角江 崇

© 2014 SPIE. We report frequency estimation of loudspeaker diaphragm vibrating at high speed by parallel phase-shifting digital holography which is a technique of single-shot phase-shifting interferometry. This technique records multiple phaseshifted holograms required for phase-shifting interferometry by using space-division multiplexing. We constructed a parallel phase-shifting digital holography system consisting of a high-speed polarization-imaging camera. This camera has a micro-polarizer array which selects four linear polarization axes for 2 × 2 pixels. We set a loudspeaker as an object, and recorded vibration of diaphragm of the loudspeaker by the constructed system. By the constructed system, we demonstrated observation of vibration displacement of loudspeaker diaphragm. In this paper, we aim to estimate vibration frequency of the loudspeaker diaphragm by applying the experimental results to frequency analysis. Holograms consisting of 128 × 128 pixels were recorded at a frame rate of 262,500 frames per second by the camera. A sinusoidal wave was input to the loudspeaker via a phone connector. We observed displacement of the loudspeaker diaphragm vibrating by the system. We also succeeded in estimating vibration frequency of the loudspeaker diaphragm by applying frequency analysis to the experimental results.

We have developed an algorithm which can record multiple two-dimensional (2-D) gradated projection patterns in a single three-dimensional (3-D) object. Each recorded pattern has the individual projected direction and can only be seen from the direction. The proposed algorithm has two important features: the number of recorded patterns is theoretically infinite and no meaningful pattern can be seen outside of the projected directions. In this paper, we expanded the algorithm to record multiple 2-D projection patterns in color. There are two popular ways of color mixing: additive one and subtractive one. Additive color mixing used to mix light is based on RGB colors and subtractive color mixing used to mix inks is based on CMY colors. We made two coloring methods based on the additive mixing and subtractive mixing. We performed numerical simulations of the coloring methods, and confirmed their effectiveness. We also fabricated two types of volumetric display and applied the proposed algorithm to them. One is a cubic displays constructed by light-emitting diodes (LEDs) in 8×8×8 array. Lighting patterns of LEDs are controlled by a microcomputer board. The other one is made of 7×7 array of threads. Each thread is illuminated by a projector connected with PC. As a result of the implementation, we succeeded in recording multiple 2-D color motion pictures in the volumetric displays. Our algorithm can be applied to digital signage, media art and so forth. © 2014 SPIE.

インテグラルフォトグラフィによって自然光下で三次元物体を撮影し,得られた画像からホログラムを作成してホログラフィック像を再生する手法がある.この手法により,自然光下での記録が困難であったホログラフィの欠点が解消された.しかし従来は,得られる再生像の視域角が約5度と小さく,人間が再生像を三次元物体として視認するための運動視差が十分に得られなかった.本論文では,インテグラルフォトグラフィを入力としたホログラフィック再生像の広視域化について検討した.その結果,記録時に用いるレンズアレイの焦点距離を短くすることで,得られる再生像の視域角を約15度に拡大することに成功した.

In case of color hologram, GS(Gerchberg-Saxton) algorithm takes much calculation time. Therefore, we have devised a fast method of speckle noise reduction of color hologram using the color space conversion from RGB color space to YCbCr color space in which the down sampling of the color difference component is used.

© 2013 ITE and SID. Holographic projection inherently requires no lenses, reconstructs images with high contrast and reconstructs color images with one spatial light modulator. In this paper, we demonstrate a speckle-reduced zoomable holographic projection. This holographic projection realizes the zoom function using a numerical method, called scaled Fresnel diffraction. In addition, the speckle noise of projected images is reduced by the combination of optimized holograms, a lowspeckle laser and a vibrating multi-mode fiber.

© 2013 ITE and SID. We tried to display the real-time reconstructed 3-D image consisting of a large number of object points. We propose one-colored time-division electroholography using the persistence of vision. Finally, we succeed to display a reconstructed 3-D image consisting of 44, 647 object points using a NVIDIA GeForce GTX TITAN at 12 fps.

© 2013 ITE and SID. Real-time electroholography requires the high computational performance. The study of fast parallel computation using excellent cost-effective and general-purpose computer system as multi-GPU system is very important. We proposed the parallel algorithm to compute multiple computer-generated holograms using multi-GPU cluster system with infiniband network simultaneously.

© 2013 ITE and SID. We proposed a real-time time-division color electroholography using a USB-to-Parallel module for simple synchronous control of one-chip RGB LED. The proposed system is low-priced. Host PC can directly synchronize the lighting of one-chip RGB LED with the CGH computation by using Message Passing Interface (MPI).

We constructed a high-speed four-dimensional (4-D) microscope for dynamically moving biological specimens. By use of parallel phase-shifting digital holography, 3-D behavior and phase distribution were captured at 150,000 frames-per-second. © OSA 2012.

We propose a combination of recording wavelengths of color digital holography using spectral estimation for improvement of color reproduction, and numerically confirmed that the color differences were greatly reduced by the combination. © OSA 2012.

Using parallel phase-shifting digital holography with a high-speed camera, the authors succeeded in phase-shifting interferometry at the rate of 180,000 fraames/s. Motion pictures of three-dimensional image of dynamically moving objects were demonstrated. © 2012 OSA.

単一波長を用いた単一露光2照射角位相接続法を紹介する。2照射角位相接続法は単一波長で急峻な段差に対しても高精度3次元形状計測可能な技術であるが,単一露光計測が従来不可能であった。我々は,ホログラムの空間分割多重記録と偏光を利用することにより単一露光での計測を可能にする。本方式の提案と種々のディジタルホログラフィへの適用,計算機シミュレーションによる有効性確認と実証例までを報告する。