Stereoscopic and Polerized imaging

SIDDHARTH AYER DHARMENDRABHAI (08DCE025) 1

INTRODUCTION
 Stereoscopy refers to a technique for creating or enhancing the illusion of depth in
an image by presenting two offset images separately to the left and right eye of
the viewer. Both of these 2-D offset images are then combined in the brain to give
the perception of 3-D depth.

 Three strategies have been used to accomplish this
1. have the viewer wear eyeglasses to combine separate images from two offset
sources
2. have the viewer wear eyeglasses to filter offset images from a single source
separated to each eye
3. have the light source split the images directionally into the viewer's eyes (no
glasses), Autostereoscopy


HISTORY
Stereoscopy creates the illusion of three-dimensional depth from images on a two-
dimensional plane. Human vision needs some aid to see those illusion:
Like,
1. Stereopsis
2. Accommodation of the eyeball (eyeball focus)
3. Occlusion of one object by another
4. Subtended visual angle of an object of known size
5. Linear perspective (Parallel edges)
6. Vertical position
7. Haze, desaturation, and a shift to bluishness
8. Change in size of textured pattern detail


All of above, Leaving first two, Are available in the form of paintings, pictures and
television.
Stereoscopy is the enhancement of the illusion of depth in a photograph, movie, or
other two-dimensional image by presenting a slightly different image to each eye,
and thereby adding the first of these cues (stereopsis) as well.
Stereoscopy is also used in stereograms for entertainment purpose. Stereoscopy is
useful in viewing images rendered from large multi-dimensional data sets such as are
produced by experimental data.


VISUAL REQUIREMENT
Anatomically, there are 3 levels of binocular vision required to view stereo images:

1. Simultaneous perception
2. Fusion (binocular 'single' vision)
3. Stereopsis

These functions develop in early childhood. Some people who have strabismus disrupt
the development of stereopsis, however orthoptics treatment can be used to
improve binocular vision. A person's stereoacuity determines the minimum image
disparity they can perceive as depth.


SIDE BY SIDE
Traditional stereoscopic photography consists of creating a 3-D illusion starting from a
pair of 2-D images, a stereogram. The easiest way to enhance depth perception in
the brain is to provide the eyes of the viewer with two different
images, representing two perspectives of the same object, with a minor changes to
the both parallel view eye balls.

Each of the two 2-D images preferably should be presented to each eye of the viewer so
that any object at infinite distance seen by the viewer should be perceived by that
eye while it is oriented straight ahead, the viewer's eyes being neither crossed nor
diverging. When the picture contains no object at infinite distance, such as a horizon
or a cloud, the pictures should be spaced correspondingly closer together.


CHARACTERISTICS
Little or no additional image processing is required. Under some circumstances, such as
when a pair of images is presented for crossed or diverged eye viewing, no device or
additional optical equipment is needed.

The principal advantages of side-by-side viewers is that there is no loss of brightness so
images may be presented at very high resolution and in full spectrum color.


FREEVIEWING
Freeviewing is viewing a side-by-side image without using a viewer.

The parallel view method uses two images not more than 65mm between corresponding
image points; this is the average distance between the two eyes. The viewer looks
through the image while keeping the vision parallel.

The cross-eyed view method uses the right and left images exchanged and views the
images cross-eyed with the right eye viewing the left image and vice-versa.


TRANSPARENCY VIEWERS
Pairs of stereo views are printed on film which is then mounted around the edge of a
cardboard disk, images of each pair being diametrically opposite. A lever is used to
move the disk so as to present the next image pair. A series of seven views can thus
be seen on each card when it was inserted into the View-Master viewer. These
viewers were available in many forms both non-lighted and self-lighted and may still
be found today.

Low-cost folding cardboard viewers with plastic lenses have been used to view images
from a sliding card and have been used by computer technical groups as part of
annual convention proceedings. These have been supplanted by the DVD recording
and display on a television set. By exhibiting moving images of rotating objects a
three dimensional effect is obtained through other than stereoscopic means.


HEAD MOUNTED DISPLAY
The user typically wears a helmet or glasses with two small LCD or OLED displays with
magnifying lenses, one for each eye. The technology can be used to show stereo
films, images or games, but it can also be used to create a virtual display. Head-
mounted displays may also be coupled with head-tracking devices, allowing the user
to "look around" the virtual world by moving their head, eliminating the need for a
separate controller.

Augmented stereoscopic vision is also expected to have applications in surgery, as it
allows the combination of radiographic data (CAT scans and MRI imaging) with the
surgeon's vision


3D VIEWERS
Active

Liquid crystal shutter glasses
Glasses containing liquid crystal that block or pass light through in synchronization with
the images on the computer display, using the concept of alternate-frame
sequencing.


Passive
Linearly polarized glasses
To present a stereoscopic motion picture, two images are projected superimposed onto
the same screen through orthogonal polarizing filters. The projectors can receive
their outputs from a computer with a dual-head graphics card. The viewer wears
low-cost eyeglasses which also contain a pair of orthogonal polarizing filters. As each
filter only passes light which is similarly polarized and blocks the orthogonally
polarized light, each eye only sees one of the images, and the effect is achieved.
Linearly polarized glasses require the viewer to keep his head level.


Circularly polarized glasses
To present a stereoscopic motion picture, two images are projected superimposed onto
the same screen through circular polarizing filters of opposite handedness. The
viewer wears low-cost eyeglasses which contain a pair of analyzing filters of opposite
handedness. The result is similar to that of stereoscopic viewing using linearly
polarized glasses, except the viewer can tilt his or her head and still maintain
left/right separation (though the tilt will still affect the brain's ability to fuse the two
images and correctly perceive depth).

Other Technologies:
1. Infitec glasses
2. Inficolor 3D


COMPLEMENTARY COLOUR ANAGLYPH
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. 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.

Other Technologies
1. Colour code 3d


CHROMADEPTH METHOD AND GLASSES
The ChromaDepth procedure of American Paper Optics is based on the fact that with a
prism, colors are separated by varying degrees. The ChromaDepth eyeglasses
contain special view foils, which consist of microscopically small prisms. This causes
the image to be translated a certain amount that depends on its color. If one uses a
prism foil now with one eye but not on the other eye, then the two seen pictures –
depending upon color – are more or less widely separated. The brain produces the
spatial impression from this difference.


AUTOSTEREOSCOPY
Autostereoscopy is any method of displaying stereoscopic (3D) images without the use
of special equipment or glasses on the part of the viewer. Because headgear is not
required, it is also called "glasses-free 3D".
The technology includes two broad classes of displays:
1. those that use head-tracking to ensure that each of the viewer's two eyes sees a
different image on the screen,
2. those that display multiple views so that the display does not need to know where
the viewers' eyes are directed.


OTHER DISPLAY METHODS
1. Autostereograms: More recently, random-dot Autostereograms have been created
using computers to hide depth information in a field of apparently random noise, so
that until viewed by diverging or converging the eyes in a manner similar to naked
eye viewing of stereo pairs, the subject of the image remains a mystery.

2. Pulfrich effects: In the classic Pulfrich effect paradigm a subject views, binocularly, a
pendulum swinging perpendicular to his line of sight. When a neutral density filter
(e.g., a darkened lens -like from a pair of sunglasses) is placed in front of, say, the
right eye the pendulum appears to take on an elliptical orbit, being closer as it swings
toward the right and farther as it swings toward the left.

3. Lenticular prints: Lenticular printing is a technique by which one places an array of
lenses, with a texture much like corduroy, over a specially made and carefully aligned
print such that different viewing angles will reveal different image slices to each eye,
producing the illusion of three dimensions, over a certain limited viewing angle.


TAKING PICTURES
It is necessary to take two photographs for a stereoscopic image. This can be done with two
cameras, with one camera moved quickly to two positions, or with a stereo
camera incorporating two or more side-by-side lenses.
Many of the conventional cameras used the film for 35 mm transparency slides, and the new
stereoscopic cameras utilized the film to make stereoscopic slides. The Stereo Realist camera
was the most popular, and its 5P picture format became a standard.
The beginning of the 21st century marked the coming of the age of digital photography. Stereo
lenses were introduced which could turn an ordinary film camera into a stereo camera by
using a special double lens to take two images and direct them through a single lens to
capture them side-by-side on the film.


Longer base line for distant objects "Hyper Stereo"
If a stereo picture is taken of a large, distant object such as a mountain or a large
building using a normal base it will appear to be flat. This is in keeping with
normal human vision, it would look flat if you were actually there, but if the
object looks flat, there doesn't seem to be any point in taking a stereo picture,
as it will simply seem to be behind a stereo window, with no depth in the scene
itself, much like looking at a flat photograph from a distance.
For making stereo images featuring only a distant object the camera positions can
be separated by a larger distance than the adult human norm of 62-65mm. This
will effectively render the captured image as though it was seen by a giant, and
thus will enhance the depth perception of these distant objects, and reduce the
apparent scale of the scene proportionately.


Shorter baseline for ultra close-ups "Macro stereo"
When objects are taken from closer than about 6 1/2 feet a normal base will produce
excessive parallax and thus exaggerated depth when using ortho viewing methods.
At some point the parallax becomes so great that the image is difficult or even
impossible to view. For such situations, it becomes necessary to reduce the baseline
in keeping with the 1:30 rule.


Stereoscopic Motion Measurement (6D-Vision)
6D-Vision tracks points with known depth from stereo over two or more consecutive
images and fuses the data. The result is an improved accuracy of the 3D-position and
an estimation of the 3D-motion (velocity and direction) of the considered points at
the same time.


Stereoscopic and Polerized imaging

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