Written by Tomi Engdahl at 1996-1997 and contents last updated at January 1998 Links checked and corrected August 1999
Our ability to see stereo-vision comes from each of our eyes seeing a slightly different view of the world. Our brain integrates these two images into one three-dimensional picture. The key element in producing the stereoscopic depth effect is parallax. Parallax is the horizontal distance between corresponding left and right image points. The stereoscopic image is composed of two images generated from two related perspective viewpoints, and the viewpoints are responsible for the parallax content of a view. For more information check Creating Good Stereo-Vision Images and Stereographics Handbook by Lenny Lipton. Sci.virtual-worlds newsgroup web site has useful FAQs about 3D technology.
Electro-stereoscopic displays provide parallax information to the eye by using a method related to that employed in the stereoscope. The 3D display systems normally in use use on of the following methods:
Color filter glasses were one of the oldest 3D glasses. The system works so that both eyes have a different color filter in front of them. This causes that left eye can only see few colors and right eye some other colors. When the led eye's colors are used to draw the emage which it should see and same is used for right eye, the combined image can be viewed with suitable glasses in 3D. The most common color combinations are red+green and blue+green. The color filtering limits that there are only few possible colors in use in th epicture so the images made using this method are not very nice to look.
Color filter glasses have been used in 3D movies and some early computer games. The advantage of this method is that the 3D material can be stored to any standard color video media and viewed with normal display devices as long as you wear the right color filter glasses. The galsses are very inexpensive beacuse you only need very cheap plastic filters for them. You can even make your own glasses from piece of cardboard and suitable filters (standard lighting GEL numbers R26 and R83 should be quite suitable for red+green glasses).
This technique causes colors in the image to be compromised because you have too many different colros in different eyes. Practically you loose almost all your color, so you can see objects coming out of the screen but they are gray. The colors also create some eyestrain and distortion.
This method is usually used with projection displays when 3D material needs to be displayed. Every viewer has to wear special glasses which have two polarizing lenses which have their polarization directions adjusted to be 90 degrees different. This makes is possible that left eye sees it's picture without problems but everything ment to right eye (sent out at different polarization) seems to be black. Same applies also to right eye.
The material which has to be shown is typically projected using two projectors (film projector, slide projector or video projector) which each have polarizing lenses in front of them (adjusted to meet the polarization directions of the glasses). The projection surface must be specially made so that it does not do any harm to the polarization (many traditional projection surface materials are not suitable, silver stripe screen is recommended). The advantage of this method is that the pictures can be in full color and the viewing glasses are still quite inexpensive.
In the LCD shutter glass 3D display, the left and right images are alternated rapidly on the monitor screen. When the viewer looks at the screen through shuttering eyewear, each shutter is synchronized to occlude the unwanted image and transmit the wanted image. Thus each eye sees only its appropriate perspective view. The left eye sees only the left view, and the right eye only the right view.
A field-sequential 3D (stereoscopic) video signal is a normal video signal (PAL, NTSC or SECAM) which has been specially recorded with left and right images stored on the even and odd fields of the video signal. The 3D video signal is usually viewed while wearing a pair of LCD shutter glasses which only allow the left eye to see left images and the right eye to see right images.
If the images (the term "fields" is often used for video and computer graphics) are refreshed (changed or written) fast enough (often at twice the rate of the planar display), the result is a flickerless stereoscopic image. This kind of a display is called a field-sequential stereoscopic display.
Lenny Lipton has develloped this technology very much: he holds many patents and has commercially used this technology. For more information on this subject check article a STEREOSCOPIC IMAGING TECHNOLOGY: A Review of Patents and the Literature by Michael Starks.
Format Fields/Sec Medium Video viewing hardware Interlace, NTSC 60 NTSC Normal TV, odd/even field sync box Interlace, PAL 50 PAL Normal TV, odd/even field sync box Side-by-side, NTSC 120 NTSC View/Record box, computer monitor Side-by-side, PAL 100 PAL View/Record box, computer monitor Above-and-Below 120 PC Sync-Doubling Emitter, VGA monitor Stereo-Ready 120 Workstation Normal workstation monitor White-Line-Code 70-90 PC White line code decoder box for glasses
Here is a short summary of 3D glass controlling schemes for computer displays (taken from 3D PC Systems page):
+-------------+---------------+----------+-----------------+----------+ | 3D Method |Vertical Output| Fields |Effective Refresh| Vertical | | | Frequency |per Second|Rate for a Stereo|Resolution| | | of video card | | Field Pair | | +-------------+---------------+----------+-----------------+----------+ |Interlaced | 60Hz | 60Hz | 30Hz | half | +-------------+---------------+----------+-----------------+----------+ |Page Flipping| 60Hz | 60Hz | 30Hz | full | +-------------+---------------+----------+-----------------+----------+ |Sync-Doubled | 60Hz | 120Hz | 60Hz | half | +-------------+---------------+----------+-----------------+----------+
The biggest drawback of LC-Shutterglasses besides the compatibility and ergonomy issue is Crosstalk. Due to the persistance of the monitor tube, the inability of the LC-panels to block the light entirely, sync errors and other factors one see "Ghostimages" sometimes. The right eye sees some residue of the image dedicated to the left eye and vice versa.
For more information different techniques on presenting 3D image on computer screen and controlling the shutter glasses, check Stereographics Handbook Chapter 4.
Another common scapegoat for inadequate hardware, software, and lack of stereo training is flicker, which is most noticeable in standard frequency (e.g. 60 Hz) field sequential systems. It varies with many factors, especially screen brightness, screen size and room illumination. The image may still flicker even at 120 Hz screen refresh if the image is not updated in the proper way. Decreasing the level of ambient illumination in the room can reduce the room flicker to imperceptible levels. Reducing screen luminosity with brightness and contrast controls will reduce image flicker to low or imperceptible levels.
There have been many methods for controlling the LC shutter glasses. The liquid crystal shutter elements (size usually 3/4"x1") itself have to be driven using AC voltage, because DC would destroy the liquid crystals. The driving signals are typically around 3-8V and frequency is usually fre hundred Hz. The shutter elements are usually designed so that when no voltage is connected to them you can see through them and when you apply the AC control voltage those elements become black.
The most common way to connect the glasses is that the LC shutter glasses are wired to a controller which is connected to video source what you want to watch (usually computer or VCR). Sometimes IR or other wireless links are used between the glasses and controller. Using IR or radio link enables easily controlling multiple glasses from one controller.
Controller itself is connected to video source thoug some suitable connector. If you are watching stereo program from VCR, the controller get the LC glass controlling info from the video signal. This same method is used also in many computer interfaces. There are fre different ways to get the controlling info from video signal and they are shown quite well in Stereographics Handbook. Some system do not just take the info from the sync signals, but they actually modify the video signal.
In PC virtual reality applications serial port and parallel port interfaces become quite common. In this implementation the software takes care of changing the data in display memory and sends the signal to which eye the picture is to the PC glass controller through serial or parallel port. The most widely used implementations of this technique have been very simple circuit which have used one or two ouput pins for telling what eye should be visible and what should not be. Sega 3D glass serial port interface is quite classical this kind of interface. Serial port interface have also been used with Commodire Amiga and Apple Macintosh.
Commodore Amiga joystick port is bidirectional. It has power output and it can be used for controlling small peripherals like LC shutter glass interface. AMI VR system has used this method. Using joystick port has also the same limitations like serial and parallel port interfaces: software has to handle the controlling of LC shutter glasses.
When 3D grpahics has become more and more used, some workstation manufacturers have put special ports to their 3D graphics adapter for easy interfacing of 3D LC shutter glasses. Nowadays Silicon Graphics workstations have a LC shutter glass interface as a standard feature.
3D display devices a a necessity for generating virtual reality environment. The only way to make the filling that you are really inside the virtual reality word is to show the virtual world around you in 3D. There have been many methods for generating 3D displays, but the most common of them used with computers are LC shutter glasses and head mount displays (HMD). For more information about both of those devices can be found from 3D Device Support Page and The Virtual Reality Homebrewer's Handbook.
Sega 3D glasses are simple and inexpensive LCD shutter glasses used in many homebrew virtual reality systems. Those glasses can be used in combination with normal computer monitor to show realistic 3D pictures. If youn't know what those glasses look like, too at this picture.
Sega designed special glasses for it's video game console to be able to produce 3D video games. Those glasses used LCD shutter method for producing 3D images. In this method the picture is snown to different eyes after each other. The LCD panels in front of both eyes are controlled so that one eye sees one screen image and the other eye sees the second image etc. With normal TV it was possible to show 25 or 30 images per second (depending on TV standard used) to both eyes. The image flickers quite much, but gives well noticable 3D effect. 3D games for sega game consoles did not sell very well and Sega dropped those glasses from it's product lines.
Ever since the Sega 3D glasses are used in many home virtual reality projects. There is free software support for those glasses in some nice VR programs (for example rend386). One of the problem for home experiments have been to figure out how to connect those glasses to PC.
There have been two approaches for controlling the glasses form the computer: serial port and parallel port. For connecting the glasses to those PC ports, the small adapater box (made for Sega game console) is practically useless. The home VR experiments had to devellop their own circuit. The program which runs in computer must them make sure that the display contents in the screen in changed for every fram and the state od the shutter glasses is changed acoording that.
I have built one circuit for interfacing sega 3D glasses to PC serial port and you can find more information about the circuit I used from my article Sega 3D glass interfacing.
3D Magic is a 3D shutter glass system from 3DTV corporation. The glasses are connected to PC parallel port using a small adapter box which has connector for 3D glasse wire. The package includes 3 CD-ROM which has games, 3D graphics and other software. The list price of 3D Magic is $115.00 (1997).
IR Pro is another 3D glass package form 3DTV corporation. IR pro is designed to be operated using various computer and video sources. The $350.00 packet includes and adapter with video inputs and the LC shutter glasses. The adapter sends IR signals to control the glasses, so you don't need any wiring between the adapter and LC shutter glasses.
Photo 3D from 3DTV corporation is a LC shutter glass product for viewing 3D photos on PC screen. The system comes with StereoVisors, serial or parallel port interface, StereoPro software for merging PCX or GIF files and Photo CD with sample stereo pairs.
StereopPro from 3DTV corporation includes LC shutter Visor, computer interface and StereoPro software for merging stereo pairs in PCX or GIF formats. The computer interfaces avaialble are parallel port, serial port and Amiga joystick port interface.
Apec makes VR97 LC Shutter Glasses which are designed to view 3D images on PC screen. Those glasses support interlaced stereo display and work under Windows 95. The glasses itself are designed so that they can be worn also with eyeglasses. The glasses support monitor frequencies up to 120 Hz and are connected to the PC using an adapter which plugs to PC monitor connection.
StereoGraphics® is the worldwide leader in 3D stereo visualization products and prototyped the first flickerless field-sequential electro-stereoscopic display in 1981. CrystalEyes®, introduced in 1989, were the first untethered liquid crystal 3D glasses.
CrystalEyes are LC shutter glasses made by Stereographics. The glasses promise to provide flickerless picture at 120 Hz refresh rate using above-and-below format.
CrystalEyes incorporate liquid crystal shutters that alternate between transparent and opaque at 120 frames per second, synchronized with a 120 Hz stereo-ready monitor using an infrared signal. When the left image is displayed, the left lens of the eyewear opens while the right lens closes-displaying the correct image to the correct eye. The result is a non-flickering, full-color, true stereo 3D image.
CrystalEyes are available with or for most major stereo-ready workstations and personal computers. Platforms include Silicon Graphics, Sun, Digital and Hewlett Packard. It also runs on IBM-compatible PCs, Macintosh and NEC. And all the major monitor manufacturers produce stereo-ready monitors.
Simuleyes are LC shutter glasses designed for PC gaming made by Stereographics. The glasses use White-Line-Code (WLC) system for reading diretly from monitor video signal if the current image is for left eye or for right eye. This method makes it very easy to interface the glasses to VGA monitor connector and automatically work well with software which support this feature.
The White-Line-Code (WLC) system is used for multi-media PCs and it offers a high-quality but low-cost solution to the problem of stereo-vision imaging. This format doesn't care if the left and right fields are in interlace or progressive scan modes, and it doesn't care about the field rate.
On the bottom of every field, for the last line of video, white lines are added to signify whether the field is a left or a right. The last line of video was chosen because it is within the province of the developer to add the code in this area immediately before the blanking area (which is not accessible to the developer). When our electronics see the white line, it is prepared to shutter the eyewear once the vertical sync pulse is sensed.
Crystaleyes 2 is a high end LC shutter glasses from Stereograhics. They are deigned to be interfaced to workstation which have built in support for 3D glasses (like Silicon Graphics workstations).
CrystalEyes 2 eyewear links liquid crystal shutters and an infrared emitter. The eyewear, shutters 60 times per eye per second in synchronization with alternating left- and right-eye views presented on the display. The mind then fuses the two perspectives into one high-resolution, full-color, flicker-free stereo image.
CrystalEyes development on workstation platforms is a straightforward process. Nearly all SGI hardware systems built in the last five years (and all systems currently shipping) include built-in hardware support for CrystalEyes. Many other workstations also include CrystalEyes support right out of the box.
Using Open GL a developer can take advantage of special extension functions to create stereoscopic applications. These functions enable the developer to check whether the hardware is stereo-ready, easily switch into and out of stereoscopic display mode, and draw to either or both of the eye buffers. And platforms that don't use Open GL generally have their own set of built-in stereo functionality.
CrystalEyes VR is a LC Shutter glass system combined with head position feedback system. The glasses are made by StereoGraphics Corp.
StereoGraphics Corp. SimulEyes VR shuttering LCD glasses provide true stereoscopic 3D viewing to multimedia and game users. The PC user can experience true 3D on a PC for under $150 with SimulEyes VR.
The video boards used in multimedia PCs conform to the IBM 8514 1024 by 768 standard, an interlaced format operating at approximately 90 fields per second. SimulEyes VR takes full advantage of this high field rate and flicker is practically imperceptible. And for non-interlaced DOS games, page swapping offers a fast action mode at 70Hz and 80Hz.
For more information how the glasses work in practice check the review at Coming Soon magazine.
CyberBoy is a LCD shutter glass kit for PC gaming by Woobo. The glass is connected to PC serial port and controlled by software.
CyberJoy is a LC sutter glass which connectrs to PC VGA output poer using small connector box. There is mostly game support for this product. The product is made by Woobo.
CyberRay is a 8-bit ISA interface card for interfacing LC shutter glasses to PC. This product connects to PC bus and VGA card and controls the LC shutter glasses. Software is designed to work with DOS and Windows. The product is made by Woobo.
CyberView is LC shutter glasses designed to be connected to other Wooboo Electronics devices mentioned above. The glasses have built-in earphones and use 12V positive control voltage. The product is made by Woobo.
3-D SPEX is inexpensive ($99) LC shutter glasse designed for PC gaming. The glasses connect to PC parallel port and need a SVGA color monitor which supports 100 Hz refresh rate. The video card must support VESA 1.2 under DOS.
The http://www.vrex.com:80/vrsurfer/vrsurfer.htmVR Surfer kit ($99) contains wireless 3D eyewear, IR transmitter, VGA dongle, video cable, power supply, configuration software and an assortment of games and applications (games, 3D video and 3D images).
3D-MAX from Kasan Electronics combines a pair of high speed LCD shutter glasses and a PC-adapter for low list price. Built in VGA-compatibility provides immediate hookup to DOS and Windows based computers. Software drivers allows 3D stereo capability to be added to DOS and Windows based applications without major development effort. (According a news article in sci.virtual.worls newsgroup written by Fred Cass (cass%pcbuoa.dnet.dec.com@mrnews.mro.dec.com) there are some problems with some video card and Windows 95).
Some more detailed info from the product from Curt Swartzwelder (Curts@cris.com):
I work for Kasan Electronics in Korea and we make LCD shutter glasses for stereoscopic viewing. We call our product 3D-MAX, and it is shipping in Europe, Japan, Russia, and other countries world wide. We expect to launch 3D-MAX in U.S. and Canada in the first quarter of 1995. Reveal Computer Products will carry 3D-MAX in computer retailers everywhere.
The basic 3D-MAX kit includes a pair of LCD glasses, an IBM PC interface board, driver software and in the U.S. market, games such as Descent: Destination Saturn, Magic Carpet, and several Knowledge Adventure products. Retail price is expected to be under $200.
3D-MAX provides flicker-free operation on standard PC monitors in the following stereo rssolutions:
320x200 320x400 640x480 800x600 512x700 1024x768 1024x7003D engines such as Renderware by Criterion and BRender by Argonaut support 3D-MAX right out of the box, giving their users the ability to create stereo graphic and virtual reality applications with minimal effort.
Additional information is available at Kasan's WWW site: http://www.kasan.co.kr
Sincerely, Curt Swartzwelder Overseas Marketing Manger Kasan Electronics Co. LTD curt@pcvr.kasan.co.k
The table is collected from the information available in web about those 3D glasses. Because the information available is far from complete there is lots of details from many glasses missing.
Model Control signal Fields/sec Price Applications 3DTV 3DMagic ???? Wired $115 PC Games, PC VR 3DTV IR-PRo Video signal IR 50/60* $325 3D video 3DTV Photo 3D Serial/parallel Wired 3D picture viewing 3DTV SEGA Glass Connector Wired 60 Modificated for PC 3DTV AMI VR Jostick port* 50/60* Amiga 3D 3DTV StereoMac 3D Serial port Apple Macintosh 3DTV StereoPro ser/par/joystick PC, Amiga CrystalEyes ??? 120 PC 3D CAD Crystaleyes 2 Connector IR Workstations CrystalEyes VR ??? PC VR, feedback Simuleyes White-line-code 90 PC Games 3DMAX VGA feature conn Wired 87-120 PC Games Apex VR97 Monitor connector Wired up to 120 3D images under Win95NOTE: The details marked with * are my assumptation of the correct information in situations where the information is not available from manufacturer. The information is collected indirectly (like if normal TV operation is mentioned then normal TV frequencies are used). Do not thake those as absolute truths.
For more information about head mounted displays read Virtual Reality: Introduction to infographic technologies, VRresource VR article collection and sci.virtual-worlds Head Mounted Displays (HMD) Frequently Asked Questions (FAQ)
CyberMaxx Virtual Reality Helmet helmet was manufactured by VictorMaxx. It had a resolution of 267x225(color triads) for its LCD screens. Its angular resolution is 12.58 arc minutes per pixel. Its field of view is 56 degrees. Because the product is discontinued some components of that HMD unit are available in the surplus market. Halted Specialities sells some of the components used to make that HMD unit (for example LCD screens and optics). They also have a good technical description of the electronics used in CyberMaxx HMD.
VFX1 from Forte Technologies has a resolution of 278x204(color triads) for its LCD screens. Its angular resolution is 10.36 arc minutes per pixel. Its FOV is 48 degrees. The HMD has also head position feedback. Forte is now Interactive Imaging Systems and they are continuing HMD devellopment.
Virtual i-glasses are a lightweight head mounted display (HMD) from company called Virtual i-o. Accorhing news articles that company is now out of business (also web site that was at http://www.vio.com/ is down). Virtual glasses stock is now at surplus markets (check companies like The VR Resource and Ilixco. Virtual i-glasses are capable of displaying both 2-D and 3-D images in full color with stereo sound. The product includes head tracking to give head movement information to games. The product is compatible with PCs, televisions, VCRs, laserdisc players, and electronic gaming systems.
SpaceHelmet Model 1 is a dual LCD helmet with ca. 180,000 pixels/eye and weight of 1 lb. SpaceHelmet is a low cost and light weight stereoscopic stereophonic HMD from 3DTV.
Dynovisor HMD is a HMD which connects to TV, LD, VCD, VCR, DVD, Camcorder, PC and Game Consoles. It integrates a display and audio system one HMD device which should give very wide screen look to games.
Scuba FX is a HMD display device manufactured by Philips Immersion Products. Scuba FX sits on the players head, and like a scuba mask, seals off the eyes from all incoming light. Inside the mask is a LCD screen that displays the game across players near entire field of view (Horizontal 40 Degrees, Vertical 30 Degrees). The display is high resolution full color active matrix LCD panel with 180,000 active dots. Scuba FX is designed to accept NTSC signals from popular video games, VCR, TV and PC which have NTSC video output (needs graphics card with TV output or VGA to Tv converter). The display claims to reach 400 TV lines horizonal resolution.
Sound is piped in through speakers beside each ear. Games that utilize true stereo are made more effective due to this stereo environment. Philips plans to market the device at around $300 and the places where the device can be bought are listed in Scuba FX web page.
The Virtual Reality Homebrewer's Handbook by Robin Hollands has a nice article how to build a Head Mount Display yourself. The project article "Project: Biocular Head Mounted Display" is available at the website of the book.
3D television and video have been a hot topic among science fiction people. Many methods have been tried to accomplish 3D television, but no solution have yet found their way to mass markets for every home. There are many solutions nowadays available as you can see from the product list.
StereoPlate from 3DTV corporation is a electrically controlled polarizing plate that fits on any three tube video projector so viewers see 3D with inexpensive polarizing paper glasses. The system requires a polarization preserving screen.
3D Theatre from 3DTV corporation is a system for playing back 3D videos. The system includes Wired LCD shutter glasses, 3D glass to video interface, 3D VCR casette (NTSC, PAL or SECAM), cables and power supply. The system enable you to watch stereo movies on your own television, and more 3D movies are available from 3DTV corporation.
Crystaleyes video system from Stereographics corporation is a complete system for generating and playing back flicker free 3D videos. The system uses special recording and playback unit, but the storage medium is standard video recorder.
The View / Record Unit takes industry-standard video signals from two unmodified cameras, stores them in buffers, and simultaneously generates two output signals: an RGB stereo signal, ready for real-time output on a stereo-ready monitor or large-screen stereo projector; and a compressed video signal, ready for standard transmission or for recording onto laserdisc or a single standard video tape, such as S-VHS or Hi-8
Once the compressed signal has been recorded or transmitted, the Playback Unit converts it into a flicker-free RGB stereo signal, which can be viewed through CrystalEyes stereo eyewear on a stereo-ready monitor or the CrystalEyes Projection System. An optional dual signal output board provides independent left and right video output signals, allowing playback of stereo images through two standard video projectors, or head-mounted display.
The Institute for the Exploration of Virtual Realities in University of Kansas has made experiments in creating 3D video tapes. They have showed that is possible to generate your own 3D videos with quite simple hardware. You can use two genlocked video cameras and a field sequential stereo video converter to make your own 3D videos. Those videos can be stored to ordinary VCR and they can be watched using 3D LC shutter galsses which have video interface.
If you consider building the circuit it would be a good idea to read also the notes.
Analogygraph pictures are coded so that left eye image uses blue colors and right eye uses red color. The image itself can be in any popular image format (typically JPEG or GIF).
Typical stereo pair images are photographed or computer generated as two images which ore jusr in parellel in one image file (left eye image on left and right eye image on right). Teh images are directly viewable using parallel "free-viewing". This storing method dos not limit the used picture format in any way.
Another modification is stereo pair images designed for cross-eyed viewing. THe only difference in cross-eyed viewing images is that the left and right image places are swapped (left eye picture is on right side and right eye image is on lefts side). The format is otherwise similar to the normal stereo pair above.
Interlaced stereo images are designed to be viewed with 3D glasses which use interlaced 3D method. Viewing those interlaced pictures are easy, you just load those to screen in interlaced screen mode and start viewing then with 3D LCD shutter glasses. The interlaced images are composed so that every other scan-line is for diffent eye (for example first scan line is for left eye and second is for right eye, third is for left etc.). I have not seen any real standard should the first line be for left or right eye. Because every other scan line belong to different images you must be very careful not to do anything to the picture which will distort it too much (do not scale the picture or compress too much using JPEG compression). Interlaced stereo images in web are typically stored in GIF format, but they can also use JPEG format if this is done carefully (JPEG causes artifacts to picture and using too much compression can distort 3D effect).
JSP images are just plain normal JPEG fiels which contain stereo picture pair. JSP format is used by X-eye 3D glasses.
When you have the hardware, you need also some software to use with your nice 3D hardware. Writing 3D programs is quite time consuming, but fortunately there are many 3D programs freely available.
