Abstract: An apparatus for detecting one or more contours of an image formed on a screen. The apparatus comprises a scanner for raster scanning pixels located on scan lines extending in paralllel with each other in the X direction of a two-dimensional coordinate system to successively produce binary pixel data regarding the scanned pixels. The binary pixel data have a first value representing a background forming pixel or a second value representing an object forming pixel. The binary pixel data are transferred to a pixel data matrix stored therein. The pixel data matrix includes pixel data regarding two adjacent pixels located on the next scan line. The latter two adjacent pixels are respectively adjacent to the former two adjacent pixels in the Y direction of the two-dimentional coordinate system. The apparatus also comprises a processing circuit which receives the pixel data matrix transferred thereto from the pixel data matrix forming circuit for producing data indicating the image contour(s).