A method is provided for establishing an overlay image to be displayed from medical image datasets of a recording region of a patient registered with one another containing at least two items of different image information. The method includes establishing, for at least a part of the overlay image, an image value of the overlay image at an image position by addition or subtraction of an image value of at least one base image dataset of the medical image datasets at the image position and a modified image value of at least one modification image dataset of the medical image datasets at the image position dependent on the image value of the base image dataset at the image position.
