A coherent optical method for generating contours from stereophotographs by using a grating as a spatial filter is proposed. The relationship between parallax and light amplitude distribution in the spectrum plane, the effect of spatial filtering and the final light amplitude distribution in the image plane are analysed theoretically. The superposition of the amplitude transmittances of the stereophotographs in the object plane of a 4f system, when illuminated with a beam of coherent light, will result in numerous sets of straight interference fringes in the speotrnm plane, with eaoh set ooresponding to a set of points with the same parallax, i. e., a contour line. When a grating is used to provide spatial filtering, only one Set of fringes is allowed to transmit through the grating, while others are blocked off. Then a contour will appear in the image plane of the system. Different grating spaoings oorespond to different contour positions and a change in the position of the grating will lead to bright or dark contours. Stright and circular contours are obtained by using two experimental models, a slope and a conio. Experimental results with contonrs in different positions and having different values of brightness are given in the paper. Because it is unnecessary to measure parallax point by point, the method has the advantage of quickness. In our experiment, two stereophotographs are superposed on one photosensitive plate incoherently to achieve amplitude addition so as to reduce the requirement on the system.