RASTER EDGE DETECTING METHOD

PURPOSE:To detect a raster edge without making arrangements even when the size of a cathode ray tube(CRT) is different by calculating the center of gravity for a peak position in the peak of data obtained by a differentiating operation by floating point arithmetic. CONSTITUTION:A raster pattern 1a generated by a signal generator 7 is displayed on the screen of a CRT 1 as a measuring object, the upper, lower, right and left sides of the raster is caught by cameras 2a-2d in order to measure the position and size of the raster pattern 1a, and this image is stored in video memories 3a-3d. When thus stored data are differentiated by an arithmetic unit 4, the longitudinal axis shows the picture element address of the video memory corresponding to the difference of adjacent brightness, the axis (abscissa) shows the address corresponding to a position in the horizontal direction of the picture, and the peak is the same position as a raster edge. Concerning the position of a peak Po, the center of gravity is calculated by the floating point arithmetic at the arithmetic unit 4 and therefore, the raster edge can be detected with accuracy higher than the resolution of the camera and the video memory.