A Method for Digital Video Camera Calibration for Luminance Estimation 2017-01-1368
Mapping the luminance values of a visual scene is of broad interest to accident reconstructionists, human factors professionals, and lighting experts. Such mappings are useful for a variety of purposes, including determining the effectiveness and appropriateness of lighting installations, and performing visibility analyses for accident case studies. One of the most common methods for mapping luminance is to use a spot type luminance meter. This requires individual measurements of all objects of interest and can be extremely time consuming. Luminance cameras can also be used to create a luminance map. While luminance cameras will map a scene’s luminance values more quickly than a spot luminance meter, commercially available luminance cameras typically require long capture times during low illuminance (up to 30 seconds). Previous work has shown that pixel intensity captured by consumer-grade digital still cameras can be calibrated to measure luminance. Taking a digital still image and converting this image into a luminance map even further reduces the measurement time. Regardless of whether one uses a digital still camera, luminance camera, or a spot type luminance meter, there is still the constraint that the user must be stationary in the scene for some period of time. This can be challenging if capturing a luminance map of an open roadway is desired, especially if the user will be capturing luminance from a driver’s perspective and location in a vehicle. In this paper, the authors present a methodology for calculating luminance from a digital video camera. The presented methodology allows for the user to mount a camera near the driver’s eye location and to drive through a scene capturing video. Still images from the video are then exported and analyzed, creating a luminance map. The resulting luminance estimates were compared to luminance values measured with a Konica Minolta LS-100 and our methods were shown to result in repeatable and accurate luminance measurements of an entire scene utilizing a quick, simple and safe capturing technique.