Exact mask-based occlusion processing in large-scale computer holography for 3D display

Recently, a very efficient mask-based technique for CGH, called the switch-back technique, has been proposed to perform silhouette light-shielding efficiently. In this algorithm, the fields behind polygons are shielded by binary mask patterns, called silhouette masks, which are generated by orthogonal projection of the polygon shape. Thus, the mask plane is parallel to the hologram but not parallel to the polygon. As a result, there are many small gaps between neighboring masks. Background fields that should be shielded by the masks sometimes leak out from the gaps. Viewers perceive the gaps as many cracks in the surfaces of the reconstructed object. To get over the problem, exacter algorithm than silhouette light-shielding, called surface light-shielding, has been proposed using rotational transform of wave-fields, but it was too time-consuming to apply it for large-scale CGHs. In this report, we propose a novel occlusion processing technique using improved surface light-shielding to calculate large-scale CGHs without any cracks. Actual large-scale CGHs are demonstrated to confirm validity of the algorithm.