Many lighting methods used in computer graphics such as indirect illumination can have very high computational costs and need to be approximated for real-time applications. These costs can be reduced by means of upsampling techniques which tend to introduce artifacts and affect the visual quality of the rendered image. This paper suggests a versatile approach for accelerating the rendering of screen space methods while maintaining the visual quality. This is achieved by exploiting the low frequency nature of many of these illumination methods and the geometrical continuity of the scene. First the screen space is dynamically divided into separate sub-images, then the illumination is rendered for each sub-image in an adequate resolution and finally the sub-images are put together in order to compose the final image. Therefore we identify edges in the scene and generate masks precisely specifying which part of the image is included in which sub-image. The masks therefore determine which part of the image is rendered in which resolution. A step wise upsampling and merging process then allows optically soft transitions between the different resolution levels. For this paper, the introduced multi-resolution rendering method was implemented and tested on three commonly used lighting methods. These are screen space ambient occlusion, soft shadow mapping and screen space global illumination.
@cite_21: Ambient occlusion is a lighting model that approximates the amount of light reaching a point on a diffuse surface based on its directly visible occluders. It gives perceptual clues of curvature and spatial proximity. Like [Mittring 2007] and [Shanmugam and Arikan 2007], we propose a real-time ambient occlusion computation as a postprocessing pass mainly based on a depth image from the eye’s point of view. This approach requires no scenedependent precomputations and is applicable to dynamic scenes. Our proposed method does not have the overocclusion issue from [Shanmugam and Arikan 2007] and samples inside the radius of influence, unlike [Mittring 2007].
@cite_1: In this chapter we do not present one specific algorithm; instead we try to describe the approaches the German company named Crytek took to find certain rendering algorithms that work well together. We believe this information is valuable for anyone that wants to implement similar rendering algorithms because often the implementation challenges arise when combining with other algorithms. We will also describe briefly the path to it as that covers alternative approaches you also might want to consider. This is not a complete description of everything that was done on the rendering side because for this chapter we picked certain areas that are of interest specifically for this audience and limited ourselves to a presentable extend. The work presented here takes significant advantage of research done by the graphics community in recent years and combines it with novel ideas developed within Crytek to realize implementations that efficiently map onto graphics hardware.
Screen Space Ambient Occlusion (SSAO) is a real-time approximation of the occlusion of ambient light by local geometry. The technique was first presented by Mittring @cite_1 and further developed and improved (e.g. by @cite_21 ).