On Mon, 19 Jan 2004 03:37:46 GMT, Mike Coslo
wrote:

It is a source of great amusement to listen to people dissing one or
the other - NTSC or PAL, or even SECAM.

They all suck very much. Trying to decide which one sucks the most is a
waste of time.

Most probably correct. And what disturbs me most is that nobody has
come up with something better available to the consumer "in general" I
mean, maybe I'm expecting too much from an industry that has not been
able to control "ghosting" effects in the end credits (white lettering
on black background) on a reasonably new TV set when fed with S-Video
from a digital source.

OTOH, SECAM is a bit more complex than NTSC or PAL. To the best of my
understanding, they actually send the chroma portion of the signal
*after* the luminance, so sets that are fit for SECAM gotta have a
delay line somewhere to brinc Chroma and Luminance back together,
IIRC?

And what about and adaption of "our" SSTV standards to "Fast Scan"
television? Would that work within reasonable parameters?


Volker

hnmm wrote:
Human eyes can detect the refresh rate flicker up to a certain
frequency. My peripheral vision can detect the 120 Hz flicker
of florescent lights as well as flicker in computer monitors.
Drives me crazy.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:

hnmm wrote:
Human eyes can detect the refresh rate flicker up to a certain
frequency. My peripheral vision can detect the 120 Hz flicker
of florescent lights as well as flicker in computer monitors.
Drives me crazy.

The scan rate of most computer monitors is closely related to multiples
of the scan rate of a NTSC television signal scan rate. This leads to a
signal that is often twice the rate of NTSC scan. But since the monitors
are not synchronized, the computer monitor will show lighter and darker
areas depending on it's scan rate. Computer monitors will vary in their
"look" on television, from a whole screen flicker to a darker colored
bar that works it's way down the screen. This is all due to the scan
rate frequencies.

- Mike KB3EIA -

On Sat, 03 Jan 2004 20:09:14 GMT, Mike Coslo
wrote:

Cecil Moore wrote:

hnmm wrote:
Human eyes can detect the refresh rate flicker up to a certain
frequency. My peripheral vision can detect the 120 Hz flicker
of florescent lights as well as flicker in computer monitors.
Drives me crazy.

The scan rate of most computer monitors is closely related to multiples
of the scan rate of a NTSC television signal scan rate. This leads to a
signal that is often twice the rate of NTSC scan. But since the monitors
are not synchronized, the computer monitor will show lighter and darker
areas depending on it's scan rate. Computer monitors will vary in their
"look" on television, from a whole screen flicker to a darker colored
bar that works it's way down the screen. This is all due to the scan
rate frequencies.

Yes, the exception would be if the monitors and the TV camera are
synchronized, as might be done with the news set.

Happy trails,
Gary (net.yogi.bear)
------------------------------------------------
at the 51st percentile of ursine intelligence

Gary D. Schwartz, Needham, MA, USA
Please reply to: garyDOTschwartzATpoboxDOTcom

"Mike Coslo" wrote in message
t...
Cecil Moore wrote:

The scan rate of most computer monitors is closely related to multiples
of the scan rate of a NTSC television signal scan rate.

How do you work that out? NTSC is 60Hz (30Hz Interlaced)
So Most CRT monitors run at 70Hz, 75Hz, 85Hz and maybe 100Hz for a high end
monitor at 1024*768

Where is the link between the vertical refresh rates?

Have a google search for Vesa refresh rates for more info.

Robin.. ( I used to work for NEC building computer monitors before NEC
pulled out of manufacturing them in the UK)

Robin,

I *haven't* worked in this area, but I still knew this comment was misplaced
since I've seen all kinds of scan freqs over the years.

--
Steve N, K,9;d, c. i My email has no u's.

"Robin" wrote in message
...
"Mike Coslo" wrote in message
t...
Cecil Moore wrote:

The scan rate of most computer monitors is closely related to multiples
of the scan rate of a NTSC television signal scan rate.

How do you work that out? NTSC is 60Hz (30Hz Interlaced)
So Most CRT monitors run at 70Hz, 75Hz, 85Hz and maybe 100Hz for a high
end
monitor at 1024*768

Where is the link between the vertical refresh rates?

Have a google search for Vesa refresh rates for more info.

Robin.. ( I used to work for NEC building computer monitors before NEC
pulled out of manufacturing them in the UK)

On Sat, 03 Jan 2004 10:38:53 -0800, hnmm wrote:


I think the question was a bit different than the answers I've been
seeing.

IF I understand the question, he wants to know why when a monitor is
shown on TV it flickers, but not when actually looking at the monitor.

When video taping, TV sets AND computer monitors will flicker. It's
due to the differences in scan rates on the monitors compared to the
camera.

Even when they are running the same frequency there will still be the
appearance of either a rolling image, or a moving bar as the scan will
not be perfectly in sync between the camera and the monitor. If
they are the same frequency the dark line on the screen will not move.
It's rare to see one where the monitor and camera sync pulses are ...
well...in sync. When that happens the TV screen looks normal.

The image on a computer monitor and a TV screen consist of a bunch of
almost horizontal lines. With a TV set the image starts at the top
and is drawn every other line, one at a time. When the line reaches
the bottom it has completed one frame. It returns to the top and draws
in the lines that were skipped in the first frame. This noticeably
reduces the perceived flicker.

Computer screens may use the same method or they may draw the entire
image on one pass. Their much higher sweep rate may allow them to do
so without a noticeable flicker.

As to regular monitor flicker, I only notice it occasionally in my
peripheral vision, but not when viewed directly. Part of that is due
to the persistence of the phosphor, but with TV sets and monitors the
persistence is very short. OTOH viewing a TV screen under
fluorescent lighting can really accentuate the flicker.

You should see a moving image on a longer persistence phosphor. They
smear....


Roger Halstead (K8RI & ARRL life member)
(N833R, S# CD-2 Worlds oldest Debonair)
www.rogerhalstead.com

.