Viewing stereo images

Using stereo anaglyph (red/green) images from the Mars Rover lander, this tutorial shows how to separate the images into left/right pairs suitable for 'cross-eyed' viewing.
Resources needed: Photodesk

The Mars Rover landing craft have stereo cameras on board, designed to replicate the view a human would get on the surface of Mars. Many of the published images are in anaglyph format -- a pair of left/right images combined into one, each with its own colour and designed to be viewed with special glasses which filter each colour appropriately.

While viewing such images is easy, you do need a pair of appropriate glasses, and the technique does not allow true colour. There are other ways to view stereo images without special equipment, such as the 'cross-eye' technique. This does require some practice to get the effect, but the results can be much better and it allows true colour viewing.

(There are many methods of viewing stereo images. One interesting recently developed technique involves rapid animation, as can be seen here. Warning: contains some nudity.)

It's easy to create your own stereo images -- just take two pictures of the same scene with the camera moved a couple of inches between shots. Here's one you can use to practice 'cross-eyed' viewing on:

You'll need to be able to see all of this image (800x600 screen size minimum). Position your head directly in front of the screen, and ensure your head is level. Relax your eyes, and with a bit of practice the images will merge -- if you've ever been able to see 'magic eye' images, the technique is much the same. One trick is to put your finger on the screen surface, focus on it, and gradually move it closer to your eyes. Once you've done it once, it becomes much easier.

After a successful landing on 3 January 2004, the Mars Exploration Rover Spirit started taking pictures with its stereo camera. These were made available in anaglyph form, but it's easy to separate the pictures out for 'cross-eyed' viewing. Here's a typical image:

If you have a pair of red/green glasses, you'll be able to see the 3D effect. If not, here's what to do.

• Load this image into Photodesk.
• Unless you've got a big monitor, scale the image so you'll be able to see 2 copies of it side by side. Half-size is about right.
• Click on the Channels icon (second from left on the toolbar) to open the channels window.
• Click on the #1 icon, which will cause the red channel only to be displayed. If you switch between that and the green (#2) display, you'll be able to see the image move slightly.
• Now save out each channel. Click on the word "Red", and it should highlight. Click Menu over the window and go to Channel 'Red'>Save>. The quickest way to get a display is to drop the sprite icon straight into Paint.
• Repeat for the green channel.
• Align the two Paint windows next to each other. The 'green' sprite should go on the left, and the 'red' on the right (Photodesk usefully gives the sprites appropriate names). Here's the result:

  Green channel

  Red channel

You may notice some glitches in the images. These are caused by imperfect stiching together of the various frames; presumably JPL will release better quality ones at some point.

Here are a few more images, each presented as a red/green anaglyph and a pair of stereo images. All are courtesy JPL/NASA.

Notes

• There's a newsgroup devoted to stereo imaging: alt.binaries.pictures.stereo
• Some more hints on viewing stereo images can be found at various sites linked to from here (Google search).
• Source images can be found at the JPL Mars Rover site.