The sharpness of the lesion boundary and the contrast between the lesion and the surrounding skin
provide important diagnostic information in the assessment of pigmented skin lesions. This paper presents a
new method for computing these parameters by employing an edge model based on a sigmoid function. For
each radial profile of the lesion, optimal parameters are found by using an iterative least-squares method. The
level and nature of variability of these parameters along the boundary will be correlated with lesion diagnosis
in a future study. The method also returns the location equivalent to “zero-crossing” for each profile, thus
producing a lesion outline. Additionally, the spread of the pigment beyond the zero-crossing point is
computed, thus showing the lesion extent
