Anaglyphs are probably the most widely used and recognizable stereo images. Their red and blue or cyan images, superimposed and slightly offset from one another are instantly recognizable to almost everyone because of their extensive use in comic books, 3D movies, and Mars Rover images (marsrover.nasa.gov/gallery/3d). Anaglyph stills and movies are also common on the Internet because you can save them in whatever file format a photo sharing or social networking site requires. Once uploaded all visitors need to view them is an inexpensive pair of red/cyan anaglyph glasses and a standard 2D TV or monitor. If you don't have anaglyph glasses you can buy them from a number of on-line sources. You may also find them at movie rental stores and sometimes where comic books are sold although the colors won't always be red and cyan. If you wear reading glasses, wearing them along with anaglyph glasses noticeably sharpens the image.

Once you become aware of anaglyphs, they seem to be everywhere. For example, Google Maps now displays street views in anaglyph 3D by right-clicking many street view images and selecting 3D mode on or 3D mode off. Also, the US National Park Service has anaglyphs of many of their parks ready for viewing at 3dparks.wr.usgs.gov.

You can see that the cyan image to be viewed by the left eye is offset to the left of the red image due to parallax at the time the pictures were taken.

Anaglyphs are popular but they have cons as well as pros:

PROS

• Anaglyphs can be any size from very small to very large. Also, since the two images are superimposed, they take up half the space of side-by-side images.
• You can view anaglyphs in books, as prints, projected with a 2D digital projector, and displayed on standard 2D TV screens or computer monitors. Anaglyph movies can also be played using any DVD player, or even a VHS tape player.
• The images can be viewed without special hardware and software other than the glasses.
• Anaglyph glasses are very inexpensive and can be bound or otherwise inserted into publications such as comic books and magazines.

CONS

• Anaglyph images tend to look dark, muted and desaturated, especially reds, because the colored lenses used to view the images remove and alter the light passing through them. To offset this to some extent you can increase the brightness of the light under which you view prints and turn up the brightness on your computer monitor.
• They look odd in 2D when not wearing anaglyph glasses.
• They can't be reproduced in black and white because colors are needed to direct each image in the stereo pair to the correct eye.
• Best results are achieved when images are prepared for a specific display and specific glasses. This is a problem since a lot of people then view them on-line through widely varying cheap glasses on displays with poorly adjusted colors.

The Principles

The principle of 3D anaglyphs was first proposed in 1853 by Wilhelm Rollmann and then adapted to practical use by Ducos du Hauron in 1891. Anaglyphs traditionally used a superimposed pair of colored images, usually cyan on the left and red on the right, with one image offset slightly from the other due to parallax at the time they were taken. When viewed through a pair of glasses with lenses of the same colors as the images but reversed so red is on the left and cyan on the right, the image appears in 3D. The principle behind this is that a color in a picture disappears when viewed through a filter of the same color, and appears black when viewed through a filter of a complementary color.

Based on the concept of complementary colors here is what happens when you view a red/cyan anaglyph through red/ cyan glasses. (If you have a pair of anaglyph glasses use them to view the color star above as you follow the discussion.)

• The red filter over the left eye displays the red parts of the image as white and the cyan parts as black. Whites and blacks are seen as is.
• The cyan filter over the right eye displays the cyan parts of the image as white and the red parts as black. Again, whites and blacks are seen as is.

As a result of this filtering of colors only the left eye sees the cyan image and only the right side sees the red one. Other colors in the scene are also affected, though not as much so you can see color anaglyphs.

Standard Anaglyph Glasses

Many anaglyph glasses were originally red and blue which was fine for viewing red and blue 3D line drawings such as those found in comic books. However, when viewing full-color photographs they have their shortcomings. For this reason other color combinations are now used—the most popular being red and cyan because cyan improves some colors, especially lighter skin tones, green foliage and blue skies. This is because the cyan filter lets through a range of colors from blue to green. The quality of the color filters in the glasses you use make a difference. Reds are usually consistent from one pair to another but cyan varies widely both in hue and saturation. There are those who think that, all else being equal, glasses with a lighter cyan work best because the lighter cyan lets you see more colors in a full-color image.

In addition to lens colors, another affect on image viewing is the optical quality of the lenses which range from cheap paper versions to those with plastic frames and molded acrylic lenses. Some of these later glasses are available with a diopter power to correct the focus shift in the image passing through the red filter. Some people, especially the nearsighted, find this correction uncomfortable because it causes the left and right lenses to have different magnifications. However, for others, having both eyes focus on the same point increases image sharpness and improves contrast.

Other Anaglyph Glasses

To improve viewing full-color anaglyph photos and movies the filters used in your lenses make a difference in the quality of colors you perceive and ghosting—when one eye sees the image meant for the other. In addition to red and cyan lenses, there are also the following glasses in play and you can learn more about them on the Internet. Some of these are patent protected proprietary systems used mainly for movies or print media when the glasses are distributed along with the media to be viewed. The reason there are so many new developments in this area is because a large percentage of the potential audience wants to be able to display 3D stills and movies on their existing home 2D equipment.

• Anachrome™ glasses (www.anachrome.com) use a more transparent cyan filter to retain more of the colors, letting a little red through to improve skin tones. Also, when taking pictures to be viewed with these glasses, the offset or parallax between the two images—called the baseline—can be reduced by moving the camera lenses closer together. Images captured this way have less disparity and look almost normal when viewed without glasses. (Baselines are discussed in Chapter 3.) The closely related Mirachrome glasses have more diopter power, and are for close viewing on small screens. This system works best when photographs are taken and processed specifically for it.
• Triscopic glasses (www.trioscopics.com) have a green left lens and magenta right.
• TriOrviz glasses (www.trioviz.com) have a magenta left lens and green right.
• ColorCode 3-D (www.colorcode3d.com) have an amber left lens and dark blue right. This color system was developed for use with the NTSC television standard that poorly displayed the traditional red channel.

Creating Anaglyphs

Until the digital era, colored filters were used over the camera lenses and the same colors were used in the viewing glasses. Today the camera filters have been replaced by software so the original images in the stereo pair are not affected at the time they are captured and can be used just like any other full-color 2D photos. There are many software programs available that create anaglyphs from stereo pairs including StereoPhoto Maker and Photoshop, both of which are discussed in Chapter 4. As you’ll see in that chapter the following types of anaglyphs can be made from a stereo pair with the click of a mouse in StereoPhoto Maker:

Phantograms

Phantograms, which are technically called stereo anamorphic images, and which StereoPhoto Maker calls "popup anaglyphs," are anaglyphs taken, often of simple subjects, from the same angle they will be viewed from. For example, after photographing a subject 3 feet away with the camera at a 45° angle the stereo pair are printed, laid on a flat surface and viewed from 3 feet away at a 45° angle using anaglyph glasses. The effect is very realistic. If you are viewing images on a laptop, or using a monitor with a tilt capability, tilt the top away from you, ideally at a 45° angle.

Viewing Phantograms on a vertical computer screen lets you see the 3D effects but doesn’t give you the dramatically realistic effect. Since most phantograms are shot with the camera pointed down and at an angle, that’s how they should be viewed. Creating these images is beyond the scope of this book but the process, which is admittedly technical, is described in detail in StereoPhoto Maker’s Help. Just search for "Popup Anaglyphs").