1. A method of assigning colours to an image or part thereof, comprising: selecting a sequence of colours for assignment to the image or part thereof; determining a minimum intensity I MIN within the image or part thereof; determining a maximum intensity I MAX within the image or part thereof; and determining relative intensity values RIV(i) for each pixel or voxel i according to: RIV ( i ) = f ( I ( i ) - I M IN I M AX - I M I N ) where I(i) is an intensity of pixel or voxel i, and ƒ is a preselected function (such as to re-arrange the normalized values); and assigning colours to at least some pixels in the image or part thereof based on the relative intensity values and an order of each of the colours in the sequence.