Anaglyph 3D is a stereoscopic 3D effect achieved by overlaying images in different colors with corresponding filters for each eye. The colors are usually chromatically opposite — most typically red and cyan.
History The oldest known description of anaglyph images was written in August 1853 by W. Rollmann in Stargard and described his "Farbenstereoscope" (color stereoscope). He had the best results when viewing a yellow/blue drawing with red/blue glasses. Rollmann found that with a red/blue drawing the red lines were not as distinct as yellow lines when viewed through the blue glass.
In 1858, in France, delivered a report to l'Académie des sciences describing how to project three-dimensional magic lantern slide shows using red and green filters to an audience wearing red and green goggles. Subsequently, he was credited with being responsible for the first realization of 3D images using anaglyphs.
Louis Ducos du Hauron produced the first printed anaglyphs in 1891. This process consisted of printing the two negatives which form a stereoscopic photograph onto the same paper, one in blue (or green), one in red. The viewer would then use colored glasses with red for the left eye and blue or green for the right eye. The left eye would see the blue image which would appear black, while it would not see the red; similarly the right eye would see the red image, which would also register as black. Thus, a three-dimensional image would result.
William Friese-Green created the first three-dimensional anaglyphic motion pictures in 1889, which were publicly exhibited in 1893. 3-D films enjoyed something of a boom in the 1920s. As late as 1954, films such as Creature from the Black Lagoon remained very successful. Originally shot and exhibited using the polarized 3D system, Creature from the Black Lagoon was successfully re-issued at a later date in an anaglyph format so it could be shown in cinemas without the need for special equipment.
The American photographic artist Claudia Kunin began using this rendering technique to produce fine art prints in 2010.
The shortened form "3-D" was in use in specialized technical literature by the early 1950s, and its popularization is generally associated with that decade. In 1953, anaglyph images began appearing sporadically in newspapers, magazines, and comic books.
Production
Anaglyph from stereoscopic pairs A stereoscopic pair is a pair of images from slightly different perspectives captured at the same time. Objects closer to the cameras have greater differences in appearance and position within the image frames than objects farther from the camera.
Historically, cameras captured two black-and-white images from the perspective of the left and right eyes, which were projected or printed together as a single image, one view through a red filter and the other side through a contrasting color such as blue or green or cyan. 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. This is called channel mixing, a kind of digital compositing or blending.
In the 1970s, filmmaker Stephen Gibson filmed direct anaglyph blaxploitation and adult films. His "Deep Vision" system replaced the original camera lens with two color-filtered lenses focused on the same film frame. In the 1980s, Gibson patented his mechanism.
Many computer graphics programs provide the basic tools (typically layering and adjustments to individual color channels for color filtering) required to prepare anaglyphs from stereoscopic pairs. In a simple workflow, the left eye image is filtered to remove blue and green, which is achieved by multiplying each pixel in the left image by solid red (#FF0000). The right eye image is filtered to remove red, by multiplying its pixels by solid cyan (#00FFFF). The two images are usually positioned in the compositing phase with close overlay registration of the main subject, and are then combined using an additive blend mode. Plugins for some of these programs, as well as dedicated anaglyph-preparation programs, are available to automate the process and require the user to choose only a few basic settings.
Stereoscopic conversion (single 2D image to 3D) There also exist methods for making anaglyphs using only one image, a process called stereo conversion. In one, individual elements of a picture are horizontally offset in one layer by differing amounts with elements offset further having greater apparent changes in depth (either forward or back depending on whether the offset is to the left or right). This produces images that tend to look like elements are flat standees arranged at various distances from the viewer similar to cartoon images in a View-Master.
A more sophisticated method involves use of a depth map (a false color image where color indicates distance, for example, a grayscale depth map could have lighter indicate an object closer to the viewer and darker indicate an object further away).The two best methods for creating anaglyphs from only one image. As for preparing anaglyphs from stereoscopic pairs, stand-alone software and plug-ins for some graphics apps exist which automate production of anaglyphs (and stereograms) from a single image or from an image and its corresponding depth map.
As well as fully automatic methods of calculating depth maps (which may be more or less successful), depth maps can be drawn entirely by hand. Also developed are methods of producing depth maps from sparse or less accurate depth maps. A sparse depth map is a depth map consisting of only a relatively few lines or areas which guides the production of the full depth map. Use of a sparse depth map can help overcome auto-generation limitations. For example, if a depth finding algorithm takes cues from image brightness an area of shadow in the foreground may be incorrectly assigned as background. This misassignment is overcome by assigning the shaded area a close value in the sparse depth map.
Mechanics Viewing anaglyphs through spectrally opposed glasses or gel filters enables each eye to see independent left and right images from within a single anaglyphic image. Red-cyan filters can be employed because our vision processing systems use red and cyan comparisons, as well as blue and yellow, to determine the color and contours of objects.Exercises in Three Dimensions: About 3D , Tom Lincoln, 2011
In a red-cyan anaglyph, the eye viewing through the red filter sees red within the anaglyph as white, and the cyan within the anaglyph as black. The eye viewing through the cyan filter perceives the opposite.Exercises in Three Dimensions: About 3D
Actual black or white in the anaglyph display, being void of color, are perceived the same by each eye. The brain blends the red and cyan-channeled images much as it does in regular binocular viewing, but due to the color filtering only green and blue are strongly perceived by the eye behind the cyan filter while red is blocked by that filter.
A red filter allows red light to pass and blocks blue and green, so a red object appears bright through the red lens but dark through cyan. Conversely, colors composed of blue and green (cyan) pass through the cyan filter and are not seen by the red filter. In this way, each eye receives separate information for depth perception and the brain integrates the two views.
Types
Complementary color
Complementary color anaglyphs employ one of a pair of complementary color filters for each eye. The most common color filters used are red and cyan. Employing tristimulus theory, the eye is sensitive to three primary colors: red, green, and blue. The red filter admits only red, while the cyan filter blocks red, passing blue and green (the combination of blue and green is perceived as cyan). If a paper viewer containing red and cyan filters is folded so that light passes through both, the image will appear black. Another recently introduced form employs blue and yellow filters. (Yellow is the color perceived when both red and green light passes through the filter.)
Anaglyph images have seen a resurgence since the early 2000s because of the presentation of images on the Internet. Where traditionally, this has been a largely black & white format, recent digital camera and processing advances have brought very acceptable color images to the internet and DVD field. With the online availability of low cost paper glasses with improved red-cyan filters, and plastic framed glasses of increasing quality, the field of 3D imaging is growing quickly. Scientific images where depth perception is useful include, for instance, the presentation of complex multi-dimensional data sets and stereographic images of the surface of Mars. With the recent release of 3D DVDs, they are more commonly being used for entertainment. Anaglyph images are much easier to view than either parallel sighting or crossed eye stereograms, although these types offer more bright and accurate color rendering, especially in the red component, which is commonly muted or desaturated with even the best color anaglyphs. Also, extended use of the anaglyph glasses can cause discomfort, and the afterimage caused by the colors of the glasses may temporarily affect the viewer's visual perception of real-life objects. In the mid-2000s, cross-view prismatic glasses with adjustable masking have appeared, offering a wider image on modern HD video and computer monitors. A compensating technique, commonly known as Anachrome, uses a slightly more transparent cyan filter in the patented glasses associated with the technique. Processing reconfigures the typical anaglyph image to have less parallax to obtain a more useful image when viewed without filters.
Compensating focus diopter glasses for red-cyan method Simple sheet or uncorrected molded glasses do not compensate for the 250 nanometer difference in the wavelengths of the red-cyan filters. With simple glasses, the red filter image can be blurry when viewing a close computer screen or printed image since the retinal focus differs from the cyan filtered image, which dominates the eyes' focusing. Better quality molded plastic glasses employ different diopter strengths in each lens to compensate for this. The direct view focus on computer monitors has been recently improved by manufacturers providing secondary paired lenses, fitted and attached inside the red-cyan primary filters of some high-end anaglyph glasses. They are used where very high resolution is required, including science, stereo macros, and animation studio applications. They use carefully balanced cyan (blue-green) acrylic lenses, which pass a minute percentage of red to improve skin tone perception. Simple red/blue glasses work well with black and white, but the blue filter is unsuitable for human skin in color.
(ACB) 3-D (ACB), which stands for “Anaglyphic Contrast Balance”, is a patented anaglyphic production method by Studio 555. Retinal rivalry of color contrasts within the color channels of anaglyph images is addressed.
Contrasts and details from the stereoscopic pair are maintained and re-presented for view within the anaglyph image. The (ACB) method of balancing the color contrasts within the stereoscopic pair enables a stable view of contrast details, thus eliminating retinal rivalry. The process is available for red/cyan color channels but may use any of the opposing color channel combinations. As with all stereoscopic anaglyphic systems, screen or print, the display color should be RGB accurate and the viewing gels should match the color channels to prevent double imaging. The basic (ACB) method adjusts red, green and blue, but adjusting all six color primaries is preferred.