Angles Of View
Lenny Lipton is the founder and Chairman of the Board of StereoGraphics Corporation in San Rafael, California. Mr. Lipton has been a pioneer in the development of 3D projection systems and is the inventor of the first practical electronic stereoscopic products for computer graphics and video applications. Also the author of numerous books and articles on film and film making, Mr. Lipton can be reached at Lenny@crystaleye.com . He is interviewed here on the subject of
3D - Just Another Dimension?Da-Lite: Three dimensional imaging is experiencing a noticeable resurgence. May we suppose that this renewed interest is driven by parallel developments in computer technology?
Lipton: Yes. The marriage of electronic displays and computers with binocular stereoscopic displays is a good one. It actually turns out to be easier to make a dependable 3D product using a computer graphics monitor and time sharing or time multiplexing techniques than it is to go into a neighborhood theater and turn it into a stereoscopic theater.
Nevertheless , a major change which has taken place in the projection of stereoscopic movies is that, in the last decade or so, you can find them being shown on a regular, continuing, and ongoing basis, particularly in theme parks.
Da-Lite: Are these movies well produced?
Lipton: Yes. They are well shot and well projected, in the sense that there are no technical screw ups such as the projectors getting out of synch or all kinds of other awful things. They have a dedicated projectionist who’s in the booth all the time and not down at the candy counter or running about the other fourteen theaters in the multiplex. And you need that expert technician which the theme parks can provide but which just isn’t practical for a neighborhood theater.
Da-Lite: Is this part of the reason 3D has enjoyed only a cyclical popularity?
Lipton: It is true to say that stereoscopic imaging has had an erratic history in terms of commercial acceptance. There have been a lot of problems, technical problems which have been difficult to overcome.
Da-Lite: What are some of these problems?
Lipton: Stereoscopic projection requires two images, one for each eye. Both of these images have to be of the same brightness. So the upper right hand corner of the right image has to be as bright as the upper right hand corner of the left image. And that’s true on a point-by-point basis across the entire screen.
If, for example, the right image which is being projected has a lot of vignetting and the left image doesn’t, it’s going to feel very bad to look at.
Da-Lite: Is the ordinary viewer going to be able to tell why he feels that it’s bad?
Lipton: No. Because these things are not seen in the visual world; these mistakes can only occur in a stereoscopic display. So if one image is out of focus, or one image is higher than the other or contains different color values, you’ll feel uncomfortable looking at it, but you’d have to be an expert to diagnose the problem exactly.
Typically the discomfort a viewer feels is referred to some other part of the body. Occasionally people will say their eyes hurt but usually it’s a headache or a feeling of nausea that’s experienced. Sometimes instead of stereoscopic images, bad projection will produce pseudoscopic images.
Da-Lite: Whatever are they?
Lipton: Pseudoscopic is when the left eye is seeing the right image and vice versa. Now that’s something you never see in the visual world and its very strange and confusing.
Da-Lite: So if you pump left-eye data through the right eye...?
Lipton: It doesn’t add up to a stereo image. You get a conflict of cues; the stereoscopic cues will conflict with the monocular cues.
There are many ways you can perceive depth and see a three dimensional image in the real world. When you look around this office there are lots of depth cues. For example, geometric perspective. The edges of the ceiling tiles form receding lines. Then, because I’m in front of the wall behind me, you can’t see it through me. That’s a cue called interposition. If you look out the window there at those hills, there’s a little bit of haze between us and the hills and that makes them look further away. That’s called aerial perspective. All in all, there are about half a dozen such cues.
Da-Lite: And these cues obtain in a photographed image as well?
Lipton: Sure, but when you add a stereoscopic cue that’s a pseudo stereoscopic cue, there’s a massive conflict which may actually inhibit some viewers from being able to recognize what they’re looking at!
Da-Lite: What are the ways to avoid this sort of mistake and how do you make good stereoscopic imagery?
Lipton: You’d think it would be easy, wouldn’t you? After all, it’s just a matter of the coordination of two images.
Well, you need somehow to generate or capture two images from two perspective viewpoints and those perspective viewpoints have to be related by a rule or series of rules.
Da-Lite: So, since you need to use two cameras, how far apart must they be?
Lipton: The answer that I like is, far enough apart to make a good looking picture but not so far apart that it hurts your eyes. For large scale, aerial photography you might have 20 feet between the cameras. At the other extreme, if you’re doing computer generated images of molecules, then the interaxial separation of the perspective viewpoints is going to be extremely close together.
Da-Lite: If it’s not the interaxial separation, what is the mechanism which creates the extension out of the screen?
Lipton: The principle entity in a stereoscopic image is called parallax. This refers back to your eyes. Your left and right eyes are seeing slightly different images of the visual world. Now, if you could freeze those images on your left and right retinas and, say they were on film, you removed them and then superimposed them one on top of the other, you would see that there’s a horizontal displacement of corresponding image points. The superimposition would be good vertically, but there would be some points which would laterally be displaced. And it’s that information which on the retinas is called retinal disparity.
The purpose of stereoscopic photography or computer generated imagery is to produce retinal disparity.
Da-Lite: But how does this disparity give that special depth sense?
Lipton: When you look at a display screen, your eyes are focused at the plane of the screen. And they’re also converged at the plane of the screen. This is similar to when you hold out a finger in front of your face. When you look at that finger your eyes are focused on it and they are also converged which means that the axes of the left and right eye cross or intersect at the finger.
Now when you look at a stereoscopic image on a display screen your eyes may be focused at the plane of the screen but they’re converged for differing distances, either in front or behind the plane of the screen. This is different from seeing in the real world and it uses different sets of eye muscles.
Da-Lite: Most people can remember seeing 3D movies. Are there other, more industrial applications for the technology?
Lipton: Definitely. The history of my company, for instance, has paralleled the development of the interactive computer display. The capacity of these devices to generate stereoscopic imagery enables the customer base to use workstations to do scientific visualization.
If, for instance, you’re looking at a complicated molecule and there are therefore hundreds of atoms on the screen, the way that people have tried to visualize the structure is to rotate it. This adds another monocular depth cue which is called motion parallax, which gives you a continuous change between the portions of the image that are close and the portions of the image that are far. By rotation, then, people found they could visualize a complicated shape.
The only trouble was, if you stopped it, the three dimensional effect vanished. This is why if you want to stop a complicated object and study it carefully you need to have it displayed stereoscopically.
Da-Lite: What other sorts of research employs stereo graphics?
Lipton: People in astronomy and people in computational fluid dynamics use the technology. The latter use includes wind tunnels and aircraft design, for instance.
Another use is satellite earth mapping where the aerial photographs are digitized and, when projected stereoscopically, can then be analyzed in exquisite topograpic detail.
Da-Lite: That’s a long way from throwing a spear out of a movie screen, isn’t it?
Lipton: It certainly is. The rise of multi-media PCs and their monitors have enabled a whole new approach to stereoscopic display. For computer generated imagery you have only one projector” (the monitor) and the way you produce stereo graphics is to alternate left eye, right eye information about 80 or 90 times a second.
To "see" the stereo graphics, you put on wireless active eyeware which we call CrystalEyes®. These contain liquid crystal shutters which, through an infra red link with the projection source, open and close their left lens, right lens in a manner exactly synchronized with the monitor.
Da-Lite: Can this technology be employed using CRT video projectors?
Lipton: Absolutely. It is also possible with the video projectors to use passive polarizing eyeware. This requires a liquid crystal modulator which switches the characteristic of polarized light at the video field rate, so it switches between one type and the other type of polarized light 120 times a second, and when you look through the polarizing glasses at the right kind of screen, you see stereoscopic images.
Since the screen must preserve polarization in this type of display, you need something like your Super Wonder-Lite® for front projection or one of your high-gain, profiled screens for rear. The CrystalEyes® approach of course permits you to use any screen surface you wish as it is not dependent on polarization effects.
Da-Lite: How significant is it that you’ve developed ways to get away from double projectors to create 3D?
Lipton: Extremely. My design philosophy is that I’m interested in products, not experiments. We have to make the displays work with one computer, one tape recorder, one projector. Anything else is, these days, just an experiment.
So it’s not only the rise of powerful computers and all kinds of improvements in display technology that have enabled us to make a product but also the development of these electro-optical shutters which can be opened and closed as much as 160 times per second.
Da-Lite: At such large field rates the viewer is certainly not going to see flicker, are there any other defects he might encounter?
Lipton: No. You should be able to create a perfect stereoscopic image if it’s computer generated.
Da-Lite: So what’s next?
Lipton: Next, of course, is to get rid of the glasses.