Since settling in on the red
planet, the Mars Exploration Rovers Spirit and Opportunity have sent back a
number of 3-D postcards to countless fans outfitted in red- and blue-tinted
spectacles. To some, the realistic pictures of the rocky Martian terrain may
seem magical, but the concept behind the illusion is in fact quite simple.
"Basically, 3-D pictures trick your
brain into doing what it does all the time in the real world," says Zareh
Gorjian, a graphic artist at NASA's Jet Propulsion Laboratory who makes 3-D
pictures and animations of Mars for a living, both the black-and-white
photography and the more advanced color photography.
So simple is the trick that, with a
little effort, anybody with a camera, a computer equipped with
photography-editing software, and a pair of tinted glasses can make their own
3-D pictures of Mars, family members, pets or anything else worth placing in
front of a lens.
Gorjian, who has been toying with the
technique for 10 years, transforms all sorts of pictures into 3-D feasts for the
eyes, including his latest vacation photos. "It's just fun," he says.
The key to 3-D imaging lies in
simulating a left and right eye. For the Mars Exploration Rovers, this is
accomplished with the aid of a left and right camera eye. Images from the
rovers' stereo camera lenses (either the hazard-avoidance cameras, the
navigation cameras or the panoramic cameras) are tinted in red and blue, then
merged into one blurred picture, which pops off the page when viewed through a
pair of red- and blue-tinted glasses.
"Your brain thinks it is seeing two
separate left and right images and so does what it always does -- combines them
into one picture," says Gorjian.
These basic 3-D photos are called
anaglyphs and work best when viewed in black and white. Color anaglyphs are
trickier because red and blue objects appear only to one eye. "You give up full
color when you use the red and blue glasses," says Gorjian.
Instead, he and his colleagues at JPL's
Multimission Image Processing Laboratory create 3-D color photographs using two
sophisticated techniques: polarization and infrared-transmission. In
polarization, the light from left and right eye images is polarized, or made to
travel in opposing, perpendicular directions. In infrared-transmission, left and
right eye images are flickered back and forth on a special screen faster than an
eye can blink. Both strategies require specialized glasses for viewing.
But black-and-white 3-D images do not
require fancy tools or equipment and can be snapped and clicked into being by
following these directions recommended by Gorjian:
Step 1
Start out by picking a subject. People are a good place to begin because they
tend to pop out in 3-D photography. Place the subject in a setting with a
lot of angles and depth (not in front of a flat wall), and about 10 to 15 feet
from the camera. Hold the camera steady by securing your elbows in your chest
and snap a picture. Make sure your subject stays very still, then step just a
tiny bit to the right, about the distance between your eyes or less, and take
the same picture. When you slide over for the second shot, you -- and most
importantly your camera -- should move in a parallel line.
Note: If Mars is your subject,
the pictures have already been taken for you. Scan through the raw images on the
JPL web site http://marsrovers.jpl.nasa.gov and pick out left and right eye images for your favorite photo (only images
taken by the rovers' navigation cameras, hazard-avoidance cameras and panoramic
cameras come in pairs). The stereo images will look identical, but you can tell
if an individual image is from the left or right camera eye by clicking on it
and looking at the file name displayed in the web address bar. Left camera eye
image file names will contain the letter "L" four characters in from the end,
and right eye image file names will similarly carry an "R." Two raw image
examples can be found at
http://marsrovers.jpl.nasa.gov/gallery/all
/2/n/043/2N130199337EFF0700P1817R0M1.HTML,
and http://marsrovers.jpl.nasa.gov/gallery/all/
2/n/043/2N130199337EFF0700P1817L0M1.HTML .
Step 2
The next step involves transferring the images into photography-editing
software. Any program will work as long it allows for red, blue and green color
channels to be manipulated independently. The following instructions will refer
to Adobe Photoshop. If your pictures are digital, just open them up in the
software. If your pictures are hardcopies, transfer them to a computer using a
scanner, or drop them off at a photo-developing store and ask for digital files
(any file type will work).
Step 3
Once the left and right eye pictures are open, convert them both to grayscale by
clicking on the 'Image' menu bar and selecting 'mode' then 'grayscale'. Next,
assign the left eye image red, green and blue channels by going back to the
'Image' menu bar and selecting 'mode' then 'RGB' (the image will still appear
gray). Do not repeat this step for the right eye image.
Step 4
Now you are ready to merge the left and right images. To begin, make sure the
left eye image is still selected. Open the channels display menu by clicking on
the 'Window' menu bar and choosing 'channels.' Highlight the blue and green
channels (press the shift key to highlight both at the same time). Important:
only the blue and green channels should be shaded blue. At this stage it doesn't
matter which boxes to the left of the channels show eyeballs (eyeballs indicate
which channels are displayed).
Step 5
Go back to the right eye image, select the whole thing (go to 'Select' menu bar,
then press 'all') and copy it (go to 'Edit' menu bar, then press 'copy'). Switch
back to the left eye image and paste (go to 'Edit' menu bar, then press
'paste'). Now, highlight the RGB color channel; an eyeball should appear in all
four channel boxes. At this point, you should see a blurred red and blue
picture.
An alternative to this step is to use
only the blue channel instead of the blue and green when pasting into the left
eye image.
Step 6
You are almost done. But first the left and right eye images need to be better
aligned. Start by highlighting only the red channel in the channels display menu
(it should be shaded blue). The next step is crucial because it allows the
red-tinted picture to be shifted over while the blue-tinted picture is still
visible. Go to the RGB channel and click only on the square box to the left. An
eyeball should appear in all four boxes, but only the red channel should be
shaded. Now pick a point in the center of the picture to match up; for example,
if a person is your subject, eye pupils are a good target. Zoom in on the target
by selecting the magnifying glass icon in the tool bar then click on the target
until it appears fairly large.
Step 7
Next, select the 'move' tool located in the upper right corner of the tool bar.
Using the up and down arrow keys, slide the red-tinted image over until your
target matches up and no longer shows any rings of color.
Step 8
Zoom back out. Objects toward the outside of your picture should still be haloed
in red or blue. In other words, the overall goal in this step is to limit the
colored tints as much as possible. To cut out excess red or blue at the far
edges of your picture, crop it using the crop tool, also located in the tool bar
(once you've outlined your picture with the tool, go to the 'Image' menu bar
then press 'crop').
Your creation is ready to be viewed!
Just don your paper glasses (the left eye should be tinted red) and watch the
picture jump out at you from your monitor screen or a printed picture.
Courtesy of Jet
Propulsion Laboratory |
