# How do color 3-D DVDs work with blue and red glasses?

I rented a copy of Shrek 3-D and it came with red and blue glasses

I understand monocrome 3-D comics with the left eye image one color and the right eye image the other.

And I understand color 3-D with Viewmaster, where each eye sees a different image entirely.

I understand color 3-D with polarized glasses, like at the IMAX theatre - they have two projectors and each has a different polarized filter over it, so each eye sees a different image.

But with DVD, there’s only one image for both eyes.
And without the glasses it looks like a regular cartoon, with plenty of blues and reds in it.

The glasses do seem to make some difference, not nearly as good as polarized, but some true depth perception.

So how does that work?

Red/Blue 3D works the same way as polarized 3D, except that the second image is in the red channel only, so it can be represented without a special projection setup. Back in the day, it used to be done optically. Now, it’s easier to do it digitally, and you get less colour loss. Through the red filter, you see everything except what’s in the red channel, and through the blue filter you see the red channel only.

(I do a lot of red blue 3d stuff– I’ve been obsessed ever since I saw Andy Warhol’s Frankenstein and Parasite one summer when I was a kid.)

I guess that’s not the clearest explanation. Here’s a step-by-step.

Here’s a 3D conversion I made of a 2D painting, using photoshop. Got your funny glasses on? Good!

I left the image alone for the left eye, of course. I did some tricky stuff to recreate the image as it would appear if it were solid and viewed from about two inches further right. After I had the two images, I just replaced the red channel from the first image with the red channel from the second.

Now the colours look more or less true without glasses, because the red channel more-or-less matches up with the blue and green channels. The only places you see something is odd is at the edges of things, where they don’t quite line up. This gets approximately fixed up when you look through the filters. The cyan “ghost” image you see without glasses will appear as a dark, solid image when viewed through the red filter, and invisible through the blue filter. The red “ghost” image you see will be invisible through the red filter, and solid-looking through the blue filter.

Although it’s just one image, it contains information from two images which can be split up and rerouted to the corresponding eye with the filters, and your brain works out the parallax to give you the 3D effect.

Lotsa fun!

This might help to illustrate:

I made a little 3-frame looping gif animation of the above picture.

The first frame shows the blue/green channels, the next frame is the red channel only, and the third frame is all three together.

Check it out with your glasses and it will make it clearer what’s going on. (Try looking through one eye at a time.)

Death knocking at the door. (Hieronymus Boschpainting made all 3D-like.)

Again, the colour looks normal because one eye gets the red and the other eye gets the blue and green, and the two images are similar enough to make a coherent RGB image.

I hate to disappoint you, but I don’t think you were looking at the 3-D version, but the normal version on the same DVD.

I have that DVD, and there are several options. The 3-D one looks nothing like a regular cartoon and is unwatchable without the glasses. There’s a blur of maybe an inch of red or blue around every object.

If you look at the regular version with 3-D glasses (indeed if you look at any normal TV show wearing the glasses) you will think it’s “sort of 3-D”.
I think it’s just that they add a blur around all object outlines and the eyes decide it is a depth separation and experience tells you what’s moving toward you, from normal clues like increasing size.

According to Pliny - You were exactly right. I found my error when I tried to find the Special Features screen of the DVD.

The 3-D version is really bad. Things get all out of focus and strange when too close.

And the 3-D effect of using colored glasses on regular images is something I now recall from prior inteactions with this system.
Remember some time back when the networks were competing to do 3-D shows, like a Third Rock From The Sun special? You had to get glasses someplace like 7-11.

And when you put them on you’d say, “Well it’s sort of 3-D but not great” and then they would tell you it was now time to put on the glasses- you had been watching the regular portion of the show.

**Larry Mudd **- Thanks for the links.
Unfortunately, it sort of confirms my original suspicions that colored lenses aren’t goting to work well with colored images.
The effect is there, but the second one went from browns to black and white with the glasses.
The lady went from natural color to mostly browns.
I think since you lose color from both eyes, the best originals for this sort of thing would be those with really bright colors.