Visualization of Coherent Structures of Light Transport

Abstract

Inspired by vector field topology, an established tool for the extraction and identification of important features of flows and vector fields, we develop means for the analysis of the structure of light transport. For that, we derive an analogy to vector field topology that defines coherent structures in light transport. We also introduce Finite-Time Path Deflection (FTPD), a scalar quantity that represents the deflection characteristic of all light transport paths passing through a given point in space. For virtual scenes, the FTPD can be computed directly using path-space Monte Carlo integration. We visualize the FTPD field for several example scenes and discuss the revealed structures. Lastly, we show that the coherent regions visualized by the FTPD are closely related to the coherent regions in our new topologically-motivated analysis of light transport. FTPD visualizations are thus also visualizations of the structure of light transport.

Light Shapes

“…A distinctive feature of our approach is visualizing light in the whole volume of a scene. Zirr et al (2015) commented that many of the recent visualization techniques focus on local regions only; therefore, in order to understand the global picture, a user should manually place a visualization tool around a scene to explore it. The main idea of this article is to extract important properties of light and visualize them as a 3D flow.…”

“…In comparison with existing light visualization approaches, our tool has a number of advantages. As Reiner et al (2012) stated, many of the existing methods are very complex and allow only experts to analyze the light transport (Durand et al 2005;Ramamoorthi et al 2007;Zirr et al 2015). Contrarily, we convert measurement results of complex natural light into three perceptually meaningful parameters that are intuitive also to nonexpert users.…”

“…This framework was extended by Ramamoorthi et al (2007) to gradient analysis of the basic shading steps, showing the relationship between spatial and angular effects on appearance. The technique of Zirr et al (2015) provides information about the amount of light scattering in the neighborhood of a given point. Although they produce visualizations of light throughout the whole scene, their approach seems to be hard to grasp without understanding vector field topology and also quite time consuming, since the stated computation time ranges from 1 to 5 hours.…”

“…The visualization of light transport, which shows the propagation of light through a known 3D environment, is gaining attention in the computer graphics field. Many researchers (Reiner et al 2012;Schmidt et al 2013Schmidt et al , 2016Zirr et al 2015) acknowledge the difficulty of light transport analysis and visualization because light travels in every possible direction through any point in an empty space and interacts in a complicated manner with the environment. There are a number of studies on volumetric light visualization (see Section 2.1), yet many of those provide analyses that are too complex for many users in the lighting design realm.…”

Applying Visual Analytics to Physically Based Rendering

“…One important technique within this field is dimensionality reduction. Within light transport, this has been used on quantities such as the irradiance vector field indicating the dominant light direction [CWW11] or finite-time path deflection [ZAD15]. while useful in the broader scope, such information compression may aggravate the analysis within complex scenes if only slight changes take place.…”