ILLUMINATION SYSTEM FOR TRANSFORMING CONVENTIONAL RAINBOW HOLOGRAPHIC DISPLAYS INTO ACHROMATIC DISPLAYS
Original Publication Date: 1988-Apr-30
Included in the Prior Art Database: 2004-Apr-04
Xerox Disclosure Journal
Rainbow holograms 20, in conventional Dr. S. B e n t o m and stereogram format, produce impressive 3-D displays using whitelight illumination. The holograms present an image in a single spectral hue that varies with the vertical viewing angle as shown in Figure 1, When the position of the hologram and illumination source is fixed, the viewed color is a function of viewing angle which is determined by the observer's height. This can pose problems with display effectiveness. Benton, the inventor of rainbow holography said, "The saturated spectral hues presented by rainbow holographic stereograms sometimes detract from their image content, so that we have sought to achromatize the images, to render them in the neutral black-to-white hues more familiar in photography". This is done during recording exposure by moving the projected image above the green axis 22 in order to offset viewing toward the blue axis 24, and below the green axis to offset viewing toward the red axis 26 (see Figure 2). White light is thus produced and the image appears black and white when a sufficient range of wavelengths is presented about the axis. The recording technique is complex, and requires multiple optical transfer steps and accurate control of spectral dispersion to prevent color fringing and loss of image sharpness (see Figure 3). Conventional illumination sources universally adopted for hologram viewing approximate point source types usually placed at a distance of about 6' to 10' from the hologram.