stereoscopy (2)

DEPARTMENT OF INFORMATION TECHNOLOGYRegional College For Education Research and Technology- Jaipur

Seminar session- 2010 - 2011

A

SEMINAR REPORT

ON

STEREOSCOPY

By

AMITOJ BHIMWAL

Submitted in partial fulfillment for the Award of degree of

Bachelor of Technology

Submitted to:-Mr. Bhuwan Chandra(HOD IT) Dr. Gaurav Jain (Asst. Prof.)

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A

SEMINAR REPORT

ON

STEREOSCOPY

Submitted in Partial Fulfillment for the Award ofBachelor of Technology Degree

OfRajasthan Technical University, Kota

(2010-2011)

Submitted By:- Submitted to :-Amitoj Bhimwal (07ERCIT005) Mr. Bhuwan Chandra(HOD) Dr. Gaurav Jain (Asst. Prof.)

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Preface

In the light of practical aspect of engineering we have to complete a SEMINAR REPORT. The object of this seminar in degree course is to correlate the theory with the practical aspect and to make students familiar with practical difficulties, which arise during working on the field so that they can challenges boldly while actually working in the field.

The field of information technology today has become so vast that it is difficult to know its boundaries. Usually unskilled persons are engaged in this field thus it is important and necessary to have persons with technical knowledge, so that the work can be performed with proper specification, standard and design.

While making this seminar report every care has been taken to avoid my mistake. Yet it is difficult to attain perfection, as it is my first experience to write such a report.

Amitoj Bhimwal B.tech (8th SEM) Branch IT

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CERTIFICATE

This is to certify that the Seminar entitled “STEREOSCOPY” has been carried out by AMITOJ BHIMWAL under my guidance in partial fulfillment of the degree of Bachelor of Technology in Information Technology of Rajasthan Technical University, Kota during the academic year 2010-2011. To the best of my knowledge and belief this work has not been submitted elsewhere for the award of any other degree.

Guide Examiner Head of the DepartmentDr. Gaurav Jain Mr. BHUWAN CHANDRA

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ACKNOWLEDGEMENT

I express my sincere thanks to Mr.BHUWAN CHANDRA Head of Department (IT) for guiding me right from the inception till the successful completion of the Seminar. I sincerely acknowledge him/her/them for extending their valuable guidance, support for literature, Critical reviews of training and the report and above all the moral support he had provided to me with all stages of this Seminar.

(Signature of Student)

AMITOJ BHIMWAL

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INDEX

Topics Page no.

1. Introduction 8

2. Issues in displaying stereoscopic images 9

Stereoscopic Display 9

Viewing Condition 10

3. Stereoscopic imaging 10

4. Relevance of stereoscopy to humans 11

5. Etymology 12

6. Visual requirements 13

7. Side-by-side (non-shared viewing scenarios) 13

Charecterstics 14

Freewing 15

Transparency Vision 16

Head-Mounted display 18

8. 3D viewing technology 19

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Active 19 Passive 20 Complementry color anaglyphs 21 ChromaDepth method 24 Other Display Method 26

9. Wiggle stereoscopy 29

10. Imaging methods 33

Longer Baseline 34 Baseline Selection 34

11. Stereopsis 36

History 36

12. Popular Culture 38

Computer Stereo Vision 40 Computer Stereo Display 40

13. Binocular vision 41

14. Conclusion 47

15. Refrences 48

1. INTRODUCTION7



Stereoscopic photography has been used since the beginning of the century and yet, widespread application of 3D technology has been limited [Sawdai98]. One of the main reasons for this is the difficulty in providing the right viewing environment in terms of easily accessible 3D-display technology. A second reason is the fairly limited supply of high quality stereoscopic images. Recent advances in low cost computers, hardware for stereoscopic viewing [Halnon98, Qualman98] and digital image capture have created the right conditions for the proliferation of stereoscopic imaging applications on the personal computer platform.

The creation of high quality stereoscopic images is a challenging task for a variety of reasons. The viewer’s perception of depth in a 3D application strongly depends on the image quality of the input capture device and the geometric accuracy with which the stereo images are captured. Image quality is typically evaluated in terms of color, resolution, contrast, and noise whereas geometric accuracy refers to the spatial alignment of the stereo images. If the objective of capturing stereoscopic images is the creation of a digital library for archival purposes or for scholarly study, then the amount of detail in the image is an important factor [Mintzer96]. Most of the research on image acquisition for digital libraries has been focused on issues such as faithful color reproduction and preservation of detail.

The capture of stereoscopic images poses additional challenges especially when views of an object are desired at multiple orientations. A desirable setup is one that minimizes the amount of human error, and allows for semi-automatic capture of the images. Such a setup is particularly useful in applications in which large numbers of objects need to be scanned which are difficult to handle or are of great value, such as museum pieces or jewelry. In this paper, we describe the superior performance achieved by using a high resolution, high fidelity digital camera and present our setup for a semi-automated stereoscopic capturing environment. This methodology is suitable for an application of growing importance to museums and cultural institutions in which an object is placed on a turntable and automatically scanned at multiple orientations.

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We examine in detail the various parameters that must be considered to successfully obtain stereoscopic images of objects and give guidelines for setting such parameters. These include choices related to the camera settings, such as aperture, focal length, etc., and image captures geometry such as distance of camera to the object, distance between the two camera positions, angle of elevation etc. We also examine the effect of scene composition and background selection on the quality of stereoscopic images. For capturing the stereoscopic images we use the IBM TDI-Pro 3000 [Mintzer96, Giordano99] developed at IBM Research and a Kaidan computer-controlled turntable [www.kaidan.com] for automatically obtaining multiple views of the object. For viewing we use off-the-shelf hardware from NuVision Technologies [www.nuvision3d.com] on a standard CRTmonitor.

2. ISSUES IN DISPLAYING STEREOSCOPIC VIEWS

Stereoscopic Display

The most common type of electronic stereoscopic viewing devices available is Liquid Crystal shutter glasses, such as those made by Stereo Graphics Corporation [Halnon98] or NuVision Technologies [Qualman98]. These glasses work by alternating the left and right eye shutters in sync with a left and right display field. Thus, the shutters flip alternately between opaque and clear so that only the left eye sees the screen when the left image is displayed, and only the right eye sees the screen when the right image is displayed. This method is known as page-flipped stereo. We used the shuttered LCD glasses. These are inexpensive and work with a variety of graphics cards. This was run on an IBM PC. With sufficiently high refresh rates, say in excess of 75 Hz, the flicker on the display is less noticeable.

Viewing Conditions

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The expected viewing environment is a CRT display attached to a PC. If the graphics card can support sufficiently high refresh rates, flicker should not be a problem. In any case, it is preferable to view the images in dim lighting or with monitor shades as this reduces the problem of flicker. This also helps to avoid color adaptation effects where the eye may adapt to different colored surrounds, affecting the perceived color of the object. In case accurate color reproduction is desired, it may be necessary to use standardized viewing conditions, such as D50 illumination and color-calibrate the display.

3. STEREOSCOPIC IMAGING

Stereoscopy, which is also called as stereoscopic imaging or 3-d imaging is a technique which is capable of recording the 3 dimensional visual information of an objective. More clearly it can be illustrated as the creation of illusion of depth aspect in a particular image. Stereoscopic images provide spatial information that trick a user's brain into believing and seeing depth in the images.

4. RELEVANCE OF STEREOSCOPY TO HUMAN BEING

Humans, most importantly have two eyes on the same side of the face i.e., we are able to see or concentrate on a particular object or thing with both the eyes simultaneously. Hence we have a vision which is also called as binocular vision. We have eyesight which makes us enable to watch a particular object with both eyes

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at same time. But what actually happens is that, when we watch an object we have two image formations in front of both our eyes. So now both the eye sights converge or coincide at a particular point and this is where our brain is able to overlap the whole system and we are able to calculate or understand the distance of an object or where an object is kept from us.

On the contrary, animals like deer have a sight which is also referred to as monocular vision. That is, a deer has its eyes on the opposite side of the face and thus the area of sight of vision or the area which he can see with both his eyes increases but on the other hand the brain is not able to properly overlap the system and measure the accurate distance of a particular object kept at a distance which may be moving or stationary. And hence it becomes impossible for them to see like humans.

What stereoscopy is?

Stereoscopy is basically the enhancement of the illusion of depth perspective in an autograph, movie or other 2 d image by presenting a slightly different image to each eye, and thereby adding the stereopsis concept as well.

How stereoscopy works?

The stereographic photography consists of creating a 3-D illusion starting from a pair of 2-D images. 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 deviation exactly equal to the perspectives that both eyes normally receive in binocular vision.

If eye strain and distortion are to be avoided, each of the 2-D images preferably should be presented to each eye of the viewer so that an object at infinity 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.

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When the picture contains no object at infinity distance, such as the horizon or the cloud, the pictures should be placed corresponding closer together.

Hence, the term stereoscopic imaging can be summarized in a definition as a technique to record or display 3-D information or provides the illusion of depth. It provides spatial information or provides the illusion of depth that tricks a user’s brain into believing and seeing depth in images.

5. ETYMOLOGY

The word stereoscopy derives from the Greek "στερεός" (stereos), "firm, solid"+ "σκοπέω" (skopeō), "to look", "to see".

6. VISUAL REQUIRMENT

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 orthotics treatment can be used to improve binocular vision. A person's stereo acuity determines the minimum image disparity they can perceive as depth.

7. SIDE-BY-SIDE (non-shared viewing scenarios)

Traditional stereoscopic photography consists of creating a 3-D illusion starting from a pair of 2-D images. The easiest way to enhance depth perception in the brain is to provide the eyes of the viewer with two different images,

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representing two perspectives of the same object, with a minor deviation exactly equal to the perspectives that both eyes naturally receive in binocular vision.

If eyestrain and distortion are to be avoided, 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

Stereograph published in 1900 by North-Western View Co. of Baraboo, Wisconsin, digitally restored.

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.

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The principal advantages of side-by-side viewers is that there is no diminution of brightness so images may be presented at very high resolution and in full spectrum color. The ghosting associated with polarized projection or when color filtering is used is totally eliminated. The images are discretely presented to the eyes and visual center of the brain, with no co-mingling of the views. The recent advent of flat screens and "software stereoscopes" has made larger 3D digital images practical in this side by side mode, which hitherto had been used mainly with paired photos in print form.

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; this can be difficult with normal vision since eye focus and binocular convergence normally work together.

The cross-eyed view method uses the right and left images exchanged and view the images cross-eyed with the right eye viewing the left image and vice-versa. Prismatic, self masking glasses are now being used by cross-view advocates. These reduce the degree of convergence and allow large images to be displayed.

Several methods are available to freeview.

Stereographic cards and the stereoscope

Two separate images are printed side-by-side. When viewed without a stereoscopic viewer the user is required to force his eyes either to cross, or to

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diverge, so that the two images appear to be three. Then as each eye sees a different image, the effect of depth is achieved in the central image of the three.

The stereoscope offers several advantages:

Using positive curvature (magnifying) lenses, the focus point of the image is changed from its short distance (about 30 to 40 cm) to a virtual distance at infinity. This allows the focus of the eyes to be consistent with the parallel lines of sight, greatly reducing eye strain.

The card image is magnified, offering a wider field of view and the ability to examine the detail of the photograph.

The viewer provides a partition between the images, avoiding a potential distraction to the user.

Stereograms cards are frequently used by orthoptists and vision therapists in the treatment of many binocular vision and accommodative disorders.

Vintage Stereoscopic Picture (for parallel viewing)

Vintage Stereoscopic Picture (for cross viewing)

Narrow paired images (for cross viewing)

Stereoscopic Picture of Piano Keys (for cross viewing)

Transparency Vision

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http://en.wikipedia.org/wiki/File:StereoCardNYCSmall.jpg

http://en.wikipedia.org/wiki/File:XEyeStCdNYCSmall.jpg

http://en.wikipedia.org/wiki/File:1080par.jpg

http://en.wikipedia.org/wiki/File:Piano_in_3D.jpg



Stereoscope and case – during WWII this tool was used by Allied photo interpreters to analyze images shot from aerial photo reconnaissance platforms.

The practice of viewing transparencies in stereo via a viewer dates to at least as early as 1931, when Tru-Vue began to market filmstrips that were fed through a handheld device made from Bakelite. In the 1940s, a modified and miniaturized variation of this technology was introduced as the View-Master. Pairs of stereo views are printed on translucent 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. One type of material presented is children's fairy tale story scenes or brief stories using popular cartoon characters. These use photographs of three dimensional model sets and characters. Another type of material is a series of scenic views associated with some tourist destination, typically sold at gift shops located at the attraction.

Another important development in the late 1940s was the introduction of the Stereo Realist camera and viewer system. Using color slide film, this equipment made stereo photography available to the masses and caused a surge

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in its popularity. The Stereo Realist and competing products can still be found (in estate sales and elsewhere) and utilized 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.

An advantage offered by transparency viewing is that a wider field of view may be presented since images, being illuminated from the rear, may be placed much closer to the lenses. Note that with simple viewers the images are limited in size as they must be adjacent and so the field of view is determined by the distance between each lens and its corresponding image.

Head-Mounted Display

An HMD with a separate video source displayed in front of each eye to achieve a stereoscopic effect

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

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moving their head, eliminating the need for a separate controller. Performing this update quickly enough to avoid inducing nausea in the user requires a great amount of computer image processing. If six axis position sensing (direction and position) is used then wearer may move about within the limitations of the equipment used. Owing to rapid advancements in computer graphics and the continuing miniaturization of video and other equipment these devices are beginning to become available at more reasonable cost.

Head-mounted or wearable glasses may be used to view a see-through image imposed upon the real world view, creating what is called augmented reality. This is done by reflecting the video images through partially reflective mirrors. The real world view is seen through the mirrors' reflective surface. Experimental systems have been used for gaming, where virtual opponents may peek from real windows as a player moves about. This type of system is expected to have wide application in the maintenance of complex systems, as it can give a technician what is effectively "x-ray vision" by combining computer graphics rendering of hidden elements with the technician's natural vision. Additionally, technical data and schematic diagrams may be delivered to this same equipment, eliminating the need to obtain and carry bulky paper documents.

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.

8. 3D viewers

There are two categories of 3D viewer technology, active and passive. Active viewers have electronics which interact with a display.

8.1 Active

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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. See also Time-division multiplexing.

"Red eye" shutter glasses method

The Red Eye Method reduces the ghosting caused by the slow decay of the green and blue P22-type phosphors typically used in conventional CRT monitors. This method relies solely on the red component of the RGB image being displayed, with the green and blue component of the image being suppressed.

8.2 Passive

Linearly polarized glasses

To present a stereoscopic motion picture, two images are projected superimposed onto the same screen through orthogonal porarizing filters. It is best to use a silver screen so that polarization is preserved. 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, as tilting of the viewing filters will cause the images of the left and right channels to bleed over to the opposite channel – therefore, viewers learn very quickly not to tilt their heads. In addition, since no head tracking is involved, several people can view the stereoscopic images at the same time.

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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 (circular polarizer mounted in reverse) of opposite handedness. Light that is left-circularly polarized is extinguished by the right-handed analyzer, while right-circularly polarized light is extinguished by the left-handed analyzer. 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.

The RealD Cinema system uses an electronically driven circular polarizer, mounted in front of the projector and alternating between left- and right- handedness, in sync with the left or right image being displayed by the (digital) movie projector. The audience wears passive circularly polarized glasses.

Infitec glasses

Infitec stands for interference filter technology. Special interference filters (dichromatic filters) in the glasses and in the projector form the main item of technology and have given it this name. The filters divide the visible color spectrum into six narrow bands - two in the red region, two in the green region, and two in the blue region (called R1, R2, G1, G2, B1 and B2 for the purposes of this description). The R1, G1 and B1 bands are used for one eye image, and R2, G2, B2 for the other eye. The human eye is largely insensitive to such fine spectral differences so this technique is able to generate full-color 3D images with only slight color differences between the two eyes. Sometimes this technique is described as a "super-anaglyph" because it is an advanced form of spectral-multiplexing which is at the heart of the conventional anaglyph technique.

Dolby uses a form of this technology in its dolby 3D theatres.

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Complementary color anaglyphs

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 recent resurgence 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 do offer more bright and accurate color rendering, most particularly in the red component, which is commonly muted or desaturated with even the best color anaglyphs. A compensating

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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 diopter glasses for red-cyan method

Simple sheet or uncorrected molded glasses do not compensate for the 250 nanometer difference in the wave lengths 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 a compensating differential diopter power to equalize the red filter focus shift relative to the cyan.

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 blue filter unsuitable for human skin in color.

ColorCode 3D

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Michelle Obama and Barack Obama and their party watch the commercials using ColorCode 3D during Super Bowl XLIII on February 1, 2009 in the White House theatre.

ColorCode 3D is a newer, patented stereo viewing system deployed in the 2000s that uses amber and blue filters. Notably, unlike other anaglyph systems, ColorCode 3D is intended to provide perceived nearly full colour viewing (particularly within the RG color space) with existing television and paint mediums. One eye (left, amber filter) receives the cross-spectrum colour information and one eye (right, blue filter) sees a monochrome image designed to give the depth effect. The human brain ties both images together.

Images viewed without filters will tend to exhibit light-blue and yellow horizontal fringing. The backwards compatible 2D viewing experience for viewers not wearing glasses is improved, generally being better than previous red and green anaglyph imaging systems, and further improved by the use of digital post-processing to minimize fringing. The displayed hues and intensity can be subtly adjusted to further improve the perceived 2D image, with problems only generally found in the case of extreme blue.

The blue filter is centered on 450 nm and the amber filter lets in light at wavelengths at above 500 nm. Wide spectrum color is possible because the amber filter lets through light across most wavelengths in spectrum. When presented via RGB color model televisions, the original red and green channels from the left image are combined with a monochrome blue channel formed by averaging the right image with the weights {r:0.15,g:0.15,b:0.7}.

In the United Kingdom, television station Channel 4 commenced broadcasting a series of programmers encoded using the system during the week of 16 November 2009. Previously the system had been used in the United States for an "all 3-D advertisement" during the 2009 Super Bowl for SoBe, Monsters vs. Aliens animated movie and an advertisement for the Chuck television series in which the full episode the following night used the format.

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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. The advantage of this technology consists above all of the fact that one can regard ChromaDepth pictures also without eyeglasses (thus two-dimensional) problem-free (unlike with two-color anaglyph). However the colors are only limitedly selectable, since they contain the depth information of the picture. If one changes the color of an object, then its observed distance will also be changed.

Anachrome "compatible" color anaglyph method

A recent variation on the anaglyph technique is called "Anachrome method". This approach is an attempt to provide images that look fairly normal without glasses as 2D images to be "compatible" for posting in conventional websites or magazines. The 3D effect is generally more subtle, as the images are shot with a narrower stereo base, (the distance between the camera lenses). Pains are taken to adjust for a better overlay fit of the two images, which are

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layered one on top of another. Only a few pixels of non-registration give the depth cues.

The range of color is perhaps three times wider in Anachrome due to the deliberate passage of a small amount of the red information through the cyan filter. Warmer tones can be boosted, and this is claimed to provide warmer skin tones and vividness.

Other display methodsAutostereogram

A random dot autostereogram encodes a 3D scene which can be "seen" with proper viewing technique.

More recently, random-dot autostereograms have been created using computers to hide the different images 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. A popular example of this is the Magic Eye series, a collection of stereograms based on distorted colorful and interesting patterns instead of random noise.

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Pulfrich effects

In the classic Pulfrich affect 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.

The widely accepted explanation of the apparent motion with depth is that a reduction in retinal illumination (relative to the fellow eye) yields a corresponding delay in signal transmission, imparting instantaneous spatial disparity to moving objects. This occurs because the eye, and hence the brain, respond more quickly to brighter objects than to dimmer ones.

So if the brightness of the pendulum is greater in the left eye than in the right, the retinal signals from the left eye will reach the brain slightly ahead of those from the right eye. This makes it seem as if the pendulum seen by the right eye is lagging behind its counterpart in the left eye. This difference in position over time is interpreted by the brain as motion with depth: no motion, no depth.

The ultimate effect of this, with appropriate scene composition, is the illusion of motion with depth. Object motion must be maintained for most conditions and is effective only for very limited "real-world" scenes.

Prismatic & self-masking crossview glasses

"Naked-eye" cross viewing is a skill that must be learned to be used. New prismatic glasses now make cross-viewing as well as over/under-viewing easier, and also mask off the secondary non-3D images, that otherwise show up on either side of the 3D image. The most recent low-cost glasses mask the images down to one per eye using integrated baffles. Images or video frames can be displayed on a new widescreen HD or computer monitor with all available area used for display.

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HDTV wide format permits excellent color and sharpness. Cross viewing provides true "ghost-free 3D" with maximum clarity, brightness and color range, as does the stereopticon and stereoscope viewer with the parallel approach and the KMQ viewer with the over/under approach. The potential depth and brightness is maximized. A recent cross converged development is a new variant wide format that uses a conjoining of visual information outside of the regular binocular stereo window. This allows an efficient seamless visual presentation in true wide-screen, more closely matching the focal range of the human eyes.

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. This can be done cheaply enough that it is sometimes used on stickers, album covers, etc. It is the classic technique for 3D postcards.

Displays with filter arrays

The LCD is covered with an array of prisms that divert the light from in their notebook and desktop computers. These displays usually cost upwards of 1000 dollars and are mainly targeted at science or medical professionals.

Another technique, for example used by the X3D company, is simply to cover the LCD with two layers, the first being closer to the LCD than the second, by some millimeters. The two layers are transparent with black strips, each strip about one millimeter wide. One layer has its strips about ten degrees to the left, the other to the right. This allows seeing different pixels depending on the viewer's position.

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9. WIGGLE STEREOSCOPY

This method, possibly the simplest stereogram viewing technique, is to simply alternate between the left and right images of a stereogram. In a web browser, this can easily be accomplished with an animated .gif image, flash applet or a specialized java applet. Most people can get a crude sense of dimensionality from such images, due to parallax.

Closing one eye and moving the head from side-to-side when viewing a selection of objects helps one understand how this works. Objects that are closer appear to move more than those further away. This effect may also be observed by a passenger in a vehicle or low-flying aircraft, where distant hills or tall buildings appear in three-dimensional relief, a view not seen by a static observer as the distance is beyond the range of effective binocular vision.

Advantages of the wiggle viewing method include:

No glasses or special hardware required Most people can "get" the effect much quicker than cross-eyed and

parallel viewing techniques It is the only method of stereoscopic visualization for people with limited

or no vision in one eye

Disadvantages of the "wiggle" method:

Does not provide true binocular stereoscopic depth perception

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http://en.wikipedia.org/wiki/File:Stereo_wiggle_3D.gif



Not suitable for print, limited to displays that can "wiggle" between the two images

Difficult to appreciate details in images that are constantly "wiggling" Lack of 3D illusion to those who can detect the wiggling too easily.

Most wiggle images use only two images, leading to an annoyingly jerky image. A smoother image, more akin to a motion picture image where the camera is moved back and forth, can be composed by using several intermediate images (perhaps with synthetic motion blur) and longer image residency at the end images to allow inspection of details. Another option is a shorter time between the frames of a wiggle image through the use of an animated .png.

Although the "wiggle" method is an excellent way of previewing stereoscopic images, it cannot actually be considered a true three-dimensional stereoscopic format. To experience binocular depth perception as made possible with true stereoscopic formats, each eyeball must be presented with a different image at the same time – this is not the case with "wiggling" stereo. The apparent "stereo like effect" comes from syncing the timing of the wiggle and the amount of parallax to the processing done by the visual cortex. Three or five images with good parallax produce a much better effect than simple left and right images.

Wiggling works for the same reason that a translational pan (or tracking shot) in a movie provides good depth information: the visual cortex is able to infer distance information from motion parallax, the relative speed of the perceived motion of different objects on the screen. Many small animals bob their heads to create motion parallax (wiggling) so they can better estimate distance prior to jumping. You can see this for you in a 3D movie by removing the glasses during a scene where the camera is moving: the glasses have very little additional effect at such a time.

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Taking a Picture

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 such as the Fujifilm FinePix Real 3D W1.

When using two cameras there are two prime considerations to take into account when taking stereo pictures; How far the resulting image is to be viewed from and how far the subject in the scene is from the two cameras.

How far you are intending to view the pictures from requires a certain separation between the cameras. This separation is called stereo base or stereo base line and results from the ratio of the distance to the image to the distance between your eyes. The mean interpupillary distance (IPD) is 63 mm (about 2.5 inches), but varies with age, race and gender. The vast majority of adults have IPDs in the range 50–75 mm. almost all adults are in the range 45–80 mm. The minimum IPD for children as young as five is around 40 mm. In any case the farther you are from the screen the more the image will pop out. The closer you are to the screen the flatter it will appear. Personal anatomical differences can be compensated for by moving closer or farther from the screen.

For example if you are going to view a stereo image on your computer monitor from a distance of 1000 mm you will have an eye to view ratio of 1000/63 or about 16. To set your cameras the correct distance apart you take the distance to the subject (say a person at a distance from the cameras of 3 metres) and divide by 16 which gives you a stereo base of 188 mm between the cameras.

If you intend to view the stereo image from the same distance as it is captured (e.g. a subject photographed three meters away, projected on a movie screen at a distance from the viewer of three meters) then the stereo base separation will be the same as the distance between the viewer's eyes (about 63 mm).

In the 1950s, stereoscopic photography regained popularity when a number of manufacturers began introducing stereoscopic cameras to the public.

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The new cameras were developed to use 135 film, which had gained popularity after the close of World War II. 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 the 35 mm picture format became the standard by which other stereo cameras were designed. The stereoscopic cameras were marketed with special viewers that allowed for the use of such slides, which were similar to View-Master reels but offered a much larger image. With these cameras the public could easily create their own stereoscopic memories. Although their popularity has waned somewhat, these cameras are still in use today.

The 1980s saw a minor revival of stereoscopic photography extent when point-and-shoot stereo cameras were introduced. These cameras suffered from poor optics and plastic construction, so they never gained the popularity of the 1950s stereo cameras. Over the last few years they have been improved upon and now produce good images.

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. Although current digital stereo cameras cost thousands of dollars, cheaper models also exist, for example those produced by the company Loreo. It is also possible to create a twin camera rig, together with a "shepherd" device to synchronize the shutter and flash of the two cameras. By mounting two cameras on a bracket, spaced a bit, with a mechanism to make both take pictures at the same time. Newer cameras are even being used to shoot "step video" 3D slide shows with many pictures almost like a 3D motion picture if viewed properly. A modern camera can take five pictures per second, with images that greatly exceed HDTV resolution.

The side-by-side method is extremely simple to create, but it can be difficult or uncomfortable to view without optical aids. One such aid for non-crossed images is the modern Pokescope. Traditional stereoscopes such as the

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Holmes can be used as well. Cross view technique now has the simple Perfect-Chroma cross viewing glasses to facilitate viewing.

10. IMAGING MATHODS

If anything is in motion within the field of view, it is necessary to take both images at once, either through use of a specialized two-lens camera, or by using two identical cameras, operated as close as possible to the same moment.

A single digital camera can also be used if the subject remains perfectly still (such as an object in a museum display). Two exposures are required. The camera can be moved on a sliding bar for offset, or with practice, the photographer can simply shift the camera while holding it straight and level. In practice the hand-held method works very well. This method of taking stereo photos is sometimes referred to as the "Cha-Cha" method.

A good rule of thumb is to shift sideways 1/30th of the distance to the closest subject for 'side by side' display, or just 1/60th if the image is to be also used for color anaglyph or anachrome image display. For example, if you are taking a photo of a person in front of a house, and the person is thirty feet away, then you should move the camera 1 foot between shots.

The stereo effect is not significantly diminished by slight pan or rotation between images. In fact slight rotation inwards (also called 'toe in') can be beneficial. Bear in mind that both images should show the same objects in the scene (just from different angles) - if a tree is on the edge of one image but out of view in the other image, then it will appear in a ghostly, semi-transparent way to the viewer, which is distracting and uncomfortable. Therefore, you can either crop the images so they completely overlap, or you can 'toe-in' the cameras so that the images completely overlap without having to discard any of the images. However, be a little cautious - too much 'toe-in' can cause eye strain for reasons best described here.

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Longer base line

For making stereo images of a distant object (e.g., a mountain with foothills), one can separate the camera positions by a larger distance (commonly called the "interocular") 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. However, in this case care must be taken not to bring objects in the close foreground too close to the viewer, as they will require the viewer to become cross-eyed to resolve them.

In the red-cyan anaglyphed example at right, a ten-meter baseline atop the roof ridge of a house was used to image the mountain. The two foothill ridges are about four miles (6.5 km) distant and are separated in depth from each other and the background. The baseline is still too short to resolve the depth of the two more distant major peaks from each other. Owing to various trees that appeared in only one of the images the final image had to be severely cropped at each side and the bottom.

This technique can be applied to 3D imaging of the Moon: one picture is taken at moonrise, the other at moonset, as the face of the Moon is centered towards the center of the Earth and the diurnal rotation carries the photographer around the perimeter.

Base line selection

There is a specific optimal distance for viewing of natural scenes (not stereograms), which has been estimated by some to have the closest object at a distance of about thirty times the distance between the eyes (when the scene extends to infinity). An object at this distance will appear on the picture plane, the apparent surface of the image. Objects closer than this will appear in front of the picture plane, or popping out of the image. All objects at greater distances appear behind the picture plane. This interpupillar or interocular distance will vary between individuals. If one assumes that it is 2.5 inches (about 6.5 cm), then the closest object in a natural scene by this criterion would be

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30 × 2.5 = 75 inches (about 2 m). It is this ratio (1:30) that determines the inter-camera spacing appropriate to imaging scenes. Thus if the nearest object is thirty feet away, this ratio suggests an inter-camera distance of one foot. It may be that a more dramatic effect can be obtained with a lower ratio, say 1:20 (in other words, the cameras will be spaced further apart), but with some risk of having the overall scene appear less "natural". This unnaturalness can often be seen in old stereoscope cards, where a landscape will have the appearance of a stack of cardboard cut-outs. Where images may also be used for anaglyph display a narrower base, say 1:50 or 1:60 will allow for less ghosting in the display..

Precise stereoscopic baseline calculation methods

Recent research has led to precise methods for calculating the stereoscopic camera baseline. These techniques consider the geometry of the display/viewer and scene/camera spaces independently and can be used to reliably calculate a mapping of the scene depth being captured to a comfortable display depth budget. This frees up the photographer to place their camera wherever they wish to achieve the desired composition and then use the baseline calculator to work out the camera inter-axial separation required to produce a high quality 3D image.

This approach means there is no guess work in the stereoscopic setup once a small set of parameters have been measured, it can be implemented for photography and computer graphics and the methods can be easily implemented in a software tool. One such tool is available freely from the Durham Visualization Laboratory.

Multi-rig stereoscopic cameras

The precise methods for camera control have also allowed the development of multi-rig stereoscopic cameras where different slices of scene depth are captured using different inter-axial settings, the images of the slices are then composed together to form the final stereoscopic image pair. This allows important regions of a scene to be given better stereoscopic

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representation while less important regions are assigned less of the depth budget. It provides stereographers with a way to manage composition within the limited depth budget of each individual display technology.

11. STEREOPSIS

Stereopsis (from stereo- meaning "solid" or "three-dimensional"), and opsis meaning view or sight) is the process in visual perception leading to the sensation of depth from the two slightly different projections of the world onto the retinas of the two eyes. The differences in the two retinal images are called horizontal disparity, retinal disparity, or binocular disparity. The differences arise from the eyes' different positions in the head. Stereopsis is commonly referred to as depth perception.

This is inaccurate, as depth perception relies on many more monocular cues than stereoptical ones, and individuals with only one functional eye still have full depth perception except in artificial cases (such as stereoscopic images) where stereopsis differentiates the media from their two dimensional counterparts.

History of stereopsis

Stereopsis was first described by Charles Wheatstone in 1838. ”… the mind perceives an object of three-dimensions by means of the two dissimilar pictures projected by it on the two retina…”. He recognized that because each eye views the visual world from slightly different horizontal positions, each eye's image differs from the other. Objects at different distances from the eyes project images in the two eyes that differ in their horizontal positions, giving the depth cue of horizontal disparity, also known as retinal disparity and as binocular disparity. Wheatstone showed that this was an effective depth cue by creating the illusion of depth from flat pictures that differed only in horizontal disparity. To display his pictures separately to the two eyes, Wheatstone invented the stereoscope.

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Leonardo da Vinci had also realized that objects at different distances from the eyes project images in the two eyes that differ in their horizontal positions, but had concluded only that this made it impossible for a painter to portray a realistic depiction of the depth in a scene from a single canvas. Leonardo chose for his near object a column with a circular cross section and for his far object a flat wall. Had he chosen any other near object, he may have discovered horizontal disparity of its features. His column was one of the few objects that projects identical images of itself in the two eyes.

Stereopsis became popular during Victorian times with the invention of the prism stereoscope by David Brewster. This, combined with photography, meant that tens of thousands of stereograms were produced.

Until about the 1960s, research into stereopsis was dedicated to exploring its limits and its relationship to singleness of vision. Researchers included Peter Ludvig Panum, Ewald Hering, Adelbert Amer Jr., and Kenneth N. Ogle.

In the 1960s, Bela Julesz invented random-dot stereograms. Unlike previous stereograms, in which each half image showed recognizable objects, each half image of the first random-dot stereograms showed a square matrix of about 10,000 small dots, with each dot having a 50% probability of being black or white. No recognizable objects could be seen in either half image. The two half images of a random-dot stereogram were essentially identical, except that one had a square area of dots shifted horizontally by one or two dot diameters, giving horizontal disparity. The gap left by the shifting was filled in with new random dots, hiding the shifted square. Nevertheless, when the two half images were viewed one to each eye, the square area was almost immediately visible by being closer or farther than the background. Julesz whimsically called the square a Cyclopean image after the mythical Cyclops who had only one eye.

Also in the 1960s, Horace Barlow, Colin Blakemore, and Jack Pettigrew found neurons in the cat visual cortex that had their receptive fields in different horizontal positions in the two eyes. This established the neural basis for stereopsis. Their findings were disputed by David Hubel and Torsten Wiesel, although they eventually conceded when they found similar neurons in the

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monkey visual cortex. In the 1980s, Gian Poggio and others found neurons in V2 of the monkey brain that responded to the depth of random-dot stereograms.

In the 1970s, Christopher Tyler invented autostereograms, random-dot stereograms that can be viewed without a stereoscope. This led to the popular Magic Eye pictures.

Not everyone has the same ability to see using stereopsis. One study shows that 97.3% are able to distinguish depth at horizontal disparities of 2.3 minutes of arc or smaller, and at least 80% could distinguish depth at horizontal differences of 30 seconds of arc.

12. POPULAR CULTURE

A stereoscope is a device by which each eye can be presented with different images, allowing stereopsis to be stimulated with two pictures, one for each eye. This has led to various crazes for stereopsis, usually prompted by new sorts of stereoscopes.

In Victorian times it was the prism stereoscope (allowing stereo photographs to be viewed), in the 1920s it was red-green glasses (allowing stereo movies to be viewed), in the 1950s it was polarizing glasses (allowing coloured movies to be viewed), and in the 1990s it was Magic Eye pictures (autostereograms). Magic Eye pictures did not require a stereoscope, but relied on viewers using a form of free fusion so that each eye views different images.

Geometrical basis for stereopsis

Stereopsis appears to be processed in the visual cortex in binocular cells having receptive fields in different horizontal positions in the two eyes. Such a cell is active only when its preferred stimulus is in the correct position in the left eye and in the correct position in the right eye, making it a disparity detector.

When a person stares at an object, the two eyes converge so that the object appears at the center of the retina in both eyes. Other objects around the main object appear shifted in relation to the main object. In the following

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example, whereas the main object (dolphin) remains in the center of the two images in the two eyes, the cube is shifted to the right in the left eye's image and is shifted to the left when in the right eye's image.

The two eyes converge on the object of attention.

The cube is shifted to the right in left eye's image.

The cube is shifted to the left in the right eye's image.

Because each eye is in a different horizontal position, each has a slightly different perspective on a scene yielding different retinal images. Normally two images are not observed, but rather a single view of the scene, a phenomenon known as singleness of vision. Nevertheless, stereopsis is possible with double vision. This form of stereopsis was called qualitative stereopsis by Kenneth Ogle.

If the images are very different (such as by going cross-eyed, or by presenting different images in a stereoscope) then one image at a time may be seen, a phenomenon known as binocular rivalry.

Computer stereo vision

Computer stereo vision is a part of the field of computer vision. It is sometimes used in mobile robotics to detect obstacles. Example applications include the ExoMars Rover and surgical robotics.

Two cameras take pictures of the same scene, but they are separated by a distance - exactly like our eyes. A computer compares the images while shifting the two images together over top of each other to find the parts that match. The

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http://en.wikipedia.org/wiki/File:Stereogram_Tut_Eye_Diagram.png

http://en.wikipedia.org/wiki/File:Stereogram_Tut_Eye_Diagram.png

http://en.wikipedia.org/wiki/File:Stereogram_Tut_Eye_View_Left_Eye.png

http://en.wikipedia.org/wiki/File:Stereogram_Tut_Eye_View_Left_Eye.png

http://en.wikipedia.org/wiki/File:Stereogram_Tut_Eye_View_Rigth_Eye.png

http://en.wikipedia.org/wiki/File:Stereogram_Tut_Eye_View_Rigth_Eye.png



shifted amount is called the disparity. The disparity at which objects in the image best match is used by the computer to calculate their distance.

For a human, the eyes change their angle according to the distance to the observed object. To a computer this represents significant extra complexity in the geometrical calculations (Epipolar geometry). In fact the simplest geometrical case is when the camera image planes are on the same plane. The images may alternatively be converted by reprojection through a linear transformation to be on the same image plane. This is called Image rectification.

Computer stereo vision with many cameras under fixed lighting is called structure from motion. Techniques using a fixed camera and known lighting are called photometric stereo techniques, or "shape from shading".

Computer stereo display

Many attempts have been made to reproduce human stereo vision on rapidly changing computer displays, and toward this end numerous patents relating to 3D television and cinema have been filed in the USPTO. At least in the US, commercial activity involving those patents has been confined exclusively to the grantees and licensees of the patent holders, whose interests tend to last for twenty years from the time of filing.

Discounting 3D television and cinema (which generally require more than one digital projectors whose moving images are mechanically coupled, in the case of IMAX 3D cinema), several stereoscopic LCDs are going to be offered by Sharp, which has already started shipping a notebook with a built in stereoscopic LCD. Although older technology required the user to don goggles or visors for viewing computer-generated images, or CGI, newer technology tends to employ Fresnel lenses or plates over the liquid crystal displays, freeing the user from the need to put on special glasses or goggles.

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13. BINOCULAR VISION

Binocular vision is vision in which both eyes are used together. The word binocular comes from two Latin roots, bini for double, and oculus for eye. Having two eyes confers at least four advantages over having one. First, it gives a creature a spare eye in case one is damaged. Second, it gives a wider field of view. For example, humans have a maximum horizontal field of view of approximately 200 degrees with two eyes, approximately 120 degrees of which makes up the binocular field of view (seen by both eyes) flanked by two uniocular fields (seen by only one eye) of approximately 40 degrees.

Third, it gives binocular summation in which the ability to detect faint objects is enhanced. Fourth it can give stereopsis in which parallax provided by the two eyes' different positions on the head give precise depth perception. Such binocular vision is usually accompanied by singleness of vision or binocular fusion, in which a single image is seen despite each eye's having its own image of any object.

Field of view and eye movements

Some animals, usually prey animals, have their two eyes positioned on opposite sides of their heads to give the widest possible field of view. Examples include rabbits, buffaloes, and antelopes. In such animals, the eyes often move independently to increase the field of view. Even without moving their eyes, some birds have a 360-degree field of view.

Other animals, usually predatory animals, have their two eyes positioned on the front of their heads, thereby allowing for binocular vision and reducing their field of view in favour of stereopsis. Examples include eagles, wolves, and snakes.

Some predator animals, particularly large ones such as sperm whales and killer whales, have their two eyes positioned on opposite sides of their heads. Other animals that are not necessarily predators, such as fruit bats and some primates also have forward facing eyes. These are usually animals that need fine

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depth discrimination/perception; for instance, binocular vision improves the ability to pick a chosen fruit or to find and grasp a particular branch.

When the eyes move laterally, in the same direction, this is called a version. When the eyes move in opposite directions, to an object closer than where the eyes are pointing or farther than where the eyes are pointing, this is called a vergence. When the eyes move in, it is a convergence eye movement; when the eyes move out, it is a divergence eye movement.

Some animals (including some humans, notably exotropes) use both of the above strategies. A starling, for example, has laterally placed eyes to cover a wide field of view, but can also move them together to point to the front so their fields overlap giving stereopsis. A remarkable example is the chameleon, whose eyes appear to be mounted on turrets, each moving independently of the other, up or down, left or right. Nevertheless, the chameleon can bring both of its eyes to bear on a single object when it is hunting, showing vergence and stereopsis.

Binocular summation

Binocular summation means that the detection threshold for a stimulus is lower with two eyes than with one. There are two forms. First, when trying to detect a faint signal, there is a statistical advantage of using two detectors over using one. Mathematically, the advantage is equal to the square root of 2, about 1.41. Second, when some cells in the visual cortex receive input from both eyes simultaneously, they show binocular facilitation, a greater level of activity than the sum of the two activities evoked separately from each eye. Any advantage in using two eyes in detection task over 1.41 is credited to this sort of mechanism, dubbed neural summation.

Binocular interaction

Apart from binocular summation, the two eyes can influence each other in at least three ways.

Pupillary diameter. Light falling in one eye affects the diameter of the pupils in both eyes. One can easily see this by looking at a friend's eye

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while he or she closes the other: when the other eye is open, the pupil of the first eye is small; when the other eye is closed, the pupil of the first eye is large.

Accommodation and vergence. Accommodation is the state of focus of the eye. If one eye is open and the other closed, and one focuses on something close, the accommodation of the closed eye will become the same as that of the open eye. Moreover, the closed eye will tend to converge to point at the object. Accommodation and convergence are linked by a reflex, so that one evokes the other.

Interocular transfer. The state of adaptation of one eye can have a small effect on the state of light adaptation of the other. Aftereffects induced through one eye can be measured through the other.

Utrocular discrimination

Utrocular discrimination is the ability to tell, when both eyes are open, to which eye a monocular stimulus was shown.

Singleness of vision

Once the fields of view overlap, there is a potential for confusion between the left and right eye's image of the same object. This can be dealt with in two ways: one image can be suppressed, so that only the other is seen, or the two images can be fused. If two images of a single object are seen, this is known as double vision or diplopia. Fusion of the images from the two eyes is considered to be separate from stereopsis for at least two reasons. First, some disorders of binocular vision, such as strabismus can spare fusion but abolish stereopsis. Second, the depth of an object either much nearer to or farther from where the eyes are fixating can be accurately judged despite the images of the object appearing double.

Fusion of images occurs only in a small volume of visual space around where the eyes are fixating. Running through the fixation point in the horizontal plane is a curved line for which objects there fall on corresponding retinal

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points in the two eyes. This line is called the empirical horizontal horopter. There is also an empirical vertical horopter, which is effectively tilted away from the eyes above the fixation point and towards the eyes below the fixation point. The horizontal and vertical horopters mark the centre of the volume of singleness of vision. Within this thin, curved volume, objects nearer and farther than the horopters are seen as single. The volume is known as Panum's fusional area (it's presumably called an area because it was measured by Panum only in the horizontal plane). Outside of Panum's fusional area (volume), double vision occurs.

Eye dominance

When each eye has its own image of objects, it becomes impossible to align images outside of Panum's fusional area with an image inside the area. This happens when one has to point to a distant object with one's finger. When one looks at one's fingertip, it is single but there are two images of the distant object. When one looks at the distant object it is single but there are two images of one's fingertip. To point successfully, one of the double images has to take precedence and one be ignored or suppressed (eye rominance). The eye of the image that takes precedence is called the dominant eye.

Allelotropia

Because the eyes are in different positions on the head, any object away from fixation and off the plane of the horopter has a different visual direction in each eye. Yet when the two monocular images of the object are fused, creating a Cyclopean image, the object has a new visual direction, essentially the average of the two monocular visual directions. This is called allelotropia. The origin of the new visual direction is a point approximately between the two eyes, the so-called cyclopean eye. The position of the cyclopean eye is not usually exactly centered between the eyes, but tends to be closer to the dominant eye.

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Binocular rivalry

When very different images are shown to the same retinal regions of the two eyes, perception settles on one for a few moments, then the other, then the first, and so on, for as long as one cares to look. This alternation of perception between the images of the two eyes is called binocular rivalry.

Disorders of binocular vision

To maintain stereopsis and singleness of vision, the eyes need to be pointed accurately. The position of each eye in its orbit is controlled by six extraocular muscles. Slight differences in the length or insertion position or strength of the same muscles in the two eyes can lead to a tendency for one eye to drift to a different position in its orbit from the other, especially when one is tired. This is known as phoria. One way to reveal it is with the cover-uncover test. To do this test, look at a cooperative person's eyes. Cover one eye of that person with a card. Have the person look at your finger tip. Move the finger around; this is to break the reflex that normally holds a covered eye in the correct vergence position. Hold your finger steady and then uncover the person's eye. Look at the uncovered eye.

You may see it flick quickly from being wall-eyed or cross-eyed to its correct position. If the uncovered eye moved from out to in, the person has exophoria. If it moved from in to out, the person has esophoria. If the eye did not move at all, the person has orthophoria. Most people have some amount of exophoria or esophoria; it is quite normal. If the uncovered eye also moved vertically, the person has hyperphoria (if the eye moved from up to down) or hypophoria (if the eye moved from down to up). Such vertical phorias are quite rare. It is also possible for the covered eye to rotate in its orbit. Such cyclophorias cannot be seen with the cover-uncover test; they are rarer than vertical phorias.

During the cover-uncover test, a person with some phoria will notice a brief episode of double vision or diplopia after uncovering the eye. This is a

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normal consequence of the eye's being briefly misaligned. If the diplopia is enduring, that is considered a disorder.

The cover-uncover test can also be used for more problematic disorders of binocular vision, the tropias. In the cover part of the test, the examiner looks at the first eye as he or she covers the second. If the eye moves from out to in, the person has exotropia. If it moved from in to out, the person has esotropia. People with exotropia or esotropia are wall-eyed or cross-eyed respectively. These are forms of strabismus with amblyopia. When the covered eye is the non-amblyopic eye, the amblyopic eye suddenly becomes the person's only means of seeing.

14. CONCLUSION

We have successfully analyzed the various aspects and perspectives of stereoscopic vision. It can be briefly summarized as-

The stereographic photography consists of creating a 3-D illusion starting from a pair of 2-D images. 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 deviation exactly equal to the perspectives that both eyes normally receive in binocular vision.

If eye strain and distortion are to be avoided, each of the 2-D images preferably should be presented to each eye of the viewer so that an object at infinity 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 infinity distance, such as the horizon or the cloud, the pictures should be placed corresponding closer together.

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Hence, the term stereoscopic imaging can be summarized in a definition as a technique to record or display 3-D information or provides the illusion of depth. It provides spatial information or provides the illusion of depth that tricks a user’s brain into believing and seeing depth in images.

15. REFRENCES

BOOKS

1. Stereo Views: An Illustrated History & Price Guide by John S. Waldsmith

2. The World of Stereographs by William Culp Darrah

INTERNET

• http://wikipedia.org

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http://www.amazon.com/World-Stereographs-William-C-Darrah/dp/0965051315/ref=cm_lmf_tit_2/189-8766380-4600958



Seminar Observer’s ReportName Observations Remarks/marking(10)

Note: Seminar will be treated as Void in case of non presence of Observer, Guide, HoD Observers can be Principal

sir, Director sir, Dean sir.

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stereoscopy (2)

Documents

d technology

bachelor of technology

d display technology

education research

y baseline selection

stereoscopic viewing

degree of bachelor

image quality