Validation of the Cycles render engine for creation of physically correct lighting models. 2019-01-1004

It is often desired to depict an accident scene using images or video in a manner that fairly and accurately represents what an observer could see at the actual scene. This can be accomplished by taking calibrated photographs or video of a recreated scene with substantially similar lighting conditions. This process requires significant coordination of the physical features at the scene. It can also be difficult to precisely control the motion and timing of moving features such as pedestrians and vehicles. The result is fixed in that the you capture specific scenarios with specific conditions with the selected field of view and perspective of the cameras used. Alternatively, three -dimensional computer modeling and physically-based rendering (PBR) can be used to recreate an accident scene to produce images and video that fairly and accurately represents what an observer could see at the actual scene. PBR is a rendering method to create synthetic images and video by accurately simulating how light interacts in the three -dimensional environment. Specifically, the process presented in this paper utilizes the Cycles render engine within Blender. This allows for the accident scene to be recreated in a three-dimensional environment including the natural and artificial light sources. As we are concerned with accurately representing the light in the scene, it is necessary to create light sources within Cycles that represent the real-world light sources. The light sources in Cycles are quantified by several variables, including strength, color, and size. The strength and size variables determine the self-emitted radiance of the light source and requires further explanation to determine the relationship between these variables in Cycles and real-world lighting quantities. The color variable describes the light color as either an RGB value or as a color temperature value. In this paper, we define and validate the relationship between strength units in Cycles and real-world lighting and provide a method to create a three-dimensional scene with correct natural and artificial lighting to accurately and fairly depict a scene with respect to lighting, visibility and contrast. This was accomplished by taking photographs, luminance and illuminance measurements of an exemplar scene under varying light conditions. The exemplar scene, including the lighting, was created in Blender and the luminance values of the computer-generated scene were compared to the luminance values measured at the scene. The final rendered images were also qualitatively compared to the calibrated photographs taken at the scene.