To control printing in a printer image data of an edge region of a printing medium is received, then it is determined if the edge region contains a pixel whose gray level is higher than a predetermined gray level. The image data is updated by lowering gray levels if the edge region contains the pixel whose gray level is higher than the predetermined gray level. Then, a ribbon is heated to transfer dye on the ribbon to the printing medium according to a result of updating the gray levels of the image data.