Axially moving a lenslet array for high-resolution 3D images in computational integral imaging

Image Enhancement of Computational Reconstruction in Diffraction Grating Imaging Using Multiple Parallax Image Arrays

This paper describes an image enhancement method of computational reconstruction for 3-D images with multiple parallax image arrays in diffraction grating imaging. A 3-D imaging system via a diffraction grating provides a parallax image array (PIA) which is a set of perspective images of 3-D objects. The parallax images obtained from diffraction grating imaging are free from optical aberrations such as spherical and chromatic aberrations that are always involved in the 3-D imaging via a lens array. The diffraction grating imaging system for 3-D imaging also can be made at a lower cost system than a camera array system. However, the parallax images suffer from the speckle noise due to a coherent source; also, the noise degrades image quality in 3-D imaging. To remedy this problem, we propose a 3-D computational reconstruction method based on multiple parallax image arrays which are acquired by moving a diffraction grating axially. The proposed method consists of a spatial filtering process for each PIA and an overlapping process. Additionally, we provide theoretical analyses through geometric and wave optics. Optical experiments are conducted to evaluate our method. The experimental results indicate that the proposed method is superior to the existing method in 3-D imaging using a diffraction grating.

Optical 3D object security and reconstruction using pixel-evaluated integral imaging algorithm

Under the framework of computational integral imaging, an optical 3D objects security and high-quality reconstruction method based on pixel-evaluating mapping (PEM) algorithm is proposed. In this method, the pixel crosstalk caused by noneffective pixel overlap is effectively reduced by a pixel-evaluated mask, which can improve the image quality of the reconstructed 3D objects. Meanwhile, compared with the other computational integral imaging reconstruction methods, our proposed PEM algorithm can obtain more accurate pixel mapping weight parameters, thereby the reconstructed 3D objects provide higher quality. In addition, the nonlinear feedback shift register cellular automata algorithm is proposed to increase the security of the proposed method. We have experimentally verified the proposed 3D objects encryption and reconstruction algorithm. The experimental results show that the proposed method is superior to the other computational reconstruction methods.

Depth reconstruction with coaxial multi-wavelength aperture telecentric optical system

An optical system to measure depth information is proposed here. The proposed optical system has double coaxial multi-wavelength apertures, which makes it possible to simultaneously take an orthogonal projection image and a perspective projection image with these two images separated by wavelengths. The three-dimensional physical position of an object can be derived with the ratio of the radial distances of these separated images with the centers located on the optical axis. Validation of the system by a ray-tracing simulation and an experiment shows that the proposed optical system can be used for depth reconstruction.

Wavelet-based iterative perfect reconstruction in computational integral imaging

We propose a new computational integral imaging (CII) method via the iterative perfect reconstruction technique to improve the visual quality of reconstructed 3D scenes. As is well known, images reconstructed by CII suffer from artifacts and, as a result, degradation of visual quality. As solutions to this problem, the regularization and iterative back-projection (IBP)-based super-resolution (SR) reconstruction algorithms have been shown to be effective for high-visual-quality reconstruction. However, computation of the regularization algorithm is very expensive, and the IBP algorithm is very sensitive to noise in the deblurring process. To address these challenges, we propose an iterative perfect reconstruction algorithm that addresses the issues of low visual quality and noise sensitivity. Experimental results indicate that our proposed method outperforms the conventional SR reconstruction-based CII methods.

Designing optical 3D images encryption and reconstruction using monospectral synthetic aperture integral imaging

This paper realizes an optical 3D images encryption and reconstruction by employing the geometric calibration algorithm to the monospectral synthetic aperture integral imaging system. This method has the simultaneous advantages of improving the quality of 3D images by eliminating the crosstalk from the unaligned cameras and increasing security of the multispectral 3D images encryption by importing the random generated maximum-length cellular automata into the Fresnel transform encoding algorithm. Furthermore, compared with the previous 3D images encryption methods of encrypting 3D multispectral information, the proposed method only encrypts monospectral data, which will greatly minimize the complexity. We present experimental results of 3D image encryption and volume pixel computational reconstruction to test and verify the performance of the proposed method. Experimental results validate the feasibility and robustness of our proposed approach, even under severe degradation.

Optical encryption via monospectral integral imaging

Optical integral imaging (II) uses a lenslet array and CCD sensor as the 3D acquisition device, in which the multispectral information is acquired by a color filter array (CFA). However, color crosstalk exists in CFA that diminishes color gamut, resulting in the reduced resolution. In this paper, we present a monospectral II encryption approach with a monospectral camera array (MCA). The monospectral II system captures images with the MCA that can eliminate color crosstalk among the adjacent spectral channels. It is noteworthy that the captured elemental images (EIs) from the colored scene belong to grayscale; the colored image encryption is converted to grayscale encryption. Consequently, this study will significantly save the calculation load in image encoding and decoding (nearly reduced 2/3) compared with the similar works. Afterwards, an optimized super-resolution reconstruction algorithm is introduced to improve the viewing resolution.

Copyright protection for elemental image array by hypercomplex Fourier transform and an adaptive texturized holographic algorithm

In practical applications of three-dimensional integral imaging, the captured elemental image array (EIA) needs to be stored and delivered through the Internet. Therefore, there is an urgent need for protecting the copyright of EIA against piracy and malicious manipulation. In our work, we propose a copyright protection algorithm for EIA by combining the use of the modified hypercomplex Fourier transform (HFT) and the adaptive texturized holographic algorithm. The modified HFT can accurately extract the features from each elemental image. According to these features, we embed watermark into the visually less noticeable regions of the EIA to increase the visual perception. In addition, an adaptive texturized holographic algorithm is proposed to increase the robustness. Finally, the analytical performances are contrasted with simulation results where the imperceptibility and robustness of the proposed method are evaluated against standard attacks.

Robust copyright protection using multiple ownership watermarks

Generally, conventional transform (DWT and DFT, etc.) -based watermarking techniques provide only one spectrum plane for embedding the watermark, thus the embedding watermark information can be easily removed. To solve this problem, we propose an efficient cellular automata (CA) based watermarking method that CA transform (CAT) with various gateway values can provide many transform planes for watermark embedding according to various CA rules. In this paper, multiple ownership watermarks are first recorded in the form of an elemental image array (EIA), simultaneously, and then the recorded EIA as the watermark data is embedded into the CAT coefficient. An additional advantage of this proposed method is that EIA is composed of many elemental images and each elemental image has its own property of watermarks. Even though most data of elemental images are lost, the watermarks can be reconstructed from the remaining elemental images successfully. Experimental results show that the proposed technique provides good image quality and is robust in varying degree to some image processing attacks.

Three-dimensional integral imaging with flexible sensing

We present to the best of our knowledge the first report on three-dimensional (3D) integral imaging capture and reconstruction method with unknown poses of sensors placed on a flexible surface. Compared to a conventional integral imaging system, where a lenslet or sensor array is commonly located on a planar surface, the flexible sensing integral imaging system allows sensors to be placed on a nonplanar surface that can increase the field of view of the 3D imaging system. To obtain the poses of the sensor array on a flexible surface, an estimation algorithm is developed based on two-view geometry theory and the camera projective model. In addition, a super-resolution image is generated from a sequence of low-resolution 2D images with sub-pixel shifts. Super-resolution 3D reconstruction results at different depths are presented to validate the proposed approach.

Superresolution of 3-D computational integral imaging based on moving least square method

In this paper, we propose an edge directive moving least square (ED-MLS) based superresolution method for computational integral imaging reconstruction(CIIR). Due to the low resolution of the elemental images and the alignment error of the microlenses, it is not easy to obtain an accurate registration result in integral imaging, which makes it difficult to apply superresolution to the CIIR application. To overcome this problem, we propose the edge directive moving least square (ED-MLS) based superresolution method which utilizes the properties of the moving least square. The proposed ED-MLS based superresolution takes the direction of the edge into account in the moving least square reconstruction to deal with the abrupt brightness changes in the edge regions, and is less sensitive to the registration error. Furthermore, we propose a framework which shows how the data have to be collected for the superresolution problem in the CIIR application. Experimental results verify that the resolution of the elemental images is enhanced, and that a high resolution reconstructed 3-D image can be obtained with the proposed method.

Tilted elemental image array generation method for moiré-reduced computer generated integral imaging display

In this paper, we propose a tilted elemental image array generation method for computer generated integral imaging display with reduced moiré patterns. The pixels of the tilted elemental image array are divided into border pixels and effective pixels. According to the optimal tilted angle, the effective pixels are arranged with uniform arrangement. Also, a pixel mapping method is proposed. Appropriate experiments are carried out and the experimental results show that not only the color moiré patterns are reduced remarkably, but also the resolution of the reconstructed 3D images are improved through the proposed method.

Three-dimensional imaging and visualization using off-axially distributed image sensing

This Letter presents an off-axially distributed image sensing (ODIS) system for three-dimensional (3D) imaging and visualization. The off-axially distributed sensing method provides both lateral and longitudinal perspectives for 3D scenes even though the sensor moves along a slanted, one-dimensional path. A 3D volume is generated from a set of recorded images by use of a computational algorithm based on ray backprojection. Preliminary experimental results are presented to illustrate the feasibility of the proposed system. To the best of our knowledge, this is the first report on 3D imaging and visualization using ODIS.