"images per second" (for LC shutter systems)

[P3D John W Roberts <roberts@xxxxxxxxxxxxxxxxx>]

There were several posts Monday on a useful terminology to describe how
many times per second an image is flashed to each eye (bearing in mind
that it's not always a new image - IMAX uses each one twice). Images
per second was suggested, with the comment that there may already be
a more descriptive term.

On first reading (which is probably a good indication), I found the term
confusing - I thought it applied to the number of *new* images per second
(24 frames per second for each eye, in the case of IMAX).

In the computer monitor / flat panel display industry, the most common
term I've come across to describe how frequently the screen is "redrawn"
is "refresh rate". Refresh rate just indicates how often the picture is
put up on the display, without implying that it's a new picture each time.
On CRTs and some kinds of FPDs, the refresh rate has to be kept fairly high
to prevent visible flicker. I suspect the term came from the refresh cycles
needed by DRAM memory devices.

Perhaps it would be useful to also apply this term to - er - time-multiplexed
stereo display systems, such as those which use LC shutters. But since
we're talking about separating the left and right signal paths, it would
be good to add "per eye".

So we could say that the IMAX LC shutter system has a refresh rate of
48 Hz per eye.

Now what term to state that the film provices 24 new images per second for
each eye? "New image rate"? "Image replacement rate"?

John R


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