Posted by Jeff Rife on 04/16/06 00:47

Gene E. Bloch (spamfree@nobody.invalid) wrote in alt.tv.tech.hdtv:
> > A CRT progressively-scanned at 60Hz with a phosphor that took 1/30th of a
> > second to decay would result in the same image as on an LCD. Do the
> > math for a moment to figure out why.
>
> Obviously I have done that math. That's why I posted what I did, in a
> second attempt to show you that each pixel on an LCD changes when its
> next value comes in, not shortly after being illuminated.

Yes, but at some point it changes. And that change takes a long time.
So long that there are almost two complete progressive scans of the
display before the first pixel "changes" to what it should have been
based on the *first* frame.

Think about that for a moment.

It means that before the first pixel is finished being set to the value
it should be based on the first frame, the second frame is already there
and changing the value again...in a sense, refreshing it.

This is *exactly* the same behavior you would see if the phosphor on a
CRT had a very long persistance. Sure, the LCD doesn't need refreshing,
but the effect is identical to a long-persistance CRT.

That means that you aren't actually verifying that the LCD remains "on"
all the time...you're just verifying that the persistance of an LCD pixel
is very, very long compared to that of a CRT.

And, if you had a CRT with the same 15-30ms persistance, you would see
*exactly* the same effects as on an LCD, which would include smearing.
On the other hand, even though an LCD is continuously "on", if the pixel
update time ever drops low enough, you would see some of the same effects
that you see on a CRT (including strobing and flicker at low frame
rates). They would not be as pronounced unless you had frames that
changed quite a bit, but they would still be there.

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