system by use of a beam projector that is located at a distance from the mirror-array plane.     

Compression scheme of sub-images using Karhunen-Loeve transform in three-dimensional integral imaging

In this paper, a compression scheme of sub-image-transformed elemental images using Karhunen-Loeve transform (KLT) in three-dimensional integral imaging is proposed. The proposed scheme provides improved compression efficiency by improving the similarity between elemental images using sub-image transformation. To test the proposed scheme, various elemental images of 3D objects are picked up and the compression process is carried out using KLT. From the experimental results, it is showed that the proposed compression scheme gives us an improved efficiency of 26% as compared with the conventional compression method.     

A feature-based robust digital image watermarking scheme using bandelet transform

Desynchronization attacks are among the most difficult attacks to resist, for it can desynchronize the location of the watermark and hence cause incorrect watermark detection. The design of an image watermarking scheme that is robust against desynchronization attacks is challenging. Based on a multi-scale SIFT (scale invariant feature transform) detector and Bandelet transform theory, we propose a new content based image watermarking algorithm with good visual quality and reasonable resistance toward desynchronization attacks. Firstly, the stable image feature points are extracted from the original host by using the multi-scale SIFT detector, and the local feature regions (LFRs) are constructed adaptively according to the feature scale theory. The Bandelet transform is then performed on the LFRs. Finally, the digital watermark is embedded into the LFRs by modifying the significant Bandelet coefficients. By binding the watermark with the geometrically invariant image features, the watermark detection can be done without synchronization error. Experimental results show that the proposed image watermarking is not only invisible and robust against common signal processing such as sharpening, noise adding, JPEG compression, etc., but also robust against the desynchronization attacks such as rotation, translation, scaling, row or column removal, cropping, etc.     

Continuous imaging space in three-dimensional integral imaging

We report an integral imaging method with continuous imaging space. This method simultaneously reconstructs real and virtual images in the virtual mode, with a minimum gap that separates the entire imaging space into real and virtual space. Experimental results show that the gap is reduced to 45% of that in a conventional integral imaging system with the same parameters.     

Effects of device resolution on three-dimensional integral imaging

We present the effects of a finite number of pixels in elemental images on the resolution and the depth of focus in three-dimensional integral imaging (II). We show that the number of pixels in elemental images determines not only the lateral resolution but also the depth resolution. The minimum number of pixels required in each elemental image is calculated to avoid depth-of-focus degradation. We evaluate how II system performance degrades as the number of pixels in each elemental image changes. The product of the depth of focus and the lateral resolution squared is used as the performance metric.     

A novel fragile watermarking scheme for image tamper detection and recovery

We propose a fragile watermarking scheme capable of image tamper detection and recovery with a blockwise dependency mechanism.Initially,the image is divided into blocks with size of 2×2 in order to improve image tamper localization precision.By combining image local properties with human visual system,authentication data are acquired.By computing the class membership degree of each image block property,data are generated by applying k-mean clustering technique to cluster all image blocks.The recovery data are composed of average intensity obtained by truncating the two least significant bits(LSBs) of each pixel within each block.Finally,the logistic chaotic encrypted feature watermark consisting of 2-bit authentication data and 6-bit recovery data of image block is embedded into the two LSBs of each pixel within its corresponding mapping block.Experimental results show that the proposed algorithm does not only achieve superior tamper detection and locate tiny tampered positions in images accurately,it also recovers tampered regions effectively.     

Integral three-dimensional imaging with digital reconstruction

A computed three-dimensional (3-D) display system based on integral imaging is presented. The 3-D image is reconstructed by numerical processing of an optically observed image array formed by a microlens array. The algorithm for reconstructing 3-D images is robust, and it enables us to obtain the images viewed from arbitrary directions. This computer-based image retrieval makes it possible to improve qualities of the image such as contrast, brightness, and resolution by numerical techniques. Also, this method eliminates the need for special purpose optical equipment such as high-quality liquid-crystal display and micro-optics components to display the 3-D images. We present experimental results of 3-D image reconstruction to test and verify the performance of the algorithms and the imaging system.     

A novel blind digital watermarking algorithm for embedding color image into color image

A robust and blind watermarking technique for dual color images is proposed in this paper. According to the energy concentrating feature of DCT, the two-level DCT is introduced and used to embed color watermark image into color host image, which is completely different with the traditional DCT. For reducing the redundancy of watermark information, the original color watermark image is compressed by the proposed compression method. After two-level DCT, nine AC coefficients in different positions of each sub-block are selected and quantified to embed watermark information. Moreover, only the extraction rules are used to extract watermark from the watermarked image without resorting to the original host image or watermark image. Experimental results show that the proposed watermarking algorithm can effectively improve the quality of the watermarked image and the robustness of the embedded watermark against various attacks.     

A novel chaos-based bit-level permutation scheme for digital image encryption

Confidentiality is an important issue when digital images are transmitted over public networks, and encryption is the most useful technique employed for this purpose. Image encryption is somehow different from text encryption due to some inherent features of image such as bulk data capacity and high correlation among pixels, which are generally difficult to handle by conventional algorithms. Recently, chaos-based encryption has suggested a new and efficient way to deal with the intractable problems of fast and highly secure image encryption. This paper proposes a novel chaos-based bit-level permutation scheme for secure and efficient image cipher. To overcome the drawbacks of conventional permutation-only type image cipher, the proposed scheme introduced a significant diffusion effect in permutation procedure through a two-stage bit-level shuffling algorithm. The two-stage permutation operations are realized by chaotic sequence sorting algorithm and Arnold Cat map, respectively. Results of various types of analysis are interesting and indicate that the security level of the new scheme is competitive with that of permutation-diffusion type image cipher, while the computational complexity is much lower. Therefore the new scheme is a good candidate for real-time secure image communication applications.     

A novel clutter rejection scheme in color flow imaging

In ultrasound color flow imaging systems, it is important to suppress the clutter signals originated from stationary and slowly moving tissue sufficiently. Without sufficient clutter rejection, the estimation of the blood flow velocity will be inaccurate, and the imaging quality will be poor. In this paper we present a new clutter rejection scheme involving first down-mixing the clutter signals to zero frequency and then cancelling the stationary echo by subtracting the signals from two consecutive pulses. This stationary echo cancelling scheme is easy to be realized with small computational power, and is adaptive to the clutter signals. Theoretical analysis and simulation using RF data prove that it's an efficient and practical clutter rejection scheme for color flow imaging.     

Information capacity gain by time-division multiplexing in three-dimensional integral imaging

We evaluate improvements in information capacity gained by use of time-division multiplexing (TDM) in three-dimensional integral imaging (II) systems. This analysis supports the motivation for two TDM methods in II [Opt. Lett. 27, 324 (2002); 1144 (2002)] that we previously developed.     

基于人眼视觉的集成成像三维显示分辨率的比较

为了对不同集成成像系统三维显示应用中的视觉分辨效果进行表征, 提出了一种基于人眼视觉的集成成像三维显示分辨率的分析比较方法. 通过分析集成成像三维显示系统的分辨率与人眼在最佳显示观看距离下分辨本领的关系, 定义了相对分辨率参数, 分析了其与集成成像三维显示实际观看时视觉分辨效果的关系. 研究结果表明, 透镜阵列的大小对集成成像三维显示的视觉分辨效果有重要的影响. 针对两个系统实例的理论计算结果表明, 系统间的相对分辨率参数差异是传统分辨率差异的1.75倍, 实验结果与理论分析一致. 该研究方法对三维显示分辨率的评价有一定的指导意义.     

集成成像三维显示系统显示性能的研究进展

集成成像三维显示技术是利用透镜阵列获取和显示立体图像的一种三维显示技术。本文首先综述了集成成像三维显示系统的特点,考虑其系统性能主要受分辨率、景深和观看视场角的限制,对近年来集成成像三维显示系统在增大分辨率、景深和观看视场角方面的研究进展做了综合论述,比较分析了各种改进方法的优劣。最后,对我国集成成像三维显示技术的研究现状进行了总结,并简述了本研究小组在该领域取得的若干研究成果。     

A novel blind color images watermarking based on SVD

Since the color image watermark has more bit information, it is a challenging problem to design a robust and blind color watermarking scheme for copyright protection. In this paper, a blind watermarking scheme based on singular value decomposition (SVD) is proposed. By analyzing the orthogonal matrix U via SVD, it is found that there exists a strong similarity correlation between the second row first column element and the third row first column element. Hence, this paper utilizes this property for image watermarking. Firstly, the 4 × 4 non-overlapping pixels block of each component in color host image is processed by SVD. And then, the color watermark is embedded by slightly modifying the value of the second row first column element and the third row first column one of U matrix, and the modified relation can be utilized to extract watermark. Experimental results, compared with the related existing methods, show that the proposed color image scheme has stronger robustness against most common attacks such as image compression, filtering, cropping, noise adding, blurring, scaling and sharpening et al.     

一种基于混沌和分数阶傅里叶变换的数字水印算法

基于混沌序列及离散分数阶傅里叶变换,提出了一种基于混沌和分数阶傅里叶变换的数字水印算法,并对算法及抗攻击性能进行了仿真分析.结果表明,该算法简单有效,对JPEG压缩、噪声、滤波等攻击具有良好的鲁棒性. 关键词： 数字水印 混沌 分数阶傅里叶变换 鲁棒性     

Real-time sensing and three-dimensional display of far outdoor scenes based on asymmetric integral imaging

A new asymmetric integral imaging (AII) system for real-time pickup and three-dimensional (3-D) display of far outdoor scenes based on dynamic-pixel-mapping (DPM) is proposed. DPM is a digital process to transform the elemental images captured with a lens array into the perspective-variant object images (POIs) whose structures are matched with those of display lenses, where the orders of pixels in each POI are reversely mapped, and then capture a set of virtual elemental images (EIs) at the specific depth planes from the back-propagated POIs. This DPM enables an asymmetrical use of pickup and display lens arrays, allowing the long-ranged pickup of far outdoor scenes and their resolution-enhanced 3-D reconstruction. Experiments with a pair of pickup and display lens arrays whose pitches and focal lengths are given by 7.5 mm, 30 mm and 1.2 mm, 8 mm, respectively, show that the effective pickup-range and resolution of the proposed system have been increased up to 6 m and 1600×1600 pixels, respectively, from 0.064 m and 480×480 pixels of the conventional systems employing the same pickup and display lens arrays. In addition, experiments with an implemented test bed confirms that the proposed system can provide real-time 3-D images in 25 frames per second.     

Improved viewing resolution of three-dimensional integral imaging by use of nonstationary micro-optics

We propose the use of synchronously moving micro-optics (lenslet arrays) for image pickup and display in three-dimensional integral imaging to overcome the upper resolution limit imposed by the Nyquist sampling theorem. With the proposed technique, we show experimentally that the viewing resolution can be improved without reducing the three-dimensional viewing aspect of the reconstructed image.     

Efficient compression of motion-compensated sub-images with Karhunen-Loeve transform in three-dimensional integral imaging

An approach to highly enhance the compression efficiency of the integral images by applying the Karhunen-Loeve transform (KLT) algorithm to the motion-compensated sub-images is proposed. The sub-images transformed from the elemental images picked-up from the three-dimensional (3D) object might represent the different perspectives of the object. Thus, the similarity among the sub-images gets better than that among the elemental images, so that an improvement of compression efficiency of the sub-images could be obtained. However, motion vectors occurred among the sub-images might result in an additional increase of image data to be compressed. Accordingly, in this paper, motion vectors have been estimated and compensated in all sub-image in advance. Then the KLT algorithm was applied to these motion-compensated sub-images for compression. It is shown from some experimental results that compression efficiency of the proposed method has been improved up to 24.44%, 40.62%, respectively, on the average compared to that of the conventional KLT compression method and that of the JPEG.     

A block-based watermarking scheme for image tamper detection and self-recovery

In this paper, we present an effective block-based digital fragile watermarking scheme for image tamper detection and recovery. The proposed scheme embeds watermarks consisting of the authentication data and the recovery data into image blocks. It adopts parity check and the intensity-relation check to thwart various malicious attacks. In the tamper detection process, instead of independently testing the embedded authentication data of each block, we take the block-neighbourhood into account and utilize a hierarchical structure to determine the legitimacy of image blocks. Experimental results show that the proposed scheme can effectively resist collage attack, vector quantization (VQ) attack and constant-average attack, while sustaining superior accuracy of tamper localization. Furthermore, the results reveal that the tampered images can be successfully self-recovered with acceptable visual quality.