Re: [photo-3d] Shutter glasses - Hz vs. MHz

[Chris Bruns <cmbruns@xxxxxxxxxxx>]

Hi Dan and Dan-

  There seems to be some units confusion here.  Please forgive the pedantic
discussion that follows.

  I believe that the units that the units under discussion are vertical refresh
rates, and should be in units of Hz (Hertz = per second).  Thus a vertical
refresh rate of 120 Hz means that the video screen is completely redrawn 120
times per second.  The human eye can perceive "flicker" when high-contrast
regions are updated at less than about 60Hz in the center of the field of
vision, and below about 75 Hz in the peripheral vision.

  The maximum vertical refresh rate of BOTH the monitor and video card should be
considered when contemplating a LCS glasses setup.  120 Hz is always beautiful
and flicker-free in my experience.  Below 90 Hz is unbearable.  Because the
monitor sends separate images to each eye, the vertical refresh rate must be
divided by two to get the per-eye refresh rate.  120 Hz on the monitor equals 60
Hz per eye with LCS glasses.

  Much of the units confusion can be attributed to the fact that there is also a
"bandwidth" specification for both monitors and video cards which is in fact in
units of MHz (mega-Hertz = millions of Hertz).  Unfortunately for the confusion
problem, this number is often roughly of the same order as the vertical refresh
rate at 1024x768 resolution (times a million, of course).  The bandwidth,
however, is not directly relevant to the usability of LCS glasses.  The maximum
vertical refresh rate (expressed in Hz) is.  However, for a given vertical
refresh rate, a higher bandwidth will permit a higher maximum resolution.

  Most but not all modern graphics cards and large monitors support 120 Hz
vertical refresh rates.  A bit of careful shopping is all that is required to
get suitable hardware.

  The "mhz" units in the previous postings would seem to refer to milli-hertz
(thousandths of Hertz) which is very slow indeed.  This is quite incorrect.

  Sorry about the pedantic diatribe.

-Chris Bruns


Dan Shelley wrote:

> >I saw the annonucement yesterday for the shutter glasses and was looking
> >at the requirements. They indicate that at least an 85mhz refresh rate
> >should be used and that 120mhz would be much better. Anyone know of a video
> >card that has that sort of refresh at 32 bit color and high res?
>
> Not being an expert in this area by any means, but having used LCS glasses
> for years, I can say that these numbers are in reference to the refresh rate
> of your monitor.
>
> Most "cheapo" monitors run at a refresh rate of 60 mhz, some at 72mhz and
> that is one reason why extended computer use in front of those monitors can
> cause some eye strain. The higher the refresh rate, the less flicker there
> is - so - the more comfort there is. The image appears to be more "solid",
> and the difference is physically noticable by some users.
>
> Looking at a screen with LCS glasses at 85 mhz will still present a flicker
> - OK for some, but far too annoying for me. 120mhz is the best option for
> JPS images as far as I am concerned - at 640x480 for that matter... WHY
> 640x480 YOU ASK??? =) Simply because many people who DO have monitors that
> can display 120mhz images, can only do so at that lower resolution. Is that
> a problems for end image quality? No. The "viewer" program resets the
> resolution mode from 800x600 or 1024x768 or whatever to 640x480, shows you
> the image full screen, and when you are done, takes you back where you
> started. You still get an amazing, full screen image.
>
> Enough for now... Any questions or comments?
>
> Dan Shelley
> dshelley@xxxxxxxxxxxx
>