What Is the Role of Color in Dermoscopy Analysis?

For the last two decades, several Computer-Aided Diagnosis (CAD) systems have been developed with the aim of aiding dermatologists to classify Pigmented Skin Lesions (PSL). The majority of these systems usually rely on shape-, colorand texture-based features to classify the lesions. Even though some systems have already achieved good results, the ideal set of features, to be extracted from the images, remains unknown. A possible course of action to determine the best set of features is to separately assess their role. The aim of this thesis is to assess what is the role of color in dermoscopy analysis and to determine which descriptor performs best, considering a rich set color spaces and color descriptors. In order to fulfill this goal, two different CAD systems, whose classification is solely based on color features, were developed. The first is based on the principle that lesions are uniform and can be represented by a set of global parameters. This approach has been adopted by the majority of the works described in the literature. On the opposite, the second system does not regard lesions as homogeneous and, thus, does not use a single model to represent them. Therefore, in this system, lesions are divided into several patches which are considered to contain uniform parts of the lesions. Both systems were tested by using three different types of color descriptors and two different classifiers. Furthermore, the dermoscopy images were, separately, represented by using seven different color spaces. The best performance (SE = 100% and SP = 93%) was achieved by both CAD systems using the unidimensional color histogram as the image descriptor and images represented in the opponent color space. These results show that color features play a major role in dermoscopy analysis.