(1) | Page Flipping Page flipping is the highest quality method of producing time-sequential stereoscopic display. It is primarily used with non-interlaced (or progressive scan) displays (which display all the lines of the frame in one go, not half/half as in interlacing). Page flipping works by flipping between two pages of video memory (of the video card) every time a new image (frame) is to be displayed. One 'page' will hold the left perspective image and the other 'page' will hold the right perspective image. The flipping can be performed by your video card's BIOS (the better solution) or a device driver could be installed which will watch the progress of the video card generating the video signal. The result is a sequence of left perspective image and right perspective image frames. Problems:
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(2) |
Row-Interleaved Image + Interlaced Display Interlacing is probably the easiest method and is what is used in (PAL and NTSC) 3D video systems (i.e. field-sequential DVDs and VHS video tapes available from various suppliers). Interlacing means that first the odd lines of the image are drawn on the screen (the odd field) and then the even lines of the image are drawn on the screen (the even field). If the image is constructed of odd lines from the right perspective image and the even lines from the left perspective image, the interlaced nature of the display will mean that first a right image will be displayed and then the left image will be displayed (left and right images will be alternately displayed - time or field-sequentially). When viewed through LC shutter glasses synchronised with the field rate, each eye will see a different image. Problems:
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(3) | Sync Doubling Sync Doubling (or sub-fields) works by dividing your existing screen into halves (the top half and the bottom half). Your software puts the left image of a stereo-pair into the top half of the display and the right image of a stereo-pair into the bottom half of the display. After your video card generates its normal video signal, an external black box adds an extra vertical sync pulse to the video signal (at the vertical mid-point of the screen). The monitor will now see the video signal differently from before and will display the first half of the video signal (which used to be the top half of your screen) as a full screen image and then the second half of the video signal (which used to be the bottom half of your screen) as a full screen image. So again, there will be left and right images being displayed alternately (time sequentially). LC shutter glasses can be synchronised with these images to allow you to see a 3D image. Problems:
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(4) | Line Blanking A row-interleaved 3D image is displayed by the video card in progressive-scan video mode (i.e. not interlated-scan). A dongle plugs into the VGA port of the computer and the monitor plugs into the back of the dongle. The dongle actively blacks out alternate lines of the video signal. In the first frame it blacks out the odd numbered lines, and in the next frame it blacks out the even numbered lines, and this sequence then repeats. The video signal will then be an alternating sequence of left and right "frames". The dongle usually also drives a pair of LCS glasses. The line-blanking method could be seen as a method of converting a progressive-scan video signal to interlace-scan, however the resultant video signal is still progressive-scan, it's just that the relevant lines have been blacked out. Problems:
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There are some animated GIFs at the Catalyst web site which
beautifully illustrate the operation of the first three of these systems.
If you are having problems with my descriptions, check out the images.
interlacing: http://www.frostbit.com/Catalyst/interlace.html
page flipping: http://www.frostbit.com/Catalyst/pageflip.html
sync double: http://www.frostbit.com/Catalyst/syncdouble.html#syncdouble
NB: Some of their descriptions are a bit wrong in places and exhibit a
bias towards the sync double technique which I guess is understandable
because their system uses the sync-double technique.
The VR Surfer (VREX) also supports line-blanking.
A comprehensive list of 3D LCS glasses is available here:
www.stereo3d.com/shutter.htm
The following table illustrates what happens with the various 3D display methods with regards to image refresh rates: (borrowed in part from Catalyst's web site)
3D Method | Vertical Output Frequency of video card# | Fields per Second | Effective Refresh Rate for a Stereo Field Pair | Vertical Resolution |
Page Flipping | 60Hz | 60Hz | 30Hz | full |
Interlaced | 60Hz | 60Hz | 30Hz | half |
Sync-Doubled | 60Hz | 120Hz | 60Hz | half |
Line-Blanked | 60Hz | 60Hz | 30Hz | half |
Here's a modified version of that table where a 120Hz update rate is required:
3D Method | Vertical Output Frequency of video card# | Fields per Second | Effective Refresh Rate for a Stereo Field Pair | Vertical Resolution |
Page Flipping | 120Hz | 120Hz | 60Hz | full |
Interlaced | 120Hz | 120Hz | 60Hz | half |
Sync-Doubled | 60Hz | 120Hz | 60Hz | half |
Line-Blanked | 120Hz | 120Hz | 60Hz | half |
See this white paper:
nVIDIA "3D Stereo Technical Brief"
www.nvidia.com/object/LO_20010605_6971.html (271 kB pdf)
The following paper goes into substantially more detail on this topic and lists other types of displays which are compatible with LCS 3D glasses:
Woods, A.J. (2005) "Compatibility of Display Products with Stereoscopic Display Methods", in Proceedings of the International Display Manufacturing Conference 2005 (IDMC'05), ISBN 957-28522-2-1, Taipei, Taiwan, 22-24 February 2005. (39kB pdf)