Progress in optics and information technologies promotes an emerging research field for imaging called computational imaging. Owing to combinatorial diversity of optical encoding and computational decoding, various kinds of high-functional and high-performance imaging are developed as a framework of computational imaging. Fundamental reasons of the active development of the technology are not only tremendous increase of computational power but also availability of efficient optical devices, such as a microlens array for light field acquisition/display and spatial light modulators for light distribution control. This special issue intends to provide an overview of this research field including light field imaging/display, digital holography, novel phase imaging, and single pixel imaging. Marriage of optics as a physical system and a current information technology is considered as quite modernized and promising. This special issue is expected to show a signpost for the readers requiring unconventional imaging methodologies.

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Light field imaging and display have attracted a great attention in the field of 3D image acquisition, processing, and display. To develop a light field acquisition and display system is a great challenge because the acquisition/display devices require tens or hundreds of higher numbers of ‘pixels’ than conventional 2D imaging and display devices. In this paper, we point out that computational photography and display technologies can be a solution for the problem. By combining the conventional 2D acquisition/display devices and associated computation, we can reduce the number of pixels for acquisition/display of the light field. We first introduce ray space concept and address light field acquisition/display as sampling and reconstruction of ray space data. Then we show how such compressive acquisition and compressive display can be realized in terms of ray space data acquisition and display.

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This review paper introduces a new type of microscope that enables simultaneous recordings of phase and fluorescence data and retrieves them in three-dimensions. Conventional microscopes take fluorescence and phase information in sequential manner, and it is far satisfying for fast reactions in living cells. In both imaging, digital holographic techniques are applied. For phase imaging, typical Mach-Zehnder interferometer is applied whilst common-path off-axis fluorescence digital holography is applied to fluorescence imaging. Individual and combined methods were verified by experiments results. We believe that the concept of multimodal digital holographic microscopy and the proposed method will push forward the life science to unprecedented level.

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Phase imaging technique based on the transport of intensity equation (TIE) has been increasingly investigated in recent years because of some unique advantages such as non-interferometric method, simple optical system, no need to phase unwrapping, and availability of incoherent light source. We describe a phase imaging technique using TIE. Also, we describe a single-shot phase imaging technique using TIE, which can acquire phase information of high-speed moving object. The principle of the technique and numerical simulation results are presented.

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Diffractive imaging is a class of reference-free phase (complex amplitude) imaging and it has advantages of simplicity of the optical hardware and imaging speed over other phase imaging techniques. This paper reviews our recent research activities in diffractive imaging, especially, by introductions of compressive sensing and machine (deep) learning.

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This paper introduces single pixel imaging (SPI) and its applications. SPI is an imaging method that uses a bucket detector instead of a 2D detector like CCD or CMOS sensors. For detecting 2D information, the illuminated light projected by a projector has spatial patterns. Because SPI is attractive from the viewpoint of its simple setup, it is widely used in sensing or industrial applications and can be categorized into analytical imaging (as SPI and compressive sensing) and correlation imaging (as ghost imaging). In this paper, each particular feature and principle are introduced.

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Theorem of light field optics is different from conventional imaging optics in its paradigm. In light field optics, the position and the direction of rays are recorded as they are instead of an image, which is light amplitude distribution on a plane. Using light field optics 3D volume image can be reconstructed from data shown on a flat display. And it is not necessary that reconstructed image is optically conjugated with display plane. I introduce theorem of light field optics and its applications.

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