A technique for printing black text on a colored background, in which the graphics are broken down into three categories: text, polygons, and images when the incoming graphic information is a Page Description Language data file. The images are compared using sum of absolute difference devices, which have arithmetic parts, and accumulators. 4 when the atomic ratio of the alkali metal atom relative to 10 atoms of Mo is taken as A and the atomic ratio of the copper atom relative to 10 atoms of Mo is taken as B in MoaPbVcCudYeZfOg where Y represents cesium or the like; Z represents iron or the like; and a to g represent each an atomic ratio of each element relative to 10 atoms of Mo.