Re: IMAX

[P3D Oliver Dean <3d-image@xxxxxxxxxxxxxx>]

> John Roberts wrote:
> 
> >If my information is correct, the IMAX 3D frame rate for each
> >eye is a solid 48 frames per sec, which would be considerably better
> >than the 30 fps for each eye with my flickery Toshiba.
> 
> Your Toshiba glasses are showing 60 FIELDS per sec, compared with 48 or 96
> fields/sec at IMAX, where each field is truly a 'frame' of film. 
> 
> I, too, have been led to believe that each frame of film is double
> shuttered, yielding 96 alternations/sec, thus no noticable flicker.  There
> is also considerably less brightness on an IMAX screen, compared with a TV,
> further helping in flicker reduction.
> 
> 
> Ray Hannisian
>  

Hi, Ray!

The quotation you cited was mine, not John Roberts'. Sorry --I was a bit
careless with my terminology in this paragraph; I was trying to make a
point about the flicker rate and my terms are not correct.  Anyway, in
an earlier post that Noel Archambault of IMAX made (and which I didn't
see until after I had posted the above), he outlined in detail what the
IMAX scheme actually is, which
is a camera frame rate of 24 fps for each eye, with each frame being
projected twice, so that each eye gets 48 interruptions per second; I
don't know the correct "official" term for this second rate -- it isn't
fields per second (there are no fields in a cinema), and it isn't frames
per second either, because that is already in use for the 24 fps rate.  

Maybe we should coin a term, call it "images per second," in the sense
of "interruptions or number of flickerss per second," abbreviated to
"ips," so that we can compare flicker rates of cinema images with the
fields per second of the interlaced tv images or the frames per second
of computer "page flipping" or "sync doubling" systems (see Jon Gross'
excellent desciptions of these on his web site at: http://www.neotek.org
-- and click on the "3D Theory" button).  Terminology in this area is a
bit confusing and could be helped, I think, by such a new term (unless
there is one already I haven't heard about).

Just to show how this term could clarify things: Ray, your comment that
the Toshiba glasses show 60 fields per second, while correct, means that
each eye is seeing only 30 fields per second. well below the flicker
threshold for most of us.  If we state that the rate is 30 ips, we can
then compare it to the IMAX rate, which Noel reports is is 48 ips for
each eye. It becomes clear that the IMAX rate is above the flicker
threshold while the Toxhiba rate is below it, and this seems to be borne
out by observation.

Thanks for your comment!  
-- 
Oliver Dean -- 3d-image@xxxxxxxxxxxxxx
Dominguez Hills (near Los Angeles), Calloushernia, USA


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