1. A method of reducing the size of data representing an image in a graphical display wherein the data comprises triangle strings representing polygons that form the image, the method comprising: determining a size of a pixel in the image; comparing the size of a pixel in the image to a narrowest dimension of a polygon that encompasses the pixel; determining a number of triangles in a triangle string that represents the polygon; if the narrowest dimension of the polygon is larger than the image size, reducing the number of triangles in the triangle string using triangle decimation; and if the polygon is similar to the image size, leaving the number of triangles in the triangle string unchanged.