3D Display Technologies Overview(1) - Device required

By Andy from Digital Tiger, 2nd, Dec. 2008, all rights reserved

Anaglyphs
The anaglyph method has been used for years to represent stereo pairs and it was a salient
technique in old 3D movies and comic books. Colored filters cover each eye, red/green, red/blue or
red/cyan filters being the most common. One eye image is displayed in red and the other in green,
blue or cyan so that the appropriate eye sees the correct image. Since both images appear
simultaneously, it is a time-parallel method. The technique is easy to produce using simple image
processing techniques and the cost of viewing glasses is very low. Grayscale images are most
common. Pseudo color or poly-chromatic anaglyphs are becoming more common. If correctly
done, anaglyphs can be an effective method for presenting stereo images.

Vectographs
Polaroid’s Vectograph process was introduced by Edwin Land in 1940. The earliest
Vectograph images used extensively were black-and-white polarizing images formed by iodine ink
applied imagewise to oppositely oriented polyvinyl alcohol (PVA) layers laminated to opposite
sides of a transparent base material. The iodine forms short polymeric chains that readily align with
the oriented polymeric molecules and stain the sheet. The chemistry is analogous to that of
uniformly stained iodine polarizers, such as Polaroid H-sheet, used in polarizing filters for stereo
projection and in 3-D glasses used for viewing stereoscopic images (see [2] for more details).
In 1953 Land demonstrated three-color Vectograph images formed by successive transfer of
cyan, magenta, and yellow dichroic dyes from gelatin relief images to Vectograph sheet. Unlike
StereoJet digital inkjet printing described below, preparation of Vectograph color images required
lengthy, critical photographic and dye transfer steps. Although the process produced excellent
images, it was never commercialized.

StereoJet
The StereoJet process, developed at the Rowland Institute for Science in Cambridge,
Massachusetts, provides stereoscopic hardcopy in the form of integral, full-color polarizing images.
StereoJet images are produced by inkjet printing, forming polarizing images by the use of inks
formulated with dichroic dyes. Paired left-eye and right-eye images are printed onto opposite
surfaces of a multilayer clear substrate, as shown in Fig. 4.
Figure 4 StereoJet substrate
The two outer layers, formed of an ink-permeable polymer such as carboxymethylcellulose,
meter the ink as it penetrates the underlying image-receiving layers. The image-receiving layers are
formed of polyvinyl alcohol (PVA) molecularly oriented at 45 degrees to the edge of the sheet. As
the dye molecules are adsorbed they align with the oriented polymer molecules and assume the
same orientation. The two PVA layers are oriented at 90 degrees to one another, so that the images
formed have orthogonal polarization.
StereoJet transparencies are displayed directly by rear illumination or projected by overhead
projector onto a non-depolarizing screen, such as a commercially available lenticular “silver”
screen. No attachments to the projector are needed, as the images themselves provide the
polarization. StereoJet prints for viewing by reflected light have aluminized backing laminated to the
rear surfaces of StereoJet transparencies.

ChromaDepth
Chromostereoscopy is a phenomenon in optics commercialized by Richard Steenblik [2]. The
technique originally used double prism-based glasses which slightly deflect different colors in an
image, laterally displacing the visual positions of differently colored regions of an image by
different amounts. The prisms are oriented in opposite directions for each eye, resulting in different
images being presented to each eye, thereby creating a stereo pair (Fig. 5). Production
chromostereoscopic glasses, marketed under the name ChromaDepth 3-D, utilize a unique microoptic
film that performs the same optical function as double prism optics without the attendant
weight and cost. Images designed for viewing with the ChromaDepth 3-D Glasses use color to
encode depth information. A number of color palettes have been successfully employed, the
simplest of which is the RGB on Black palette: on a black background red will appear closest, green
in the middleground, and blue in the background. Reversal of the optics results in the opposite
depth palette: BGR on Black.
Figure 5 Superchromatic glasses
A peculiar feature of the ChromaDepth 3-D process is that the user does not have to create a
stereo pair. A single ChromaDepth 3-D color image contains X, Y, and Z information by virtue of
the image contrast and the image colors. The stereo pair seen by the user is created by the passive
optics in the ChromaDepth 3-D Glasses. The primary limitation of the ChromaDepth 3-D Process
is that the colors in an image cannot be arbitrary if they are to carry the image’s Z dimension, so the
method will not work on arbitrary images. The best effects are obtained with images that are
specifically designed for the process and with natural images, such as underwater reef photographs,
that have natural coloring fitting the required palette.
Another limitation is that some color “fringing” can occur when viewing CRT images. The
light emitted from a CRT consists of different intensities of red, green, and blue; any other color
created by a CRT is a composite of two or more of these primary colors. If a small region of a
composite color, such as yellow, is displayed on a CRT, the ChromaDepth 3-D Glasses optics may
cause the composite color to separate into its primary components, blurring the region.
ChromaDepth 3-D High Definition Glasses reduce this problem by placing most of the optical
power in one eye, leaving the other eye to see the image clearly.
The ChromaDepth 3-D technique can be used in any color medium. It has found wide
application for use with laser shows and with print, video, television, computer graphic,
photographic slide, and Internet images. Many areas of research have benefited from the use of
ChromaDepth 3-D, including interactive visualization of geographic and geophysical data
Transparency Viewers
Cheap plastic and cardboard slide viewers are available for viewing 35 mm. stereo slides from
many companies like Reel 3D Enterprises (http://stereoscopy.com/reel3d/index.html). The user
places the left eye view in the left slot and the right eye view in the right slot and then holds them up
to the light. This is a standard technique for checking the mounding of slides for correct
registration.


Field Sequential Devices
StereoGraphics Systems
Although there are many manufacturers of active and passive glasses systems, StereoGraphics
is a well known company that has produced high quality CRT and RGB projector based stereo
systems for years. The quality of their hardware is excellent and we report on it here.
The active StereoGraphics shutters called CrystalEyes (Fig. 6) are doped, twisted-nematic
devices. They “open” in about 3 ms and “close” in about 0.2 ms. The shutter transition occurs
within the vertical blanking period of the display device and is all but invisible. The principal figure
of merit for such shutters is the dynamic range, which is the ratio of the transmission of the shutter
in its open state to its closed state. The CrystalEyes system is in excess of 1000:1. The
transmission of the shutters is commonly 32%, but because of the 50% duty cycle the effective
transmission is half that. Their transmission should be neutral and impart little color shift to the
image being viewed.
The field of view (FOV) varies also. Ninety-seven degrees is typical. SGI can operate at a speed
of up to 200 fields per second. The cost for eyewear and emitter is $1000.
Figure 6 Active Glasses CrystalEyes System
Passive systems have a lower dynamic range than active eyewear systems. The phosphor
afterglow on the CRT causes ghosting, or image cross talk, in this type of system. In order to
minimize the time that the modulator is passing an unwanted image, electrode-segmentation can be
used. The modulator’s segments change state moments before the CRT’s scanning beam arrives at
that portion of the screen. The consequence of this action is a modulator that changes state just as
the information is changing. This increases the effective dynamic range of the system and produces
a high quality stereo image. This technique is used by StereoGraphics in their ZScreen system (Fig.
7). A Monitor ZScreen system costs $2200
Figure 7 Passive Glasses ZScreen System
On personal computers that do not have a stereo sync output, the above-and-below format is
used. The left image is placed on the top half of the CRT screen and the right image on the bottom
half, thus reducing the resolution of the image. Chasm Graphics makes a software program called
Sudden Depth that will format the images in this way. Now, the stereo information exists but needs
an appropriate way to send each L/R image to the proper eye. The StereoGraphics EPC-2 performs
this task.
The EPC-2 connects to the computer’s VGA connector and intercepts the vertical sync signal.
When enabled, the unit adds an extra vertical sync pulse halfway between the existing pulses. The
result causes the monitor to refresh at twice the original rate. This in effect stretches the two images
to fill the whole screen and show field sequential stereo. The EPC-2 acts as an emitter for
CrystalEyes or can be used a device to create a left / right signal to drive a liquid crystal modulator
or other stereo product. The EPC-2 is the same size as the other emitters and has approximately the
same range. The cost is $400.

The Pulfrich Technique
Retinal sensors require a minimum number of light photons to fire and send a signal to the
visual system. By covering one eye with a neutral density filter (like a lens in a pair of sunglasses),
the light from a source will be slightly time delayed to the covered eye. Hence, if an object is in
motion in a scene, the eye with the filter cover will see the position of the object later than the
uncovered eye. Therefore, the images perceived by the left and right eyes will be slightly different and the visual system will interpret the result as a stereo pair.
If the motion of an object on a display device is right to left and the right eye is covered by the filter, then a point on the object will be seen by the left eye before the right eye. This will be interpreted by the visual system as positive parallax and the object will appear to move behind the stereo window. Similarly, an object moving from left to right will appear in front of the display device. The reader can implement the technique easily using one lens of a pair of sunglasses while watching TV.

The Fakespace PUSH Display
Fakespace Lab’s PUSH desktop display uses a box shaped binocular viewing device with
attached handles which is mounted on a triad of cylindrical sensors (Fig. 8) The device allows the
user to move the viewing device and simulate limited movement within a virtual environment. The
field of view can be as large as 140 degrees on CRT based systems. The cost is $25,000 US for the
1024x768 CRT and $9,995 US for the 640x480 LCD version
Figure 8 The Fakespace Lab’s PUSH Desktop Display
A variation which permits more viewer movement is the Boom (Fig. 9). The binocular viewing
device is attached to a large arm configured like a 3D digitizer that signals the position of the viewer
using sensors at the joints of the arm. The viewer motion is extended to a circle with 6’ diameter.
Vertical movement is limited to 2.5’. The Boom sells for $60,000 US. A hands free version is
available for $85,000 US.

Tags:stero,3D,Anaglyphs,Vectograph