1. A method of measurement of mitotic activity from histopathological specimen image data, the method comprising the steps of: a) identifying pixels in the image data having luminances associated with mitotic figures; b) selecting from among the identified pixels a reference pixel which is sufficiently close in position and luminance to another identified pixel to provide a reference colour; c) locating pixels in the image data with luminances sufficiently close to that of the reference colour to indicate potentially mitotic figures; d) incrementing image regions corresponding to potentially mitotic figures from the located pixels by adding pixels thereto, potential increments to image regions being implemented or rejected by according to whether or not their luminances are sufficiently close to respective image region luminances and sufficiently far from an image data background luminance; e) selecting grown image regions on the basis of thresholds for image region area, compactness and width/height ratio; and f) counting selected grown image regions as actually indicating mitotic figures on the basis of a threshold for number of such regions.