Rendering - Experimental Ideas & Implementations 2015

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https://diglib.eg.org/handle/10.2312/12636

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Browsing Rendering - Experimental Ideas & Implementations 2015 by Subject "I.3.7 [Computer Graphics]"

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    Efficient Visibility Heuristics for kd-trees Using the RTSAH
    (The Eurographics Association, 2015) Moulin, Matthias; Billen, Niels; Dutré, Philip; Jaakko Lehtinen and Derek Nowrouzezahrai
    Acceleration data structures such as kd-trees aim at reducing the per-ray cost which is crucial for rendering performance. The de-facto standard for constructing kd-trees, the Surface Area Heuristic (SAH), does not take ray termination into account and instead assumes rays never hit a geometric primitive. The Ray Termination Surface Area Heuristic (RTSAH) is a cost metric originally used for determining the traversal order of the voxels for occlusion rays that takes ray termination into account. We adapt this RTSAH to building kd-trees that aim at reducing the per-ray cost of rays. Our build procedure has the same overall computational complexity and considers the same finite set of splitting planes as the SAH. By taking ray termination into account, we favor cutting off child voxels which are not or hardly visible to each other. This results in fundamentally different and more qualitative kd-trees compared to the SAH.
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    Filtering Environment Illumination for Interactive Physically-Based Rendering in Mixed Reality
    (The Eurographics Association, 2015) Mehta, Soham Uday; Kim, Kihwan; Pajak, Dawid; Pulli, Kari; Kautz, Jan; Ramamoorthi, Ravi; Jaakko Lehtinen and Derek Nowrouzezahrai
    Physically correct rendering of environment illumination has been a long-standing challenge in interactive graphics, since Monte-Carlo ray-tracing requires thousands of rays per pixel. We propose accurate filtering of a noisy Monte-Carlo image using Fourier analysis. Our novel analysis extends previous works by showing that the shape of illumination spectra is not always a line or wedge, as in previous approximations, but rather an ellipsoid. Our primary contribution is an axis-aligned filtering scheme that preserves the frequency content of the illumination. We also propose a novel application of our technique to mixed reality scenes, in which virtual objects are inserted into a real video stream so as to become indistinguishable from the real objects. The virtual objects must be shaded with the real lighting conditions, and the mutual illumination between real and virtual objects must also be determined. For this, we demonstrate a novel two-mode path tracing approach that allows ray-tracing a scene with image-based real geometry and mesh-based virtual geometry. Finally, we are able to de-noise a sparsely sampled image and render physically correct mixed reality scenes at over 5 fps on the GPU.
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    High Performance Non-linear Motion Blur
    (The Eurographics Association, 2015) Guertin, Jean-Philippe; Nowrouzezahrai, Derek; Jaakko Lehtinen and Derek Nowrouzezahrai
    Motion blur is becoming more common in interactive applications such as games and previsualization tools. Here, a common strategy is to approximate motion blur with an image-space post-process, and many recent approaches demonstrate very efficient and high-quality results [Sou13,GMN14]. Unfortunately, all such approaches assume underlying linear motion, and so they cannot approximate non-linear motion blur effects without significant visual artifacts.We present a new motion blur post-process that correctly treats the case of non-linear motion (in addition to linear motion) using an efficient curve-sampling scatter approach. We simulate plausible non-linear motion blur in 4ms at 1920 1080 and our approach has many desirable properties: its cost is independent of geometric complexity, it robustly estimates blurring extents to avoid typical over- and under-blurring artifacts, it supports unlimited motion magnitudes, and it is less noisy than existing techniques.
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    Interactive Global Illumination Effects Using Deterministically Directed Layered Depth Maps
    (The Eurographics Association, 2015) Aalund, Frederik Peter; Frisvad, Jeppe Revall; Bærentzen, Jakob Andreas; Jaakko Lehtinen and Derek Nowrouzezahrai
    A layered depth map is an extension of the well-known depth map used in rasterization. Multiple layered depth maps can be used as a coarse scene representation. We develop two global illumination methods which use said scene representation. The first is an interactive ambient occlusion method. The second is an interactive singlebounce indirect lighting method based on photon differentials. All of this is implemented in a rasterization-based pipeline.
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    MBVH Child Node Sorting for Fast Occlusion Test
    (The Eurographics Association, 2015) Ogaki, Shinji; Derouet-Jourdan, Alexandre; Jaakko Lehtinen and Derek Nowrouzezahrai
    Optimal BVH layout differs among ray types. To accelerate shadow rays, the use of a specialized traversal order, optionally with an additional data structure has been proposed. In this paper we show how sorting child nodes of MBVH (Multi Bounding Volume Hierarchy) improves the performance of occlusion test without changing the topology of the data structure.We introduce a cost metric suitable for MBVH which takes into account the distribution of representative rays, and prove that the cost can be minimized by sorting child nodes based on a very simple criterion. Our method is very easy to implement and requires only small amounts of storage and preprocessing time for sorting. We also demonstrate how rendering performance can be improved by up to 10% in conjunction with various algorithms.
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    Practical Rendering of Thin Layered Materials with Extended Microfacet Normal Distributions
    (The Eurographics Association, 2015) Guo, Jie; Qian, Jinghui; Pan, Jingui; Jaakko Lehtinen and Derek Nowrouzezahrai
    We propose a practical reflectance model for rendering thin transparent layers with different sides varying in roughness and levels of gloss. To capture the effect of subsurface reflection, previous methods rely on importance sampling for each light-surface interaction. This soon becomes a computationally demanding task since a recursive sampling scheme is required to handle multiple internal reflections. In this paper, we first provide a comprehensive analysis of the relationship between the directional distribution of scattered light and the roughness of each layer boundary using joint spherical warping. Based on the analysis, we generalize the traditional microfacet theory for layered materials and introduce the extended normal distribution function (ENDF) to accurately model the behavior of subsurface reflection. With the ENDF, the number of sampling processes can be reduced to only once for each bounce of subsurface reflection. We demonstrate that our BSDF model based on the ENDF is easy to be implemented on top of Monte Carlo sampling based offline renderers and it incurs little computational overhead. Moreover, it can be also efficiently used in real-time applications with the help of GPU acceleration.