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BBC Codecs and black hair



 
 
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  #1  
Old February 6th 15, 09:53 PM posted to uk.tech.digital-tv
Vir Campestris
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Posts: 439
Default BBC Codecs and black hair

Is it just me, or do the Beeb have a problem with dark hair?

I've noticed it before on TOTP1979, where if someone with an Afro jumps
up and down the hair lags behind. But it's old stuff, coming off old
film, and probably cheaply digitised. And Afro haircuts are sadly
lacking these days.

But tonight I noticed Miliband's hair doing it on the news.

Andy
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  #2  
Old February 7th 15, 08:27 AM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
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Posts: 2,246
Default BBC Codecs and black hair

On Fri, 06 Feb 2015 22:53:49 +0000, Vir Campestris
wrote:

Is it just me, or do the Beeb have a problem with dark hair?

I've noticed it before on TOTP1979, where if someone with an Afro jumps
up and down the hair lags behind. But it's old stuff, coming off old
film, and probably cheaply digitised. And Afro haircuts are sadly
lacking these days.

But tonight I noticed Miliband's hair doing it on the news.


It's an inevitable feature of severe bit-rate reduction applied to
video material. The processing delay seems to depend slightly on
brighness, so that light and dark parts of the picture appear to
become detached from each other and look as if they're connected by
elastic. It's been there all along, even if you've never noticed
before, though now that you have noticed you'll never be able not to
see it, ever again.

The situation that bugs me the most is an arty portrait shot where the
two sides of the subject's face are lit to very different brightness
levels, and there is slight movement because the director has decided
to try to take a steady shot with a hand held camera, but you'll soon
spot lots of other examples. We've probably just got to live with it.

Rod.
  #3  
Old February 7th 15, 09:54 AM posted to uk.tech.digital-tv
Brian Gaff[_2_]
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Posts: 1,003
Default BBC Codecs and black hair

Maybe its some kind of alien possession we have hitherto been unaware of?
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Vir Campestris" wrote in message
o.uk...
Is it just me, or do the Beeb have a problem with dark hair?

I've noticed it before on TOTP1979, where if someone with an Afro jumps up
and down the hair lags behind. But it's old stuff, coming off old film,
and probably cheaply digitised. And Afro haircuts are sadly lacking these
days.

But tonight I noticed Miliband's hair doing it on the news.

Andy



  #4  
Old February 7th 15, 09:58 AM posted to uk.tech.digital-tv
Brian Gaff[_2_]
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Posts: 1,003
Default BBC Codecs and black hair

A friend reckons that grass at some certain distance looks like the worms
are having a disco, as he describes it. One assumes its when the depth of
field is good due to bright lighting and a certain resolution is where the
artefacts start to affect the picture. I am given to understand dense
undergrowth if panned slightly does this as well.
Not being able to see is probably a good thin nowadays by the sound of it.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Roderick Stewart" wrote in message
...
On Fri, 06 Feb 2015 22:53:49 +0000, Vir Campestris
wrote:

Is it just me, or do the Beeb have a problem with dark hair?

I've noticed it before on TOTP1979, where if someone with an Afro jumps
up and down the hair lags behind. But it's old stuff, coming off old
film, and probably cheaply digitised. And Afro haircuts are sadly
lacking these days.

But tonight I noticed Miliband's hair doing it on the news.


It's an inevitable feature of severe bit-rate reduction applied to
video material. The processing delay seems to depend slightly on
brighness, so that light and dark parts of the picture appear to
become detached from each other and look as if they're connected by
elastic. It's been there all along, even if you've never noticed
before, though now that you have noticed you'll never be able not to
see it, ever again.

The situation that bugs me the most is an arty portrait shot where the
two sides of the subject's face are lit to very different brightness
levels, and there is slight movement because the director has decided
to try to take a steady shot with a hand held camera, but you'll soon
spot lots of other examples. We've probably just got to live with it.

Rod.



  #5  
Old February 7th 15, 10:42 AM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
external usenet poster
 
Posts: 2,246
Default BBC Codecs and black hair

The thing I notice most with grass, or trees, or anything with lots of
distributed fine detail, is that it all becomes a blur as soon as the
camera pans, even quite slowly. Subtitles can also become quite
mangled sometimes if the camera pans. Presumably the processing needed
for a stationary picture full of detail is just at the limits of what
the system is capable of handling. Designed by engineers, redesigned
by accountants, no doubt.

Rod.

On Sat, 7 Feb 2015 10:58:57 -0000, "Brian Gaff"
wrote:

A friend reckons that grass at some certain distance looks like the worms
are having a disco, as he describes it. One assumes its when the depth of
field is good due to bright lighting and a certain resolution is where the
artefacts start to affect the picture. I am given to understand dense
undergrowth if panned slightly does this as well.
Not being able to see is probably a good thin nowadays by the sound of it.
Brian

--
From the Sofa of Brian Gaff Reply address is active
"Roderick Stewart" wrote in message
.. .
On Fri, 06 Feb 2015 22:53:49 +0000, Vir Campestris
wrote:

Is it just me, or do the Beeb have a problem with dark hair?

I've noticed it before on TOTP1979, where if someone with an Afro jumps
up and down the hair lags behind. But it's old stuff, coming off old
film, and probably cheaply digitised. And Afro haircuts are sadly
lacking these days.

But tonight I noticed Miliband's hair doing it on the news.


It's an inevitable feature of severe bit-rate reduction applied to
video material. The processing delay seems to depend slightly on
brighness, so that light and dark parts of the picture appear to
become detached from each other and look as if they're connected by
elastic. It's been there all along, even if you've never noticed
before, though now that you have noticed you'll never be able not to
see it, ever again.

The situation that bugs me the most is an arty portrait shot where the
two sides of the subject's face are lit to very different brightness
levels, and there is slight movement because the director has decided
to try to take a steady shot with a hand held camera, but you'll soon
spot lots of other examples. We've probably just got to live with it.

Rod.


  #6  
Old February 7th 15, 11:08 AM posted to uk.tech.digital-tv
Davey
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Posts: 2,310
Default BBC Codecs and black hair

On Sat, 07 Feb 2015 12:55:34 +0100
Martin wrote:

On Sat, 07 Feb 2015 11:42:06 +0000, Roderick Stewart
wrote:

The thing I notice most with grass, or trees, or anything with lots
of distributed fine detail, is that it all becomes a blur as soon as
the camera pans, even quite slowly. Subtitles can also become quite
mangled sometimes if the camera pans. Presumably the processing
needed for a stationary picture full of detail is just at the limits
of what the system is capable of handling. Designed by engineers,
redesigned by accountants, no doubt.


I've never noticed the subtitles blurring. Are both problems caused
by the TV and not caused by what is transmitted?


I also have not noticed any problems as described with the subtitles.
They have enough of their own without additional ones.

--
Davey.
  #7  
Old February 7th 15, 12:11 PM posted to uk.tech.digital-tv
Roderick Stewart[_3_]
external usenet poster
 
Posts: 2,246
Default BBC Codecs and black hair

On Sat, 7 Feb 2015 12:08:51 +0000, Davey
wrote:

The thing I notice most with grass, or trees, or anything with lots
of distributed fine detail, is that it all becomes a blur as soon as
the camera pans, even quite slowly. Subtitles can also become quite
mangled sometimes if the camera pans. Presumably the processing
needed for a stationary picture full of detail is just at the limits
of what the system is capable of handling. Designed by engineers,
redesigned by accountants, no doubt.


I've never noticed the subtitles blurring. Are both problems caused
by the TV and not caused by what is transmitted?


I also have not noticed any problems as described with the subtitles.
They have enough of their own without additional ones.


The TV's own locally generated subtitles are unaffected. I refer to
foreign language programmes where the subtitles are embedded as part
of the video signal. Sometimes the lettering can jitter side to side
or break up during a rapid pan. Presumably the decoding circuitry,
which for bit rate reduced material partly depends on interpolating
between frames, is having difficulty deciding what is supposed to be
moving and what is not.

Rod.
  #8  
Old February 7th 15, 12:20 PM posted to uk.tech.digital-tv
David Woolley[_2_]
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Posts: 550
Default BBC Codecs and black hair

On 07/02/15 11:42, Roderick Stewart wrote:
The thing I notice most with grass, or trees, or anything with lots of
distributed fine detail, is that it all becomes a blur as soon as the
camera pans, even quite slowly. Subtitles can also become quite


One would expect that. Digital TV periodically sends a complete frame,
but between them it sends information on how sections of the picture
have moved (you can see this when a picture begins to pixelate and an
old frame gets moved around on top of a later frame, for the bits of the
later picture that are moving.

At the next level, it transmits the difference between the result of the
above, and image being encoded, but if there are changes over a large
area, it is likely to choose to send them in low resolution, and fill in
the detail later. It will be using JPEG type coding for this and will
be allocating very few bits to the high spatial frequencies.

This is all supposed to rely on the eye not seeing lots of detail when
things are moving.

Note that digital TV codec standards specify how to decode the signal.
How the signal is encoded is an open design choice as long as the result
is reasonable, once decoded. This means different encoders may
prioritise different aspects of the image quality and still be compliant
coders.

mangled sometimes if the camera pans. Presumably the processing needed
for a stationary picture full of detail is just at the limits of what
the system is capable of handling. Designed by engineers, redesigned
by accountants, no doubt.


For a stationary picture, you may have several seconds to fill in the
fine detail.

  #9  
Old February 7th 15, 01:36 PM posted to uk.tech.digital-tv
Davey
external usenet poster
 
Posts: 2,310
Default BBC Codecs and black hair

On Sat, 07 Feb 2015 13:11:34 +0000
Roderick Stewart wrote:

On Sat, 7 Feb 2015 12:08:51 +0000, Davey
wrote:

The thing I notice most with grass, or trees, or anything with
lots of distributed fine detail, is that it all becomes a blur as
soon as the camera pans, even quite slowly. Subtitles can also
become quite mangled sometimes if the camera pans. Presumably the
processing needed for a stationary picture full of detail is just
at the limits of what the system is capable of handling. Designed
by engineers, redesigned by accountants, no doubt.

I've never noticed the subtitles blurring. Are both problems caused
by the TV and not caused by what is transmitted?


I also have not noticed any problems as described with the subtitles.
They have enough of their own without additional ones.


The TV's own locally generated subtitles are unaffected. I refer to
foreign language programmes where the subtitles are embedded as part
of the video signal. Sometimes the lettering can jitter side to side
or break up during a rapid pan. Presumably the decoding circuitry,
which for bit rate reduced material partly depends on interpolating
between frames, is having difficulty deciding what is supposed to be
moving and what is not.

Rod.


Ah. To me, 'subtitles' meant the subtitles that I normally use, there
was no differentiation.

--
Davey.
  #10  
Old February 7th 15, 04:11 PM posted to uk.tech.digital-tv
Mark Carver
external usenet poster
 
Posts: 7,633
Default BBC Codecs and black hair

On 07/02/2015 13:11, Roderick Stewart wrote:

The TV's own locally generated subtitles are unaffected. I refer to
foreign language programmes where the subtitles are embedded as part
of the video signal. Sometimes the lettering can jitter side to side
or break up during a rapid pan. Presumably the decoding circuitry,
which for bit rate reduced material partly depends on interpolating
between frames, is having difficulty deciding what is supposed to be
moving and what is not.



Yes, I've noticed the same on the captions during the world cup last year.

As you say it can be a problem when there's text as part of the coded
video signal. If you see it on optional viewer selected subtitles, then
it can only be the processiong of your screen itself, gasping for beath,
so pretty unlikely to happen, unless you have a particularly cheap and
nasty screen.


--
Mark
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