| Summary: | 博士 === 國立臺灣大學 === 電子工程學研究所 === 104 === Illumination is essential for synthesizing images. From real-time rendering, interactive rendering to light transport simulation, these fields exploit efficiency in producing illumination according to different application targets. In this dissertation, we will introduce our efficient rendering techniques for rendering illumination with plausible quality, from architecture to algorithm perspective.
The dissertation starts from exploiting a power-aware rendering architecture for a conventional GPU pipeline. From hardware perspective, we aim at reducing the pixel threads to save processor power dissipation in the forward rendering pipeline. Since illumination usually reveals smooth variation, instead of lighting every rasterized pixel, we sparsely sample pixels for lighting and interpolate the un-shaded pixels per tile basis during ROP phase. The screen-space approximated lighting technique is realized in a 16-core mobile GPU chip prototype, which is fabricated with TSMC 45nm technology. In our evaluation, the processor execution can reduce about 40% to 50% while performing forward lighting.
The hardware-based approach is a simplified filtering technique and limited by the tile basis. Extended from the hardware-based approach, we propose a screen-space geometry-aware bilateral filter for sparsely lit pixels. With randomly illuminated screen pixels, the screen-space lighting approximation considers deferred geometric properties, including normal and position. Empirically, we can merely shade 20% to 30% screen pixels in average with satisfactory reconstruction quality.
Moreover, indirect illumination is the soul of global illumination which enhances the visual realism for either real-time or interactive rendering applications. In addition to direct illumination, we approximate the first bounce indirect illumination. Our technique is based on a simplified point-based geometry, which is indexed via voxel grids. Through sparse ray marching for examining occluded voxels, we propose a visibility filter for associating batches of visible voxels to smooth visibility estimation. Therefore, the first bounce indirect illumination can be approximated with the possible point light sources. Regarding performance, the proposed technique can produce indirect illumination in an interactive rate from 1 to 2 fps.
Ultimately, we extend the point-based geometry to approximate path tracing. To efficiently query the intersection for vertex connection, we propose a hybrid lookup hierarchy. The lookup structure is composed of point samples, clustered planes and voxel grids. Through utilizing a voxel-based query approach on coarse voxels, the rough estimate can be used for locally connecting the possible path vertex via the lookup structure. As a result, the variance of a synthesized image can be rapidly reduced in a few seconds with plausible visual quality.
Our evaluation reveals compelling performance results, from architecture to parallel implementations, from real-time graphics to light transport simulation, meanwhile delivering plausible visual quality. In summary, the dissertation can be regarded as an extensive study in major efficient rendering topics for approximated illumination.
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