A method for reducing the dimensionality of a spatially registered signal derived from the optical properties of a sample , comprising the steps of: - providing a wavelength-tunable light source that emits primary radiation (P) with time-variant wavelength, - sampling location points of the sample with the primary radiation (P), - collecting secondary radiation (S), wherein the secondary radiation (S) is a portion of the primary radiation (P) reflected by the sample , - generating an interferometer-based detection signal for a plurality of sample areas that respectively contain at least one location point by means of a detection unit , wherein the detection signal is generated in the form of a differential signal between two output signals of a beam splitter that respectively receives reference radiation (R) and secondary radiation (S) at two inputs, and wherein the reference radiation (R) is a portion of the primary radiation (P) that is not routed to the sample , wherein depth information of the sample is coded in the frequency of the detection signal, and - determining a brightness value for at least one of the sample areas from the associated detection signal, characterized in that the brightness value is determined from a radiofrequency power component of the detection signal for the individual sample area, wherein the radiofrequency power component is determined using a radiofrequency power detector in an analog measurement, wherein the radiofrequency power component is determined in a frequency range from and including 3 kHz to 30 GHz or in at least one frequency sub-range thereof, so that depth-resolved information with an axial resolution of less than 20 μm is used for the determination of the brightness value. - providing a wavelength-tunable light source that emits primary radiation (P) with time-variant wavelength, - sampling location points of the sample with the primary radiation (P), - collecting secondary radiation (S), wherein the secondary radiation (S) is a portion of the primary radiation (P) reflected by the sample , - generating an interferometer-based detection signal for a plurality of sample areas that respectively contain at least one location point by means of a detection unit , wherein the detection signal is generated in the form of a differential signal between two output signals of a beam splitter that respectively receives reference radiation (R) and secondary radiation (S) at two inputs, and wherein the reference radiation (R) is a portion of the primary radiation (P) that is not routed to the sample , wherein depth information of the sample is coded in the frequency of the detection signal, and - determining a brightness value for at least one of the sample areas from the associated detection signal, characterized in that the brightness value is determined from a radiofrequency power component of the detection signal for the individual sample area, wherein the radiofrequency power component is determined using a radiofrequency power detector in an analog measurement, wherein the radiofrequency power component is determined in a frequency range from and including 3 kHz to 30 GHz or in at least one frequency sub-range thereof, so that depth-resolved information with an axial resolution of less than 20 μm is used for the determination of the brightness value. <EOS>