EGSR15: 26th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/14329

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Browsing EGSR15: 26th Eurographics Symposium on Rendering by Subject "Raytracing"

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    Improved Half Vector Space Light Transport
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Hanika, Johannes; Kaplanyan, Anton; Dachsbacher, Carsten; Jaakko Lehtinen and Derek Nowrouzezahrai
    In this paper, we present improvements to half vector space light transport (HSLT) [KHD14], which make this approach more practical, robust for difficult input geometry, and faster. Our first contribution is the computation of half vector space ray differentials in a different domain than the original work. This enables a more uniform stratification over the image plane during Markov chain exploration. Furthermore, we introduce a new multi chain perturbation in half vector space, which, if combined appropriately with half vector perturbation, makes the mutation strategy both more robust to geometric configurations with fine displacements and faster due to reduced number of ray casts. We provide and analyze the results of improved HSLT and discuss possible applications of our new half vector ray differentials.
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    Manifold Next Event Estimation
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Hanika, Johannes; Droske, Marc; Fascione, Luca; Jaakko Lehtinen and Derek Nowrouzezahrai
    We present manifold next event estimation (MNEE), a specialised technique for Monte Carlo light transport simulation to render refractive caustics by connecting surfaces to light sources (next event estimation) across transmissive interfaces. We employ correlated sampling by means of a perturbation strategy to explore all half vectors in the case of rough transmission while remaining outside of the context of Markov chain Monte Carlo, improving temporal stability. MNEE builds on differential geometry and manifold walks. It is very lightweight in its memory requirements, as it does not use light caching methods such as photon maps or importance sampling records. The method integrates seamlessly with existing Monte Carlo estimators via multiple importance sampling.
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    Portal-Masked Environment Map Sampling
    (The Eurographics Association and John Wiley & Sons Ltd., 2015) Bitterli, Benedikt; Novák, Jan; Jarosz, Wojciech; Jaakko Lehtinen and Derek Nowrouzezahrai
    We present a technique to e ciently importance sample distant, all-frequency illumination in indoor scenes. Standard environment sampling is ine cient in such cases since the distant lighting is typically only visible through small openings (e.g. windows). This visibility is often addressed by manually placing a portal around each window to direct samples towards the openings; however, uniformly sampling the portal (its area or solid angle) disregards the possibly high frequency environment map. We propose a new portal importance sampling technique which takes into account both the environment map and its visibility through the portal, drawing samples proportional to the product of the two. To make this practical, we propose a novel, portal-rectified reparametrization of the environment map with the key property that the visible region induced by a rectangular portal projects to an axis-aligned rectangle. This allows us to sample according to the desired product distribution at an arbitrary shading location using a single (precomputed) summed-area table per portal. Our technique is unbiased, relevant to many renderers, and can also be applied to rectangular light sources with directional emission profiles, enabling e cient rendering of non-di use light sources with soft shadows.