ingoldsb@ctycal.COM (Terry Ingoldsby) (08/24/89)
I'd like to start a discussion on computer generated holography in
general, and 3D computer generated holograms (CGH) in particular. If this
should go elsewhere, then please tell me. I thought it fit here since
CGH is the ultimate computer graphics.
I have dabbled in 2D computer generated holograms, producing them on a
computer and reproducing them using a laser. I recently heard that
some researchers (at MIT?) had been playing around with 3D stuff. Does
anyone know how they are doing it? Is anyone else interested in this
topic?
--
Terry Ingoldsby ctycal!ingoldsb@calgary.UUCP
Land Information Systems or
The City of Calgary ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsbnews@blackbird.afit.af.mil (News System Account) (08/25/89)
In article <441@ctycal.UUCP> ingoldsb@ctycal.COM (Terry Ingoldsby) writes: >I'd like to start a discussion on computer generated holography in >general, and 3D computer generated holograms (CGH) in particular. If this >should go elsewhere, then please tell me. I thought it fit here since >CGH is the ultimate computer graphics. > >I have dabbled in 2D computer generated holograms, producing them on a >computer and reproducing them using a laser. I recently heard that >some researchers (at MIT?) had been playing around with 3D stuff. Does >anyone know how they are doing it? Is anyone else interested in this >topic? The research at MIT, that I`m aware of, is being conducted by Steve Benton. He's producing Synthetic Holographic Stereograms. In general they produce a series of perspective views using convential computer graphic techniques. Each image is then projected with laser light onto a sheet of holographic film from the angle corresponding to its computed viewpoint. The effect is to provide the visual properties of an actual hologram. This works because each eye receives a different perspective view. As you move around you get the stereoscopic effect, hence 3-D. There have been several articles written in the SPIE journals. Volume 761 has one titled "Alcove Holograms for Computer_Aided Design". As far as work being done on actual 3-D CGH, the Air Force Institue of Techology is doing some work in this area. They are using points to describe an object and then calculating the light propogated from a point on the object to every point in the hologram plane. This is being done without the use of Fourier analysis. Anyway, the calculated intensity pattern is plotted out and photo-reduced onto a holographic plate. tom
halazar@mit-amt.MEDIA.MIT.EDU (Michael Halle) (08/25/89)
Your summary is correct. The work we are doing here at MIT (under
Steve Benton) generally uses computer graphics to make the images, and
then lets "Mother Nature" do all the hard stuff (figuring out the
holographic fringe pattern formed on the image of the film). Even
more work is saved by eliminating vertical parallax in the final image.
In other words, the object in the hologram will move naturally as the
viewer moves side to side, but will not change in perspective as the
viewer moves up and down.
Traditional, hard-core CGH forces the computer to bear the cost of
determining which fringe goes where. Much more time is spent
computing the image then actually composing it. That's because of the
cost of computing the fringe pattern is proportional (polynomially,
usually) to the complexity of the image (how many points are in the
picture). In a holographic stereogram, the cost is constant. We
generally render between 100 and 1000 side to side views of an object,
each view anywhere from 640x480 pixels and up. Holograms made from
these images are full color and white light viewable "snapshots" of
any sort of three dimensional computer graphics. Size for our work is
typically 20x25 cm, but can be up to about 1m square. We are also
working on ways to make the image dynamic, in the spirit of 3D video.
Our research is a combination of making better holograms and exploring
uses for them. CAD/CAM and medical imaging are two of our major foci.
We hope that by introducing people to the technology now, we can help
holography be widely useful by the time technology and funding permit
high quality images to be mass-produced quickly.
Here's a couple of holographic stereogram references:
@inproceedings{benton:sur,
author = {Stephen A. Benton},
title = {Survey of Holographic Stereograms},
booktitle = {Processing and Display of Three-Dimensional Data},
year = 1983,
organization = {SPIE} }
@inproceedings{benton:pho,
author = {Stephen A. Benton},
title = {Photographic Holography},
booktitle = {Optic in Entertainment},
year = 1983,
organization = {SPIE} }
If you are interested in further information, let me know.
--Michael Halle
Spatial Imaging Group
MIT Media Laboratoryingoldsb@ctycal.COM (Terry Ingoldsby) (08/26/89)
In article <1306@blackbird.afit.af.mil>, news@blackbird.afit.af.mil (News System Account) writes: > The research at MIT, that I`m aware of, is being conducted by Steve Benton. > He's producing Synthetic Holographic Stereograms. In general they produce > a series of perspective views using convential computer graphic techniques. > Each image is then projected with laser light onto a sheet of holographic > film from the angle corresponding to its computed viewpoint. The effect > is to provide the visual properties of an actual hologram. This works because > each eye receives a different perspective view. As you move around you get > the stereoscopic effect, hence 3-D. In other words, the same as `Leslie' hologram referred to by another poster. Also similar to a white light space shuttle hologram I saw a few years ago. > > There have been several articles written in the SPIE journals. Volume > 761 has one titled "Alcove Holograms for Computer_Aided Design". > > As far as work being done on actual 3-D CGH, the Air Force Institue of > Techology is doing some work in this area. They are using points to > describe an object and then calculating the light propogated from > a point on the object to every point in the hologram plane. This > is being done without the use of Fourier analysis. Anyway, the > calculated intensity pattern is plotted out and photo-reduced > onto a holographic plate. Do you know if they use 2D or 3D Fourier? When I made my 2D holograms I basically used a 2D FFT to calculate the diffraction pattern of an aperture, mixed in a reference beam and output the resulting pattern to a monitor. There I photographed it (and reduced its size) so that I could reproduce it using a laser. Note that the laser is not necessary for reproduction; it can be reproduced in the computer but its not as much fun. A professor I had once mentioned that he thought that 3D holography worked because film emulsion was 3D (in comparision to the wavelength of light). I'm not sure if he was correct. If that is true, do I have to use a 3D FFT? How do I get it on the emulsion? Since a normal hologram does not give a full 3D (ie. 360 degree) image could the calculations be restricted (ie. not use a 3D FFT). I can also see how a sort of super glorified ray-tracing effort would allow you to calculate the interference of all the light reflected from a 3D object, but surely the calculations would require more computer power than is currently available. (This is as much a question as a statement). -- Terry Ingoldsby ctycal!ingoldsb@calgary.UUCP Land Information Systems or The City of Calgary ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb
eugene@eos.UUCP (Eugene Miya) (08/27/89)
Actually this raises an interesting question: everybody is
trying to anonymous FTP 2-D images, etc. We should probably start to
consider the small, but growing database of holograms. We could
store the source code to generate them rather than the images themselves
since it presents a staggering storage problem. We have few rendering
systems, but this will probably grow in time as well. Perhaps
some space could be set aside at media-lab as an Internet repository.
Another gross generalization from
--eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov
resident cynic at the Rock of Ages Home for Retired Hackers:
Ex-Voyager Program member
"You trust the `reply' command with all those different mailers out there?"
"If my mail does not reach you, please accept my apology."
{ncar,decwrl,hplabs,uunet}!ames!eugene
Live free or die.jh@tuna.MIT.EDU (John Underkoffler) (08/27/89)
Wavefronts And You: The Holographic Scoop ----------------------------------------- In response to Terry Ingoldsby's holo-worthy posting, it is not necessarily the case that 3-D holography is reliant on a three-dimensional film emulsion for its operation. The simplest kind of transmission holograms employ diffraction (which, as we know, is a phenomenon whereby waves of light are `perturbed' or `annoyed' after propagation through some region of spatially varying opacities) through a photographically recorded fringe pattern in a high-resolution but otherwise workaday emulsion. As far is the imaging properties of the beast are concerned, the film emulsion is merely a two-dimensional mask of opaque fringes in a transparent field. A theoretically infinitely thin [2-D, then] emulsion can contain a complete record of the moving wavefronts which represent a fully three-dimensional scene; no information is lost, unlike many transatlantic telephone conversations. Of course, certain kinds of holograms do depend on an emulsion of finite thickness, so I can't be entirely trusted to tell the truth. An example is any kind of reflection hologram (a hologram for which the illumination is on the same side of the film as the viewer), which is similar to an interference filter in its use of many nested, gently curved fringes, roughly parallel to the plane of the film. A few notes on "real" Computer Generated Holograms (as we call the fringe-calculated variety, as contrasted with Holographic Stereograms, which may or may not employ a computer to generate the myriad perspective views which become optically assembled in a fairly non-thrilling manner) seem in order. First off, the preponderance of CGHs made using FFTs is the result of a lucky coincindence in nature: if you allow a certain distribution of light to propagate a long way, what you get looks mathematically something like the Fourier Transform of the distribution you started with. This made a lot of people who wore white lab jackets and used terms like "Mach-Zender Interferometer" and "apodization" very happy when they realized it. Basically, it meant that if they wanted to compute what the fringes in a holographic recording of an dismayingly distant two-dimensional transparency would be, they wouldn't have to use the dreadful ray-tracing method mentioned by Terry. Of course, that meant that the only kind of holograms that they could make were ones which featured images of dismayingly distant two-dimensional transparencies. Such images became quite popular, of course. In short, then, FFTs can be used to generate fringe patterns for a very highly constrained class of holographic images, because a 2-D spatial Fourier Transform happens to be a really good approximation to the actual thing for that sadly flat class. But we want CGHs which display non-flat objects! It is therefore not feasible to use the Fourier Transform shortcut. Instead, you have to go ahead and play Momma Nature and use the ray-tracing method; that is, you do what nature does when it makes a hologram [er...], which is that light from each infinitesimal object in the scene you're depicting propagates to each location on the holographic film, unless it's precluded from reaching certain locations because of occlusion by other objects. Thus, the contribution from each little spot of light in your scene has to be communicated to each little location in the holo-film. The number of each of these is `a lot', as we say in the business. Example-numbers and statistics are boring, so I won't give any, but think of something staggering and then square it a few times to get a rough estimate of the number of propagation-computations that're necessary. However, the problem is luckily not so computationally intractable as Ms./Mr./Dr. Ingoldsby fears. There are many ways to cheat. One of these is that we can dispense quickly with vertical parallax: because your eyes are situated horizontally (in order to fill out your face, as my colleague Mr. Halle noted), most people don't notice if they cannot look over or under objects. Therefore, you can get away with propagating light from each scene-point only to hologram-points which are at the same vertical level with them. Already, the problem is reduced by a few orders of magnitude. For homework, think of other ways to make computation of holograms easier. Tommy Mouser's estimate of 6 Cray2-days for the computation of a one-inch-square hologram is consequently slightly misfounded. Using, among other computation reduction techniques, elimination of vertical parallax, we routinely compute two-by-two-inch holograms in a few minutes on an HP 835 workstation. You and your friends can have fun making CGHs in your spare time! John Underkoffler Pasteurizer, Spatial Imaging Group MIT Media Lab jh@media-lab.media.mit.edu
mcdonald@uxe.cso.uiuc.edu (08/29/89)
> However, the problem is luckily not so computationally >intractable as Ms./Mr./Dr. Ingoldsby fears. There are many ways >to cheat. One of these is that we can dispense quickly with >vertical parallax: because your eyes are situated horizontally >(in order to fill out your face, as my colleague Mr. Halle noted), >most people don't notice if they cannot look over or under objects. Unfortunately, doing this generates a flat, unlifelike image. You can't look under or over objects, true, but the subjective effect is even worse than that. In our Illini Union museum room, about 100 yards from my office, is presently a large display of holographic art, some real 3D, some 2D-ish. Believe me, the real Ohhhhhhhh's come from the folks looking at the full 3D transmission ones!!! Doug McDonald
halazar@mit-amt.MEDIA.MIT.EDU (Michael Halle) (08/30/89)
If the holograms in your museum are white-light viewable transmission holograms, they almost definitely have no vertical parallax. That's because (see my earlier posting) different vertical perspectives would blur together in different colors, creating an unsightly mess. (A full parallax white light transmission hologram is called a full aperture hologram. The horizontal parallax only (HPO) transmission hologram is the Benton or rainbow hologram.) Try tipping your head sideways and see if the image goes flat. White light reflection holograms are another story; they can retain vertical parallax and not blur out (too much) in white light. There are many, many ways to ruin a hologram, especially a computer generated stereogram. Eliminating vertical parallax has not, in our experience, proven to be one of them. Really, most people don't notice. Some of these ways do, however, include: moving the object instead of the viewer (light sources don't look right); rotating the object (object swings around, exhibits keystone distortion); not matching rendering to holographic setup (assorted terrible things); and not carefully registering the frame sequence (jumpy image). And there are plenty of publicly displayed examples of them all...that's in part because many people don't know or can't do the process exactly the right way. That doesn't mean their images don't "sort-of" work, or that the entire idea is flawed. I don't know of anyone who has done studies on the effect of resolution in synthetic holography. We can't really compete with the full bandwidth of a true hologram, so a computer image is bound to be quantitatively inferior (in information content) to the "real thing". Is it good enough for real-life people? We'll see. Also, field of view is usually limited to about 30 degrees for the most common stereograms. We've got work in the pipeline that pushes that past 90 degrees. The images are extremely good, quite convincing even with medium resolution (640x480) input images. And no vertical parallax. --Michael Halle Spatial Imaging Group MIT Media Laboratory
jh@tuna.MIT.EDU (John Underkoffler) (08/30/89)
$^!@~ )*%#@ However, the problem is luckily not so computationally $^!@~ )*%#@ intractable as Ms./Mr./Dr. Ingoldsby fears. There are many ways $^!@~ )*%#@ to cheat. One of these is that we can dispense quickly with $^!@~ )*%#@ vertical parallax: because your eyes are situated horizontally $^!@~ )*%#@ (in order to fill out your face, as my colleague Mr. Halle noted), $^!@~ )*%#@ most people don't notice if they cannot look over or under objects. $^!@~ Unfortunately, doing this generates a flat, unlifelike image. $^!@~ You can't look under or over objects, true, but the subjective $^!@~ effect is even worse than that. $^!@~ $^!@~ In our Illini Union museum room, about 100 yards from my office, $^!@~ is presently a large display of holographic art, some real $^!@~ 3D, some 2D-ish. Believe me, the real Ohhhhhhhh's come from the $^!@~ folks looking at the full 3D transmission ones!!! $^!@~ $^!@~ Doug McDonald Eliminating vertical parallax does not generate flat, unlifelike images. Bad rendering generates flat, unlifelike images. If the two eyes of a non-deformed viewer are looking at a stereogram and are intercepting two different-viewpoint views which are indistinguishable from the real-life views she would be intercepting by viewing an analagous real scene instead, then of course her psychovisual perception is identical to that engendered by the real scene. If, on the other hand, the views have been rendered on a Sinclair ZX80 running CrayolaRealistic BlenderMan, then her wonderfully perceptive visual processing faculties will feel understandably put out. It is my long-distance guess that the Illini Union museum room does not, at this time, feature any holographic stereograms which have been recorded with the proper geometry and whose views have been rendered in a manner worthy of, say, Edward Hopper's admiration. This is a pity. The museum room is invited to examine some of our latest efforts in the field of synthetic holography, which humbly proffer startling solidity and tangibility and have generated their own little smorgasboard of Ohhhhhhhh's. John Underkoffler Tweezermaster, Spatial Imaging Group MIT Media Laboratory jh@media-lab.media.mit.edu
eugene@eos.UUCP (Eugene Miya) (08/30/89)
In article <632@mit-amt.MEDIA.MIT.EDU> jh@tuna.MIT.EDU (John Underkoffler) writes: >Eliminating vertical parallax does not generate flat, unlifelike images. >Bad rendering generates flat, unlifelike images. Not really true. I think that criteria for judging 3-D imagery have to be developed. I won't even try to inumerate the criteria. Many companies try to render the color mandrel. By chance it had some characteristics: color, fine resolution, etc. I think we have to develop some test case pieces. You must view a lot of 3-D before judging the quality (different systems) of good holograms. If you don't, you will get spoofed. Please, continue this discussion on comp.graphics. We have to think about the issue. BTW there exist quite a series of Voyager holographic "movies" going back to Jupiter. I won't try to justify why the Lab doesn't put the current set of images on the net except to say it gives something to people like Ed Stone, Brad Smith, and the rest of the investigators who pushed for this mission in 1972: tenure. The cost of these is about $500 a copy contact the Lab. We as US taxpayers may have paid for the mission, but an agreement was made with these men who proposed this mission at a time when space was not popular: we give you access to this data for a year in advance of your colleagues for your time in the management of this mission. We as readers should respect this. Some people see this as PR, these men see this as their data and their livelihood. Remember this when you FTP these images which will eventually get out (and your can get the earlier planets right now). If you want to argue this, follow up to sci.space, not comp.graphics. Another gross generalization from --eugene miya, NASA Ames Research Center, eugene@aurora.arc.nasa.gov resident cynic at the Rock of Ages Home for Retired Hackers: "You trust the `reply' command with all those different mailers out there?" "If my mail does not reach you, please accept my apology." {ncar,decwrl,hplabs,uunet}!ames!eugene Live free or die.
mcdonald@uxe.cso.uiuc.edu (09/01/89)
>If the holograms in your museum are white-light viewable transmission >holograms, they almost definitely have no vertical parallax. That's There seem to be two different kinds in the display: Single color (nominally) reflection with white light shining on them. There are deep red ones and light green ones. These are full three dimensional images of small objects, plus one which is not a hologram at all but rather two different holographic mirrors, one on top of another, one of them flat and one curved, so the viewer sees two reflections of himself. The green one show color fringes rather badly, but all are very nicely full 3D. The transmission ones appear not to be holograms at all, in the usual sense. They are holographic images of two different images of the same (large) subject, made with an ordinary camera, and put onto the holographic film so that if you stand in the right place the 1st order diffraction images of one picture reaches your right eye, the 1st order of the other reaching your left eye. You move your head right or left and see the spectrum of the light source. Put your head in the wrong spot and you can get different orders into each eye. These are NOT a success. It would seem wrong to call something "a hologram of such and such an object" if the viewer cannot refocus his eye on different distances in that object , and cannot look at different views: above, below, left, right. By this criterion, the second of the above are not holograms of the original subjects - they are holograms of flat photographics prints (or transparencies). I have never seen holograms illuminated by white light that looked remotely as good as ones illuminated by a HeNe or Ar or Kr laser. Doug McDonald