1. A method of rendering an image comprising at least one light source, a first, shadow-casting object with a second, shadow-receiving object located on the side of the first shadow-casting object remote from said at least one light source, the method comprising: generating a shadow mask which identifies for each of a plurality of pixels on the shadow receiving surface a grey level representing the intensity of shadow in each pixel, the intensity being determined utilizing the distance between the shadow-casting object and the shadow-receiving object.