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Posted by Gene E. Bloch on 04/14/06 18:55
For fun, as well as in a spirit of intellectual honesty, I did an
experiment today.
I took the lens elements out of a Wollensak Rapax leaf shutter (almost
as old as I am) so I could look through it at several LCD devices (an
LCD TV, a desktop monitor, and a laptop monitor) and one CRT device (a
TV). I triggered the shutter at 1/400 sec while looking towards each of
the respective screens in turn.
On the CRT TV I saw a fraction of a picture (a horizontal band taken
from the whole). The band was in a different location each time,
because I couldn't synchronize my trigger finger with the vertical
pulse :-)
In each LCD device I saw the entire picture every time. Every time.
Always. On the LCD TV, that was true for both standard def an high def.
This corroborates ~P~ (and me) 100%.
Gino
On 4/14/2006, ~P~ posted this:
> Jeff,
>
> DECAY TIME: Look it up, it's all related to phosphor based CRT displays,
> not digital technologies. When a phosphor is struck with a charged
> particle, it lights up, then fades out. LCD is not phosphor based, nor is
> DLP, or LCoS. Plasma is... I wonder how that would affect not 60hz rates?
>
> But, with LCD, there is no decay of the image over time because the pixels
> maintain a specific state for the entire time. If a LCD operated at 1/10hz.
> That's one frame every 10 seconds - it would display that frame and then
> wait for the next frame. It would not fade out, it would not go to black,
> it would not have a color change, or a light intesity change. It would be
> like me putting a book on a shelf - it would sit on that shelf until I took
> it down. It wouldn't change or go away, it would just sit there. 10
> seconds later, when I pulled that book down and put up a new book, that new
> book would happily sit there until I took it down - 10 seconds later.
>
> Telling it to go to a new state has to do with pixel response time, not
> refresh rate. This is a very serious issue with LCD but much less so with
> other digital display technologies. Lower refresh rates are actually
> handled a bit better by LCD displays since they aren't asked to make as many
> changes per second as they are with 60hz rates. It is common that people
> see 8ms response times rated for pixels, and don't realize that is a full
> on/full off measurement. The real challenge for the LCD pixels and where
> they are slow is going from slightly on, to almost all the way on or
> vice-versa. The intermediary changes are what take the most time. This is
> what results in most of the smearing. Artifacts should only come from poor
> processing.
>
> NOTE: Strobing indicates that pixels go to black prior to going to a new
> state - this is not the case. They go from 10% red to 20% red without first
> going to black. Accuracy does not create strobing. Pixel decay, from CRTs,
> that is to quick DOES cause strobing. But, I'm not talking CRT and to many
> people are stuck in a CRT world.
>
> I'm not disagreeing at all with issues related to motion smearing due to
> poor pixel response time. I am saying that at 24hz we still would likely
> have issues with LCD because pixel response is a bit slow - no matter what.
> But, this would possibly be less dramatic than it is with 60hz processing.
> With DLP and LCD projection where response time is much faster, we likely
> wouldn't see any smearing issues and the persistentcy of frames allows
> perfect 24hz reproduction - identical to original films.
>
> I know you want to argue this, and it is possible the slowest we will ever
> see is displays rated for 48hz output. But, we will see 24hz output from
> Blu-ray this year. This will be one of the first times people will see
> that, and then we can judge for ourselves. I am hoping we will see true
> 24hz displays, but it may not be practical since processing is always
> required all over the place with digital displays and chips have to be
> developed to handle that processing. Optoma HD81? Meh, may take longer for
> my point to be made... or fully rebuked.
>
> "Jeff Rife" <wevsr@nabs.net> wrote in message
> news:MPG.1ea8ed8d68c73bfe98a46d@news.nabs.net...
>
> And, once again, you show your complete lack of knowledge. It takes
> close to 1/30th of a second to change most LCD pixels. The fact that
> this is *more* time than the refresh rate of 1/60th of a second is why
> the artifacts are smearing instead of strobing. A CRT with such a slow
> decay rate for its phosphor will have the same effect.
>
> If LCDs ever get really, really fast, then you'll start to see some
> strobing artifacts, because despite your squawking to the contrary,
> the entire display is *not* refreshed at the same time. This is also
> why a 24Hz refresh would start to show strobing and flicker on an LCD:
> because the pixel decay time would finally be below the refresh rate.
--
Gene E. Bloch (Gino)
letters617blochg3251
(replace the numbers by "at" and "dotcom")
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