A processing system includes a setting module for capturing Cyan, Magenta, Yellow and K data of a foreground and selecting one from the Cyan, Magenta, Yellow and K data in order to set gray values of remaining three of the Cyan, Magenta, Yellow and K data as “0”; a coupler module for capturing the Cyan, Magenta, Yellow and K data of the background and combining the Cyan data of the foreground and background into a Cyan data group, the Magenta data of the foreground and background into a Magenta data group, the Yellow data of the foreground and background into a Yellow data group and the K data of the foreground and background into a K data group; and a print module for printing, out the Cyan, Magenta, Yellow and K data groups one above another in an overlapping manner.