1. A method for displaying an image at a desired level of opacity on a pixel-oriented display of a computer, said image being formed by a plurality of rows of tiles, each tile having a predetermined number of pixels, comprising the steps of: (a) determining the desired level of opacity of the image; (b) selecting a dither pattern corresponding to the desired level of opacity; (c) displaying the pixels in each tile in a row according to the dither pattern; (d) creating a new dither pattern by shifting the dither pattern by a random number of bits; (e) displaying the pixels of each tile in another row corresponding to the new dither pattern; repeating steps (d) and (e) for each row of said image.