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Sample Decorrelation in BRDF Preconvolution for Image Based Lighting

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auzaiffe

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Sample Decorrelation in BRDF Preconvolution for Image Based Lighting is a January 2026 blog post by auzaiffe about a seam artifact in split-sum IBL LD cubemap prefiltering, found while reimplementing Unity HDRP-style IBL.

It reviews Karis-style FGD and LD terms, then shows how reusing one sample sequence per pixel plus an orthonormal frame that flips across X+ and X- face centers mirrors the pattern and creates a discontinuity. HDRP RenderDoc captures illustrate the bug. Fixes include blue-noise offsets, per-pixel seeds, basis-free VNDF sampling, and stochastic basis rotation.

It is for advanced real-time engineers implementing IBL preconvolution or auditing HDRP as a reference. Microfacet BRDF and importance sampling basics are assumed.

The article is a free WordPress post with diagrams, before and after images, and references.

It is a concrete debugging write-up for face-center seams in preconvolved environment lighting.