Luminance maps from High Dynamic Range imaging: calibrations and adjustments for visual comfort assessment

Luminance maps created on the basis of High Dynamic Range Imaging (HDRI) is a technique increasingly used to study the visual environment. But creating HDR images with commercially affordable equipment requires an extensive calibration process to ensure that luminance data and derived spatial information is correct. This paper aims to provide an overview of the necessary steps for the most commonly used HDR calibration process, based on the self-calibration routines in hdrgen/Photosphere. It also addresses commonly made mistakes and aspects requiring special attention. The described steps are: the capture of multiple exposure photographs, the response curve derivation, the HDR image generation, the vignetting and neutral density filter correction, the calibration adjustment by spot luminance measurement and the geometrical reprojection. A detailed description of the geometrical reprojection is included in this paper, since this topic has not yet been described in the literature relating to HDRI, although needed for certain lens types and glare analysis.