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Stripes on TV



 
 
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  #1  
Old December 7th 16, 07:30 PM posted to uk.tech.digital-tv
Scott[_2_]
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Posts: 1,171
Default Stripes on TV

We were talking about this at the office this morning. At one time
certain patterns involving stripes were banned on TV because they
caused blurring of the picture. Was this an analogue artifact or does
it affect digital also? Does it affect HD as well as SD?
  #2  
Old December 7th 16, 07:46 PM posted to uk.tech.digital-tv
NY
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Posts: 959
Default Stripes on TV

"Scott" wrote in message
...
We were talking about this at the office this morning. At one time
certain patterns involving stripes were banned on TV because they
caused blurring of the picture. Was this an analogue artifact or does
it affect digital also? Does it affect HD as well as SD?


It certainly affected analogue, both PAL and NTSC, but not (AFAIK) France's
SECAM which had different artefacts. The colour information overlapped the
monochrome information in the spectrum, in such a way that in a static image
the two did not interfere, but if there was the slightest movement, the two
interfered and fine detail was decoded as spurious colour. It was called
"cross colour".

As far as I know, there isn't any such interference with digital.

  #3  
Old December 7th 16, 08:58 PM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 500
Default Stripes on TV

On 07/12/16 20:46, NY wrote:
The colour information overlapped the monochrome information in the
spectrum, in such a way that in a static image the two did not
interfere, but if there was the slightest movement, the two interfered
and fine detail was decoded as spurious colour. It was called "cross
colour".



You didn't need movement for cross-colour, although movement would make
it more obvious, as it was a sort of moire fringe that moved much faster
than the object causing it.

It peaked at the colour sub-carrier frequency, which meant that, in
modern, pixel terms, it was when it was close to having alternate pixels
black and white on a horizontal line.

Although I can't say I have noticed it, in theory, you could get a
similar effect with amateur and even semi-professional, digital cameras,
as they don't have a sensor for each colour, but rather a single sensor
with a filter with red green and blue spots (or is that cyan, magenta
and yellow) aligned with the pixels (a Bayer pattern).
  #4  
Old December 8th 16, 06:44 AM posted to uk.tech.digital-tv
Brian Gaff
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Posts: 6,370
Default Stripes on TV

Several reasons fotor this. In the old analogue system you could get an
effect on fine detail around the frequency of the 4.43 oscillator for the
colour decoder. It was supposed to be filtered but you cold still see it on
some test signals.
Then there were effects of a kind of strobing interference pattern and the
interference on old crt screens. Lots of other problems besides of course.
On digital, from what I'm told the main issue is quantization and
compression artefacts making things either look wrong or go blocky at times.
Obviously the more data you throw away the worse its going to look
This is also my main gripe with MP3 audio, to my mind a bit like cassettes
vs vinyl , but sadly nobody much seems to care any more.

Brian

--
----- -
This newsgroup posting comes to you directly from...
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"Scott" wrote in message
...
We were talking about this at the office this morning. At one time
certain patterns involving stripes were banned on TV because they
caused blurring of the picture. Was this an analogue artifact or does
it affect digital also? Does it affect HD as well as SD?



  #5  
Old December 8th 16, 06:56 AM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 6,370
Default Stripes on TV

When I first read this sub line I thought you meant that you had camouflaged
your set.
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Scott" wrote in message
...
We were talking about this at the office this morning. At one time
certain patterns involving stripes were banned on TV because they
caused blurring of the picture. Was this an analogue artifact or does
it affect digital also? Does it affect HD as well as SD?



  #6  
Old December 8th 16, 08:34 AM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 959
Default Stripes on TV

"David Woolley" wrote in message
news
On 07/12/16 20:46, NY wrote:
The colour information overlapped the monochrome information in the
spectrum, in such a way that in a static image the two did not
interfere, but if there was the slightest movement, the two interfered
and fine detail was decoded as spurious colour. It was called "cross
colour".



You didn't need movement for cross-colour, although movement would make it
more obvious, as it was a sort of moire fringe that moved much faster than
the object causing it.

It peaked at the colour sub-carrier frequency, which meant that, in
modern, pixel terms, it was when it was close to having alternate pixels
black and white on a horizontal line.


I thought that the whole point was that the colour sub-carrier frequency was
chosen (*) so the frequency components at integer multiples of the line
frequency for the colour information sat half-way between those of the
monochrome information, so as to minimise interference. Any movement shifts
those frequencies and the upper-sideband will move in the opposite direction
to the mono so the two will overlap.


(*) odd number of line frequency multiples

  #7  
Old December 8th 16, 11:18 AM posted to uk.tech.digital-tv
NY
external usenet poster
 
Posts: 959
Default Stripes on TV

"Brian Gaff" wrote in message
news
Several reasons fotor this. In the old analogue system you could get an
effect on fine detail around the frequency of the 4.43 oscillator for the
colour decoder. It was supposed to be filtered but you cold still see it
on some test signals.


I think the 4.43 signal is mainly the converse problem: the carrier
manifesting itself as fine dot-patterning on the luminance. Cross colour is
at a variety of frequencies - whenever the colour frequencies (at multiples
of the line frequency) overlap with the corresponding ones for luminance.
The diagrams I've seen show a series of frequencies (like the teeth of a
comb) for chroma which *should* interleave with the corresponding ones for
luma, but if they don't, the "teeth" of one overlap with those of the other
instead of neatly enmeshing.

Then there were effects of a kind of strobing interference pattern and
the interference on old crt screens. Lots of other problems besides of
course.
On digital, from what I'm told the main issue is quantization and
compression artefacts making things either look wrong or go blocky at
times.
Obviously the more data you throw away the worse its going to look


That is the crucial thing - it's not the quantisation and compression that
is the problem per se, it's the *amount* of compression and therefore the
amount of info that is thrown away.

This is also my main gripe with MP3 audio, to my mind a bit like cassettes
vs vinyl , but sadly nobody much seems to care any more.


I agree that there are some horrible MP3 files out there. I find that MP3
compression at 160 kbps or greater (for stereo) is indistinguishable from
the original WAV or CD. Anything less than 96 (or 60 for mono) and it's not
a pleasant experience :-(

Vinyl suffers from its own problems which to my ears are more noticeable:
background "sandpaper noise" and crackles and pops due to dust and
scratches. I have had some supposedly good pressings of classical music
(where there are more quiet periods that make background noise noticeable)
where there is appalling noise. It's not tape hiss, it's much more
noticeable frying eggs and crackling fire noise which I presume is a rough
surface on the grooves.

It's the difference between distortion and artefacts on digital compression,
and noise (continuous and impulse) on vinyl.

  #8  
Old December 8th 16, 03:22 PM posted to uk.tech.digital-tv
tim...[_2_]
external usenet poster
 
Posts: 320
Default Stripes on TV


"Scott" wrote in message
...
We were talking about this at the office this morning. At one time
certain patterns involving stripes were banned on TV because they
caused blurring of the picture. Was this an analogue artifact or does
it affect digital also? Does it affect HD as well as SD?


I thought it was a film with Bill Murray?

tim



  #9  
Old December 9th 16, 09:39 AM posted to uk.tech.digital-tv
Brian Gaff
external usenet poster
 
Posts: 6,370
Default Stripes on TV

I need to be listening at 192 kbit mp 3 to be totally easy minded. The main
issue seems to occur when some nutter has compressed it expanded it then
recompressed it again. You can often hear this as a gritty sound or almost a
modulation noise on loud passages and voices.
With regard to video, not seen current output but when i could see, grass
that looke lkike paint occasionally looking lkike a mass attack of wororms,
signage that wobbles about and some very peculiar colouring of peoplees
faces as if there were not enough hues of pink available are what I
remember.

As for the colour problems on analogue, comb filtering was used a lot
particularly in video machines which did clean it up but sadly tended to
make effects come and go making them more obvius. For example I never could
wath

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"NY" wrote in message
...
"Brian Gaff" wrote in message
news
Several reasons fotor this. In the old analogue system you could get an
effect on fine detail around the frequency of the 4.43 oscillator for the
colour decoder. It was supposed to be filtered but you cold still see it
on some test signals.


I think the 4.43 signal is mainly the converse problem: the carrier
manifesting itself as fine dot-patterning on the luminance. Cross colour
is at a variety of frequencies - whenever the colour frequencies (at
multiples of the line frequency) overlap with the corresponding ones for
luminance. The diagrams I've seen show a series of frequencies (like the
teeth of a comb) for chroma which *should* interleave with the
corresponding ones for luma, but if they don't, the "teeth" of one overlap
with those of the other instead of neatly enmeshing.

Then there were effects of a kind of strobing interference pattern and
the interference on old crt screens. Lots of other problems besides of
course.
On digital, from what I'm told the main issue is quantization and
compression artefacts making things either look wrong or go blocky at
times.
Obviously the more data you throw away the worse its going to look


That is the crucial thing - it's not the quantisation and compression that
is the problem per se, it's the *amount* of compression and therefore the
amount of info that is thrown away.

This is also my main gripe with MP3 audio, to my mind a bit like
cassettes vs vinyl , but sadly nobody much seems to care any more.


I agree that there are some horrible MP3 files out there. I find that MP3
compression at 160 kbps or greater (for stereo) is indistinguishable from
the original WAV or CD. Anything less than 96 (or 60 for mono) and it's
not a pleasant experience :-(

Vinyl suffers from its own problems which to my ears are more noticeable:
background "sandpaper noise" and crackles and pops due to dust and
scratches. I have had some supposedly good pressings of classical music
(where there are more quiet periods that make background noise noticeable)
where there is appalling noise. It's not tape hiss, it's much more
noticeable frying eggs and crackling fire noise which I presume is a rough
surface on the grooves.

It's the difference between distortion and artefacts on digital
compression, and noise (continuous and impulse) on vinyl.



 




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