Projects distant lighting onto low-order spherical harmonics. Nine coefficients reproduce diffuse irradiance from any environment to within a percent, because the cosine lobe is itself a strong low-pass filter.
supersedescorrects · extends
classifiesspecializes · part-of
substitutes forapproximates · alternative-to
depends onrequires · validates
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approximatesis a cheaper stand-in for Image-Based Lightingnine coefficients capture all diffuse irradiance
References
An Efficient Representation for Irradiance Environment Maps — Ramamoorthi, Hanrahan — 2001 · link