Abstract: A color filter is provided for use with an imager which has a plurality of discrete collection sites. The filter has a plurality of color filter elements arranged in rows aligned with the collection sites. Two elements of the filter overlay a scan line of the imager in one television field, and each of the rows has a repeating sequence, e.g., 6, of at least two independent colors. The adjacent rows in the filter have their color sequences shifted by two elements. A demultiplexing scheme is disclosed, which features a high-frequency luminance signal having a constant colorimetric composition.

Abstract: A variable index-of-refraction optical medium of certain minimum thickness and periodicity with respect to the wavelength of incident light--if it meets certain specified constraints with respect to (1) relative indices-of-refraction of both its internal structure and that of its surroundings and (2) relative values of incident wavelength to periodicity and the relative indices-of-refraction--operates to produce both angularly-dependent subtractive-color filter reflection spectra and subtractive-color filter transmission spectra in accordance with its physical parameters. Such filters are suitable for use as authenticating devices for sheet-material authenticated items.