An optical model of the appearance of blemishes in digital photographs
Adrian Zamfir, Alexandru Drîmbărean, Marta Zamfir, Vasile V. Buzuloiu, Eran Steinberg, Dan C. Ursu · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 2007
Changing the lens of a DSLR camera has the drawback of allowing small dust particles from the environment to be attracted onto the sensors' surface. As a result, unwanted blemishes may compromise the normally high quality of photographs. The particles can be removed by physically cleaning the sensor. A second, more general approach is to locate and remove the blemishes from digital photos by employing image processing algorithms. This paper presents a model that allows computing the physical appearance (actual size, shape, position and transparency) of blemishes in a photograph as a function of camera settings. In order to remove these blemishes with sufficient accuracy, an initial algorithm calibration must be performed for any given pair camera-lens. The purpose of this step is to estimate some parameters of the model that are not readily available. To achieve this, a set of "calibration images" must be carefully taken under conditions that will allow the blemishes to become easily identifiable. Then, based on the metadata stored in the photo's header, the actual appearance of the blemishes in the given photograph is computed and used in the automatic removing algorithm. Computing formulas and results of our experiments are also included.