Posted by ~P~ on 04/15/06 16:16

Pixel by pixel, top to bottom, is likely in the 1/5000th of a second range.
Very, VERY fast. The data is processed digitally, not analog. So, even if
a digital display is fed an analog sequence, it will put that sequence into
a frame buffer, where it analyses that frame and typically the two or three
before/after it to perform deinterlacing. Then, it passes the entire frame
on (digitally) to the display for a frame update. The entire process
requires 2 or 3 frames to have been fully fed to the digital display, so it
may run 2-3 frames behind 'real time'. But, when it is done processing a
frame, it passes on the entire frame buffer so that it is clear and ready
for the next frame - and it is measured in Mhz, not hz.

The statement that requires row-by-row updating is not correct and has no
facts to back it up. Digital displays (all) are capable of updating an
entire row at a time, in any order that makes sense and will tell the entire
SCREEN to update within a fraction of the time that CRT requires for the
whole screen. The pixels, due to response time, may then take 1/20th of a
second to actually get to that new state - or they may take 1/200th of a
second - or faster depending on the technology involved. LCD flat panels
are the slowest. Plasma, DLP, and LCD rear projection are much faster.

LCD's do not capture images, those are CCDs (charged coupled devices) and
they do exactly what you say and exist in the digital domain. Further, they
act like a CCD on your digital camera. Not only is the entire frame
captured at once, it typically is tied to a shutter speed that captures
actual motion as a 'blurring' effect. Like a film camera which captures the
ENTIRE frame at once. A film camera shoots 24 frames per second, but, it
doesn't have a shutter speed of 1/1000th of a second - or 1/24th of a
second. It shoots somewhere between. Likely about 1/20th of a second or
so. So, you capture the blurring of motion which keeps video from looking
jaggy - like it is stepping from frame to frame. That motion blurring is
VITAL to make motion look smooth on screen. This same motion is captured in
a CCD and it most definitely does not do it using scan lines. It is
hundreds - if not thousands - of times faster in caputring an image than CRT
could hope to display it.

In all honesty, I am unfamilar with what was used prior to CCDs for
capturing video. I know that a LOT of television shows were shot using film
because it was superior to video in a lot of ways. But, what was used
before CCDs? That's likely 25 other websites and newgroups. :o)



"Jan B" <nospam@nospam.se> wrote in message
news:4440e4d2.109134196@news.individual.net...

-This pussles me a little.
-My understanding from above is that it takes some time for an LCD
-panel to update the complete picture, row by row.
-But how long time does it take from top to bottom?

-The original video (TV) method (don't know if still used in studio
-cameras) used tubes that were scanned in the same way as a 50/60Hz CRT
-monitor. The motion portrayal would be correct this way as the
-scanning is the same at "both ends".

-Now consider an LCD sensor of the type that integrates and stores one
-frame (or half frame) nearly instantaneous.

-When such a camera pans horisontally over a vertical object like a
-pole and the video is displayed on a CRT that takes nearly a field
-period to scan from top to bottom I would expect to perceive a tilted
-object "moving" across the screen. This is since the scanning at the
-bottom would lag the top when displaying but not at the recording.

-Have anybody noticed such effects?

-The opposite would be visible if the video is shot with the scanning
-method and was displayed with instantaneously (or to fast) refresh one
-complete frame/field at a time.

-The arguments for introducing strobing and row-by-row illumination for
-LCD panels (refer to Philips "Clear LCD" development) is that our
-brain gets disturbed by the "sample-and-hold" effect as we try to
-follow what should be a smooth motion.
-(The row-by-row syncronised ON/OFF illumination would work around a
-slow pixel response time.)

-The arguments says that the strobing/deacy from a CRT is better from
-this aspect but I have a problem understanding how that can help when
-there is a lag in the strobing between top and bottom parts of the
-picture and that lagging is different from what is shot in the film
-frame .

-Hope somebody can explain.
-/Jan

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