A new method of skin erythrosis evaluation in digital images

In the clinical field, reproducible and comparable assessments of skin color are needed for objective evaluation of lesions and efficacy of treatments. In order to provide objective, quantitative color information in skin lesions, devices such as reflectance spectrophotometer and reflectance colorimeter have been successfully used during the past decade, though they are too expensive and technically complex to be handled in routine clinical situations. Reflectance skin color measurements require direct contact of the probe with the skin, and the compression significantly influences readings. Color measurements obtained from digitized images have been proposed as a simple and cost-effective way to evaluate skin color and promote efficacy of treatments. The disadvantage is its direct and close relation to the ambient light: even if an accurate control of subject illumination is provided, readings vary between different laboratories. We propose a standard system for computerized color image analysis of skin erythrosis modification after Intense Pulsed Light (IPL) treatments, making it possible to compare readings taken by different observers in different environmental light conditions. The goal of our study is the introduction of fixed color internal controls in digital imaging in order to calculate a normalization factor of measurements, resulting not in a method of absolute quantification of erythema or erythrosis but in a method that provides the possibility of translation and comparison of the red values between systems in different environmental conditions. Between December 2004 and May 2005 we evaluated 30 patients at the Department of Plastic and Reconstructive Surgery at the University "La Sapienza" of Rome. Three points of standard colored paper (Red Green Blue) were applied with a plastic pattern (standard intersection lines) and white point in non involved area for skin control. For every patient we took a series of pictures pre-treatment and after a standard cycle of 5/6 IPL. We evaluate the grade of reproducibility of our procedure with a careful analysis of pre-treatment digital images obtained in different environmental conditions. The statistic analysis of the standard deviation between the values of R obtained (using different light conditions), and the respective normalized valor (normalized to the referent image), did not show any significant statistical difference and allows us to achieve our goal: the reproducibility of the results.