Spectral zonal filter

Claim 1

A substantially two-dimensional light modulation filter for use in preparing from colored light representing a scene an image transparency suitable for producing by Fourier transform and spatial and spectral filtering techniques a projected image of said scene in prescribed colors, which may be natural or artificial, from ''''n'''' light components representing respective spectral zones of said colored light where ''''n'''' is an integer greater than one, said filter having a plurality of ''''n'''' periodic functions each extending throughout the area of said filter and having a unique azimuthal characteristic in the area of the filter for passing light representative of a unique wavelength band corresponding to a selected one of said spectral zones, said functions overlapping each other, the configuration of said functions being such that the light transmittance of said filter is expressed as the product: (x, lambda ) P (x) .P (x) .--P (x) Where: (x, lambda ) is the mathematical representation of the total filter with transmittance a function of spatial coordinates x and wavelength lambda ; P (x) is the periodic function corresponding to the wavelength band lambda i with azimuthal characteristic Alpha i; and lambda i is the average wavelength in the band from lambda i- Delta lambda i to lambda i + Delta lambda i, each periodic function being comprised of periodic alternately spectrally neutral elements and color filter elements capable of passing light limited to a unique wavelength band corresponding respectively to a selected one of said spectral zones, said neutral elements and said color filter elements occupying different fractions of the period length of said function such that light in said unique wavelength band is transmitted through said filter in a minor fraction of said period length and substantially blocked in a major fraction of said period length, said minor fraction being substantially smaller than said major fraction.