4 January 2008 A method for compressing off-axis digital hologram with spectrum shifting
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Abstract
Large amounts of communication bandwidth and memory space is occupied to transmit and store digital hologram on account of its enormous data volume. It is necessary to compress the information of digital hologram for effective transmittance and storage. After theory of off-axis hologram is studied, it is found that at most half of the information is useful for reconstructing image. A new method is proposed to compress the information, according to the spectrum character of off-axis hologram. The sampling frequency is reduced by shifting the useful information of digital hologram from high-frequency section to low-frequency section. Therefore, the information is compressed. The detailed procedure is expressed as follows. (1) To filter the hologram with a high-pass filter, whose cut off frequency is equal to the difference between frequency of reference beam and the highest frequency of object beam. (2) To multiply every row of the filtered hologram by a cosine sequence, whose frequency is equal to the difference between frequency of reference beam and the highest frequency of object beam. (3) To filter the processed hologram with a low-pass filter. (4) To subsample the hologram with a sampling frequency as four times as the highest frequency of the object. As thus, the digital hologram is compressed to half size of the original one at least. Moreover, higher compression rate will be obtained if the subsampled hologram is compressed with other methods. The theoretical analysis and experimental results are presented.
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Yong Li, Fang Song, Hui Wang, Hongzhen Jin, Haihua Zhang, "A method for compressing off-axis digital hologram with spectrum shifting", Proc. SPIE 6832, Holography and Diffractive Optics III, 68320A (4 January 2008); doi: 10.1117/12.754682; https://doi.org/10.1117/12.754682
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