Anaglyph image





Anaglyph images are used to provide a stereoscopic 3d effect, when viewed with 2 color glasses (each lens a different color). Images are made up of two color layers, superimposed, but offset with respect to each other to produce a depth effect. Usaully the main subject is in the center, while the forground and background are shifted laterally in oposite directions. The picture contains two differently filtered colored images, one for each eye. When viewed through the "color coded" "anaglyph glasses", they reveal an integrated stereoscopic image. The visual cortex of the brain fuses this into perception of a three dimensional scene or composition.

Anaglyph images have seen a recent resurgence due to the presentation of images and video on the internet, CDs, and even in print. Low cost paper frames or plastic-frammed glasses hold accurate color filters, that typically, after 2002 make use of all 3 primary colors. The current norm is red for one channel (usually the left) and a combination of both blue and green in the other filter. That equal combination is called cyan in technical circles, or blue-green. The cheaper filter material used in the past, dictated red and blue for convenience and cost. There is a material improvement of full color images, with the cyan filter, especially for accurate skin tones.

Video games, theatrical films, and DVDs can be shown in the anaglyph 3D process. Practical images, for science or design, where depth perception is useful, include the presentation of full scale and microscopic stereographic images. Examples from NASA include Mars Rover imaging, and the solar investigation, called STEREO, which uses two orbital vehicles to obtain the 3D images of the sun. Other applications include geological illustrations by the USGS, and various online museum objects.

Anaglyph images are much easier to view than either parallel sighting or crossed eye stereograms. However, these side-by-side types offer bright and accurate color rendering, not easily achieved with anaglyphs.

With the techniques outlined below it is possible to convert stereo pairs from any source into anaglyph images.

Producing anaglyph images
In historical methods using camera filters, on film, two images from the perspective of the left and right eyes are projected or printed together as a single image, one side through a red filter and the other side through a contrasting color such as blue or green or mixed cyan. As outlined below, one may now, typically, use an image processing computer program to simulate the effect of using color filters, using as a source image a pair of either color or monochrome images. Since the turn of the 21st century, most filtering, both in glasses and processing have favored primary red, for the left eye, and cyan (which is equal parts blue and green) for the right eye. These 3 colors cover the entire visible spectrum, providing more natural color. Popular professional programs such as Adobe Photoshop provide the basic digital tools for processing of anaglyphs. They do not provide instruction for anaglyph in their basic documentation. Various websites offer free instruction related to Photoshop. Simple, low cost programs, dedicated to anaglyph creation, are also available. In practice, the left eye image is filtered to remove blue & green. The right eye image is filtered to remove red. The two images are usually positioned in the compositing phase in close overlay registration. In Photoshop, for example a function called "screen" allows the two filtered layers to be combined transparently, on each other, although the compositing can also be done by pasting into the selected channels.

How Anaglyph works
Viewing anaglyphs through appropriately coloured glasses results in each eye seeing a slightly different picture. In a red-blue anaglyph, for instance, the eye covered by the red filter sees the red parts of the image as "white", and the blue parts as "black" (with the brain providing some adaption for colour); the eye covered by the blue filter perceives the opposite effect. True white or true black areas are perceived the same by each eye. The brain blends together the image it receives from each eye, and interprets the differences as being the result of different distances. This creates a normal stereograph image without requiring the viewer to cross his or her eyes.

3D in the movies
From 1952 to 1955, 3D movies became very popular with more than 40 titles enjoying wide distribution, then lost ground as the competing Cinemascope widescreen systems became heavily promoted by major studios. Contrary to "revisionist" claims, 98 percent of the screenings in theaters in the fifties were presented in polarized, dual-projector interlocked format, not in the anaglyph format with colored glasses, according to authoritive American 3D historians Ray Zone and Dan Symnes and veteran Hollywood 3D producers, Allan Silliphant, the late Arch Obler in their public statements. There was a resurgence of 3D interest in the sixties,seventies and eighties due to the simplification of stereo polarized projection in two "single strip" processes pioneered by Obler (Spacevision) and Silliphant (Stereovision). Stereovision remained the main format for 35mm theatrical distribution of 3D until the emergence of the larger, IMAX 70mm 3D format.

Modern 3D movies
Spy Kids 3D was commercially successful in theaters using anaglyph paper glasses in 2003. The DVD did not sell or rent well, due to video retailers not wanting to deal with the paper glasses. Polar Express, in 2004, used the superior IMAX polarized method for 3D. That film made $62 million dollars in less than 90 theaters over two holiday seasons. It earned 14 times as much as the 2D version of the film,per screen, which is "un-precedented". A second, anaglyph film, 2005 by Robert Rodriguez, The Adventures of Shark Boy & Lava Girl failed to recover investment by many millions. The film had been processed in a highly "desaturated" 3D style, which was not very appealing. Disney released their 2005 Chicken Little in about 84 theaters, in digital polarized 3D. It earned nearly 3 times the gross of the much wider 2D release. 6 new films were slated for 3D release in 2006. They include Monster House, portions of the IMAX version of Superman Returns, The Ant Bully, Open Season, Nightmare before Christmas (converted to 3D), Fly Me to the Moon, all in polarized 3D. Anaglyph may have more applicability in the home market, should this crop of polarized 3D films prove commercially viable in theaters. At this point, anaglyph offers the only practical method for wide distribution of 3D home DVDs, or HD broadcasting in 3D, without costly electronic glasses.

Conversion from 2D flat to 3D anaglyph
In recent years computer technology and professional skills have made it practical to convert still images, movies & video to 3D. Color anaglyph looks particularly good in HD, with animation content. See NASA Illustration converted to Anachrome 3D. A feature film like Star Wars might cost as much as $10 million to convert for theater showing. The HD DVD 3D version might cost a fifth of that amount.

Note: Information below relates to "traditional methodology", not the newer techniques, mentioned above.

Viewing


A pair of eyeglasses with two filters of the same colors, once used on the cameras (or now simulated by image processing software manipulations) is worn by the viewer. In the case above the red lens over the left eye allows only the red part of the anaglyph image through to that eye, while the cyan (blue/green) lens over the right eye allows only the red and green parts of the image through to that eye. Portions of the image that are red will appear dark through the cyan filter, while portions of colors composed only of green and blue will appear dark through the red filter. Each eye therefore sees only the perspective it is supposed to see.

Red sharpened anaglyph glasses
Simple paper, uncorrected gel glasses, cannot compensate for the 250 nanometer difference in the wave lengths of the red-cyan filters. With simple glasses, the red filtered image is somewhat blurry, when viewing a close computer screen or printed image, The (RED) retinal focus differs from the image through the (CYAN) filter, which dominates the eyes' focusing. Better quality, molded acrylic glasses frequently employ a compensating differential diopter power to balance the red filter focus shift relative to the cyan, which reduces the inate softness of red filtered light.

The correction is only about 1/2 + diopter,on the red lens. However, some people with corrective glasses are bothered by difference in lens diopters, as one image is a slightly larger magnification, than the other. Though endorsed by many 3D websites, the diopter "fix" effect is still somewhat controversial. Some, especialy the nearsighted, find it uncomfortable. There is about a 400% improvement in accuity with a molded diopter filter, and a noticable improvement of contrast and blackness. The American Amblyopia Foundation, uses this feature in their plastic glasses for school screening of children's vision, judging the greater clarity as a significant plus factor.

Anachrome filters
Plastic glasses, developed in recent years, provide both the diopter "fix" noted above, and a change in the (CYAN) filter. The formula provides intentional "leakage" of a minimal (2%) percentage of red light with the conventional (BLUE/GREEN) range of the filter. This assigns, two eyed, "redness cues" to objects and details, such as lip color, and red clothing that are fused in the brain. Care must be taken, however, to closely ovelay these (RED) areas into near-perfect registration, or "ghosting" will be annoying. Anachrome formula lens, work well with black & white, but can provide excellent results when the glasses are used with conforming, "anachrome friendly" images. The US Geological Survey, has posted thousands of these "conforming", full-color images on their popular 3D site, which depicts the geology and scenic features of the U.S. National Park System. By convention, anachrome images try to avoid excess seperation of the cameras, and parallax, thereby reducing the ghosting that the extra color bandwidth introduces to the images.

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Making an anaglyph image
The following method assumes that the stereo pair is available as a digitized image and that access to general purpose image processing software and computer is available.

Starting with a pair of color images, or a sepia (toned) image, first convert each to grayscale (shades varying between black and white). Select the right image and paste it into a new document. Convert the new document to color (it still looks black and white, with all channels identical). Returning to the grayscale stereo pair select only the red channel of the left image and copy that channel to the clipboard. Select new the anaglyph document as the destination window. Using the channels window select the red channel and paste in the left image. The images may then be flattened, color adjustments applied as outlined below, and the image saved in an approprate transmission and viewing format such as JPEG.

Anaglyphs containing color information
Using color images, replace the red channel of the right-eye image with the red channel of the left-eye image. Here's how: select the entire right eye image (if the original is a crossed eye stereogram this will be on the left) and make a new document. Paste the right eye image in. Move the selection to the left eye image (with consideration as above for crossed eye stereograms) and using the channels dialog select the red channel. Copy the red channel from this source image. Select the new document and select the red channel. Paste the left eye image into the red channel. Depending upon the colors this might look rather good as a color image (but not exactly true to the original color). Eye sensitivity balance can be improved by selecting the green channel and reducing it using a linear curve selection (e.g. reduce to 12.5%). Select the blue channel and reduce somewhat less (e.g. reduce by 5%). This action compensates for the eye's lower sensitivity to red and its high sensitivity to green, but may induce bleed through (you may see ghost images on one side or to each side of an object). Without the anaglyph glasses the picture will appear reddish and somewhat dimmer, but the overall effect is improved when the glasses are used. The dimness can be corrected by increasing the overall brightness 15 to 20% and the contrast 10 to 15%. All of these adjustments will depend upon color balance, brightness, and contrast of the original image and the nature of the subject material.

Using color information, it is possible to obtain reasonable (but not accurate) blue sky, green vegetation, and appropriate skin tones. Color information appears disruptive when used for brightly colored and high contrast objects such as signage, toys, and patterned clothing when these contain colors that are close to red or cyan.

Depth adjustment
(The adjustment suggested in this is section is applicable to any type of stereogram but is particularly appropriate when anaglyphed images are to be viewed on a computer screen or on printed matter.)





Those portions of the left and right images that are coincident will appear to be at the surface of the screen. Depending upon the subject matter and the composition of the image it may be appropriate to make this align to something slightly behind the nearest point of the principal subject (as when imaging a portrait). This will cause the near points of the subject to "pop out" from the screen. For best effect, any portions of a figure to be imaged forward of the screen surface should not intercept the image boundary, as this can lead to a discomforting "amputated" appearance. It is of course possible to create a three-dimensional "pop out" frame surrounding the subject in order to avoid this condition. If the subject matter is a landscape, you may consider putting the frontmost object at or slightly behind the surface of the screen. This will cause the subject to be framed by the window boundary and recede into the distance. Once the adjustment is made, trim the picture to contain only the portions containing both left and right images. In the example shown above, the upper image appears (in a visually disruptive manner) to spill out from the screen, with the distant mountains appearing at the surface of the screen. In the lower modification of this image the red channel has been translated horizontally to bring the images of the nearest rocks into coincidence (and thus appearing at the surface of the screen) and the distant mountains now appear to recede into the image. This latter adjusted image appears more natural, appearing as a view through a window onto the landscape.



Scene composition
In the toy images to the right, the shelf edge was selected as the point where images are to coincide and the toys were arranged so that only the central toy was projecting beyond the shelf. When the image is viewed the shelf edge appears to be at the screen, and the toy's feet and snout project toward the viewer, creating a "pop out" effect.

Dual purpose, 2D or 3D "compatible anaglyph" technique
Since the advent of the internet, a variant technique has developed where the images are specially procesed to minimize visible mis-registration of the two layers. This technique is know by various names, the most common, associated with diopter glasses, and warmer skin tones, is Anachrome. The USGS, in their extensive National Park (Scenic) 3D website, uses this closer overlay technique. (See external links). The technique allows most images to be used as large thumbnails, while the 3D information is encoded into the image with less parallax than conventional anaglyphs.

In comics
These techniques have been used to produce 3-dimensional comic books, mostly during the early 1950s, using carefully constructed line drawings printed in colors appropriate to the filter glasses provided. The material presented were typically short graphic novels of a war story, horror, or crime/detective nature - similar in content to some modern Japanese manga. These genres were largely eliminated in the US by the rise of the Comics Code Authority. Anaglyphed images were of little interest for use in the remaining comics, which emphasized bright and colorful images, unsuited for use with the viewing and production methods available at the time, which were usually red-green rather than red-cyan.

In fine arts
Some maintainers of internet web sites have added depth information to images of famous paintings, further processing these to produce color anaglyph images. Chu, a Graffiti artist from the UK has created largescale, improvised, anaglyphic murals, most notably for the UK premiere of Donnie Darko.