In Computer-Generated Hologram (CGH), random phases are often added to diffuse the object light. However, due to this effect, speckle noise, which is a deterioration in image quality, occurs. In this study, we generated a hologram that suppresses the influence of speckle by calculation so that the light wave converges to the viewpoint. The viewing zone is limited by this method, it can be applied to Head-Mounted Display (HMD) type CGH or Eye tracking type electronic holography. The effectiveness of the proposed method was confirmed by simulation and actual optical reproduction.
Computer-generated hologram (CGH) has a serious problem that stereoscopic images are deteriorated by speckle noise. In analog holography, statistical characteristics of speckle noise were theorized, but it is difficult to apply the theory to CGH, which is effected by computerization such as sampling, quantization and so on. In this paper, we focused on point-based method which is one of the calculation methods of CGH and objectively evaluated the effect of the density of arrange point light sources on speckle noise. We evaluated the image quality by PSNR, considering the resolution of the eye. By objective evaluation, we confirmed the effect on speckle noise by changing the density of point light sources.
Computer-generated holography (CGH) is the ideal 3D display technology because we can observe the reconstructed image without 3D fatigue. Holograms are made by computer simulation of light propagation. We used the point-based methods which considers virtual objects as a set of point light sources to calculate object light. Generally, in the recording process of a hologram using the point-based method, the phase of each point on the object surface is randomized in order to diffuse object light, which is called a “random phase”. A random number for implementing a random phase is called a “random phase number”. However, applying a random phase causes “speckle noise” on the surface, due to complicated interference between reflected lights. We examined the relationship between the characteristics of the random phase number and the state of the reconstructed image surface. We focused on the reflection characteristics of the reconstructed image and the speckle noise, in particular. To measure the speckle noise, we used a criterion called “speckle contrast”. In this paper, we examined the relationship between the randomness of the surface phase and the speckle contrast. We confirmed that there are random numbers whose speckle contrast depends on phase variances and random numbers whose speckle contrast does not depend on phase variances
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