Shadow Penumbras for Complex Objects by Depth-Dependent Filtering of Multi-Layer Depth Images

Abstract

January 12, 1999This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. Abstract. This paper presents an efficient algorithm for filtering multi-layer depth images (MDIs) in order to produce approximate penumbras. The filtering is performed on a MDI that represents the view from the light source. The algorithm is based upon both ray tracing and the z-buffer shadow algorithm, and is closely related to convolution methods. The method's effectiveness is demonstrated on especially complex objects such as trees, whose soft shadows are expensive to compute by other methods. The method specifically addresses the problem of light-leaking that occurs when tracing rays through discrete representations, and the inability of convolution methods to produce accurate self-shadowing effects. PREPRINT

Occlusion Textures for Plausible Soft Shadows*

“…Our work is similar in spirit to that of Keating and Max [KM99] but the field of application is completely different. Their approach does not aim at real time and targets ray-tracing.…”

“…Our approach is inspired by previous work [KM99, SS98] and obtains real‐time performance for highly complex scenes using off‐the‐shelf graphics hardware. In general, our solution is not physically correct, as is no current real‐time method, but it often compares well to the reference solution.…”

Precomputed radiance transfer for real-time rendering in dynamic, low-frequency lighting environments

“…Shadow maps, containing depths from the light source's point of view, were first used by Williams [43] to simulate point light source shadows. Many extensions of the basic technique, some suitable for real-time rendering, have since been described: percentage-closer filtering [35], which softens shadow edges, layered depth maps [26] and layered attenuation maps [1], which more accurately simulate penumbra shape and falloff, and deep shadow maps [29], which generalize the technique to partially transparent and volume geometry. All these techniques assume point or at least localized light sources; shadowing from larger light sources has been handled by multi-pass rendering that sums over a light source decomposition into points or small sources [17][27] [36].…”

Plausible Image Based Soft Shadows Using Occlusion Textures

“…It is closely related to [24] and results in alias free, not soft, shadows, just like [32]. In [20], the scene is replaced by an MDI (Multiple depth image) obtained on the CPU, and ray-tracing is performed against this alternative representation. There are several similarities to our method and we will have a more precise discussion in section 4.…”

“…Our approach is inspired by previous work [20,26] and exploits current graphics hardware to obtain real-time performance for highly complex scenes.…”