PURPOSE:To detect the corner point, attitude, etc., of the line edge of a body to be measured easily at a high speed with high precision by detecting a point where the absolute value of the brightness gradient of a variable density image is larger than a specific value and the direction of the brightness gradient changes by more then a specific value as the corner point. CONSTITUTION:A differentiation device 4 reacts to a coordinate signal along an imaginary line from an edge detecting device 7 and processes the variable density image signal of the body to be measured corresponding to plane coordinates stored in an image input device 1, thereby outputting a brightness gradient signal. Then, the device 7 detects the edge of the image on the basis of the absolute value of the brightness gradient from an absolute value arithme tic device 5 which is larger than the specific value. A corner detecting device 8 performs arithmetic along the edge to decide on the point where the absolute value of the brightness gradient from the device 5 is larger than a specific value and the output of a direction arithmetic device 6 which processes the direction of the brightness gradient changes by more than the specific value as the corner of the body to be measured, thereby detecting the corner point, attitude, etc., easily with high precision.
展开▼
