Photometric calibration is the process of determining the relationship between the output of a digital imaging system (such as a camera) and the actual physical light intensity in a scene. This calibration is essential for accurately measuring or estimating attributes such as color, brightness, and texture from images. By calibrating the imaging system, researchers are able to ensure that the measurements taken from the images are reliable and consistent across different scenes and lighting conditions. Various techniques are used for photometric calibration, including using known reference objects in the scene, capturing images under controlled lighting conditions, and using specialized calibration charts or targets.