In message <
0c6cnXGGCZ4zUvv5nZ2dnZfqn_cAAAAA@brightview.co.uk> at Fri,
19 May 2023 02:23:58, NY <
me@privacy.net> writes
On 10/05/2023 13:49, J. P. Gilliver wrote:
I thought, now the light source is displays is not the actual raster
on a CRT but a steady backlight, strobing was a thing of the past -
or at least heavy strobing. But in
https://twitter.com/BBCWillVernon/status/1656226547634774016 (once I
click the play button), I see - I'm not sure if it is a monitor or >>viewfinder - with strobing so strong it reminds me of the relays of
NASA headquarters in the moonshot days.
Anybody?
That strobing is really obnoxious. Reminds me of 1970s news reports
from NTSC-land where no 30-to-25 Hz standards converter was available
at short notice so they pointed a 25 Hz camera (either video or 16 mm
film) at a TV showing original 30 Hz US footage. Usually preceded by
Reginald Bosanquet or Sandy Gall apologising for "the poor picture
quality in the next report".
(That's what I meant by "the relays of NASA headquarters" - room full of computer monitors, strobing horribly. I used to think - before I was old
enough to realise what was happening - "how do they stand using
those?".)
If I view my computer or laptop monitor (60 Hz or 120 Hz refresh) with
a PAL video camera (CCD rather than tube sensor) I can see a faint
rippling. Likewise for a UK 50 Hz TV viewed through a GoPro that can
only work at 30 Hz. But nothing like as bad as the camera that recorded
the Will Vernon footage.
Yes, because these days the light source in your monitor, or TV, is
_not_ the scanning electron beam, but a steady backlight - the slight
rippling is from the interaction with the update, see below. If you were
to point your GoPro or even video camera at a CRT display, strobing
would be back.
The "Will Vernon footage" was looking over the shoulder of someone
filming the wonderful Steve Rosenberg, playing things to do with the
2023 Eurovision, so would have been in the last few weeks, which is what prompted my post: the equipment would presumably all have been modern, including the monitor that was strobing (it didn't _look_ to be a CRT
one - too thin, though quite bulky so not _ultra_-modern); even if the
camera _taking_ the "footage" was an old tube one, I wouldn't have
expected such strobing. I presume it wasn't visible live, otherwise the
camera operator - the guy with headphones - would surely have complained (especially as it was more or less in his peripheral vision, sort of
above him). So I was puzzled why the strobing we see is so bad. Any
thoughts?
Do camera viewfinders/monitors tend to display each frame for almost
the full 1/25 or 1/30 second, or is there a significant period of unlit >screen between each frame? I've noticed that some car brake lights
I can't see any reason to turn the backlight off at all, and as it would involve extra circuitry (and involving power semiconductors), I doubt it
is done at all. I don't think, with modern displays, "between each
frame" has a meaning, for the whole image: I think the pixels are
refreshed at frame (or field) rate, but sequentially, so there isn't a
time when the whole image doesn't have some part changing, so there
isn't a between-frame gap. A lot of modern resolution/frame-rate
standards don't even have the blanking period - line or field.
(If you've got an old camera with a CRT viewfinder, that's different.)
flicker very badly when seen by a dashcam, and I wonder whether that is
more noticeable if the LEDs in the brake lights have a short mark:space
ratio (to achieve the required brightness) as well as the pulsing
frequency being mismatched with the camera frame rate.
Certainly the latter. I think in quite a lot of modern cars, they don't
_have_ separate tail, brake, and rear fog lights, but just change the mark:space ratio to provide the three functions.
(P. S.: my spell checker doesn't know "backlight", and suggests >>"jacklight" - a word I've never heard of! Anyone heard of it?)
The only words following "jack" that spring to mind are hammer, rabbit,
off and shit ;-) I've never heard of jacklight.
Thanks to the person who found an OED example! I'm often
puzzled/surprised by spellcheckers. I suppose it's _possible_ that at
some point I mistyped it with the J, and then when it queried it I hit
"add to dictionary". (Most spellcheckers make doing that by mistake only
too easy - and then it's tedious to correct - you have to find where the dictionary _is_ for a start, then figure out how to edit it.) The most surprising one I came across was when I used the word blazon - which
means to describe in heraldic terms (e. g. a coat of arms) - and the
'checker _did_ know the word.
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf
I don't like activity holidays. I like /inactivity/ holidays.
- Miriam Margolyes, RT 2017/4/15-21
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