PURPOSE: To obtain the information having a small error even in a low-contrast region or a considerably noisy region, by obtaining a parallax for each spectrum by means of a pair of multispectrum images and synthesizing these parallaxes.

CONSTITUTION: The parallax is obtained with each spectrum of a multispectrum image by means of the mutual correlation coefficient Rxy(l) of a single band. These parallaxes are then synthesized by the simple sum, the weighted linear sum or product, etc. to obtain the coorelation value of a pair of images which are obtained by photographing the same point at different angles. Then the coordinates (x, y) are obtained for the position where the correlation coefficient has a peak, and the parallax is obtained by obtaining the degree of shift of the position coordinates. Furthermore the height of an object on the ground is obtained by the above-mentioned parallax, and the reduced scale is compensated between an input image and the actual length