Luminance maps from High Dynamic Range imaging: photometric, radiometric and geometric calibrations

Luminance maps created on the basis of High Dynamic Range Imaging is a technique increasingly used to study the visual environment. But creating HDR images with commercially affordable equipment requires a tedious calibration process, during which several steps could go wrong without anyone noticing it. This paper aims to provide an overview of the HDR calibration process, including different options, attention points and common mistakes. For inaccuracies and errors to be more easily detected and corrected, it is essential to understand each transformation applied to the images. Therefore, the capture of multiple exposure photographs, the response curve derivation, the HDR image generation, the vignetting and neutral density filter correction, the absolute calibration, and the geometrical reprojection stages are addressed. A more detailed description of the geometrical reprojection, especially required when working on glare assessment, is given as this topic has not yet been dealt with in the literature.