A new method for color image subtraction is proposed in this paper. The two color images encoded separately by two three-primary color gratings with an effective halfperiod shift of color fringes in one step are recorded on the same black-white film. The three-color gratings are formed in real-time by in torference of symmetric orders of 2-D grating diffraction and three-color filters, and the half-period change of color fringes is realized by simple polarization spatial filters. The intensity subtraction of two oolor images then can be obtained easily by decoding in a, white liglit processor. An experimental example is given.