ABSTRACT
A Fresnel Zone Aperture (FZA) mask for a lensless camera, an ultra-thin and functional computational imaging system, is beneficial because the FZA pattern makes it easy to model the imaging process and reconstruct captured images through a simple and fast deconvolution. However, diffraction causes a mismatch between the forward model used in the reconstruction and the actual imaging process, which affects the recovered image's resolution. This work theoretically analyzes the wave-optics imaging model of an FZA lensless camera and focuses on the zero points caused by diffraction in the frequency response. We propose a novel idea of image synthesis to compensate for the zero points through two different realizations based on the linear least-mean-square-error (LMSE) estimation. Results from computer simulation and optical experiments verify a nearly two-fold improvement in spatial resolution from the proposed methods compared with the conventional geometrical-optics-based method.
ABSTRACT
The Fresnel-zone-aperture lensless camera using a fringe-scanning technique allows non-iterative well-conditioned image reconstruction; however, the spatial resolution is limited by the mathematical reconstruction model that ignores diffraction. To solve this resolution problem, we propose a novel image-reconstruction algorithm using the wave-optics-based design of the deconvolution filter and color-channel image synthesis. We verify a two-fold improvement of the effective angular resolution by conducting numerical simulations and optical experiments with a prototype.
ABSTRACT
We propose a new type of lensless camera enabling light-field imaging for focusing after image capture and show its feasibilities with some prototyping. The camera basically consists only of an image sensor and Fresnel zone aperture (FZA). Point sources making up the subjects to be captured cast overlapping shadows of the FZA on the sensor, which result in overlapping straight moiré fringes due to multiplication of another virtual FZA in the computer. The fringes generate a captured image by two-dimensional fast Fourier transform. Refocusing is possible by adjusting the size of the virtual FZA. We found this imaging principle is quite analogous to a coherent hologram. Not only the functions of still cameras but also of video cameras are confirmed experimentally by using the prototyped cameras.
ABSTRACT
Bovine viral diarrhea virus (BVDV) field isolates show genetic and antigenic diversity. At least 14 subgenotypes of BVDV-1 and 4 of BVDV-2 have been identified in Artiodactyla worldwide. Of these, 6 subgenotypes of BVDV-1 and 1 of BVDV-2 have been isolated in Japan. Previously, we reported that each subgenotype virus expresses different antigenic characteristics. Here we investigated the reactivity of neutralizing antibodies against representative strains of Japanese BVDV subgenotypes using sera from 266 beef cattle to estimate the prevalence of this epidemic virus among cattle in Japan. Antibody titers at concentrations at least 4-fold higher than antibodies against other subgenotype viruses were considered subgenotype specific. Subgenotype-specific antibodies were detected from 117 (80.7%) of 145 sera samples (69.7% against BVDV-1a, 1.4% against BVDV-1b, 8.3% against BVDV-1c, and 1.4% against BVDV-2a). The results suggest that neutralization tests are useful in estimating currently epidemic subgenotypes of BVDV in the field.
