and
CROSS-EYED VIEWING
HUMAN VISION IN THREE DIMENSIONS
WHY SOME PEOPLE CANNOT SEE IN 3-D
LAW ENFORCEMENT 3D PHOTOGRAPHY
APPENDICES
Law Enforcement is responsible for investigating crimes, identifying and arresting the suspects, and presenting evidence to a judge and jury in court. In order to objectively perform these duties, police need to gather accurate information and clearly explain the crime scene and physical evidence in a court of law. Part of this information is the documentation of the incident. Documenting an incident has always been divided into three categories: notes, sketch and photography. The notes or written police report is simply documenting the scene with the written word. In order to show the incident photos are taken to represent the scene. Then lastly a sketch or drawing is completed. The drawing will be drawn to scale giving the perspective or measurements of the scene.
This method of recording an incident has been the standard for years. The major drawback to this is that the visual documents of sketches and photographs are two-dimensional. This greatly restricts the actual visualization of the incident requiring a careful cross referencing of the details in order to understand it.
We live in a three-dimensional world and the technology of creating images three dimensionally has been in existence and has been used since long before the turn of the century. Yet in law enforcement we often find ourselves trying to analyze it using two dimensional devices, photographs and sketches. By using various techniques we can fool our eyes into believing that we are seeing three dimensions. Sometimes we can fool our eyes into performing comprehensive diagnostic analyses, making critical medical decisions, and formulating strategic military plans. We use this information to inform, educate and entertain.
We often take our eyes for granted. At the speed of light information rushes through our pupils and into our heads, where our brains process it. We learn about the rays of light, the cornea, the lens, and the retina in elementary school but no one ever stops to explain one of the real mysteries of vision and the world we live in: our perception of three dimensions.
We depend on 3-D information to make decisions about every waking moment. How big is that step? How deep is that river? How far away is that traffic sign? How tall is that building? Is that my car being towed away down the street? Engineers, geographers, cartographers, doctors, and scientists all use three-dimensional information to make important decisions that affect our daily lives, yet law enforcement has yet to realize the benefits of three-dimensional information.
Why doesn't law enforcement use 3-D documentation to record the incident? This paper will attempt to answer this question and demonstrate how to produce 3-D documentation in both drawings and photography.
As you read through this paper you will observe several images have the (3D) next to them. If you are able to freeview stereo images then click on the (3D) and you will see three photos side by side. The left two images are for parallel viewing while the right two images are for cross-eyed viewing. For some it may be easier to print the images then view them with the appropriate viewer.
The word "stereo" originates from the Greek and means "relating to space"2. Today the word "stereo" usually refers to stereophonic sound. Originally the term was associated with stereoscopic pictures, which were either drawn or photographed. In order to avoid confusion with stereophonic sound the term 3-D, which of course stands for three-dimensional, is applied.
As persons we live in a three-dimensional environment. Without a feeling for space, we can not move within it. Our perception of space is created almost exclusively by our mind, based on input from our eyes. There are many ways to orient oneself in space, by perspective, gradation of color, contrast and movement.
The lenses of the eyes in a healthy human being project two slightly different pictures to the retinas, which are then transformed, by the brain, into spatial representation. The actual stereoscopic spatial observation is a result of this combined perception through both eyes, where the differences between two perspectives are interpreted relating to depth or distance. If you close one eye and look around, everything will seem flattened out. The size and shape and distance of things will be very difficult to judge. The slight differences in the perspective between the left and right eye views are known as stereo parallax.
Although you don't look at things with only one eye, the ordinary camera does! The ordinary camera with only one lens (eye) records a single perspective. Since there is no parallax, the image when viewed makes flat pictures without any depth. Size and shape and distance are even harder to judge in a flat picture than they are when the real scene is viewed with one eye. Parallax helps us determine instantly if one thing is in front of another. That's why it takes a camera with two lenses to capture the image in three-dimensions.
The normal photograph is only one-eyed. It is photographed using a single lens, and therefore cannot convey a true spatial perception. It is only a flat picture. By using two camera lenses and imitating the interocular distance of the eyes, we can create three-dimensional images.
To be able to see in three-dimensions requires input from two properly functioning eyes. For the brain to perceive three-dimensions, image data from two independent sources with slightly different points of views are combined, the brain analyzes the difference. These differences tell the brain that one object is farther away than the other. This process of combining and analyzing two images into one three-dimensional image is known as binocular or stereoscopic vision.
The fundamental benefit of stereoscopic vision is called depth perception. From the time we are old enough to cross the streets by ourselves we are taught to look both ways before crossing. But without the ability to properly judge the distance of the oncoming cars, this gesture is of little value. Depth perception enables us to gauge distances in a relative sense with a remarkable degree of accuracy.
There is however another component necessary to perceive three dimensions, knowledge and experience. If you look around at your desktop, you will probably see a paper clip, a pen or a stapler, all of which are familiar objects. If an unfamiliar object such as a gemstone is thrown onto the desktop you are able to make an immediate judgment as to its size, relative to the other objects. Your experience with the familiar objects enables you to quickly draw a conclusion about the new one.
Other visual clues include shading, shadowing, or environmental effects such as light intensity. At times it is difficult to distinguish between stereoscopic effects and visual clues or monocular effects.
At a great distance, objects appear to be flat whether you use two eyes or one. The real benefits of stereoscopic vision are realized at distances ranging from the closest focusing distance of the eye to about 200 feet; this is because of the average eye spacing of approximately 2 1/2 inches.
The basis of three-dimensional vision lies in using two independent captured images from slightly separated points of view, see figure 3. The brain processes and interprets these images, and makes the calculations needed to determine the relative position of the objects in the viewed scene using information from both images.
Many factors contribute to the quality of three-dimensional vision. The distance between the eyes, the quality of the image, the ability of the eyes to focus each image, the speed at which the image is focused, and the general health of the viewer's nervous system all contribute to the process of analyzing images. A complete treatise is beyond the scope of this paper but it is important to understand that the overall process of vision is one of the most complex human attributes.
The distance between our eyes is set by nature and there isn't much we can do about it. Because our brains develop visual analysis abilities as we develop and grow, any compensation needed by the brain to accommodate abnormal eye separation is done automatically. For point of discussion, the average interpupillary separation for adult males is 65 to 66 millimeters. Women average two to three millimeters less. Children reach an interpupillary separation of 55 millimeters by the age of 10. Although this is not incredibly important to normal vision, it has a lot to do with building stereoscopic viewing devices.
In spite of all that has been said about how humans can see in 3D, some unlucky souls are simply not able to perceive three-dimensions. No matter how hard they try, they are unable to gather enough information to properly asses the situation and draw three-dimensional clues about it. The degree of their inability varies, depending on several factors. Impaired vision, physical abnormalities, environmental factors and color blindness may all contribute to 3-D problems.
The true discoverer of stereoscopy is Sir Charles Wheatstone, an English physicist. He first lectured on the subject on June 21, 1833 to the Royal Society of London. His was an accidental discovery made while working on an acoustical experiment with drawn pictures.
On August 19, 1839 the Frenchman Daguerre disclosed his method of generating permanent photographic images, thereby making it possible not only to draw stereograms but to photograph them as well.
In 1849 the first true stereo camera with two lenses was built by English physicist David Brewster.
The stereo craze diminished before the turn of the century and did not surface again until around 1920, when the 45 x 107 mm stereo cameras came into existence.
With the appearance of color 35 mm slide film in the late 1930 the stereo craze again began to flourish. Polarization filters were discovered and stereo projection was developed.
In the late 1940's (after World War II) a new wave of stereo photography came into existence using the new smaller 35 mm cameras. The American format was 24 X 23 mm or 5 sprocket and called "Realist" ( after the Milwaukee-based camera ). In Europe the format was 30 X 23 mm or 7 sprocket and called "European". The normal 35mm camera has a format of 36 X 24 mm or 8 sprocket.
During this same time period the historic View Master was produced. This unique system used 35mm slide film but had a format of 8 X 11 mm and required a special cutter to produce this format. The View Master system is world renowned, but has always been considered a "toy".
Starting in the early 1950's several manufacturers entered the stereo camera market. Some of these manufactures are the Three Dimensional Company (TDC), Tower, Wirgin, Delta, Realist, Kodak, Universal Stere-All, Revere 33, Stereo Graphic and the Leader. There were over 40 different models of 35mm stereo cameras manufactured. By far the two most popular, but still in use today, are the Stereo Realist and the Kodak Stereo.
Several SLR camera attachments were also made to "split" the full frame image of a normal 8 sprocket format into two 18mm wide frames: commonly known as "half frames". Special attachments allowed the photographer to use his own ordinary SLR to create stereo pictures. This system had several drawbacks and never really became popular.
The revival of 3-D photography in the 1980's and 1990's began in 1981 with the introduction of the four lensed NIMSLO 3-D camera. This camera was designed to produce lenticular 3-D prints for viewing without a viewer. Although this camera was most convenient to use and view, the 3-D content of the pictures could not compare to the quality of a conventional pair of 3-D images in a viewer.
The current 3D cameras on the market are the FED Boy from the Ukraine and an RBT 35mm Stereo camera from Germany. The Fed Boy is a European format 35mm whereas the RBT is two full frame cameras joined together.
Interest in 3-D is increasing, as evidenced by the introduction of new 3-D cameras, 3-D video systems, 3-D computer graphics, Virtual Reality, and the advancement of 3-D technology in medicine, science, military and many other areas. Holography, for example, provides a totally novel approach to 3-D imaging and other 3-D opportunities. There is little that cannot be photographed in 3-D, and with the correct camera technique, results can be dramatic.
Currently there are several stereo camera clubs throughout the world. The most noted of these are in Chicago, Illinois, Detroit, Michigan, Columbus, Ohio and California. There are three Organizations that perpetuate stereo photography. These Associations are the National Stereoscopic Association, The International Stereoscopic Union and the Stereoscopic Society of America. See appendix C for addresses of organizations The National Stereoscopic Association held a joint conference in Atlanta, Georgia recently and more than 900 people from all over the world attended.
Along with these international associations there are also 3D Groups on all the major on-line computer services, the most active being the "Photo-3D" group on the Internet.
All forms of three dimensional imagery are discussed in these computer groups. These include photography, drawings, Ray Tracing, Analog, Virtual Reality and 3D Video. Techniques as well as media for 3D imagery are discussed.
There are several methods of capturing a 3-D image with photography. The simplest method is using a 3-D camera. The modern (since 1940's) 3-D camera is a camera that uses 35mm film. Most of the 3-D cameras in use today are vintage cameras of the 1950's. In 1980 Nimslo produced a 4 lens camera that was used to make lenticular prints but failed to attract the buying power of the public. Stereo enthusiasts bought the camera and converted it to true 3-D use. Instead of using all 4 lenses the stereo enthusiast used only the outside two lenses. This gave an interocular separation of about 2 1/4 inches, sufficient for scenes from about 6 feet to 20 feet in depth.
The typical stereo camera has two lenses separated by approximately 2 1/2 inches, the same distance that the average human's eyes are separated. The camera takes two pictures at once, each lens recording a slightly different perspective, just as the human eyes capture two slightly different images. These images are then viewed using a print or slide viewer, depending on the type of film used. Each viewer has two separate viewing lenses so when viewing the image the left eye sees only the left image and the right eye sees only the right image. The mind then combines these images to form one image in three dimensions. A simple device of this nature is the View Master viewer and reels we all were familiar with as children.
Another method of taking two photographs at once is to use two identical cameras side-by-side and activate them simultaneously. The problem with this method is the lens separation is greater than 2 1/2 inches. This greater separation then produces an image which is slightly miniaturized, an effect called "Hyperstereo". If the lenses are closer together than 2 1/2 inches the images appear to be larger than normal and are called "Hypostereo". When the lens spacing of the camera and viewer matches the eye spacing of the person viewing the images that is called "Orthostereo".
Another method to capture 3-D images is to use a single camera and shift your weight from one leg to the other leg between the two consecutive exposures, thus separating the images by about 2 1/2 inches. The problem with this method is that if there is any change of camera angle or movement, such as trees blowing in the wind, between the exposures the 3-D image will be spoiled.
A third method is to use a camera mounted on a slide bar thus controlling horizontal and vertical movement between exposures. This method is ideal for "table top" photography or macro photography when the object photographed does not move between exposures.
There are several methods for mounting photographs or slides for viewing. I will not attempt to demonstrate these methods or dwell in greater detail on the techniques used in stereo photography. Instead I refer you to the Bibliography at the end of this paper for reference material.
The question of "Why should three-dimensional photography be used in law enforcement" is simply answered by answering the question "Do you need to visualize depth relationships?" Have you ever had someone try to explain to you the traffic accident they were involved in? The first thing they do is to verbally describe the scene. If you indicate you don't understand they will then draw you a diagram of the scene. In essence they are trying to get you to visualize two-dimensionally what they saw three-dimensionally. Not only is this situation difficult for the layman to understand; police officers have the same difficulty.
A recent traffic accident that I witnessed occurred like this. A car was traveling in the right of two northbound lanes. The car approached a four way intersection controlled by traffic lights. The traffic light for the north bound traffic turned from green to yellow to red, then a few seconds later the east and westbound traffic were given the green light. The car traveling north in the right lane did not stop for the red traffic light and struck a van traveling east through the intersection. This van then struck another unit. This third unit was stopped at the light to make a left hand turn to go from westbound to southbound. Clear as mud? This is an example of a verbal description. Does that help? Using a sketch or a diagram to reconstruct the accident scene helps in understanding the verbal description.
Now using a stereoscopic viewer examine the 3-D photos of the same scene. You should now be able to perceive depth. Which is easier to understand the verbal description or the three-dimensional image? Probably the combination of the two is ideal. Yet I have rarely seen three dimensional photography used to document traffic accident scenes.
In what other areas of law enforcement would three dimensional imagery be beneficial? How about crime scenes? The typical rules of documentation, notes, photographs and sketches are applied here also. Handwritten notes are taken to aid in preparing a formal written report later. The notes verbalize what the scene looks like, describes conditions found at the scene, and indicate where the scene is located, where the items of evidence are located, and what occurred at the scene.
Next photographs are taken to give a pictorial representation of the scene then a diagram or sketch is prepared to put things into perspective. The following is a typical crime scene report of a burglary.
On May 25, 1988 Sgt. Baldwin was requested to process a business burglary at a McDonald's restaurant. Upon arriving at the scene Sgt Baldwin was advised that the burglars had forced open a side door to the restaurant and removed a large safe from the office. The safe was found in a barn a short distance away from the business.
Sgt. Baldwin made the following observations: The burglars had used a prying tool to force open the side door to the McDonald's restaurant. Drag marks from the safes' wheels were observed on the tile floor leading from the office to the side door across the tile floor. The drag marks were observed on the asphalt leading away from the building to a barn a short distance away. Inside the abandoned barn was the safe. The safe had been pried opened and the contents removed. The burglars had "peeled" the front door of the safe, exposing the locking mechanism. They had then reached inside the peeled door and manipulated the locks, thus opening the safe.
The description of the scene is accompanied by a diagram to give perspective to the scene. The photographs of the scene give the viewer a pictorial representation of the crime scene. However only 3D pictures of the safe can give "true perspective" and aid the viewer in understanding the written description and "flat" photographs.
Here is an example of a death investigation scene.
On June 25, 1994 Sgt. Baldwin was requested to process a death investigation at a residence in Anytown, Illinois. The officers at the scene advised Sgt. Baldwin that the victim had been discovered deceased in his bedroom by his sister. The victim had apparently shot himself with a shotgun. The victim had been despondent the past several weeks and had talked of suicide.
In examining the scene Field Supervisor Baldwin made the following observations: The victim was dressed in a blue T-shirt, Blue cotton shorts, white socks and white gym shoes. The victim was lying on his right side. A Winchester 12 gauge shotgun was lying next to the victim. A shotgun shell was "stove piped" in the chamber. Blood spatter, skin tissue, skull fragments and brain tissue were splattered in all directions from the victim. A gun cabinet was present in the room. The gun cabinet door was standing open and a box of Remington 12 gauge Deer Slugs was on the cabinet shelf. The box was opened. To the east of the victim Field Supervisor Baldwin observed three holes in a tile of the suspended ceiling. The holes were in close proximity to each other. Field Supervisor Baldwin observed the wadding from a shot gun shell wedged inside two of the ceiling tile holes.
This written description is followed by a diagram and then photographs to give the investigator visual clues as to what the crime scene looked like. However when followed by 3D photographs the investigator gets a "true perspective" of the scene.
Space and discretion limit the use of additional photographs of the scene; however, viewing the one photograph in 3-D discloses the benefit of 3-D pictures of crime scenes.
Where else can 3-D photographs be helpful in law enforcement? Actually, in every facet of law enforcement. Wherever visual documentation is required, 3-D photography should be used.
Three dimensional sketches have been in use for several years now. Law enforcement has failed to use this visual imagery to its fullest extent.
In the past, drawings, whether of traffic accidents or crime scenes, were always drawn flat. The viewer could only imagine how this incident looked in the real world of three dimensions. Later, scale models were made to help the viewer visualize the incident in three dimensions. This process was quite good, but the models were extremely costly and time consuming to build.
About ten years ago three dimensional drawings were introduced to law enforcement. This technique did help the viewer with perspective but it still lacked true three-dimension quality.
The latest aid to completing three-dimensional drawings is the computer. There are several software packages now available which produce what are called 3-D images. Any single view of something is a flat image. The only three-dimensional qualities are things like shadows and perspective. However, if these same computer images are "shifted" or viewed from two slightly "shifted" different perspectives (at least a 3 inch separation) they will be seen as true 3-D.
"Although stereoscopic photographs are used as evidence, their admissibility has not been passed upon by an appellate court except in two early cases decided over eighty years ago. In an Illinois case it was held not error to admit in evidence stereoscopic views of a bridge and embankment where the plaintiff was injured when a horse pulling his sleigh became frightened and ran off the embankment leading to the bridge. The court allowed in evidence a stereoscope to aid the jury in examination of the views. (Ill. - City of Rockford vs Russell, 9 ILL.App. 229 (1881)). In an Iowa case the trial court rejected stereoscopic views of the plaintiff's property taken the day after injuries were caused by a large flow of water. The Appellate court held that the stereographs ought to have been admitted because they were competent evidence to show the condition of the property after the alleged injuries. (Iowa - German Theological School vs City of Dubuque, 17 NW 153, 64 Iowa 736 (1883))."3
There is no difference in theory between present day stereo photography and that in use when stereo photographs were declared admissible in evidence in the 1880's. The only difference is that present day stereo photographs are more reliable and more realistic because of the employment of color photography, and therefore, since there was no question about the admissibility of the duly verified and relevant stereo photographs in the 1880's there certainly should be no question now.
In more recent times there was a newspaper report of stereo color slides being projected in a homicide trial in Chattanooga, Tennessee in 1950. In 1966 stereo color slides were admitted as evidence in a federal court at Wichita, Kansas in a suit charging three major oil companies with pollution of Walnut River. It is certain that stereo pictures have been used as evidence in other trial cases but it is difficult to obtain this information due to the lack of reference to stereo pictures in the appellate court opinions.
The legal requirements for three-dimensional drawings are the same as for normal drawings of traffic accident or crime scenes: the dimensions must be accurate and the scale must be stated. The newer technology of video enhanced "3-D" recreations of the event may have problems with admissibility in court but the use of stereo photographs has a long history of admissibility.
The use of 3-D images, whether photographs or drawings, does have an important role in visualizing an incident. Perspective in viewing has always been advantageous rather then detrimental to the viewer. Problems with 3-D photography in its current form include: the extra work required to properly view the images, the possibility that the person viewing the image has a visual defect preventing them from seeing the image in 3-D, and the lack of modern equipment to capture and properly view the images.
In order for the public and law enforcement to accept these 3-D images the process must be fairly easy to produce and should not require a separate viewing device. The future is nearer then most people think. 3-D television is currently being produced in Australia and Japan. The use of 3-D images in drawings are already here in the form of video animation.
Law enforcement is gradually being persuaded to selectively use three-dimensional images. Video animation is currently used in criminal, traffic, and civil cases by both prosecution and the defense attorneys. 3-D photography has been used in recent civil cases but law enforcement officials are still reluctant to use 3-D photography in criminal cases. This barrier is crumbling but will not totally disappear until people are able to see three-dimensional images without the use of mechanical viewers. Holography, video animation and digitization of images will, in the near future, make viewing three-dimensional images a norm rather then a rarity.
1 Fritz G. Waach, Stereo Photography, Self Edition, Reel 3-D Enterprises, Culver City, CA, 1995, 1:5
2 Douglas E. Wolfgang, Adventures in 3-D, Que Corp., 1:9
3 Charles C. Scott, Photographic Evidence,2nd Edition, Chapter 24, St. Paul, West Publishing, 1991
Brown, Theodore. Stereoscopic Phenomena of Light and Sound. Facsimile of 1903 Edition. Culver City, California. Reel 3-D Enterprises. 1994
Burder, David FRPS and Pat Whitehouse FRPS. Photographing in 3-D 3rd ed. Surrey. England. The Stereoscopic Society. 1992
Dalzell, J. Moir, Practical Stereoscopic Photography, 2nd Edition, London, The Technical Press, 1953
Dinwiddie, James H.. Tips and Techniques for Better Stereo Pictures. Chicago, Illinois. Chicago Stereo Camera Club. 1994
Ferwerda, Jac G.. The World of 3-D. The Netherlands. 3-D Book Productions. 1987
Hyzer, William G., "Scientific 3-D Photography", Photomethods. Volume 32. Number 1. January 1989. pp 12-13
McKay, Herbert C., Three Dimensional Photography. Minneapolis, Minnesota. American Photography. 1951
Morgan, Hal and Dan Symmes. Amazing 3-D. Boston, Massachusetts. Steam Press. 1982
Morgan, Willard D. and Henry M. Lester. Stereo Realist Manual. New York City, New York. The Fountain Press. 1954
Pinsky, Susan and David Starkman. Reel 3-D News. Culver City, California. Reel 3-D Enterprises. 1979
Piper, Charles A.. The Technical Page. Stereo Club of Southern California. 1989
Scott, Charles C., Photographic Evidence, 2nd Edition. Chapter 24. Stereoscopic Photography. St. Paul, Minnesota. West Publishing. 1991
Waach, Fritz G.. Stereo Photography. Self Edition. Culver City, California. Reel 3-D Enterprises. 1995
Wolfgram, Douglas E.. Adventures in 3-D . Carmel, Indiana. Que Corporation. 1993
APPENDIX A
Always have the pictures, the viewer, and your eyes lined up straight. Adjust the distance for your own eyes.
This will never do! If you do not fuse the stereo pictures immediately, chances are that you have the pictures tilted.
Most people can fuse the pictures through the viewer right away. However, if you have any trouble, relax, and start from the beginning. Depending on your viewing distance, you may see an extra strip of picture on each side of the fused stereo. If you do, just disregard it.... or move the viewer just a little further away from your eyes to make the strips disappear.
Try out the stereo viewer on this stereo pair. Adjust the picture and viewer for your own eyesight as described above.
APPENDIX B
The technique of viewing side-by-side 3-D pairs without a stereo viewer is called "free-viewing". The 3-D examples in this paper may be free-viewed as follows. Like any new experience, a little practice will be required to see the 3-D images clearly. Practice and be patient: the effort is worthwhile.
Hold a piece of stiff cardboard at your reading distance, hold card between your eyes and the pictures. Draw the pictures slowly away from the eyes while fixing each eye on the same prominent feature in each picture.
Remember, practice makes perfect and this does require a lot of practice. However, once you have trained your eyes, you will then find "free-viewing" stereo pictures easy. The trick is in training your eyes!
APPENDIX C
The International Stereoscopic Union
Paul Milligan, (American Representative)
508 La Cima Circle, Gallup, New Mexico 87301
The Stereoscopic Society of America
1677 Dorsey Avenue, Suite C, East Point, Georgia 30344
The Photographic Society of America
Stereo Division Membership
Director P. Sweezey
4594 Las Lindas Way, Carmichael, California 95608
Reel 3-D Enterprises, Inc.
P.O. Box 2368, Culver City, California 90231
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