Positioning device

Abstract

In a positioning device, a maximum-value/minimum-value calculating section calculates the maximum value and minimum value of densities with respect to each of a target image and a reference image that has been preliminarily stored. Further, based upon the maximum values and minimum values of densities of the two images, a barrel-shifter gradation conversion section carries out bit shifts of the original images of the two images respectively so as to allow them to contain effective bits related to contrast, and gradation-converts the respective images so as to have numbers of density levels that are fewer than the original numbers of density levels thereof, thereby outputting the resulting images that have been gradation-converted. With this arrangement, even if the contrast of an original image is poor, it is possible to reduce the amount of calculations for finding the degree of similarity between the reference image and the target image without impairing the operation accuracy in finding the degree of similarity. Therefore, even if the contrast of an original image is poor, it is possible to carry out an effective rough search by using a rough search section. Moreover, since the degree of similarity is found with high precision with a minimum of the amount of calculations, the circuit scale can be minimized to the corresponding extent.