Excerpt from HMP 7 Chapter 3
Color Holography
One of the goals of holographers worldwide has been to develop cost-effective techniques that result in affordable full color, fully-dimensional images. The ability to produce such realistic-looking hologram images outside research laboratories will undoubtedly aid all aspects of the medium.
Commercial holographers would certainly benefit – clients have been asking for (and expecting) true color images for years. Many jobs have been lost when the words ‘monochromatic’, ‘multi-color’ or ‘pseudo-color’ have been uttered by holographers to potential customers. Technical achievements that we know are extraordinary and viable are less exciting to those expecting to see images like those created by Hollywood’s special effects teams.
Holographic artists would also benefit if they could easily add realistic colors to their three dimensional images -- the market for holographic fine art might even be resurrected. Imagine the frustration of painters and photographers if they were confined to using only shades of red or green or gold in their work...and if creating combinations of these few colors proved difficult and expensive, if not impossible. It’s no wonder the majority of holographic artists do not prosper.
If the technology to produce realistic images were affordable and accessible, many new applications for holography would certainly result. The entire field would regain some of the attention it once held among visual artists and the general public (and which it seemingly lost over the past decade to the fast moving digital imaging industry).
Steady Progress Has Been Made
Over the past two decades, great strides in true color imaging have been made by holographers working in their various fields. Embossed holographers have gradually increased their palate of available colors to the point where, theoretically, almost any hue can be generated using existing technology. More importantly, embossed holographers have been able to accurately reproduce the colors typically found on printed materials and computer monitors. In practice, even the most difficult colors to depict (e.g., flesh tones) can be, and have been, reproduced.
Holographers working with dichromated gelatin (DCG) have also produced notable achievements in color reproduction. Unfortunately, further research in this area has been slowed by economic restraints -- there seems to be no point in pursuing such labor intensive manufacturing techniques, since they result in relatively small, glass-encased holograms that are impractical to mass produce for most commercial applications.
The silver-halide reflection camp has consistently struggled to make more colorful display holograms. Years ago, a handful of determined artists developed tricks that produce a reasonably realistic-looking apple, pear and banana, using only HeNe lasers and red sensitive emulsions. As methods became perfected, many worthwhile images were produced on glass and film – but customers willing to order large volumes of these holograms were rare. Even with today’s technology these multi-color holograms remain difficult and expensive to make, especially in the sizes requested by corporate clients.
True color reflection holograms were sporadically displayed at technical conferences but never mass produced. However, new developments in panchromatic emulsions should invigorate holographers interested in working with silver-halide. Affordable materials are becoming available. This is a very exciting time for holographers with access to the right lasers.
Another very promising field of research in full color holographic imaging revolves around photopolymer recording materials. Although successful results were achieved a decade ago in the lab, corporate managers decided it wasn’t yet cost effective to bring the existing technology to market. New developments in panchromatic photopolymers and more efficient mass replication equipment may change the situation. Many holographers are now working closely with photopolymer suppliers to refine production methods and make them more feasible to utilize.
To give our readers a progress report about the state of color reflection holography, we’ve consulted with an acknowledged leader in the field, Hans Bjelkhagen. His article follows.
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