ABSTRACT
Vitiligo is an acquired pigmentary skin disorder and the vitiligous areas are visually paler in contrast to normal skin or completely white due to the lack of pigment melanin. The course of vitiligo is unpredictable where the vitiligous skin lesions may remain stable for years before worsening. To monitor the efficacy of vitiligo treatments, dermatologists observe the disease directly, or indirectly over time using digital photos based on the Physician's Global Assessment (PGA) scale. The progression of vitiligo treatment can be very slow and can take more than 6 months. It is observed that dermatologists find it visually hard to determine the areas of skin repigmentation due to this slow progress and thus the observations are made after a longer period. Here, a tool that enables dermatologists to determine and quantify areas of repigmentation objectively over a shorter period during treatment has been developed using digital image processing techniques. Fundamentally, skin colour is due to the combination of skin histological parameters, namely pigment melanin and haemoglobin. However, in digital imaging, colour is produced by combining three different spectral bands, namely red, green and blue (RGB) but with appropriate processing, spatial distributions of melanin and haemoglobin in skin image could be determined. Using principal component analysis as a dimensional reduction tool, the two-dimensional subspace can be represented by its first and second principal components. Independent component analysis is employed to convert the two-dimensional subspace into skin images that either represent skin areas due to melanin or haemoglobin. From the melanin skin image, vitiligous skin lesions are identified as skin areas that lack melanin and segmented. The difference in the vitiligous surface areas between skin images before and after treatment will be expressed as a percentage of repigmentation in each vitiligo lesion. Results of preliminary and preclinical trial study show that the vitiligo monitoring system is able to determine repigmentation progression objectively and thus treatment efficacy on a shorter time period. It is found that all the percentages obtained using the system are within the PGA range as verified by dermatologists. Thus, the vitiligo monitoring system is highly accurate and found consistent in comparison to PGA performed by dermatologists.
