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25 March 1999 Computer-generated holograms with pulse-width modulation for multilevel 3D images
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In this report, computer-generated holograms (CGH's) which have the ability to reconstruct multi-level 3-D images under white light are described. For trial fabrication of the CGH, an electron beam printing system (EBPS) which is capable of recording interferogram data (IFD) with submicron precision is utilized. Because EBPS is controlled with on-off switching, IFD needs to be transformed into minute rectangle cells with their locations corresponding to the fringe. In our previous report, the intensity of the IFD was quantized into 2 levels with the median threshold, and then transformed into the cells. By this method, the location information of the IFD can be retained, while the intensity information, which is essential to reconstruct the tone of images, cannot. To solve this problem, pulse-width modulation (PWM), in which the intensity is quantized into multi levels is used, then the cell width is determined in proportion to the quantized intensity value, and applied to the IFD transformation. As a result of this experiment, in which 8 leveled PWM is applied to the IFD transformation, a 7 level-shaded pyramid is found to be sufficient, and therefore the effectiveness of the transforming method for reconstructing multi-level 3-D images has been confirmed experimentally.
© (1999) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Tomohisa Hamano, Mitsuru Kitamura, and Hiroshi Yoshikawa "Computer-generated holograms with pulse-width modulation for multilevel 3D images", Proc. SPIE 3637, Practical Holography XIII, (25 March 1999);

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