History of Anaglyph images
Though it was implemented shortly
after the invention of stereography itself, the anaglyph has
long been a highly recognizable but lowly stepchild in the arena
of 3-D. Using complementary colored red and blue lenses for left
and right eye image selection is a cost-effective way to present
a 3-D image, but many people are troubled by the color
bombardment different to each eye necessary for the effect.
Despite this, the anaglyph has proliferated and continues to do
so as a viable means of stereographic presentation.
Increasingly, though the anaglyph is an inherently
monochromatic, or black-and-white system, stereographic artists
are using a fuller palette of color in the creation of this
unique form of 3-D image. The polychromatic, or full color,
anaglyph has had a relatively limited use up to the present day
but new computer software promises to increase its application
in a variety of media.
When stereoscopic views became tremendously popular in the
1850s, different investigators sought alternative means of
displaying the stereo image. Helmholtz, in his Treatise on
Physiological Optics, cites the work of Rollman, who in 1853
illustrated the principle of the anaglyph using blue and red
lines on a black field with red and blue glasses to perceive the
effect. By 1858, Joseph DAlmeida began projecting
three-dimensional magic lantern slide shows using red and blue
filters with the audience wearing red and blue goggles.
Printed Anaglyphs
The work of DAlmeida was continued by Molteni but it is to Louis
Ducos Du Hauron of Algiers that we owe the first printed
anaglyphs. Many of the 3-D pioneers, like Du Hauron, the Lumiere
brothers and Frederick E. Ives, were exploring the nature of
color in photography and it was through this work that their
invention of anaglyphic processes came about. The thrust of
their efforts was to create a more perfect replication of nature
through photographic reproduction and the attempts to capture
color as well as 3-D information in an image can be seen as an
expression of that goal.
To Du Hauron we must credit the discovery of subtractive
filtration, the active principle behind the anaglyph. In his
1869 book titled Les Couleurs en Photographie, Du Hauron
disclosed many major facts concerning principles of color in
both photography and printing. Seven years previous, in a letter
of 1862 Du Hauron had written: Physical Solution of the Problem
of Reproducing Colors by Photography.--The method which I
propose is based on the principle that the simple colors are
reduced to three --red, yellow and blue--the combinations of
which in different proportions give us the infinite variety of
shades we see in nature.
By exposing black and white negative film through filters of
these colors, a three-color separation is produced. This is the
underlying principle behind all color printing. In 1870 a
three-color lithograph was produced by Du Hauron that
demonstrated this principle.
With subtractive filtration in the anaglyph, it can be seen that
the red lens sees the blue image and cancels out the red. The
blue sees the red and cancels blue. Because a given color filter
cancels out the same color in the photo or print it is called
subtractive.
Subtractive Filtration
When panchromatic black-and-white film, or film that sees color,
was invented in 1890 the mass reproduction of color photographs
in magazine and newspaper supplements began to take place.
Two-color anaglyphs also began to appear with many specially
printed inserts. Throughout the 1890s and up to the 1950s there
were many printed applications of the two-color anaglyph in
magazines and newspapers.
Anaglyphic Glasses
Anaglyphic glasses are
red/blue or red/green filters used for viewing print, movies, games, and computer
applications in 3-D. Anaglyphic is defined as two views of the same subject
(either moving or still) in contrasting colors and slightly offset for two
different perspectives.
A
three-dimensional effect is produced when these images are viewed with two
correspondingly colored filters (usually red/blue and sometimes red/green
lenses) matching the colors in the image. In the case of red/blue lenses,
the blue artwork is totally invisible to the right eye, and the red artwork
is totally invisible to the left eye. Each eye gets only one view of the same
picture. By restricting the proper views to the appropriate mind produces
the 3-D illusion.
In some parts of the world
(e.g. North America), red/blue is the preferred color combination, but in
other areas (e.g. Europe), red/green is the preferred combination. In the
Far East, both systems seem to be in use.
To see the examples on the page, you would need to use a pair of
red/blue anaglyphic glasses. Make sure that the red lens in on
the left eye and the blue lens is on the right eye. You can make a pair by following the instructions
at
http://www.gpsdrawing.com/gallery/infopages/anaglyphic.htm
How it Works
Figure 1 below
shows the case where the object is behind the projection plane. The projection
for the left eye is on the left and the projection for the right eye is on
the right, the distance between the left and right eye projections is called
the horizontal parallax. Since the projections are on the same side as the
respective eyes, it is called a positive parallax. Note that the maximum positive
parallax occurs when the object is at infinity, at this point the horizontal
parallax is equal to the interocular distance.
If an object is located
in front of the projection plane, then the projection for the left eye is
on the right and the projection for the right eye is on the left. This is
known as negative horizontal parallax. Note that a negative horizontal parallax
equal to the interocular distance occurs when the object is half way between
the projection plane and the center of the eyes. Negative horizontal parallax
increases as the object moves closer to the viewer. The Negative parallax
is shown in Figure 2.
An object will appear
to be at the center of the projection plane if focal plane is coincident for
both the left and right eye, as shown in Figure 3 below. It has zero
parallax because the distance between the left and right eye projections
is zero.
Off-axis Rendering
Objects that lie in front of the projection plane will appear
to "pop out" from the computer screen; objects that are behind the
projection plane will appear to be "inside" the screen. It is easier
to view stereo pairs of objects that recede into the screen; to achieve this
one would place the focal point closer to the camera than the objects of interest.
Off-axis rendering is shown in Figure 4.
The degree of the stereo effect depends on both the distance of the camera
to the projection plane and the separation of the left and right camera Too
large a separation can be hard to resolve and is known as hyperstereo. A good
ballpark separation of the cameras is 1/15 of the distance to the projection
plane. Another constraint in off-axis rendering is to ensure the negative
parallax does not exceed the eye separation. A common measure is the parallax
angle defined as P = 2 arctan(DX / (2 d)) where
DX is the horizontal separation of a projected point between the two
eyes and d is the distance of the eye from the projection plane. The
value of P should not exceed 1.5 degrees for all points in the scene.
Note P is positive for points behind the scene and negative for points
in front of the screen. It is not uncommon to restrict the negative value
of P to some value closer to 0 since negative parallax is more difficult
to fuse especially when objects cut the boundary of the projection plane.
Figure 5 illustrates the the equation for calculating the separation
of camera placement.
Creating Stereo Photograph / Movies
Using only one camera, the resulting image look rather flat.
To create a a 3-D stereo photograph, place two cameras, separated by distance
of your eyes, in front of the object. Take photographs using both cameras
at the same time. Using
Anaglyph
Maker (Freeware, written by Takashi Sekitani), merge the two pictures
together to create a 3-D photograph. With a pair of red/blue anaglyphic glasses,
you will see the photo taken by left camera with your left eye, and the photo
taken by right camera with your right eye. Figure 6 illustrates the
difference between a stereo image and a non-stereo image.
Also, it is possible to create a 3-D movie with two movie camera
using the same technique. In many 3-D theaters, the left image of movie and
the right image of movie are projected to one screen by each movie
projectors
with polarizing filters . And people wear 3D glasses that have polarizing
filters when seeing the movie. You will see the movie projected from left
projector with your left eye, and the movie projected from right projector
with your right eye.
References
3-D Glasses - http://www.3-d-glasses.com/anaglyphic.html
Calculating Stereo Pairs - http://astronomy.swin.edu.au/~pbourke/stereographics/stereorender/
STEREOeYe - http://www.stereoeye.com/index_e.html
