More 3D than 3D: Stereoscopic Defined

Let's start with reality: we live in a world where things occupy a finite volume of space at any given moment in time... Alright, maybe that's not a good way to explain this. Let me try again. Stuff we see in real life has some width, some height and some depth. Our life in our 3D world and our two eyes give us the ability to quickly and easily judge position and dimensions of objects. 3D video games try to approximate this by drawing a two image that has many of the same "depth cues" we use to judge position and shape in reality.

Looking at a picture of something, a 2D image can help us perceive some of the depth that we would have seen if we had stood at the same location as the camera: stuff that's further away appears relatively smaller than the foreground. Shadows and lighting help give us a feel for dimensions as they fall on objects. If we were to talk about video, we would see parallax in effect making it look like objects closer to the viewer move faster than objects further away. Our experience tells us that we can expect certain constants in our reality and we pick up on those and use them to judge things that look similar to reality. Video games exploit all these things to help tell our brains that there is depth in that monitor. Or maybe we're looking at a video of something that was reality. Either way, there is something major (aside from actual depth) missing.

Though we can judge 3 dimensions to a certain extent based on depth cues, having two eyes see objects from two slightly different positions is what really tells our brain that something has depth. The combination of these two slightly different images in our brain delivers tons of information on depth. Trying to play catch with one eye is tough. Just ask your neighborhood pirate.

Seeing two different images with your two different eyes, or rather presenting two different images of the same thing from slightly different positions, is what stereoscopic 3D is. It's right there in the word ... ya know ... stereo ... and scopic. Alright, moving on.

If you've ever tried looking at those "magic eye" pictures, you know what impact just stereoscopic info can have. For those who don't know, a magic eye image is a seemingly random looking pattern that when viewed with your eyes looking "through" the image reveals a hidden 3D picture. Though there is absolutely no other depth information in the picture, no lighting or shadows, no perspective projection, nothing but basic shapes that each eye picks up when you focus through the image, the 3D effect is pronounced and looks "deeper" than any 3D game out there.


This is not a sailboat.

Combining stereoscopic information with all the other depth information makes for a dramatic effect when done properly. Correct rendering and presentation of left and right eye images with proper 3D projection, lighting all that simply looks real enough to touch. Viewing a game properly rendered for stereoscopic effects can range from feeling like looking at a shoe box diorama or a popup book to looking through a window into the next room.

Hollywood tried stereoscopic 3D with anaglyphs (those red and blue images you need the red and blue glasses for), but it didn't really take off except as a sort of lame gimmick. Back in the late 90s and early this century, we saw the computer industry test the waters with active shutter glasses that worked quite a bit better. Rather than displaying a single images with both eye views superimposed requiring filtering, shutter glasses cover one eye while the entire screen displays an image rendered for the other eye. That eye is covered while the first is uncovered to see it's own full resolution full color image. When done right this produces amazing effects.

There are a couple catches though. This process needs to happen super fast and super accurately. Anyone who spent (or spends) hours staring at sub-60Hz CRTs knows that slow flicker can cause problems from eye strain to migraines. So we need at least 60Hz for each eye for a passable experience. We also need to make absolutely certain that one eye doesn't see any of the image intended for the other eye. Thus, when building active shutter glasses, a lot of work needs to go into making both lenses able to turn on and off very fast and very accurately, and we need a display that can deliver 120 frames per second in order to achieve 60 for each eye.

Early shutter glasses and applications could work too slowly delivering the effect with a side of eye strain, and getting really good results required a CRT that could handle 120Hz and glasses that could match pace. It also required an application built for stereoscopic viewing or a sort of wrapper driver that could make the application render two alternating images every frame. Requiring the rendering of an extra image per "frame" required realtime 3D software to be very fast as well. These and other technical limitations helped to keep stereoscopic 3D on the desktop from taking off.

There is still a market today for active shutter glasses and stereoscopic viewing, though there has been sort of a lull between the production of CRTs and the availability of 120Hz LCD panels. And while LCDs that can accept and display a 120Hz signal are just starting to hit the market, it's still a little early for a resurgence of the technology. But for those early adopters out there, NVIDIA hopes to be the option of choice. So what's the big deal about NVIDIA's solution? Let's check it out.

Index Not Just Another Pair of Glasses: GeForce 3D Vision at Work
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