Quick Approximation of Camera´s Spectral Response from Casual Lighting

Knowing the RGB spectral sensitivities of a camera is useful for several image processing applications. However, camera manufacturers seldom provide this information. Calibration methods for determining them can be daunting, requiring either sophisticated instruments or carefully controlled lighting. This paper presents a quick and easy method that provides a reasonable approximation of the camera response functions with only a color chart and casual unknown illuminations. Our approach is enabled by careful design of the cost function that imposes several constraints on the problem to make it tractable. In the components of the cost function, the Luther condition provides the global shape prior and the commercial lighting systems with unknown spectra provide narrow spectral windows for local reconstruction. The quality of reconstruction is comparable with other methods that use known illumination.