Yasuhiro Takaki

Hybrid holographic microscopy free of conjugate and zero-order images

The true image area that can be used for recording microscopic objects in hybrid holographic microscopy can be increased by elimination of the conjugate image and the zero-order image. We therefore added two shutters and one phase modulator to the electro-optical holographic recording system so that we could change the recording parameters and evaluate four methods of eliminating the conjugate image and the zero-order image. We found that the methods that use only the phase modulator require the recording of fewer holograms than do the methods that use the shutters and also provide reconstructed images that are less noisy.

Multi-projection of lenticular displays to construct a 256-view super multi-view display

A new super multi-view (SMV) display system that enables the number of views to be increased is proposed. All three-dimensional (3D) images generated by multiple multi-view flat-panel displays are superimposed on a common screen using a multi-projection system. The viewing zones of the flat-panel 3D display are produced in the pupils of the projection lenses and then imaged to the observation space by a screen lens. Sixteen flat-panel 3D displays having 16 views were used to construct a SMV display having 256 views. The 3D resolution was 256 x 192. The screen size was 10.3 inches. The horizontal interval of the viewing zones was 1.3 mm.

High-Density Directional Display for Generating Natural Three-Dimensional Images

A high-density directional display can produce natural three-dimensional(3-D) images by projecting a large number of directional images using directional rays. When the angle pitch of the directional rays is 0.2/spl deg//spl sim/0.4/spl deg/, more than two directional rays passing through a point in 3-D space enter the viewers eye simultaneously so that the viewers eye can focus on that point. No discrepancy appears between the convergence function and the accommodation function so that the display does not induce visual fatigue. Two different system configurations are presented: a projection configuration and a thin configuration. A prototype display based on the projection configuration was constructed. The prototype display displayed 64 directional images with directional rays having a horizontal angle pitch of 0.34/spl deg/. The screen size was 9.2 in. The preliminary experimental results showed that a viewer could focus on 3-D images produced by the prototype display.

Super multi-view display with a lower resolution flat-panel display

A lenticular-type super multi-view (SMV) display normally requires an ultra high-resolution flat-panel display. To reduce this resolution requirement, two or more views are generated around each eye with an interval smaller than the pupil diameter. Cylindrical lenses constituting a lenticular lens project a group of pixels of the flat-panel display to generate a group of viewing zones. Pixel groups generating left and right viewing zones through the same cylindrical lens are partitioned to separate the two zones. The left and right pixel groups for different cylindrical lenses are interlaced horizontally. A prototype SMV display is demonstrated.

Hologram generation by horizontal scanning of a high-speed spatial light modulator

In order to increase the image size and the viewing zone angle of a hologram, a high-speed spatial light modulator (SLM) is imaged as a vertically long image by an anamorphic imaging system, and this image is scanned horizontally by a galvano scanner. The reduction in horizontal pixel pitch of the SLM provides a wide viewing zone angle. The increased image height and horizontal scanning increased the image size. We demonstrated the generation of a hologram having a 15 degrees horizontal viewing zone angle and an image size of 3.4 inches with a frame rate of 60 Hz using a digital micromirror device with a frame rate of 13.333 kHz as a high-speed SLM.

Super multi-view windshield display for long-distance image information presentation

A three-dimensional (3D) windshield display can display driving information in the vicinity of objects in the drivers front scene. We propose a super multi-view windshield display that can present the information in a wide depth range. The super multi-view display technique provides a smooth motion parallax. Motion parallax is the only physiological cue for perceiving the depths of 3D images displayed at far distances; these cannot be perceived by other physiological cues such as vergence, binocular disparity, and accommodation. A prototype system, which generates 36 viewing zones with a horizontal interval of 3.61 mm, was constructed. The smoothness of the motion parallax and the accuracy of the depth perception were evaluated.

Increased horizontal viewing zone angle of a hologram by resolution redistribution of a spatial light modulator

The narrow viewing zone angle is one of the problems associated with electronic holography. We propose a technique that enables the ratio of horizontal and vertical resolutions of a spatial light modulator (SLM) to be altered. This technique increases the horizontal resolution of a SLM several times, so that the horizontal viewing zone angle is also increased several times. A SLM illuminated by a slanted point light source array is imaged by a 4f imaging system in which a horizontal slit is located on the Fourier plane. We show that the horizontal resolution was increased four times and that the horizontal viewing zone angle was increased approximately four times.

Speckle-free and grayscale hologram reconstruction using time-multiplexing technique

Speckle generation is an inherent problem of holography. A speckle-reduction technique employing a time-multiplexing method is proposed. Object points constituting a reconstructed image are divided into multiple object point groups consisting of sparse object points, and the object point groups are displayed time sequentially. The sparseness and temporal summation enable the suppression of speckle generation. The object point group is decomposed into multiple bit planes to represent the grayscale of object points, and binary holograms are generated from the bit plane patterns by using a half-zone plate technique. The binary holograms are displayed by a high-speed spatial light modulator.

Table screen 360-degree three-dimensional display using a small array of high-speed projectors

We propose a 360-degree three-dimensional display with a table screen, which consists of a small number of high-speed projectors and a rotating screen. Because each high-speed projector is located outside the rotating axis of the screen, multiple projectors can be aligned. The lens shift technique is used to superimpose multiple images generated by all projectors on the rotating screen. The screen has an off-axis lens function such that the rotation of the screen generates numerous viewing points on a circle. The use of multiple projectors enables an increase in the number of colors, an increase in the number of viewing points, and a reduction in the screen rotation speed. We develop an image synthesis technique for the proposed display system. A color display system employing three high-speed projectors is demonstrated.

Thin-type natural three-dimensional display with 72 directional images

High-density generation of directional images can provide natural 3D images. Directional images are orthographic projections of a 3D scene into specific directions. A number of directional images projected into different horizontal directions are simultaneously displayed into the corresponding horizontal directions with nearly parallel rays. When the number of directional images becomes large enough and the display angle pitch becomes small enough, rays from a 3D scene are virtually reconstructed. A slanted lenticular sheet technique is used to construct a thin-type natural 3D display which can generate high-density directional images. A slanted lenticular sheet is attached to a high-resolution LCD panel to construct a 2D array of 3D pixels. One 3D pixel consists of 3M x N color sub-pixels to generate M x N rays having different horizontal proceeding directions. The lenticular sheet is slanted so as to differentiate all horizontal distances from the same color sub-pixels to the axis of a lenticle in each 3D pixel. The LCD panel having the resolution of 3,840 x 2,400 is used to construct 320 x 400 3D pixels and each 3D pixel emits rays into 72 different horizontal directions with the horizontal angle pitch of 0.38° by setting M = 12 and N = 6. The slant angle was determined by considering the directivity of directional images.