A device for generating fusion images by fusioning two images, in particular medical images, comprising an image-processing computation unit (2) for fusioning the images, as well as a monitor (3) connected thereto for image output, a gray-value histogram (7, I, II) being displayable on the monitor (3) for each image of the images to be fusioned, which device is designed in such a way that, in each gray-value histogram (7, I, II) of the images to be fusioned, one or more gray-value ranges can be selected by user-controlled highlighting of one or more markings (8) on the monitor (3), as well as for generating the fusion image with the aid of the selected gray-value ranges.