1. A method of modifying half-toned pixel data for a selected pixel that contains black and does not contain a predetermined non-black primary color, the current pixel being in a half-tone cell for the predetermined non-black primary color, comprising: obtaining half-toned data for any pixels in neighboring half-tone cells for the predetermined non-black primary color that have a same intra-cell position as the selected pixel; if any of the obtained half-toned pixel data contains the predetermined non-black primary color and does not contain black, modifying the half-toned pixel data for the selected pixel to include the predetermined non-black primary color.