Occlusion processing for computer generated hologram by conversion between the wavefront and light-ray information

In the field of computational holography for three-dimensional (3D) display, the mutual occlusion of objects is one of the crucial issues. We propose a new mutual occlusion processing that is achieved by the conversion between the light-ray and wavefront on a virtual plane called ray-sampling (RS) plane located at near the interrupting object. The wavefront coming from background scene is converted into light-ray information at the RS plane by using Fourier transform based on the angular spectrum theory, then the converted light-rays are overwritten with those from interrupting object in the light-ray domain as an occlusion culling process. The ray information after the occlusion process is reconverted into wavefront by inverse Fourier transform at each RS point, then wave propagation from RS plane to hologram is computed by general light diffraction computation techniques. Since the light-ray information is used for the occlusion processing, our approach can realize a correct occlusion effect by a simple algorithm. In addition, high resolution 3D image can be reconstructed with wavefront-based technique. In the numerical simulation, we demonstrate that our approach for deep 3D scene with plural objects can realize a correct occlusion culling for varying observation angle and focusing distance.