Abstract
The image generated by binary computer-generated holograms (CGHs) always suffers from serious speckle noise. Thanks to the fast frame rate of the binary spatial light modulator, the speckle can be significantly suppressed by intensity accumulation, i.e., the sequential display of multiple CGHs of the same scene. If enough randomness is added to the CGHs, the speckle noise can be mostly averaged out. Intuitively, the quality of the reconstructed image should be proportional to the number of intensity accumulation. However, there is no simple method to predict the dependence of the average noise and accumulation number, and we can only know the results after finishing the full computation. In this paper, we propose an empirical formula of the average noise based on the speckle phenomenon in a laser projector. Using this model, we have confirmed that the randomness induced by random phase is equivalent to that induced by random down-sampling for the generation of binary CGHs. In addition, if the computational efficiency is a concern, the CGH calculated with iterations is not recommended for intensity accumulation display. Finally, there is an upper-quality limit of the reconstructed image by intensity accumulation. Thus, a strategy for efficient intensity accumulation is suggested.
Highlights
The use of a computer-generated hologram (CGH) is a promising technique for naked-eye three-dimensional (3D) display without the issue of vergence-accommodation conflict [1]
We have proposed a model to estimate the dependence of peak-signal-to-noise ratio (PSNR) on the number of intensity accumulation by binary CGHs
The model is confirmed to fit the properties of binary CGHs generated by the random phase (RP) method, the modified iterative Fresnel algorithm (MIFA), and the localized random down-sampling (LRDS)
Summary
The use of a computer-generated hologram (CGH) is a promising technique for naked-eye three-dimensional (3D) display without the issue of vergence-accommodation conflict [1]. The CGHs are applied to address a spatial light modulator (SLM), generating the light field of a 3D scene. The 3D display can be realized by using a binary SLM; i.e., the modulation is 0, π in phase or 0, 1 in amplitude [2,3,4,5,6]. The display quality of a binary SLM is usually low because of the limited degrees of freedom. Optimization algorithms, such as binary search [7,8,9] or simulated annealing [10], can be applied to improve the quality of binary CGH display, the quality of a single binary
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