Tomohiko Fujii

Compensated phase-added stereogram for real-time holographic display

A common difficulty in displaying a Fresnel hologram in real time the required calculation of huge amounts of information. We propose a novel digital hologram generation method for real-time holographic display. It depends on compensation of the phase-added stereogram, and can generate high-quality holograms rapidly. We describe a generation algorithm for the phase-added stereogram, using the fast Fourier transform (FFT) for fast calculation, and the compensated phase-added stereogram to get a reconstructed image as clear as the Fresnel hologram. Moreover, we present a method to define the optimum size of segmentation to get a clear reconstruction image and to achieve fast computation using the FFT. We have built a demonstration system to implement the proposed method. The system consists of a server, a client, and an optical holographic display system for real-time holographic display. The server generates 3-D information and transmits it on Ethernet. The client receives the information and generates a digital hologram using the compensated phase-added stereogram. Finally, the generated hologram is displayed on the optical holographic display system in real time. We have achieved display of digital holograms at 15 frames/s with 1000 object points.

Fast calculation method for computer-generated cylindrical holograms

Since a general flat hologram has a limited viewable area, we usually cannot see the other side of a reconstructed object. There are some holograms that can solve this problem. A cylindrical hologram is well known to be viewable in 360 deg. Most cylindrical holograms are optical holograms, but there are few reports of computer-generated cylindrical holograms. The lack of computer-generated cylindrical holograms is because the spatial resolution of output devices is not great enough; therefore, we have to make a large hologram or use a small object to fulfill the sampling theorem. In addition, in calculating the large fringe, the calculation amount increases in proportion to the hologram size. Therefore, we propose what we believe to be a new calculation method for fast calculation. Then, we print these fringes with our prototype fringe printer. As a result, we obtain a good reconstructed image from a computer-generated cylindrical hologram.

Improvement of Hidden-Surface Removal for Computer-Generated Holograms from CG

For computer-generated rainbow holograms (CGRHs), it is important to display surface model shaded images like computer graphics (CG). We have proposed a simple process to obtain 3-D data for CGRH from two CG images.

Disk hologram made from a computer-generated hologram.

We have been investigating disk holograms made from a computer-generated hologram (CGH). Since a general flat format hologram has a limited viewable area, we usually cannot see the other side of the reconstructed object. Therefore, we propose a computer-generated cylindrical hologram (CGCH) to obtain a hologram with a 360 deg viewable area. The CGCH has a special shape that is difficult to construct and calculation of such a hologram takes too much time. In contrast, a disk-type hologram is well known as a 360 deg viewable hologram. Since a regular disk hologram is a flat reflective type, the reconstruction setup is easy. However, there are just a few reports about creating a disk hologram by use of a CGH. Because the output device lacks spatial resolution, the hologram cannot provide a large diffraction angle. In addition, the viewing zone depends on the hologram size; the maximum size of the fringe pattern is decided on the basis of the special frequency of the output device. The calculation amount of the proposed hologram is approximately a quarter of that of a CGCH. In a previous study, a disk hologram made from a CGH was achieved. However, since the relation between the vertical viewing zone and reconstructed image size is a trade-off, the size of the reconstructed image and view zone is not enough for practical use. To improve both parameters, we modified a fringe printer to issue a high-resolution fringe pattern for a disk hologram. In addition, we propose a new calculation method for fast calculation.

Fast generation of computer-generated hologram by graphics processing unit

A cylindrical hologram is well known to be viewable in 360 deg. This hologram depends high pixel resolution.Therefore, Computer-Generated Cylindrical Hologram (CGCH) requires huge calculation amount.In our previous research, we used look-up table method for fast calculation with Intel Pentium4 2.8 GHz.It took 480 hours to calculate high resolution CGCH (504,000 x 63,000 pixels and the average number of object points are 27,000).To improve quality of CGCH reconstructed image, fringe pattern requires higher spatial frequency and resolution.Therefore, to increase the calculation speed, we have to change the calculation method. In this paper, to reduce the calculation time of CGCH (912,000 x 108,000 pixels), we employ Graphics Processing Unit (GPU).It took 4,406 hours to calculate high resolution CGCH on Xeon 3.4 GHz.Since GPU has many streaming processors and a parallel processing structure, GPU works as the high performance parallel processor.In addition, GPU gives max performance to 2 dimensional data and streaming data.Recently, GPU can be utilized for the general purpose (GPGPU).For example, NVIDIAs GeForce7 series became a programmable processor with Cg programming language.Next GeForce8 series have CUDA as software development kit made by NVIDIA.Theoretically, calculation ability of GPU is announced as 500 GFLOPS. From the experimental result, we have achieved that 47 times faster calculation compared with our previous work which used CPU.Therefore, CGCH can be generated in 95 hours.So, total time is 110 hours to calculate and print the CGCH.

Computer-generated cylindrical rainbow hologram

In this paper, we have investigated the computer-generated cylindrical rainbow hologram. Since general flat format hologram has the limited viewable area, we usually can not see the other side of the reconstructed object. There are some holograms to solve this problem. A cylindrical type hologram is well known as the 360 degrees viewable hologram. As the cylindrical holograms, there are two methods such as a multiplex hologram and a laser reconstruction 360 degrees hologram. Since the multiplex hologram consists of the many two-dimensional pictures, the reconstructed image is not the true three-dimension. In constant, a laser reconstruction 360 degrees hologram has the true three-dimensional effect. However, since the spatial resolution of the output device is not enough and the huge calculation amount, there are few reports on computer-generated cylindrical hologram. In our previous study, the computer-generated cylindrical hologram was realized as the Fresnel hologram. The calculation amount was too huge and took about 44 hours in the total calculation time, though we had used the several PCs. We propose the rainbow type computer-generated cylindrical hologram. To decrease the calculation amount, the rainbow hologram sacrifices the vertical parallax. Also, this hologram can reconstruct the image with white light. Comparison with the previous study of the Fresnel hologram, the calculation speed becomes 165 times faster. After the calculation, we print this hologram with the fringe printer, and evaluate reconstructed images.

Improvement of computer-generated disk hologram

We have been investigating the computer-generated disk hologram (CGDH). Since general flat format hologram has the limited viewable area, we usually cannot see the other side of the reconstructed object. Therefore, we proposed the computer-generated cylindrical hologram (CGCH) to realize the 360 degrees viewable hologram. However, the CGCH has the special shape, it is difficult to construct the CGCH and the calculation amount is too large. In contrast, a disk type hologram is also well known as the 360 degrees viewable hologram. Since the disk hologram is the reflective type flat hologram, the setup of reconstruction is very easy. However, there was few report of the disk hologram by the computer-generated hologram. Due to the lack of the spatial resolution of our output device, the hologram cannot provide the large diffraction angle. In addition, the viewing zone is depended on the hologram size (of course, the maximum size of the fringe pattern is decided on the special frequency of the out put device), the calculation amount is also large (calculation amount of the CGDH is about quarter of the CGCH). In our previous study, the computer-generated disk hologram was realized. However, since the relation between the vertical viewing zone and reconstructed image size is trade-off, the size of the reconstructed image and view zone is not enough for practical use. Therefore, to improve both parameters, we modified the fringe printer to output the high resolution fringe pattern for the disk hologram.

Computer-Generated Disk Hologram

It is difficult to realize a computer-generated disk hologram due to the needs of high resolution output and huge computation. We have achieved to make the computer-generated disk hologram by using the fringe printer.