Psoriasis is an inflammatory cutaneous disease of unknown origin, characterized by the appearance of red, itchy, and scaly plaques of abnormal skin. One of the most important issues that guides treatment of psoriasis is to evaluate the degree of the illness determining the psoriasis and area severity index (PASI). Dermatologists usually use visual and tactile senses to assess lesion severity, involving a subjective judgment depending on the medical practitioner. For this purpose, we propose an image processing system based on photometric stereo acquisition technique and adapted analysis criteria to evaluate skin parameters. This diagnosis aided system gives an objective and accurate evaluation of skin erythema (redness), skin thickness, and scaling, which are the three clinical parameters, with the area of lesioned skin, that determine PASI score. Thus, we estimate the intensity of erythema from the albedo map and thickness from the three-dimensional estimation of the skin surface. Finally, the combination of color and geometry results allows identifying and quantifying the skin scaling. A validation protocol with an image database that covers all parameter variation ranges is proposed, and the results show a high correlation with dermatologist scores.
In dermatology, image processing allows non-contact and non-invasive metrological measurements. Psoriasis is an incurable skin disease with an unknown origin. One of the most important tasks in the treatment of psoriasis is to evaluate the degree of the illness following a severity score. Dermatologists use visual and tactile senses to assess the lesions severity. In this article, we propose an automated methodology for assessing objectively the severity of psoriasis by measuring the physical parameters of the skin. Thus, from the colorimetry and geometry obtained by photometric-stereo, we determine the level of erythema and skin thickness. Our results show that for a low acquisition time, the scores obtained are highly correlated with those of dermatologists.