Photometric camera characterization from a single image with invariance to light intensity and vignetting

摘要

Photometric characterization of a camera entails describing how the camera transforms the light reaching its sensors into an image and how this image can be defined in a standard color space. Although the research in this area has been extensive, the current literature lacks practical methods designed for cameras operating under near light. There are two major application scenarios considered in this paper that would benefit from this type of approaches. Camera rigs for minimally-invasive-procedures cannot be calibrated in the operating room with the current methods. This comes from the fact that existing approaches need multiple images, assume uniform lighting, and/or use over-simplistic camera models, which does not allow for the calibration of near light setups in a fast and reliable way. The second scenario refers to the calibration of cellphone cameras, which currently cannot be calibrated at close range with a single image, specially if the flash is used, as there would be non-uniform lighting on the scene. In this work, we describe a method to characterize cameras from a single image of a known target. This enables both geometric and photometric calibrations to be performed on-the-fly without making assumptions on the vignetting nor on the spatial properties of the light. The presented method showed good repeatability and color accuracy even when compared to multiple-image approaches. Applications to laparoscopic cameras, generic cameras (such as cellphone cameras), and cameras other than trichromatic are shown to be viable.