Binarization of gray-scale hologram - DOC by 7J2cb2

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									                  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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