PASI Area and Erythema Scoring using YIQ Color Space

Psoriasis is an autoimmune inflammatory #skindisease, afflicting skin with red plaques that are usually covered with silvery, white scales. Many treatments exist to control psoriasis; however, unfortunately there is no definite cure. PASI (Psoriasis Area and Severity Index) measures psoriasis severity by evaluating the area, #erythema, scaliness, and thickness of the plaques, and is the gold standard method used to assess treatment performance. PASI parameters are calculated by #dermatologists manually, a time-consuming process that can lead to inconsistent and diverse results. This paper presents a computer-based automatic method to measure the area and erythema parameters of PASI. In the proposed method YCbCr and YIQ color spaces are used, and clustering is done using the K-means algorithm. Seventeen patients have been assessed in this study, and the results of ten patients with different erythema scores are presented in this paper. Results of this study showed that the proposed method is highly accurate. Other advantages of the proposed method include: differentiating moles and scars from #psoriasis patches, omitting light reflections, and reducing the calculation time by using color spaces which have linear transformation from the RGB color space.