Posted by Gene E. Bloch on 04/16/06 01:25

On 4/15/2006, Jeff Rife posted this:
> 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.

Document that, for a change.

> 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 the difference is? I think your semantics are a bit messed up here.

> 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.

You seem to have finally come around to (almost) understanding what I
am saying, even though you are phrasing it as proving that I am wrong.

Enough of this.

Gino

--
Gene E. Bloch (Gino)
letters617blochg3251
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