Matrix-based analysis of digital images: application to goniophotometric measurements with variable referential

Digital video-based luminance mapping systems require the establishment of a precise relation between the considered spatial referential and the associated pixel coordinates on the image. Such a relation may vary with the measurement conditions, and an adjustment of the geometric calibration therefore becomes necessary. In this paper, a methodology for adapting the image calibration according to the referential transformations is proposed, based on the use of a set of matrices individually associated to each spatial coordinate. These matrices are modified with analytical conversions in order to define the actual measurement situation. The description of this approach is given through an application example on a recent bidirectional goniophotometric device, based on digital imaging, proving the consistency of the adopted methodology.