Random forest based erythema grading for psoriasis

Psoriasis Area and Severity Index, or PASI score [7] is one of the most prevalent scoring indices for Psoriasis. Erythema or redness of skin is an important identifier for evaluation of PASI score. Extra subjectiveness in the evaluation of erythema has been observed, since the perception of redness can be influenced by the skin tone, ambient lighting and many other such factors which are difficult to control in a clinical setting. We propose a novel colorimetric feature for erythema grading by extending the tissue-photon interaction model [12] to make it skin tone independent. We propose to use Skellam distribution statistics as feature vectors for erythema grading. We present a random forest based technique for classification of erythema regions in Psoriasis into severe, moderate and slight categories.