Objective measurement of erythema in psoriasis using digital color photography with color calibration

Traditional metrics for evaluating the severity of psoriasis are highly subjective, which complicates efforts to identify effective treatments in clinical trials. We propose a method for the objective measurement of the psoriasis severity parameter of erythema (redness). This procedure is standardized for different camera systems and lighting environments through the usage of a color card with predetermined color values in order to calibrate the images. Quantitative measures based on the digital color images are shown to correlate well with subjective assessment of psoriasis severity collected using a standard numerical scale by a panel of dermatologists. Additionally, the color calibration process is shown to improve results.