In order for registration of images for surgery, first, a three-dimensional reference image of a surgical area of a patient before surgery is acquired. Then, a grating-pattern light is provided towards the surgical area to acquire a first measurement image. Thereafter, a preliminary registration is performed between the acquired first measurement image and a pre-acquired three-dimensional reference image. Then, a grating-pattern light is provided towards the surgical area after cutting out the surgical area to acquire a second measurement image. Thereafter, a fine registration is performed between the acquired second measurement image and the pre-acquired three-dimensional reference image based on the preliminary registration result. Thus, an accurate registration result may be acquired at low cost in a short period of time.
