The interest in holographic applications has in the latest years opened up for new optimism in the expanding holographic community. One of the reasons for this is the development of new technology in optics and computers.
There seems to have been no particular reason why holography should have been such a late developer. Although today a hologram is invariably produced by using a laser as the light source, holograms can - and have been - made by other light sources, even, most improbably, with white light. The theoretical principles underlying holography could well have been worked out as early as 1816, when Auguste Fresnel clothed Thomas Young's 1802 theory of diffraction and interference with the respectable garment of mathematical rigor, at about the same time, when the first experiments that resulted in photography where carried out. In 1856 Scott Archer discovered how to produce a light sensitive material coated on glass. The monochromatic property of the golden-yellow sodium flame was well known, and it would at that time have been just possible to make a Denisyuk-type reflection hologram.
But the history of technology tells us that inventions appear only when contemporary culture is ready for them.
In 1947 Denis Garbor carried out his experiments using visible light from a filtered mercury arc. Because of the limited coherence of his source his holographic images were restricted to transparencies little larger than a pinhead. Garbor`s two papers (A new microscopic principle and microscopy by reconstructed wavefronts) for which he was subsequently to be awarded a Nobel prize in 1971, were published respectively in 1948 and 1949.
Meanwhile, in the Soviet Union, Yuri Denisyuk was experimenting with an optical configuration that was radically different from Garbor`s. In this configuration the reference and object beams where incident on the photographic plate from opposite sides. This was achieved by placing the film plate between the light source and the subject matter, so that the portion of the reference beam not absorbed by the emulsion passed through and was reflected back from the object, forming the object beam. By 1962 Denisyuk had succeeded in producing holograms in which the image could be reconstructed using a point source of white light. This was a considerable advance in comparison to other configurations which required a monochromatic reconstruction beam.
The appearance of a workable laser in 1962 gave holography the impetus it needed. Its importance centred round the large increase in the coherent length. It now became possible to make holograms of solid objects. Leith and Upatnieks produced the first laser transmission hologram of a solid object in 1963, and Denisyuk began to produce holograms of art objects in the same year.
After this holography began to develop rapidly. A good deal of the process consisted of small improvements in optical components, holographic emulsion and processing methods, combined to a growing mastery of the techniques by practitioners.
By restricting the vertical parallax, Stephen Benton produced in 1968 a transmission hologram which could be replayed using white light.
The principle of transfer images was quickly extended to reflection holograms. Thus holograms could now be produced with an intermediate stage. Just as in creative photography, it now became possible to introduce artefacts into the final hologram.
In 1974 Michael Foster introduced a method for duplicating holograms
mechanically by using them in the same way as audiodisks. It became
possible to mass-produce holograms at very low cost, holograms
which, turned into reflection holograms by aluminium backing,
could be
used in textbooks, art publications and publicity hand-outs, and on credit cards as a security device.
The past two decades have seen many more advances in holographic technologies, such as live portraiture, natural colour and holographic stereograms made from movie and computer graphics, which the present report is about.
Production of holographic stereogram from two-dimensional photographs is an established technique. This technique was first described by De Bietetto (1969). Each image is projected in turn on to a diffusing screen, while a movable mask ( which is stepped between exposures ) is used to define a narrow strip on the holographic plate. The complete hologram then contains a series of strip exposures. When it is viewed, the observer sees the image reconstructed by a single strip. As the observer moves, the reconstructed image appears to rotate, giving the illusion of three-dimensionatity.2
Figure 1-1 Set-up for recording partitioned
holograms.
A holographic stereogram can of course be cylindrical, for all-round view. In this case, the transparencies can be made by photographing a rotating subject from a fixed position. If the subject articulates as well, each frame is a record of a particular aspect at a particular time. A rotating cylindrical holographic stereogram made from successive frames of movie film can then show an apparently three-dimensional display of a moving subject. This technique was originally invented by Cross in 1977.26
Figure 1-2 Oblique view of reflection alcove hologram.
Liquid crystals where actually discovered over 100 years ago,
but they did not find commercial applications until the invention
of the twisted nematic (TN) LCD by Schadt and Helfrich in 1971.30
By the mid-1980s, it was becoming obvious to display industry
experts that the Japanese displays industry was beginning to make
significant breakthroughs in technical developments and in the
manufacturing of liquid crystals displays (LCDs). In Japan, the
stage is nearly complete for the production of flat panel displays
(FPDs) through the end of the 1990s. The LC FPD industry is now
orders of magnitude ahead of the other FTB technologies. The research,
development, and production activities in Japan are so focused
on LCD technology that funding for advancing electroluminescent
(EL), plasma, and other FPD technologies is diminishing. In Japan,
LCDs are perceived as clearly being the leading edge technology,
but the cost and complexity of the new amorphous silicon (a-Si)
LCD factory are so extensive that the larger machines of the next
generation will not be attempted until the present generation
of machines have completely proven and been paid for.
The aim of the present thesis is to develop methods for producing holograms from computer images. In this method, holograms are made from non-existing objects, that is, images produced on the computer. This means that it is not necessary to make prototypes of a new product in order to get it visualised in 3 dimensions. The computer image of the product can be directly converted to a holographic filmplate, and the product can be shown in 3 dimensions. There are economic advantages, if it becomes possible to skip the building of prototypes, which is often a very expensive and a time consuming operation.
This thesis work builds on the conclusion drawn in Thor Erling Grahl-Nielsen diploma work NTH-1992, 24 and a further thesis work of Olav Birkelands Cand. scient thesis UIB-1994. 10
Figure 1-3 The set-up for production of holographic multi stereogram.
The purpose of the present thesis work is to examine the best methods for producing high quality holographic multi-stereograms from computer images.9 In particular, reflection and rainbow holograms are produced from master holograms by the two step method.
A hologram is a very good way to display an object in three dimensions. To make a good reflection hologram is more difficult than transmission and rainbow holograms. I believe the reflection hologram has the best chance to be a success in 3D visualisation, when this can be reproduced in white light.
In finding the right set-up for production of high quality holographic multi-stereograms, there was a great deal of optical equipment and procedures that had to be inspected. Therefore, the thesis work started with a simple holographic record of an object. When the result of the recording and developing processes were satisfactory, the set-up was changed step by step until the final set-up for the recording of high quality holographic multi-stereogram was found and tried out in some detail.
