A method of quantifying the extent of erythema around a wound of a patient is disclosed. An image (200) is captured that includes the wound, the erythema and surrounding skin. A border of the wound is identified (step 232) and a distance transform is performed (step 234) on an area of the image between the wound border and a boundary of the image to determine bands of pixels (226, 228, 230), wherein the pixels within each band are equidistant from the wound border. A representative value such as average brightness is calculated for each band (step 238), and a threshold level is defined relative to the representative value of the surrounding skin (step 240). The extent of the erythema is then calculated.