JP2941507B

PURPOSE:To accurately binarize thick and thin parts on an aerial photograph even if thick and thin parts are mixedly included while reducing the load of hardware and software. CONSTITUTION:An input circuit 1 successively reads out the images of an aerial photograph 7 plural times at respectively different sensitivity values and outputs image data in each sensitivity, an image to be binarized extracting circuit 2 successively inputs the image data of respective sensitivity values, applies compensation corresponding to the reading sensitivity of the current image data to the preceding image data subtracts the image data obtained by the compensating operation from the current image data and forms image data obtained by canceling the image part read out by the preceding reading operation through the subtracting processing and then a binarizing circuit 3 and a data synthesizing circuit 4 successively binarize and synthesize respective image data formed by the circuit 2 to form and print out the binarized image data of the photograph 7.