Real Illumination from Virtual Environments

Teaser 1 Teaser 2
Left: Room simulating normal lighting. Right: Room simulating Grace Cathedral.
Abhijeet Ghosh , Matthew Trentacoste , Helge Seetzen , Wolfgang Heidrich

Abstract

We introduce a method for actively controlling the illumination in a room so that it is consistent with a virtual world. In combination with a high dynamic range display, the system produces both uniform and directional illumination at intensity levels covering a wide range of real-world environments. It thereby allows natural adaptation processes of the human visual system to take place, for example when moving between bright and dark environments. In addition, the directional illumination provides additional information about the environment in the user's peripheral field of view. We describe both the hardware and the software aspects of our system. We also conducted an informal survey to determine whether users prefer the dynamic illumination over constant room illumination in an entertainment setting.

Active Lighting Setup

In our prototype implementation, we focus on methods that could conceivably be used in entertainment applications, such as gaming environments or home theaters. We use computer-controlled LED lights thatare distributed throughout the room. All lights are individually programmable to a 24 bit RGB color. This setup allows us not only to raise or lower the ambient light in the room, but also to create some degree of directional illumination, which results in a low-resolution dynamic room illumination approximating an environment-map for the assumed viewing position. Although the light sources are located outside of the user's direct field of view, the directional illuminationinteracts with objects inside the field of view, such as the monitor or the wall behind it. The goal of our system is to illuminate the room so that it matches a low-frequency version of the virtual scene.

The lighting system consists of 24 RGB LED lights (ColorKinetics iColor Cove), each of which can be individually programmed to a 24 bit RGB color value. We used seven poles with stands to mount the 24 light sources. The lights were positioned and oriented such that they predominantly illuminated the ceiling, as well as the walls to the left, right and in front of the viewer.

light modifications Undiffused Diffused
Left: LED Diffuser setup. Center: Undiffused LED strip. Right: Diffused LED strip.

To create a smoothly varying illumination pattern we used strong diffusers at the light sources, which also reduce color separation of the RGB elements. The diffuser for each light consist of 2" diameter transparent acrylic tubing that was cut in half along its axis, and spray-painted lightly on the outside with white plastic paint (Krylon Fusion for plastic). To avoid internal reflection losses we used reflective film to coat the inside of the light source.

Calibration

Some calibration steps are necessary in order to control the system in a way consistent with the virtual world and the image shown on the display. Geometric calibration is necessary to determine the positions of the light sources relative to the viewer, and their spread, which is modeled as a Gaussian. Photometric calibration is subsequently performed to match white points and illumination levels between the light sources and the display.

Basis images
Images of the basis functions recovered for each of the lights.

To obtain geometric calibration information, we place a reflective ball at the intended viewer position to act as a light probe. We take photographs with a web camera (Creative NX Ultra) while switching on one light at a time. We then model the impact of every light source by fitting a Gaussian to the environment map. It is centered around the direction corresponding to the brightest point in the environment map, and its standard deviation is chosen such as to minimize the RMS error.

Experiments

To test the concept, we conducted an user survey with a set of three experiments. As the evaluation criterion, we chose user preference rather than other possible criteria such as perceived realism. This choice was made due to our primary interest in entertainment applications for the current system.

Light Dark

We tested the preference of participants for directionally uniform illumination level over constant room illumination with an HDR driving video. We then tested the preference of participants for directionally localized illumination changes over uniform brightness changes with a rotation interface to explore HDR panoramas. Finally, to test the usefulness of the lighting system in combination with low-dynamic range displays, the participants were shown a footage from "Need for Speed Underground 2" on a conventional display. Comprehensive presentation of the results can be found in the paper.

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