Correct for photometric nonuniformity by multiplying by a ``UNI'' file, the reciprocal of a flat field image. Names of SDAS tables must be provided in the keywords GRAPHTAB, COMPTAB, and UNITAB. The filter names must be given in the keywords FILTNAM1 and FILTNAM2, and for f/96 also FILTNAM3 and FILTNAM4. GRAPHTAB and COMPTAB together with the filter names are used to compute the pivot wavelength of the system (optics + filters + detector). The name of the UNI file is obtained from the table identified by the keyword UNITAB. This table contains columns for wavelengths, relay names (f/48 or f/96), and UNI file names. The UNI file name is taken from the row with the correct relay name and the wavelength nearest to the pivot wavelength (i.e. their ratio is nearest to unity). This correction is not appropriate for spectrographic images.
