1. A method for culling small objects in a system for shading 3-dimensional computer graphics images comprising the steps of: subdividing a display on which an image is to be viewed into a plurality of rectangular areas; for each rectangular area deriving a list of objects in the image which may be visible in that rectangular area; using the list of objects to determine how the rectangular area should be shaded for display; characterized in that the step of deriving a list of objects comprises the step of; determining maximum and minimum values for each object in x and y directions; for each object in the image, determining a bounding box from the maximum and minimum values of the x and y coordinates of the object; determining a set of pixel sampling points from the maximum and minimum values; determining whether or not a bounding box surrounding the object covers any of the pixel sampling points; culling the object if the bounding box misses all the pixel sampling points; testing each sampling point against each edge of the object; determining from the test performed whether or not the object covers any pixel sampling point; and adding or rejecting the object from the list in dependence on the result of the determination.