1. An image processing device, comprising: an image acquisition device acquiring a taken image in which a subject is imaged; a smoothing device generating a smoothed image by smoothing the taken image; a noise extraction device extracting a difference noise component from a difference between the taken image and the smoothed image; a noise addition device adding the difference noise component to the smoothed image; a map acquisition device acquiring a distance map that represents a distribution of distances on a pixel-by-pixel basis or a region-by-region basis in the taken image; and an image combining device combining the taken image with the smoothed image on the basis of the distance map, and generating an output image.