This study proposes a technique to construct a flat-panel see-through three-dimensional (3D) display based on integral imaging. This display consists of multiple lens arrays, a transparent flat-panel ...display, and a light-blocking wall (LBW). Rays behind the display are reconstructed in front of it by combination of the lens arrays and the LBW to provide the see-through function. The combination of one of the lens arrays and the transparent flat-panel display produces full-parallax 3D images, which are superimposed on background images. The experimental system is constructed to verify the proposed technique. The see-through and superposition capabilities of the experimental system are demonstrated.
Dual-wavelength phase-shifting digital holography that selectively extracts wavelength information from five wavelength-multiplexed holograms is presented. Specific phase shifts for respective ...wavelengths are introduced to remove the crosstalk components and extract only the object wave at the desired wavelength from the holograms. Object waves in multiple wavelengths are selectively extracted by utilizing 2π ambiguity and the subtraction procedures based on phase-shifting interferometry. Numerical results show the validity of the proposed technique. The proposed technique is also experimentally demonstrated.
A simple calculation method to synthesize computer-generated holographic stereograms, which does not involve diffraction calculations, is proposed. It is assumed that three-dimension (3D) image ...generation by holographic stereograms is similar to that of multi-view autostereoscopic displays, in that multiple parallax images are displayed with rays converging to corresponding viewpoints. Therefore, a wavefront is calculated, whose amplitude is the square root of an intensity distribution of a parallax image and whose phase is a quadric phase distribution of a spherical wave converging to a viewpoint. Multiple wavefronts calculated for multiple viewpoints are summed up to obtain an object wave, which is then used to determine a hologram pattern. The proposed technique was experimentally verified.
Horizontally scanning holography can enlarge both screen size and viewing zone angle. A microelectromechanical-system spatial light modulator, which can generate only binary images, is used to ...generate hologram patterns. Thus, techniques to improve gray-scale representation in reconstructed images should be developed. In this study, the error diffusion technique was used for the binarization of holograms. When the Floyd-Steinberg error diffusion coefficients were used, gray-scale representation was improved. However, the linearity in the gray-scale representation was not satisfactory. We proposed the use of a correction table and showed that the linearity was greatly improved.
Horizontally scanning holography using a microelectromechanical system spatial light modulator (MEMS-SLM) can provide reconstructed images with an enlarged screen size and an increased viewing zone ...angle. Herein, we propose techniques to enable color image generation for a screen-scanning display system employing a single MEMS-SLM. Higher-order diffraction components generated by the MEMS-SLM for R, G, and B laser lights were coupled by providing proper illumination angles on the MEMS-SLM for each color. An error diffusion technique to binarize the hologram patterns was developed, in which the error diffusion directions were determined for each color. Color reconstructed images with a screen size of 6.2 in. and a viewing zone angle of 10.2° were generated at a frame rate of 30 Hz.
Holographic stereograms produce multiple parallax images that are seen from multiple viewpoints. Because random phase distributions are added to the parallax images to remove areas where images ...cannot be seen in the viewing area, speckles are generated in the reconstructed images. In this study, virtual viewpoints are inserted between the original viewpoints (real viewpoints) to make the interval of the viewpoints smaller than the pupil diameter of the eyes in order to remove the areas without images. In this case, regular interference patterns appear in the reconstructed images instead of the speckle patterns. The proper phase modulation of the parallax images displayed to the real and virtual viewpoints increases the spatial frequencies of the regular interference patterns on retinas so that the eyes cannot perceive them. The proposed technique was combined with the multiview-based holographic stereogram calculation technique and was experimentally verified.
Eye accommodation is considered to function properly for three-dimensional (3D) images generated by holography. We developed a horizontally scanning holographic display technique that enlarges both ...the screen size and viewing zone angle. A 3D image generated by this technique can be easily seen by both eyes. In this study, we measured the accommodation responses to a 3D image generated by the horizontally scanning holographic display technique that has a horizontal viewing zone angle of 14.6° and screen size of 4.3 in. We found that the accommodation responses to a 3D image displayed within 400 mm from the display screen were similar to those of a real object.
Conventional three-dimensional (3D) displays have a problem regarding human 3D perception. There is a conflict between vergence and accommodation, which are physiological factors of human 3D ...perception, and this conflict causes visual fatigue. Therefore, super multi-view (SMV) displays have been developed to solve this problem. In SMV displays, the interval between viewpoints is reduced such that it is smaller than the pupil diameter of the eyes. Measurements of eye responses show that the SMV displays have the effect of enlarging the depth of focus (DOF) of eyes. When 3D images are displayed in the enlarged DOF range, the vergence-accommodation conflict does not occur. However, the SMV displays must generate highdensity viewpoints. This paper describes several SMV display systems, such as the focused light array system, the multi-projection system, the flat-panel system, the hybrid system, the time-multiplexing system, and the head-mount system. Future developments are also discussed.
The Gerchberg–Saxton (GS) algorithm is a Fourier iterative algorithm that can effectively optimize phase-only computer-generated holograms (CGHs). This study proposes a new optimization technique for ...phase-only CGHs based on the gradient descent method. The proposed technique evaluates the intensity distributions of reconstructed images to directly obtain the phase distributions of the CGHs, whereas the GS algorithm equivalently evaluates the amplitude distributions of reconstructed images and extracts phase distributions from complex-amplitude distributions of the holograms using a constant-amplitude constraint. The proposed technique can reduce the errors in the reconstructed images with fewer iterations than the GS algorithm.
We propose a hologram calculation technique that enables reconstructing a shaded three-dimensional (3D) image. The amplitude distributions of zone plates, which generate the object points that ...constitute a 3D object, were two-dimensionally modulated. Two-dimensional (2D) amplitude modulation was determined on the basis of the Phong reflection model developed for computer graphics, which considers the specular, diffuse, and ambient reflection light components. The 2D amplitude modulation added variable and constant modulations: the former controlled the specular light component and the latter controlled the diffuse and ambient components. The proposed calculation technique was experimentally verified. The reconstructed image showed specular reflection that varied depending on the viewing position.
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