represents the curve over time of the intensity of the received light insofar as it corresponds to the amplitude envelope of the received light the center frequencies f 1 through f n thereof correspond as exactly as possible to the modulation frequencies f 1 through f n electrical signals that represent the intensity of the light components arising from the light sources 1 1 through 1 n in the received light supplied to the subject 6 and transmitted therethrough are thus respectively available at the outputs of the band pass filters 8 1 through 8 n these electrical signals respectively proceed to signal editing circuits 9 1 through 9 n wherein signal editing adapted to the particular examination case ensues the output signals of the signal editing circuits 9 1 through 9 n are supplied to an n 1 multiplexer 29 whose output is connected to the analog digital converter 11 per scan position thus the electronic computational unit 12 has instead of one data pair corresponding to both transirradiation directions but a plurality of data pairs available to it corresponding to the plurality n of different wavelengths each representing the two transirradiation directions for a different wavelength one can proceed in the above described way with the images produced on the basis of the data by the electronic computational unit 12 and displayed on the monitor 14 as needed the combining of image information arising from different images to form a new higher contrast image is thus not limited to the images of one image pair belonging to one of the wavelengths u03bb 1 through u03bb n on the contrary there is also the possibility of combining image information from images belonging to different wavelengths u03bb 1 through u03bb n to.