Gradation representation method using binary-weighted computer-generated hologram

A novel type of multiplexed computer-generated hologram (CGH) is designed with more than one billion of pixels per period. It consists of elementary cells divided into arbitrary-shaped polygonal apertures, the division being identical in all cells. The cells are further digitized into pixel arrays to exploit the huge space-bandwidth product of electron-beam lithography. The polygonal apertures in the same location inside the cells constitute a subhologram. With the Abbe transform that has never, to our knowledge, been used in other CGH designs, the subhologram images (subimages) are obtained with fast Fourier transforms. It is therefore possible to design a multiplexed CGH that has a size thousands of times larger than the manageable size of a conventional CGH designed with the iterative Fourier transform algorithm (IFTA). A much larger object window than that of the conventional CGH can also be achieved with the multiplexed polygonal-aperture CGH, owing to its extremely large dimensions. The multiplexed polygonal-aperture CGH is designed with the novel iterative subhologram design algorithm, which considers the coherent summation of the subimages and applies constraints on the total image, subimages, and subholograms. As a result, the noise appearing in the preceding multiplexed-CGH designs is avoided. The multiplexed polygonal-aperture CGH has a much higher diffraction efficiency than that resulting from either the preceding multiplexed-CGH designs or the conventional CGH designed by the IFTA.

We report the generation of a real-time large computer generated hologram (CGH) using the wavefront recording plane (WRP) method with the aid of a graphics processing unit (GPU). The WRP method consists of two steps: the first step calculates a complex amplitude on a WRP that is placed between a 3D object and a CGH, from a three-dimensional (3D) object. The second step obtains a CGH by calculating diffraction from the WRP to the CGH. The disadvantages of the previous WRP method include the inability to record a large three-dimensional object that exceeds the size of the CGH, and the difficulty in implementing to all the steps on a GPU. We improved the WRP method using Shifted-Fresnel diffraction to solve the former problem, and all the steps could be implemented on a GPU. We show optical reconstructions from a 1,980 × 1,080 phase only CGH generated by about 3 × 10(4) object points over 90 frames per second. In other words, the improved method obtained a large CGH with about 6 mega pixels (1,980 × 1,080 × 3) from the object points at the video rate.

An effective hologram region (EHR) based approach is presented to speed up the computation of computer generated holograms (CGHs). The object space is predivided into subspaces, and an EHR for each subspace is predefined according to the maximum spatial frequency of interference fringes, light diffraction efficiency, and CGH binarization effect. To compute the hologram of an object, the object points are first categorized according to which subspace they are located in, and then their holograms are calculated using the corresponding EHRs. As each EHR usually takes up only a portion of the hologram plate, the CGH computational load is thus reduced. This new approach is highly suitable for large hologram display systems. In addition, when compared to the reconstructed image using the conventional approach, our experimental results show that more noise can be blocked off and the reconstructed image appears sharper without noticeable brightness reduction.

Holographic display has been considered as a promising display technology. Currently, low-speed generation of holograms with big holographic data is one of crucial bottlenecks for three dimensional (3D) dynamic holographic display. To solve this problem, the acceleration method computation platform is presented based on look-up table point source method. The computer generated holograms (CGHs) acquisition is sped up by offline file loading and inline calculation optimization, where a pure phase CGH with gigabyte data is encoded to record an object with 10 MB sampling data. Both numerical simulation and optical experiment demonstrate that the CGHs with 1920×1080 resolution by the proposed method can be applied to the 3D objects reconstruction with high quality successfully. It is believed that the CGHs with huge data can be generated by the proposed method with high speed for 3D dynamic holographic display in near future.

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.

The conventional computer-generated hologram reconstructing photorealistic three-dimensional (3D) images based on ray-wavefront conversion has the disadvantage of spatio-angular resolution trade-off. In this Letter, we propose for the first time, to the best of our knowledge, a computer-generated photorealistic hologram without spatio-angular resolution trade-off based on the additive compressive light field (CLF) approach. The original light field is compressed into multiple layer images through numerical optimization based on the additive light field principle. Then, by independently calculating the wave propagation from each layer image to the hologram plane and adding them together, a CLF hologram is generated. Since the CLF information is presented through a holographic method, the advantage of high resolution in CLF is preserved while the limitation of the number of physically stacked layers (such as liquid crystal displays) is removed, leading to higher quality, larger depth of field, and higher brightness compared with a conventional CLF display. The proposed method is verified with a photorealistic optical experiment.

A hologram display technique that provides speckle-free, shaded reconstructed images is proposed. A three-dimensional object consists of object points; these object points are divided into plural object point groups that are generated in a time-sequential manner. Each object point group consists of a two-dimensional (2D) array of object points that are separated so as to prevent interference among them. Each object point group is generated by displaying a 2D array of zone plates on a high-speed spatial light modulator (SLM). The amplitude distribution of the zone plates is modulated two-dimensionally based on Phong shading to shade the reconstructed images. The 2D amplitude distribution of the zone plates is decomposed into multiple binary patterns that are displayed by the SLM in a time-sequential manner. The proposed method is experimentally verified.

We propose a new development for calculating a computer-generated hologram (CGH) through the use of multiple general-purpose graphics processing units (GPGPUs). For optimization of the implementation, CGH parallelization, object point tiling, memory selection for object point, hologram tiling, CGMA (compute to global memory access) ratio by block size, and memory mapping were considered. The proposed CGH was equipped with a digital holographic video system consisting of a camera system for capturing images (object points) and CPU/GPGPU software (S/W) for various image processing activities. The proposed system can generate about 37 full HD holograms per second using about 6K object points.

We present a novel approach for securing valuable documents using a complementary approach based on the encryption of computer-generated holograms (CGHs). The proposed approach utilizes the well-known iterative Fourier transform algorithm (IFTA) to generate a phase-only CGH for valuable digital and/or physical documents. The generated CGH is then secured by binary phase randomization, which is implemented using the symmetric encryption technique, exclusive OR (XOR). The reconstruction process for the calculated secured CGHs varied slightly depending on whether the documents were digital or physical. For digital documents, reconstruction was performed using a symmetric decryption key followed by an inverse Fourier transform (IFFT). On the other hand, the reconstruction of the physical document involved two additional processes: printing and scanning. To evaluate the quality of the digital reconstruction, the speckle signal-to-noise ratio (SSNR) was estimated for both printed grayscale and binary CGHs. The security analysis of the XOR-encrypted CGH was quantitatively evaluated to ensure the level of protection against various cryptographic attacks such as plaintext and brute-force attacks. The results revealed that the combination of phase CGHs and the XOR encryption/decryption provides robust cryptographic protection for valuable documents, benefiting document security and anti-counterfeiting.

In this paper, a fast hologram generation method based on optimal segmentation of sub-computer-generated hologram is proposed. When using the point light source (PLS) model for computer-generated hologram (CGH), the 3D object is discretized into individual object points, which are assumed to independent ideal sources. Then, the sub-CGH can be obtained by calculating the diffraction light field distribution of each ideal PLS, and the final hologram can be generated by further calculating of the sub-CGHs. In the proposed method, the contribution of any pixel in the sub-CGH generated by each ideal PLS to the final reconstructed image is calculated, and each sub-CGH is divided into the optimized diffraction areas (ODAs) and the invalid diffraction areas. Then, only the ODAs of each sub-CGH is pre-calculated and saved for further generating the final hologram. Because of the size of the ODAs are much smaller than that of the sub- CGHs, the hologram generation speed is greatly improved. The proposed method can be used to optimize most of the PLS model-based hologram generation methods. The proposed method is used to optimize the novel look-at-table (NLUT) method and wavefront recording plane (WRP) method, and both of them achieve good acceleration effect. In the optimization of the NLUT method, the sub-CGH database of the traditional NLUT method is replaced by the ODAs database. The final hologram can be generated by calling and superimposing all the ODAs. In the optimization of the WRP method, the WRP is calculated by using the ODAs instead of the sub-CGHs. Then, the final hologram is generated by using the Fresnel diffraction from the WRP to the holographic plane. With the proposed method, the calculation speed of the NLUT method and the WRP method can be significantly improved and the quality of the reconstructed image is not affected.

A procedure based entirely on computer simulation is developed for testing the quality of computer-generated holographic optical elements (CGHOEs). This new testing method may be of help in optimization techniques in the future. We introduce a mathematical quantity, the correlation, to characterize the performance of the studied CGHOE. Our procedure examines how the correlation between the object and the reconstructed image depends on various parameters of the CGHOE, such as the reference amplitude, the location and number of the object points, the number of gray levels used, and the pixel size on the hologram. To reduce computer running time, we introduce a new method for modeling the reconstruction of a computer-generated hologram (CGH): instead of using the whole information stored on the CGH, we use randomly chosen pixels (square-shaped slits) of the CGH. In this way, computer running time becomes smaller by two orders. A postquantization procedure is developed that, under certain conditions, improves the quality of the CGHOE. Our model uses amplitude holograms and 2-D objects, but in principle, there are no difficulties in extending it to phase holograms and 3-D objects.

The accuracy of digital and optical Hough transform (HT) processors is analyzed. New correction techniques to achieve improved accuracy are addressed. A new output format optical HT system using computer generated holograms (CGHs) is described and analyzed and its accuracy is found to be superior to that of digital HT processors. Its speed is much faster; the CGH space bandwidth product (SBWP) requirements are much less than for other methods; CGH error sources are addressed; and simple multiple binary exposure CGH fabrication is found to be sufficient.

We present a simple and fast calculation algorithm for a computer-generated hologram (CGH) by use of wavefront recording plane. The wavefront recording plane is placed between the object data and a CGH. When the wavefront recording plane is placed close to the object, the object light passes through a small region on the wave recording plane. The computational complexity for the object light is very small. We can obtain a CGH to execute diffraction calculation from the wavefront recording plane to the CGH. The computational complexity is constant. The total computational complexity is dramatically reduced in comparison with conventional CGH calculations.

A new approach for designing the binary phase-only hologram with arbitrary-shaped polygonal apertures is proposed. The diffraction of the aperture was computed with the analytical Abbe transform. To explore the very high number of degrees of freedom available in the computer-generated hologram (CGH) of very large pixel count, a two-step optimization including the genetic algorithm with local search for encoding binary phases of apertures followed by the direct search for floating covertices of the elementary triangular apertures was developed for high performance and low image-reconstruction error of the binary CGH.

In this paper, we introduce MIPAV (Medical Image Processing, Analysis, and Visualization software) and its plugin architecture to build the plugin for lossless image compression by the theory of cross-point regions with ideal cross-point regions on multiple bit planes. MIPAV is an open-source software, a good tool for researching and studying operations over medical images, but it does not have the tool for image compression. To build a plugin integrated into MIPAV software we use the scheme of ICRICM (Ideal Cross-point Regions for Image Compression on Multiple bit planes). This plugin can create a new output file from the original image, and the size of this output file is smaller than before. And inversely, the output file will be used in the decompression process to get the original image without any differences.KeywordsMIPAVICRICM algorithmcross pointideal cross-point regionlossless image compression