A grid of individual dots (known as pixels) that viewed together make up a shape or picture. TIFF and BMP graphic files are bitmap graphics. When describing a bitmap, them the number of 'bits' refers to the number of colours each dot can be, ie. in a 1-bit picture, each dot is either black or white; in an 8-bit greyscale, each dot can be any one of 256 shades of grey.