1. A method of quantifying the extent of erythema around a wound of a patient, the method comprising the steps of: capturing an image that includes the wound, the erythema and surrounding skin; defining a border of the wound; performing a distance transform on an area of the image between the wound border and a boundary of the image to determine bands of pixels, wherein the pixels within each said band are equidistant from the wound border; calculating a representative value for each said band; defining a threshold level relative to the representative value of the surrounding skin; identifying an erythema boundary as the band having a representative value closest to the threshold level; and calculating a characteristic value to quantify the region within the erythema boundary.