Archived from groups: alt.video.digital-tv (
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"Doug McDonald" <mcdonald@scs.uiuc.edu> wrote in message
news:c7095s$jq1$1@news.ks.uiuc.edu...
> Stephen Neal wrote:
>
> >>
> >>50i, at that display rate, is simply, absolutely, utterly,
> >>completely, UNWATCHABLE.
> >
> >
> > Interesting comments. I completely believe that that is your
experience -
> > just as I believe that some people prefer 100Hz TVs over 50Hz.
>
> Of course they are going to prefer 100HZ frame doubled! It doesn't
> have the unwatchable flicker.
Except that 100Hz sets usually have horrendous processing artefacts. I have
yet to meet a broadcast professional (camera operator, picture editor,
vision engineer etc.) who has a 100Hz set at home - and have never seen any
in use for picture monitoring in TV galleries.
They do certainly reduce large area flicker, and reduce interline interlace
twitter, however the downside is the smearing, juddering and other nastiness
they introduce.
> Personally I
> > have yet to see a 100Hz TV I could watch for any length of time.
> > Increasingly I believe that environment and familiarity influence what
we
> > see as artefacts and defects in our system.
> >
>
> 50 Hz is simply to slow: it has a terrible, completely unwatchabble,
> flicker.
>
I just love your blanket statements - I watch a lot of 50Hz TV. I do not
find it unwatchable - you seem to. By definition therefore it is not
unwatchable - you just find it to be so.
I find 100Hz TV sets unwatchable as a lot of others do - but then some
others don't. We obviously are all different and see different artefacts -
or have different perceptions.
I just sat down and watched a film sourced programme that was displayed 3:2
pulldown 60i. I found the programme watchable because of the content - but
the 3:2 pulldown flicker was annoying and distracting - yet I suspect you
may not even notice the 3:2 artefacts because familiarity has led you to
"notch them out", in the same way I probably do some aspects of 50Hz
flicker. If I look at a wall of TVs from the corners of my eye I do see the
large area flicker - but in normal viewing conditions I don't. Given that I
spend a lot of time with banks of 576/50i screens filling my field of view
it may just be that my brain is de-sensitized to this?
(I know that in the days of 405 line 50Hz UK broadcasting a lot of engineers
developed a notch filter in their hearing at 10.125kHz or whatever the
linescan was - but the minute a monitor went off-lock and started whining at
a different, but similar, frequency, they all heard it)
> > However what is odd - as I find 60Hz refresh PC displays unwatchable
(and
> > get a headache within minutes if using them).
>
> Yes, and 50 Hz is FAR worse.
>
Except that it isn't for my TV - though I'm absolutley sure it would be for
my PC monitor.
Before PCs took over the world it was common for European home computers to
use RGB monitors at 288/50p(?) or 576/50i (15.625kHz line rate, 50Hz refresh
rate) - I didn't notice the 50Hz flicker anywhere near as much as I do with
my VGA PC monitor (probably XVGA) at 60Hz. I suspect phosphor persistence
issues as well as brightness (Older UK home computers often defaulted to
white text against black, so there would be less large area flicker)
I simply don't see it as a problem with TV sets and video images - yet I
find 60Hz PC CRTs a real problem. Can't explain why (apart from differing
field of views, different persistence phosphors and different contrast
levels - PCs often have large areas of white, whereas most TV content is
more widely varying in luminance - so the flicker is less pronounced?)
>
> > I suspect it is a
> > brightness/contrast and field of view issue - PC CRT monitors often
display
> > bright white displays, and I suspect their phosphors decay quicker (to
cope
> > with higher refresh rates?).
>
> No, actually, they are all much faster than frame rate, of the order
> of line rate.
Are you sure about that in the case of TVs? I have certainly seen Sony TVs
in the UK where there is a degree of lag on a white spot moving around a
dark image (and no this is not a tubed camera issue - the images were
electronically sourced) - where you see a decaying tail behind the spot.
Not of the order of old green/amber screen VDU phosphors certainly, but
certainly nearer field than line rate.
> >
> > I have no problems with 60i or 50i viewing - and would not suggest for a
> > moment that the US move to 50i, just as I see no reason for the UK to
move
> > to a 60i HDTV system. There are perfectly valid reasons for both our
> > refresh rates
>
> There is NO valid reason for 50 HZ ... it is simply too slow.
It is only too slow - in your opinion - as a display refresh rate, not as a
capture/transmission refresh rate - as 24fps is deemed "fast enough" for a
capture/transmission system. Increasingly, modern display technologies - as
has been mentioned many times - divorce the display refresh rate from the
source material refresh rate. 50Hz as a transmission rate is fine.
> The
> poor folks saddled with 50 Hz line frequence should have used some
> system to allow a faster refresh rate, at least after the UK dumped
> 405 lines ....
Except that we introduced 625/50 (aka 576/50i) with our move to UHF in 1964
(40 years ago this year) with the launch of BBC Two. 625/50i was adopted in
the UK as it was the European standard that was emerging for mainland Europe
(as well as other parts of the Commonwealth - still significant in the
0s) - and frame rate standards conversion in those days was amazingly crude
(point a camera at a high-persistence TV, or transfer to film if live
conversion wasn't an issue) compared to line-standards conversion. Even
France ditched their 819/50 standard (10MHz channels?) for 625/50.
Sure we didn't finally ditch VHF 405/50 until the 1980s, but even if we had
we'd only have had a few Band I and Band III VHF channels to broadcast a
newer (wider than 405 bandwith) system on - and even in the mid 80s digital
video processing was not around at the consumer price point.
> there is plenty of space in your 8 MHz, and plenty
> of things like three phase power for lighting.
Quite difficult to cope with lighting flicker if you are shooting in a
location where you don't have control of the lighting though. Even now we
get 10Hz lighting flicker on some stuff shot in the US on 576/50i cameras -
normally discharge lighting causes this. It can be got around a bit with
clear-scan filtering (where you fiddle with a cameras shutter) - but if you
want to use the clearscan shuttering for another purpose (say removing PC
screen flicker - increasingly less of a problem as LCD screens replace CRTs
thankfully) you are stuffed.
There are still strong reasons for shooting video (especially higher frame
rate stuff such as 150fps SuperSloMo stuff) at the same rate as your mains
frequency - though SuperSloMo can get stuffed by discharge lighting in some
cases even if you are running at a frame rate that is a multiple of mains
frequency.
> > With 24p and 25p perfectly valid as HDTV systems - and modern display
> > devices no longer tied to broadcast refresh rates, or less
"refresh-related"
> > (i.e. many non-CRT displays no longer have a similar pulsing refresh
> > dynamic, or a raster scan and decay system in the way that a CRT system
has)
> > there is less reason for the transmission system to run at the display
> > refresh rate? On the other hand I think that for non-drama production,
50
> > or 60 Hz motion rendition is important, so any system should not be
limited
> > to 24/25/30 fps motion rendition - instead 50 or 60 Hz interlace, or
ideally
> > (as non-CRT devices cope better with them) progressive systems should be
> > used?
> That's true ... I would not in the least object to 50Hz
> progressive on an "always on" display even for sports. It would
> be fine. As a TRANSMISSION format, now that transmission and
> display are becoming uncoupled, it is OK.
Yep - that is what I am saying. We don't need to move to a new transmission
refresh rate - we could move to 576/50p as an interim (as Australia has),
720/50p or 1080/50i. The displays likely to be marketed in Europe for these
standards are likely to be non-CRT based. Unlike the US - where large 4:3
sets and now large 16:9 sets have been popular, in Europe the average screen
size has always been smaller - often because of depth and total size reasons
(our rooms are just smaller I guess!) - so direct view Plasmas, LCDs and
projectors (LCD and DLP more than CRT) are increasingly the main source of
large-screen pictures.
I'd love to be able to buy a 32" direct view HDTV CRT over here - I prefer
watching interlaced material as interlaced without it being mangled to
progressive - but there are very few direct view CRTs with the correct
inputs. (We have at least one 1080/50i HDTV channel broadcasting now in
Europe)
Steve
).
/www.dvddemystified.com
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