Liu Jung-Ping, Liao Heng-Kuang
Appl Opt. 2018 Jan 1;57(1):A215-A221. doi: 10.1364/AO.57.00A215.
In a polygon-based computer-generated hologram (CGH), the three-dimensional (3D) model is represented as a polygon, which consists of numerous small facets. Lighting effect, material texture, and surface property can be included in the polygonal model, which enables polygon-based CGH to realize high-fidelity 3D display. On the other hand, the occlusion effect is an important depth cue for 3D display. In polygon-based CGH, however, occlusion processing is difficult and time-consuming work. In this paper, we proposed a simple and fast occlusion processing method, the slice-by-slice silhouette (S) method, for generating the occlusion effect in polygon-based CGH. In the S method, the polygonal model is sliced into multiple thin segments. For each segment, a silhouette mask is generated and located at the backside of the segment. The incident light is first shaded by the mask and superimposes on the light emitted from the facets of the evaluated segment. In this way, every segment can be processed sequentially to get the resulting object light. Our experimental result demonstrates that the S method can generate a high-definition hologram with qualified occlusion effect. The computing complexity of the S method is lower than that of previous methods. In addition, the S method can be parallelized easily, and thus can be further speeded up by applying a parallel computing framework, such as multi-core CPU or GPU.
在基于多边形的计算机生成全息图（CGH）中，三维（3D）模型表示为多边形，该多边形由众多小平面组成。光照效果、材质纹理和表面属性可以包含在多边形模型中，这使得基于多边形的CGH能够实现高保真3D显示。另一方面，遮挡效果是3D显示的重要深度线索。然而，在基于多边形的CGH中，遮挡处理是一项困难且耗时的工作。在本文中，我们提出了一种简单快速的遮挡处理方法，即逐片轮廓（S）方法，用于在基于多边形的CGH中生成遮挡效果。在S方法中，多边形模型被切成多个薄段。对于每个段，生成一个轮廓掩码并将其放置在段的背面。入射光首先被掩码遮挡，然后叠加在被评估段的小平面发出的光上。通过这种方式，可以依次处理每个段以获得最终的物体光。我们的实验结果表明，S方法可以生成具有合格遮挡效果的高清全息图。S方法的计算复杂度低于以前的方法。此外，S方法可以很容易地并行化，因此可以通过应用并行计算框架（如多核CPU或GPU）进一步加速。
