TYPES OF 3D
ANAGLYPH 3D
WHAT IS ANAGLYPH 3D
Anaglyph 3D provides a stereoscopic 3D effect, when viewed with glasses where the two lenses are different (usually chromatically opposite) colors, such as red and cyan. Images are made up of two color layers, superimposed, but offset with respect to each other to produce a depth effect. Usually the main subject is in the center, while the foreground and background are shifted laterally in opposite directions.
The picture contains two differently filtered colored images, one for each eye. When viewed through the "color coded" "anaglyph glasses", they reveal an integrated stereoscopic image. The visual cortex of the brain fuses this into perception of a three dimensional scene or composition.
WHAT WE HAVE LEARNED
Anaglyph glasses work well for achieving a 3D effect, however you see a skewed sense of color because the filters in the glasses themselves are colored. One benefit of working in Anaglyph 3D is the low cost of purchasing glasses. Paper anaglyph glasses can be purchased for as little as $0.30 per pair. Another benefit that anaglyph offers is the ability to view the 3D images or video on any platform without using any additional filters, hardware, or software. You can view this 3D effect on any TV, computer monitor, or projector. You can even print an image using the correct filter colors and view the 3D effect on paper.
There are many types of anaglyph glasses which use different filter colors, however the most widely used seem to cyan/red and green/magenta. The only real reason that we can find for the different filter option have to do with how well the colors filter certain wavelengths of light. There are still a lot of discussions as to which option is better but a many times it comes down to personal preference. Although, many recently released films have distributed DVD and Blu-ray discs packaged with glasses using the green/magenta filters.
The red filter color can be achieved by using only the Red value in the RGB spectrum. This means the color contains no green or blue (R=255, G=0, B=0). The blue filter, which is technically called cyan, can be achieved by using no red, and the highest values of green and blue (R=0, G=255, B=255).
The magenta filter is built using the highest values of a combination of red and blue, and a zero value for green (R=255, G=0, B=255). The green filter is achieved by setting the highest value for green, and a zero value for red and blue (R=0, G=255, B=0).
POLARIZED 3D
WHAT IS POLARIZED 3D
Polarized 3D glasses create the illusion of three-dimensional images by restricting the light that reaches each eye, an example of stereoscopy which exploits the polarization of light.
To present a stereoscopic motion picture, two images are projected superimposed onto the same screen through different polarizing filters. The viewer wears low-cost eyeglasses which also contain a pair of different polarizing filters. As each filter passes only that light which is similarly polarized and blocks the light polarized in the opposite direction, each eye sees a different image. This is used to produce a three-dimensional effect by projecting the same scene into both eyes, but depicted from slightly different perspectives. Since no head tracking is involved, several people can view the stereoscopic images at the same time.
TYPES OF POLARIZED 3D
There are two types of polarized glasses that are widely used in the entertainment industry. The first is Linearly Polarized Glasses where two images are projected superimposed onto the same screen through orthogonal polarizing filters (Usually at 45 and 135 degrees)[1]. The viewer wears linearly polarized eyeglasses which also contain a pair of orthogonal polarizing filters oriented the same as the projector. As each filter only passes light which is similarly polarized and blocks the orthogonally polarized light, each eye only sees one of the projected images, and the 3D 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. This can make prolonged viewing uncomfortable as head movement is limited to maintain the 3D effect.
The second type is Circularly Polarized Glasses in which two images are projected superimposed onto the same screen through circular polarizing filters of opposite handedness. The viewer wears eyeglasses which contain a pair of analyzing filters (circular polarizers mounted in reverse) of opposite handedness. Light that is left-circularly polarized is blocked 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.
WHAT WE HAVE LEARNED
Early this semester we performed several tests using this type of polarization. By networking two projectors together and installing filters in front of them, we projected polarized images onto a screen. A specific type of screen called a silver lenticular (vertically ridged) screen must be used when projecting 3D polarized images. The term silver screen comes from the actual silver content embedded in the material that made up the screen's highly reflective surface. Light reflected from a motion picture screen tends to lose a bit of its polarization, but this problem is eliminated if a silver screen is used.
Polarized 3D has many benefits when viewing 3D images. One benefit is the low cost of polarized 3D glasses. You can buy a pair of circular or linear polarized 3D glasses for roughly $2.00. This price is a little bit higher than anaglyph glasses, but they are still pretty reasonably priced.
Another benefit polarized 3D offers is the fact that they do not use color filters in the glasses. This means that there is no color distortion when viewing the images on the screen.
The downside of polarized 3D comes in the cost of the projectors. While you can use 2 low-cost networked projectors, it is sometimes difficult to get both projected images to line up exactly how you want them to. There are systems that use one projector but the cost goes up. One example of this is the technology known as RealD. In the case of RealD a circularly polarizing liquid crystal filter which can switch polarity many times per second is placed on front of the projector lens. Only one projector is needed, as the left and right eye images are displayed alternately. Sony features a new system called RealD XLS, which shows both circularly polarized images simultaneously: A single 4K projector displays both 2K images above each other, a special lens attachment polarizes and projects the images on top of each other.
ACTIVE-SHUTTER 3D
WHAT IS ACTIVE-SHUTTER 3D
Active Shutter Glasses (also called Liquid crystal shutter glasses) are glasses used in conjunction with a display screen to create the illusion of a three dimensional image, an example of stereoscopy. Each eye's glass contains a liquid crystal layer which has the property of becoming dark when voltage is applied, being otherwise transparent. The glasses are controlled by an infrared, radio frequency, DLP-Link or Bluetooth transmitter that sends a timing signal that allows the glasses to alternately darken over one eye, and then the other, in synchronization with the refresh rate of the screen. Meanwhile, the display alternately displays different perspectives for each eye, using a technique called Alternate-frame sequencing, which achieves the desired effect of each eye seeing only the image intended for it.
WHAT WE HAVE LEARNED
Active-Shutter is the most widely used technology built into 3D televisions like the one that we used this semester: A 55” Samsung LED 3D Television. We also used active-shutter with our 3D computer monitors and 3D vision kits. The active-shutter technology has its drawbacks and its advantages.
One disadvantage is that a flicker can be noticeable except at very high refresh rates, as each eye is effectively receiving only half of the monitor's actual refresh rate. Modern active-shutter glasses however generally work in higher refresh rates and mostly eliminate this problem.
Until recently, the method only worked with CRT monitors; some modern flat-panel monitors now support high-enough refresh rates to work with some active-shutter shutter systems.
Active-shutter glasses are shutting out light half of the time; moreover, they are slightly dark even when letting light through, because they are polarized. This gives an effect similar to watching TV with sunglasses on, which causes a darker picture perceived by the viewer. However, this effect can produce a higher perceived display contrast when paired with LCD displays because of the reduction in backlight bleed.
Frame rate has to be double that of an ordinary stream to get an equivalent result. All equipment in the chain has to be able to process frames at double rate; in essence this doubles the hardware requirements of the equipment. This is especially noticeable when the image stream is interactively generated in real time by 3D hardware on computers.
In addition, shutter glasses tend to be much more expensive than other forms of stereoscopic glasses, with most models selling for well over $100, particularly for the standard wireless models.
Shutter glasses are also matched to the TV so it's not possible to take your shutter glasses to a friend's house if he owns a different brand 3DTV. However, efforts are being made to create a Universal 3D Shutter Glass.
There are some advantages to using this technology as well. Active-shutter glasses mostly eliminate "ghosting" which is a problem with other 3D display technologies such as RealD 3D, or Dual projector setups. Moreover, unlike red/cyan color filter 3D glasses, LC shutter glasses are color neutral enabling 3D viewing in the full color spectrum.
REFERENCES:
http://en.wikipedia.org/wiki/Anaglyph_image
