Kouichi Nitta

Image reconstruction for thin observation module by bound optics by using the iterative backprojection method

A method for reconstructing high-spatial-resolution images in an imaging system known as thin observation module by bound optics (TOMBO) is reported. We investigate a novel procedure combining a pixel-rearrangement method and iterative backprojection (IBP). Pixel rearrangement has been used until now in TOMBO, and IBP is a digital superresolution technique. We verify the effectiveness of the combined procedure with simulated and experimental results.

Advances in passive imaging elements with micromirror array

We have proposed a new passive imaging optics which consists of a grid array of micro roof mirrors working as dihedral corner reflectors. Although this element forms mirror-like images at opposite side of objects, the images are real. Because the imaging principle of the proposed element is based on accumulation of rays, the design of each light path makes many kinds of devices possible. So, we propose two variations of such a device. One device consists of an array of micro retroreflectors and a half mirror, and it can also form real mirror-like images. The advantage of this device is wide range of view, because the displacement of each retororeflector is not limited on a plane unlike the roof mirror grid array. The other consists of an array of long dihedral corner reflectors. Although this structure has been already known as a roof mirror array, it can be used for imaging. This device forms two heterogeneous images. One is real at the same side of an object, and the other is virtual at the opposite side. This is a conjugate imaging optics of a slit mirror array whose mirror surface is perpendicular to the device surface. The advantage of a roor mirror array is that the real image has horizontal parallax and can be seen in air naturally.

Iterative algorithm of phase determination in digital holography for real-time recording of real objects

We propose a numerical method to obtain complex amplitude distribution of a three-dimensional (3D) object from a digital hologram. The method consists of two processes. The first process is to measure simultaneously a hologram of the 3D object and an object intensity distribution by two image sensors. These intensity distributions give us the amplitude and absolute value of phase of the 3D object at the image sensor plane. The second process is the determination of phase distribution by a proposed iterative process based on the criterion that the reconstructed 3D object is in focus and its conjugate reconstruction is out of focus. Numerical and experimental results show the effectiveness of the proposed method.

Thin observation module by bound optics (TOMBO) with color filters

This paper demonstrates, for the first time, TOMBO color imaging system that employs color-splitting filters on each lens. A red, green, or blue color filter is allocated to each microlens instead of each pixel in conventional single-sensor color imaging system. Thus the microlens array here also makes up a color filter array of Bayer geometry. For the imaging device, a CMOS image sensor with 1040 x 960 pixels whose size is 6.25 um square was used. 8 x 8 microlens array with 750 um pitch was employed as a taking lens. Excellent color images were obtained by rearrangement, interpolation, and postdigital processing.

Three-dimensional measurement and imaging based on multicameras randomly distributed on the circumference.

We present a three-dimensional (3D) measurement and imaging based on a multicamera system. In the presented system, projected images of 3D objects are taken by cameras located at random positions on a circumference, and then the 3D objects can be reconstructed numerically. We introduce an angle correction function to improve the quality of the reconstructed object. The angle correction function can correct the angle error caused by the position errors in the projected images due to the finite pixel size of the image sensor. The numerical results show that the point source was reconstructed successfully by introducing the angle correction function. We also demonstrate experiments: the two objects are located on a rotary stage controlled by a computer, the projected images are taken by a single camera, and by using 33 projected images, the two objects are reconstructed successfully.

A method for factorization by means of digital optical computing and image compression

A method to reduce computational costs of a factorization algorithm based on two dimensional pattern processing is presented. We develop logical operations to implement a factorization in the data compressed domain. In the method, firstly, two dimensional discrete images for data processing is compressed in accordance with the presented coding. Secondly, sequences of logical operations are executed in compression domain. Finally, desired results are obtained by extraction of the compressed data after the operations. An advantaged feature of the presented method is that computational costs can be decreased by the data compression rate.

Optical Security Card by Three‐dimensional Random Phase Distribution

An optical security card based on a three‐dimensional (3D) phase object is presented. This card enables us to develop a personal authentification system and secure data storage in a highly scattering medium. The authentification is implemented by the correlation between a speckle pattern of the 3D phase object and stored speckle patterns. For secure data storage, absorption distribution is involved in a scattering volume medium. Appropriate user can only reconstruct the absorption distribution by solving inverse problem. Experimental and numerical results are presented to show the effectiveness of the proposed system.

Design of Waveguide Array for Wide and Thin Coherent Illuminator

We have proposed a waveguide array device for a wide and thin coherent illuminator. The device is numerically analyzed by beam propagation method. In the numerical evaluation, 81 beam array is designed, but the intensity fluctuation is not small. We have to modify the waveguide structure along the propagation direction.

Characteristics of 3-D image reconstruction in a system based on multi vision data acquisition and holographic display

The characteristics of image quality on a three-dimensional (3D) imaging system based on multi-vision capturing and holographic display are analyzed numerically. We compare the longitudinal resolution in holographic reconstruction with accuracy of axial positions obtained with stereogram analysis.

Three-dimensional Interface based on Digital Holography

A three-dimensional (3D) interface system based on digital holography is presented. For the development of 3D interface system, a 3D display system, a recording system of 3D objects, an information processing system of 3D manipulation, and 3D measurement system are required. In the system, the complex amplitude distribution of 3D objects is recorded as digital hologram. In the reconstruction, the complex amplitude distribution of the 3D objects or phase-only information is used. The optical reconstruction is also available. The manipulation of 3D object can be implemented by processing complex amplitude of the 3D objects in the hologram plane. We present numerical and experimental results.