1. 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.