Tomoya Nakamura

Superposition Imaging for Three-Dimensionally Space-Invariant Point Spread Functions

In this paper, we propose an aberration compensation method using superposition imaging and inexpensive postprocessing. In the method, the focusing distance and optical axis position of an imaging system with aberrations are varied over certain ranges, and the resulting images are superposed to equalize the point spread function (PSF) within a three-dimensional region and remove space variance. A sharp image of an object with a large depth-of-field and field-of-view is then reconstructed by deconvolution of the superposed image using the effective three-dimensionally space-invariant PSF. The effectiveness of the proposed method was verified by simulations assuming defocus, the five Seidel aberrations, and vignetting.

Computational superposition compound eye imaging for extended depth-of-field and field-of-view

This paper describes a superposition compound eye imaging system for extending the depth-of-field (DOF) and the field-of-view (FOV) using a spherical array of erect imaging optics and deconvolution processing. This imaging system had a three-dimensionally space-invariant point spread function generated by the superposition optics. A sharp image with a deep DOF and a wide FOV could be reconstructed by deconvolution processing with a single filter from a single captured image. The properties of the proposed system were confirmed by ray-trace simulations.

Fast method of calculating a photorealistic hologram based on orthographic ray–wavefront conversion

A computer-generated hologram based on ray-wavefront conversion can reconstruct photorealistic three-dimensional (3D) images containing deep virtual objects and complicated physical phenomena; however, the required computational cost has been a problem that needs to be solved. In this Letter, we introduce the concept of an orthographic projection in the ray-wavefront conversion technique for reducing the computational cost without degrading the image quality. In the proposed method, plane waves with angular spectra of the object are obtained via orthographic ray sampling and Fourier transformation, and only the plane waves incident on the hologram plane are numerically propagated. We verified this accelerated computational method theoretically and experimentally, and demonstrated optical reconstruction of a deep 3D image in which the effects of occlusions, transmission, refraction, and reflection were faithfully reproduced.

Single-shot acquisition of optical direct and global components using single coded pattern projection

We present a single-shot approach for separating optical direct and global components from an object. The former component is caused by direct illumination that travels from a light source to a point on the object and goes back to a camera directly. The latter one is caused by indirect illumination that travels from the light source to a point on the object through other points and goes back to the camera, such as multi-path reflection, diffusion, and scattering, or from another unintended light source, such as ambient illumination. In this method, the direct component is modulated by a single coded pattern from a projector. The modulated direct and un-modulated global components are integrated on an image sensor, which captures a single image. These two components are separated from the single captured image with a numerical algorithm employing a sparsity constraint. Ambient light separation and descattering based on the proposed scheme are experimentally demonstrated.

Computational superposition projector for extended depth of field and field of view

This Letter describes a projection system with extended depth of field (DOF) and field of view (FOV). In the proposed system, an input image is projected with varying focusing distances and optical axis directions, and the projected images are superposed on a three-dimensional screen to realize a three-dimensionally space-invariant point spread function (PSF). A target image is deconvolved, and the result is used as the input image before projection by using the superposed PSF to generate a sharp output image on the screen. This concept for extended-DOF and -FOV projection was demonstrated experimentally.

Rapid calibration of a projection-type holographic light-field display using hierarchically upconverted binary sinusoidal patterns

A projection-type holographic light-field (LF) display is a full-parallax, full-color, and glass-free three-dimensional (3D) display with a holographic optical element and a projector. The display has unique characteristics, including transparency; however, a rapid calibration method has not yet been established. In this paper, we propose a rapid calibration method for a holographic LF display without sacrificing its accuracy. The proposed method performs calibration via the projection of binary sinusoidal patterns whose frequencies are iteratively and hierarchically upconverted. Compared to the conventional method, in the proposed method, the required number of projections is reduced from linear to logarithmic with the projectors resolution. We confirm the successful reconstruction of the 3D image using the proposed method.

Efficient calculation method for realistic deep 3D scene hologram using orthographic projection

We propose a fast calculation method to synthesize a computer-generated hologram (CGH) of realistic deep three-dimensional (3D) scene. In our previous study, we have proposed a calculation method of CGH for reproducing such scene called ray-sampling-plane (RSP) method, in which light-ray information of a scene is converted to wavefront, and the wavefront is numerically propagated based on diffraction theory. In this paper, we introduce orthographic projection to the RSP method for accelerating calculation time. By numerical experiments, we verified the accelerated calculation with the ratio of 28-times compared to the conventional RSP method. The calculated CGH was fabricated by the printing system using laser lithography and demonstrated deep 3D image reconstruction in 52mm×52mm with realistic appearance effect such as gloss and translucent effect.

Autofocus for a multiscale gigapixel camera

In recent studies, the advanced wide field of view architectures for image reconstruction and exploitation (AWARE) multiscale camera, which is composed of a monocentric objective lens and an array of microcameras, was developed for the realization of snapshot wide field of view and high resolution imaging. This paper describes accelerated autofocus (AF) methods for the AWARE system based on a hierarchical spatial algorithm and an iterative temporal algorithm. In the algorithms, sensor positions of each microcamera are hierarchically scanned with contrast detection to effectively search for a focusing distance. The positions are then updated iteratively for dynamic scenes using temporal information. The algorithms are theoretically analyzed and experimentally demonstrated. The developed AF methods can be used for the realization of the temporal gigapixel imaging by the AWARE system.

Analysis of quantitative phase obtained by digital holography on H&E-stained pathological samples

The application of digital holography in cell imaging is gaining attraction as it gives quantitative information related to optical thickness without the need for staining. In contrast, conventional pathology examination uses tissues or cells that are stained to visualize the morphological structure or molecular expression with color. However, the relationship between color information and quantitative phase inside histopathology specimen is not yet well understood. In this study, we developed a system to capture both a color image and digital hologram, and those of H&E (hematoxylin and eosin)-stained liver tissue were acquired. Then, we calculated and analyzed the relationship between the textural features inside the color and phase images for hepatocellular carcinoma (HCC) histopathological specimen. Upon experimental investigation, we found that gray-level co-occurrence matrix (GLCM) textural features in phase images are useful for discriminating cancer and normal tissue, and varies between HCC grades which bring the possibility to be utilized for HCC diagnosis or classification without staining procedure.

Effectiveness of color correction on the quantitative analysis of histopathological images acquired by different whole-slide scanners

Advances in whole-slide scanning have led to research on digital pathology, including monitor-based diagnosis, feature quantification, and computer-aided diagnosis. The color variations due to the staining process and scanning device are a serious issue that should be solved in whole-slide imaging applications, and methods for color correction have been studied. Nevertheless, the effectiveness of color-correction methods in the quantitative analysis of histopathological images acquired by different whole-slide scanners (WSSs) has not been confirmed. In this work, several liver tissue samples were scanned by different WSSs, and a color-correction method for whole-slide images was applied to the digitized tissue specimens. A set of histological features were extracted from the histopathological images, both without and with color correction, to analyze the effectiveness of the color-correction method in feature quantification and cancer identification.