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

Abstract

We present a new, real-time method for rendering diffuse and glossy objects in low-frequency lighting environments that captures soft shadows, interreflections, and caustics. As a preprocess, a novel global transport simulator creates functions over the object's surface representing transfer of arbitrary, low-frequency incident lighting into transferred radiance which includes global effects like shadows and interreflections from the object onto itself. At run-time, these transfer functions are applied to actual incident lighting. Dynamic, local lighting is handled by sampling it close to the object every frame; the object can also be rigidly rotated with respect to the lighting and vice versa. Lighting and transfer functions are represented using low-order spherical harmonics. This avoids aliasing and evaluates efficiently on graphics hardware by reducing the shading integral to a dot product of 9 to 25 element vectors for diffuse receivers. Glossy objects are handled using matrices rather than vectors. We further introduce functions for radiance transfer from a dynamic lighting environment through a preprocessed object to neighboring points in space. These allow soft shadows and caustics from rigidly moving objects to be cast onto arbitrary, dynamic receivers. We demonstrate real-time global lighting effects with this approach.

HDR light probe sequence resampling for realtime incident light field rendering

“…The result of the rotation will be a full set of spherical harmonic coefficients, representing the Phong lobe in global space, ready to use for computation of (5). For lowfrequency glossy transfer, a 25 coefficient (degree 4) spherical harmonic approximation to the glossy transfer function yields satisfying results [Sloan et al 2002], and for the purposes here, a 25 coefficient approximation to a Phong model of low shininess (s ≤ 6) is used.…”

“…They showed that diffuse transfer could be accurately simulated by representing the environment illumination with a nine component spherical harmonic. Sloan et al [2002] later extended the use of spherical harmonics for Precomputed Radiance Transfer (PRT) of glossy materials, performing expensive computations as a precomputation step.…”

“…Using spherical harmonics for HDR lighting may yield problems with ringing (Gibbs phenomenon), which can be reduced by windowing [Sloan et al 2002]. A higher degree of spherical harmonic approximations of transfer functions may also be desirable if there is a higher demand on numerical accuracy, see for example [Mahajan et al 2008] for a discussion on the accuracy of different spherical harmonic approximations to the Phong transfer function.…”

A Dual Theory of Inverse and Forward Light Transport

“…First, many fast techniques for acquiring the light transport of real scenes have been proposed in recent literature [Debevec et al 2000;Masselus et al 2003;Peers et al 2006]. Precomputed light transport is popular even for synthetic rendering [Sloan et al 2002;Ng et al 2003;Hasan et al 2006]. In essence, these methods directly measure the effects of interreflections under various lighting conditions.…”

Real-time triple product relighting using spherical local-frame parameterization

“…dering for rich lighting effects, such as precomputed radiance transfer using spherical harmonics by Sloan et al [15,16] and all-frequency relighting using wavelets by Ng et al [8,9]. The former allows changing lighting and viewpoint in real-time, but limited to low-frequency illumination.…”