Determination of the Fourier Spectra of Photographic Images

The determination of the spatial frequency density in the image recorded by a film or a photographic plate is shown to be possible by the measure of the total flux transmitted when the film or plate is illuminated by a sinusoidal distribution of light superposed on the transparency. The sinusoidal light distribution is produced in the form of two-beam interference fringes. In the present instrument fringes of good contrast are obtainable at frequencies greater than 20 per millimetre. The apparatus has been used to determine the frequency spectra of slits, a line-grating and of different scenes taken by air photography.