Practical photoquantity measurement using a camera

Abstract

An image output by a camera is generally not a faithful representation of the real scene, because it undergoes a series of radiometric disturbances during the imaging process. This paper proposes a method for obtaining a more accurate measure of the light seen by a camera. Our method requires no specific calibration apparatus and only minimal supervision. Nevertheless, it is quite comprehensive, since it accounts for response function, exposure, vignetting, spatial non-uniformity of the sensor and colour balancing. Our method works in two steps. First, the camera is calibrated off-line, in a photoquantity sense. Then, the photoquantity of any scene can be estimated in-line. Our method is therefore geared to a wide range of computer vision applications where a camera is expected to give a measurement of the visible light. The paper starts by presenting a photoquantity model of the camera imaging process. It then describes the key steps of calibration and correction method. Finally, results are given and analyzed to evaluate the relevance of our approach.

Improving Local Adaptive Filtering Method Employed in Radiometric Correction of Analogue Airborne Campaigns

“…The resulting mosaic is displayed on Figure 1 and presents some radiometric inhomogeneities that seem to follow a similar pattern confirmed by considering the mean of the images as shown on Figure 2. This pattern is due to a combination of several factors: some of them are linked to external parameters, like the hotspot (Teng et al, 1997), a sum of retro-specular phenomena caused by the way aerosol and ground are interacting with sunbeams, and some to internal parameters, like the lens vignetting (Dehos et al, 2012).…”