You can make this 3-D image of Mars like this one in the same way the Rover's Pancam does. (click for larger image)

On board the Mars Exploration Rover s are a host of tools employed in the search for water on the red planet. A robotic arm and special camera serve as a chisel and magnifying glass.

Instruments called "spectrometers" gather and analyze light and other kinds of electromagnetic waves, and give clues to the chemical composition of Martian soil. But perhaps the most spectacular tool aboard the Rover is a set of stereoscopic "eyes" called the Pancam. Using 3-D images called "anaglyphs," the Pancam helps scientists steer the Rover and determine what rocks or other features to sample.

Not to mention that the Pancam will be sends live 3-D pictures of the Martian landscape!

How does the Pancam work? It works much like your eyes, using two images taken from slightly different angles to give dimension to a subject. Try this: Find an object near you to focus on. Close your left eye. Then open your left eye and close your right. Notice how the two things you see are slightly different? It's the combination of the two views that lends perspective and depth to your eyesight.

ACTIVITY
Make a 3-D Image of the Martian Landscape

You can re-create a stereoscopic image from the Mars Pathfinder mission using Adobe Photoshop. Here's how:

(If you don't have Photoshop, you can create stereographs using free software that you can download here. If you need to make 3-D glasses, you'll find instructions here.)

1) Download the starting images. The images you see on the right are thumbnails of photos taken by the Mars Pathfinder rover. You can download larger versions by clicking the images. A window will pop up with a larger version. To download them, right-click and go to "download image to disk." You can also mine the raw-data archives of daily rover images here.

Left view Right view

2) Create a document with both views. Open both right and left views. In the right view, go to Select -> All, then File -> Copy. This will put a copy of the right view on your clipboard. Then, in the left view, go to File -> Paste. This will create a new layer with the right view exactly on top of and in line with the left view. It may be helpful to rename the new layer "right view." You can do this in the layers palette, pictured at left.

3) Change color modes. In order to make anaglyphs, the pictures have to be in RGB color mode. Go to Image -> Mode -> RGB. It will ask you whether you want to flatten the layers. Say "no."
4) Change the colors of the black and white photos. In the layers palette, click on the layer with the right view to select it. Choose Image -> Adjust -> Levels. From the "Channel" pop-up, choose "Red." Type in 0 (zero) in both "Output Levels" boxes. Note that your image has turned cyan. Click OK.

5) Make a similar change with the left view layer. Select the left view in the Layers palette. Click the eyeball for the right view layer to make it invisible so you can see the left. Choose Image->Adjust->Levels. From the "Channel" pop-up, choose "Green." Type in 0 (zero) in both "Output Levels" boxes. Note that your image has turned magenta. From the "Channel" pop-up, choose "Blue" and type in 0 (zero) in both "Output Levels" boxes. Note that your image has now turned red. Click OK.

6) Make the top layer transparent. Go back to the Layers palette and click the eyeball for the right view layer to make it visible again. Make sure "right view" is selected. You need to make this layer transparent so the red layer shows through. From the pop-up menu near the top left of the Layers palette, choose "Screen".

What's going on?

Anaglyphs are a way scientists can make the Rover's Pancam and the images it sends us a sort of substitute for human eyes. There are two principles at work when you're viewing an anaglyph: depth perception and color filters.

Depth perception arises from having two images of the same thing taken from slightly different angles. You can see how your own eyes do this: Focus on a nearby object, cover first your right eye, then your left. How are the views different from each other? How is your sense of space affected?

The Pancam's lenses are similar to your eyes in that they're also set a short distance apart and take pictures from slightly different angles. You'll notice, if you put the two original pictures from the activity next to each other, that the difference between them resembles the difference between views when you covered your eyes individually. When your brain combines two flat images like these, whether they're what you see in the world around you or photos from a distant planet, it interprets the angular offset as depth.

So why adjust the color of the images? Again, this is a way of mimicking what your eyes do. Look at the final image of both perspectives composed one on top of the other. Without the glasses, both eyes see both images. But if you were standing looking at the landscape yourself, rather than looking at photos of it, each eye would only see one perspective. The 3-D glasses screen out one image from each eye.

To show yourself how this works, put your 3-D glasses on, and go to your final, layered file. Turn off the eyeball on the blue layer so that you only see the red one. Then look at the image using first just your left eye, then just your right. You'll notice that your left eye (the one behind the red lens) can see the red image quite well. But to your right eye (the one behind the blue lens) the image is nearly black. Now, turn the blue layer back on and turn the red one off, and do the same comparison. What do you see? In this way, the 3-D image tricks your eyes, so that each eye sees only one image, the way it would happen if you were actually looking at the landscape.

Going further

• Do the experiment described above again. Are the actual colors of red and blue important? Would a colorblind person be able to see the 3-D aspect of an anaglyph? How would their experience compare with that of someone who isn't colorblind?

• Turn your glasses around and look at your anaglyph with the red filter over your left eye and the blue filter over your right. Does this effect how the image looks? Why or why not?

• You can make anaglyphs from lots of other Mars pictures. You'll find them on NASA's Mars Pathfinder Stereo Pair Archive:

http://mars.jpl.nasa.gov/MPF/mpf/stereo-arc.html

• Need some 3-D glasses? Make your own!