Binarization of gray-scale hologram Fan Jiang Nov. 2006 Motivation: Computer-generated holograms (CGH's) have been investigated intensively in recent years. The most common CGH's use Fourier Transform as the diffraction theory, which can only generate gray-scale holograms. However, during the lithography, we can only write binary holograms on the mask. In the previous experiments, we used one threshold to convert the gray-scale holograms to binary holograms. The algorithm is simple, but the binarization errors cause enormous errors in the reconstruction with respect to the original object. The main object of this project is to explore and develop some better binarization methods to reduce the errors during the conversion and to get higher quality of reconstruction images. Approach: We have tried method of global threshold in the previous experiments, but the results are not satisfying. So here, I propose to try method of adaptive threshold. First, separate the hologram to some sub-holograms. Then find the proper threshold for each sub-holograms and convert them to binary sub-holograms. Finally, reconstruct the whole binary hologram and calculate the error between the original object and the reconstruct image. This method is depending mostly on how to separate the hologram to some sub-holograms. So I plan to try different ways to explore the best one. Another binarization method is proposed by "Eryi Zhang, Steffen Noehte, Christoph H. Dietrich, and Reinhard Manner". They developed a method called "Gradual and Random Binarization Algorithm" based on an interactive algorithm, combined with constrains. I will also try to use this new conversion in our own object. I will compare all the results at last and find the best one. Reference: 1) Eryi Zhang, Steffen Noehte, Christoph H. Dietrich, and Reinhard Manner, Gradual and random binarization of gray-scale holograms, Applied Optics, Vol. 34, 1995, 5987-5995. 2) 2) Chris Jacobsen, Malcolm R. Howells, A technique for projection x-ray lithography using computer-generated holograms, J. Appl. Phys. 71(6), 2993-3001.
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