Path-space manipulation of physically-based light transport

Computer graphics artists often resort to compositing to rework light effects in a synthetic image without requiring a new render. Shadows are primary subjects of artistic manipulation as they carry important stylistic information while our perception is tolerant with their editing. In this paper we formalize the notion of global shadow, generalizing direct shadow found in previous work to a global illumination context. We define an object's shadow layer as the difference between two altered renders of the scene. A shadow layer contains the radiance lost on the camera film because of a given object. We translate this definition in the theoretical framework of Monte‐Carlo integration, obtaining a concise expression of the shadow layer. Building on it, we propose a path tracing algorithm that renders both the original image and any number of shadow layers in a single pass: the user may choose to separate shadows on a per‐object and per‐light basis, enabling intuitive and decoupled edits.

Section: Related Workmentioning

confidence: 99%

Section: Limitations and Extensionsmentioning

confidence: 99%

Global Illumination Shadow Layers

Desrichard

Vanderhaeghe

Paulin

2019

“…On a higher level of abstraction, spherical plots and particle flow tools allow selective inspection of light transport [RKRD12]. Edge bundling [HvW09] applied to light path visualization reduces visual clutter and supports artists in path re‐targeting [SNM*13]. Comparison of light transport in different scene setups has so far not been handled.…”

Section: Related Workmentioning

confidence: 99%

Applying Visual Analytics to Physically Based Rendering

Simons¹,

Herholz

Petitjean

et al. 2018

Physically based rendering is a well‐understood technique to produce realistic‐looking images. However, different algorithms exist for efficiency reasons, which work well in certain cases but fail or produce rendering artefacts in others. Few tools allow a user to gain insight into the algorithmic processes. In this work, we present such a tool, which combines techniques from information visualization and visual analytics with physically based rendering. It consists of an interactive parallel coordinates plot, with a built‐in sampling‐based data reduction technique to visualize the attributes associated with each light sample. Two‐dimensional (2D) and three‐dimensional (3D) heat maps depict any desired property of the rendering process. An interactively rendered 3D view of the scene displays animated light paths based on the user's selection to gain further insight into the rendering process. The provided interactivity enables the user to guide the rendering process for more efficiency. To show its usefulness, we present several applications based on our tool. This includes differential light transport visualization to optimize light setup in a scene, finding the causes of and resolving rendering artefacts, such as fireflies, as well as a path length contribution histogram to evaluate the efficiency of different Monte Carlo estimators.

“…Numerous techniques allow a (possibly) non‐physical manipulation of light, which can be controlled directly as in the Bendy‐Lights method of Kerr et al [KPD10] or indirectly as in Nowrouzezahrai et al [NJS*11] for artistic volumetric lighting. Schmidt et al [SNM*13] combined both direct and indirect interactions, allowing manipulation of light paths and retargeting of paths according to edits in the scene. In the field of material editing, recent strides have been made by Hašan and Ramamoorthi [HR13], who built a material designer to interactively set the local (single‐scattering) albedo coefficients and by Klehm et al [KISE14], who enabled stylized property and lighting manipulation of static volumes.…”

Section: Related Workmentioning

confidence: 99%

“…Therein, lighting is not only essential to set the mood of a scene, but also to guide attention and achieve depth and realism. In existing light manipulation methods, such as path‐space manipulation [SNM*13], the light transport simulation starts anew every time an element in the scene changes. While much work pushed consistent, progressive light transport for faster convergence [GKDS12, HPJ12, KD13], individual effects such as sharp caustics may still take a long time to converge.…”

Section: Introductionmentioning

confidence: 99%

Consistent Scene Editing by Progressive Difference Images

Günther¹,

Grosch

2015

Even though much research was dedicated to the acceleration of consistent, progressive light transport simulations, the computation of fully converged images is still very time‐consuming. This is problematic, as for the practical use in production pipelines, the rapid editing of lighting effects is important. While previous approaches restart the simulation with every scene manipulation, we make use of the coherence between frames before and after a modification in order to accelerate convergence of the context that remained similar. This is especially beneficial if a scene is edited that has already been converging for a long time, because much of the previous result can be reused, e.g., sharp caustics cast or received by the unedited scene parts. In its essence, our method performs the scene modification stochastically by predicting and accounting for the difference image. In addition, we employ two heuristics to handle cases in which stochastic removal is likely to lead to strong noise. Typical scene interactions can be broken down into object adding and removal, material substitution, camera movement and light editing, which we all examine in a number of test scenes both qualitatively and quantitatively. As we focus on caustics, we chose stochastic progressive photon mapping as the underlying light transport algorithm. Further, we show preliminary results of bidirectional path tracing and vertex connection and merging.