| 摘要 |
The disclosed filter provides (1) a high contrast between black and white together with a substantially neutral black and/or (2) a gray-scale color (wavelength) characteristic which is substantially independent of luminosity, and is preferably neutral. Neutral black is achieved when two superimposed, crossed, sine-wave gratings embossed in plastic have different depths which are selected to provide a zero-diffraction-order-light transmittance wavelength selectivity characteristic for any one of the phase gratings which exhibits a minimum zero-diffraction-order-light transmittance at desired different wavelengths in the visible spectrum. A gray scale is achieved by mixing black-manifesting subareas with white-manifesting subareas. |
