1. A method of generating a coloured or shaded texture for images to be displayed on a display device or printed, the method including the steps of: (a) providing a plurality of shape elements, each shape element defining a surface; (b) providing each of the shape elements with an opacity which varies over its surface; (c) arranging the shape elements in an overlapping fashion; and (d) rendering the shade elements for output to a printer or display device, such that the overlapping opacities generate a coloured or shaded texture.