Science > Physics > Why not wear clothes with detailed patterns on tv?
| Topic: |
Science > Physics |
| User: |
"Bert Harleman" |
| Date: |
07 Dec 2006 06:29:17 PM |
| Object: |
Why not wear clothes with detailed patterns on tv? |
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order to
produce a interlaced signal at the tv's at home, you need to record the
signal (in the studio) with the same principle (interlacing). But I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Bert
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| User: "tadchem" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 05:08:26 AM |
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Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order to
produce a interlaced signal at the tv's at home, you need to record the
signal (in the studio) with the same principle (interlacing). But I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Hold a pocket comb up in front of one eye and view a half-open Venetian
blind through it - preferably from inside on a bright day.
If you align the teeth of the comb and the slats of the blind, and
adjust the distances between yourself and the blind and the comb, you
will find you are able to make the view go from bright to dark with the
slightest wiggle. You might even see your own pulse.
TV images are a grid of horizontal and vertical lines. People often
wear clothes with horizontal or vertical lines.
As Sam Wormley has suggested, look up "Moir=E9 patterns":
http://en.wikipedia.org/wiki/Moire
Tom Davidson
Richmond, VA
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 05:58:18 AM |
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"tadchem" <tadchem@comcast.net> wrote in message =
news:1165576106.771333.136730@79g2000cws.googlegroups.com...
Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes =
with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at =
home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact =
origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order to
produce a interlaced signal at the tv's at home, you need to record =
the
signal (in the studio) with the same principle (interlacing). But I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Hold a pocket comb up in front of one eye and view a half-open Venetian
blind through it - preferably from inside on a bright day.
If you align the teeth of the comb and the slats of the blind, and
adjust the distances between yourself and the blind and the comb, you
will find you are able to make the view go from bright to dark with the
slightest wiggle. You might even see your own pulse.
TV images are a grid of horizontal and vertical lines. People often
wear clothes with horizontal or vertical lines.
As Sam Wormley has suggested, look up "Moir=E9 patterns":
http://en.wikipedia.org/wiki/Moire
That isn't why.
This is:
B. The detailed pattern causes 'false colours' on the analog tv at home
http://en.wikipedia.org/wiki/PAL
When watching a football game (not USA football, but soccer) on=20
a colour TV (not USA NTSC color, but European PAL coloUr)
the referee's black and white shirt shows colour fringes as the
frequency changes by zooming the camera.=20
A guest on a lit studio news broadcast or idiot show such as Jay Leno=20
should not wear clothing with vertical stripes or checker patterns, =20
the colour fringes are disconcerting as he moves.
=
http://www.mediacollege.com/video/test-patterns/television/bbc-f1997.jpg
Notice the colour band in the stripes column on the immediate right=20
of the circle. That is not present on the original test card.
Androcles
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| User: "Richard Tobin" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 06:53:13 AM |
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In article <urceh.49149$Pk.12260@fe2.news.blueyonder.co.uk>,
Sorcerer <Headmaster@hogwarts.physics_e> wrote:
http://www.mediacollege.com/video/test-patterns/television/bbc-f1997.jpg
Notice the colour band in the stripes column on the immediate right
of the circle. That is not present on the original test card.
.... which you can see at http://www.cogsci.ed.ac.uk/~richard/tcf.png
-- Richard
--
"Consideration shall be given to the need for as many as 32 characters
in some alphabets" - X3.4, 1963.
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 07:42:22 AM |
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"Richard Tobin" <richard@cogsci.ed.ac.uk> wrote in message =
news:elbn7p$tre$1@pc-news.cogsci.ed.ac.uk...
| In article <urceh.49149$Pk.12260@fe2.news.blueyonder.co.uk>,
| Sorcerer <Headmaster@hogwarts.physics_e> wrote:
|=20
| > =
http://www.mediacollege.com/video/test-patterns/television/bbc-f1997.jpg
| >
| >Notice the colour band in the stripes column on the immediate right=20
| >of the circle. That is not present on the original test card.
|=20
| ... which you can see at http://www.cogsci.ed.ac.uk/~richard/tcf.png
|=20
Yep. Very sharp, my first colour TV had thermionic valves and never
got past the fourth band down. Nowadays I don't own a TV, I'm
not interested in soccer, kid's puppet shows at 6:00 am, reruns of=20
"The Adams Family" in monochrome, Songs of Praise, Judge Judy,
endless snooker, Oprah Winfrey, endless Wimbledon, Eastenders,
Coronation Street, telly tubbies or buying a license to support
the BBC symphony orchestra. At least the USA has voluntary
contributions for its PBS. Maybe I've just gotten older, but it sure
seems to me the quality of TV programmes is inversely proportional
to the quality of Far East TV technology.
=20
| -- Richard
| --=20
| "Consideration shall be given to the need for as many as 32 characters
| in some alphabets" - X3.4, 1963.
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| User: "tadchem" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 05:17:26 PM |
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Sorcerer wrote:
"tadchem" <tadchem@comcast.net> wrote in message news:1165576106.771333.1=
36730@79g2000cws.googlegroups.com...
Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order to
produce a interlaced signal at the tv's at home, you need to record the
signal (in the studio) with the same principle (interlacing). But I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Hold a pocket comb up in front of one eye and view a half-open Venetian
blind through it - preferably from inside on a bright day.
If you align the teeth of the comb and the slats of the blind, and
adjust the distances between yourself and the blind and the comb, you
will find you are able to make the view go from bright to dark with the
slightest wiggle. You might even see your own pulse.
TV images are a grid of horizontal and vertical lines. People often
wear clothes with horizontal or vertical lines.
As Sam Wormley has suggested, look up "Moir=E9 patterns":
http://en.wikipedia.org/wiki/Moire
That isn't why.
This is:
B. The detailed pattern causes 'false colours' on the analog tv at home
http://en.wikipedia.org/wiki/PAL
The problems of striped clothing in TV studios predates the PAL
standard or even color TV (excuse me, that's 'colour' TV for those
addicted to superfluous vowels).
I first heard of it in the early 50's when the Howdy Doody show was on
the air. Once in a while one of the kids in the "Peanut Gallery" would
show up for the show in a striped shirt or dress.
http://www.howdydoodytime.com/peanut.htm
Howdy's plaid shirt was bad, but it was at least a coarse enough
pattern that it still looked plaid on screen - except in middle
distance shots. But the kids' clothes were often simply *distracting*.
Tom Davidson
Richmond, VA
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 11:07:13 PM |
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"tadchem" <tadchem@comcast.net> wrote in message =
news:1165619846.402599.141220@j44g2000cwa.googlegroups.com...
Sorcerer wrote:
"tadchem" <tadchem@comcast.net> wrote in message =
news:1165576106.771333.136730@79g2000cws.googlegroups.com...
Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes =
with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency =
of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at =
home
I kind of understand the principle of interlacing and I read about =
the
artifacts called 'interline twitter', but I cannot find the exact =
origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order =
to
produce a interlaced signal at the tv's at home, you need to record =
the
signal (in the studio) with the same principle (interlacing). But =
I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Hold a pocket comb up in front of one eye and view a half-open =
Venetian
blind through it - preferably from inside on a bright day.
If you align the teeth of the comb and the slats of the blind, and
adjust the distances between yourself and the blind and the comb, you
will find you are able to make the view go from bright to dark with =
the
slightest wiggle. You might even see your own pulse.
TV images are a grid of horizontal and vertical lines. People often
wear clothes with horizontal or vertical lines.
As Sam Wormley has suggested, look up "Moir=E9 patterns":
http://en.wikipedia.org/wiki/Moire
That isn't why.
This is:
B. The detailed pattern causes 'false colours' on the analog tv at =
home
http://en.wikipedia.org/wiki/PAL
The problems of striped clothing in TV studios=20
How come such an argumentative old ***** as you noticed
a problem with striped clothing on a kiddy show in the early 50's=20
and claim it is down to Moir=E9 fringes?
Davidson, I don't believe you, you are an old senile fucking liar
and typical American proud prude, dude. You;ve had your say,
now shut the ***** up.
=20
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| User: "tadchem" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 04:08:51 AM |
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Sorcerer wrote:
How come such an argumentative old ***** as you noticed
a problem with striped clothing on a kiddy show in the early 50's
I have always been a little more observant than most people.
and claim it is down to Moir=E9 fringes?
The *name* may not have been around then, but the phenomenon certainly
was.
Davidson, I don't believe you,
You don't always believe empirical data, either.
you are an old senile fucking liar
and typical American proud prude, dude. You;ve had your say,
now shut the ***** up.
You've degenerated to ad hominem attacks again, as you always do when
you run out of logic.
I can *always* count on you, Sore-cerer.
Tom Davidson
Richmond, VA
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 05:28:56 AM |
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"tadchem" <tadchem@comcast.net> wrote in message =
news:1165918131.147416.201620@16g2000cwy.googlegroups.com...
Sorcerer wrote:
How come such an argumentative old ***** as you noticed
a problem with striped clothing on a kiddy show in the early 50's
I have always been a little more observant than most people.
and claim it is down to Moir=E9 fringes?
The *name* may not have been around then, but the phenomenon certainly
was.
Davidson, I don't believe you,
You don't always believe empirical data, either.
you are an old senile fucking liar
and typical American proud prude, dude. You;ve had your say,
now shut the ***** up.
You've degenerated to ad hominem attacks again, as you always do when
you run out of logic.
I can *always* count on you, Sore-cerer.
You didn't provide any logic, the NTSC 525 *line* TV system
is analogue, not a pixel array on a digital computer monitor to=20
beat with and produce any Moir=E9 fringe; there is no vertical=20
component, so shove your ad hominem attack on me back up=20
your arse, you not even close to being observant.
You can always count in me to point out ***** when I see it.=20
.
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| User: "" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
09 Dec 2006 07:49:02 AM |
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In article <1165619846.402599.141220@j44g2000cwa.googlegroups.com>,
"tadchem" <tadchem@comcast.net> wrote:
Sorcerer wrote:
"tadchem" <tadchem@comcast.net> wrote in message
news:1165576106.771333.136730@79g2000cws.googlegroups.com...
Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order to
produce a interlaced signal at the tv's at home, you need to record the
signal (in the studio) with the same principle (interlacing). But I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Hold a pocket comb up in front of one eye and view a half-open Venetian
blind through it - preferably from inside on a bright day.
If you align the teeth of the comb and the slats of the blind, and
adjust the distances between yourself and the blind and the comb, you
will find you are able to make the view go from bright to dark with the
slightest wiggle. You might even see your own pulse.
TV images are a grid of horizontal and vertical lines. People often
wear clothes with horizontal or vertical lines.
As Sam Wormley has suggested, look up "Moiré patterns":
http://en.wikipedia.org/wiki/Moire
That isn't why.
This is:
B. The detailed pattern causes 'false colours' on the analog tv at home
http://en.wikipedia.org/wiki/PAL
The problems of striped clothing in TV studios predates the PAL
standard or even color TV (excuse me, that's 'colour' TV for those
addicted to superfluous vowels).
I first heard of it in the early 50's when the Howdy Doody show was on
the air. Once in a while one of the kids in the "Peanut Gallery" would
show up for the show in a striped shirt or dress.
http://www.howdydoodytime.com/peanut.htm
Howdy's plaid shirt was bad, but it was at least a coarse enough
pattern that it still looked plaid on screen - except in middle
distance shots. But the kids' clothes were often simply *distracting*.
I had a tank top when I was child that was navy blue and white
stripes; the stripes were like a jagged houndstooth. When I ironed
that thing, I always got dizzy.
/BAH
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| User: "Sue..." |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 06:07:48 AM |
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Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact origin
of this artifact.
In answer A the cause of the problem is explained by the 'scan
frequency' of the television-camera's. I can imagine that in order to
produce a interlaced signal at the tv's at home, you need to record the
signal (in the studio) with the same principle (interlacing). But I'm
not sure this has to be at the exact same resolution. I can imagine
there's a process that can convert the recorded data to the final
screen-resolution.
Then again, I'm not sure what they mean with 'scan-frequency'.
In answer both of my descriptions are just theories.
Does anyone have a good idea what the right answer might be?
Bert
A crash course in color conversion - 6/7/2001 - EDN
To completely eliminate cross-luminance and cross-color effects, the
video material must never experience a composite-video conversion. ...
http://www.edn.com/article/CA85641.html =A92006 Google
-----
Sue...
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| User: "tadchem" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 03:45:20 PM |
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Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
Look at the image here and you'll see why:
http://www.jimzura.com/Update901/AppearanceTips.htm
Note the peculiar "pattern" superimposed on the man's jacket.
This results from the Moir=E9 interference of the detail in the jacket
(and *only* in the jacket) with the lines scanned to produce the image.
This is *not* an artifact of false color produced from RGB pixels
(which would show various colors rather than simple light/dark bands),
nor of the compression errors due to digital resampling (which would
manifest across the entire picture).
The man's jacket is evidently a fine-grained pattern of light and dark
such as a 'houndstooth' pattern. The light bands appear where the
camera 'sees' only the light part of the pattern, and the dark bands
appear where the camera sees only the dark part of the pattern.
BTW, if I were you I should ignore anything "Sorcerer" says, as he has
a nasty habit of talking out his arse. When someone calls him on an
error he vigorously defends himself to the point of hissing and
spitting like a cornered possum rather then concede a point.
Note his posts elsewhere in this thread in which he attributes the "no
stripes" rule to consequences of a European video protocol, even though
the rule has long standing here in the US where the protocol he cites
is not in use.
Tom Davidson
Richmond, VA
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 05:42:05 PM |
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"tadchem" <tadchem@comcast.net> wrote in message =
news:1165959920.519331.49550@79g2000cws.googlegroups.com...
Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes =
with
a detailed line-pattern. Why is that?
Look at the image here and you'll see why:
http://www.jimzura.com/Update901/AppearanceTips.htm
Note the peculiar "pattern" superimposed on the man's jacket.
This results from the Moir=E9 interference of the detail in the jacket
(and *only* in the jacket) with the lines scanned to produce the image.
This is *not* an artifact of false color produced from RGB pixels
(which would show various colors rather than simple light/dark bands),
nor of the compression errors due to digital resampling (which would
manifest across the entire picture).
The man's jacket is evidently a fine-grained pattern of light and dark
such as a 'houndstooth' pattern. The light bands appear where the
camera 'sees' only the light part of the pattern, and the dark bands
appear where the camera sees only the dark part of the pattern.
BTW, if I were you I should ignore anything "Sorcerer" says, as he has
a nasty habit of talking out his arse. When someone calls him on an
error he vigorously defends himself to the point of hissing and
spitting like a cornered possum rather then concede a point.
Note his posts elsewhere in this thread in which he attributes the "no
stripes" rule to consequences of a European video protocol, even though
the rule has long standing here in the US where the protocol he cites
is not in use.
Tom Davidson
Richmond, VA
The man's jacket is evidently a fine-grained pattern of light and dark
such as a 'houndstooth' pattern, but the COLOUR is red, blue, magenta,
grey and GREEN.
http://www.androcles01.pwp.blueyonder.co.uk/temp.JPG
If I were you I should ignore anything "tadchem" says, as he has
a nasty habit of talking out his arse, perhaps he's colour blind, he is=20
certainly ignorant of colour subcarriers and electronics.
When someone calls him on an error he vigorously defends himself to the
point of hissing and spitting like a cornered rat rather than concede a =
point.
The image banding is NOT caused by Moir=E9 fringes.
=20
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| User: "THE_ONE" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 06:39:17 PM |
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By the way, the colour pattern created on an NTSC TV, due to the fine
lined clothes, tends to create a case of a colour role over effect. The
colours are constantly changing.
If you are viewing a PAL TV, then this colour rolling is not as
apparent. This is because the PAL system included a design feature of
having alternating colour carrier phase. The colour carrier is
alternating back and forth 180%. This then cancels out any phase
shifting that may have occurred to the colour carrier. If the colour
carrier has shifted in one direction, then for time the carrier that is
shifted 180%, this shift is in the opposite direction related to it.
The end result is that the overall shift in the carrier is cancelled
out. This is why Most PAL TV's do not have the HUE adjust feature.
An NTSC does not have this feature, and so a Hue adjustment feature is
required.
Meanwhile on the PAL TV, the cancelling out leaves nothing but what
appears to fine Black and white bars.
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| User: "THE_ONE" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 06:56:03 PM |
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By the way, the colour pattern created on an NTSC TV, due to the fine
lined clothes, tends to create a case of a colour role-over effect. The
colours are constantly changing.
If you are viewing a PAL TV, then this colour rolling is not as
apparent. This is because the PAL system included a design feature of
having alternating colour carrier phase. The colour carrier is
alternating back and forth 180%. This then cancels out any phase
shifting that may have occurred to the colour carrier. If the colour
carrier has shifted in one direction, then for the time when the
carrier is shifted 180%, this shift is now in the opposite direction
related to colour carrier than it was previously.
The end result is that the overall shift in the carrier is cancelled
out. This is why Most PAL TV's do not have the HUE adjustment
feature.
An NTSC does not have this feature, and so a Hue adjustment feature is
required.
Meanwhile on the PAL TV, the cancelling out leaves nothing but what
appears to be fine Black and White bars when the fine lined clothes
mess with the colour carrier.
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| User: "THE_ONE" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 05:09:32 PM |
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Hello dummies.
You are not listening.
When it comes to TV signals, the colour info is separated from the
Black and White.
Way back when, all we had was the original Black and White TV. Because
of this, all we had was a simple black and white baseband Video signal.
Then came the new colour image breakthrough. But the trick was to add
color to the original Black and White signal, and do so in a manner
that would not distort the picture if still viewed on an old Black and
white TV.
That was when they decided to add a colour carrier signal that would be
added on top of the Back and White Video signal. The carrier signal is
different for PAL than it is for NTSC. But colour carriers both still
are.
As I said, your TV must then extract this colour carrier from the
signal, and then add it to the underlying black and white signal which
has now been broken down into the three RGB signals that are fed to
your TV's picture tube.
However, if the black and white signal includes frequencies that are
close to colour carrier frequency, then the TV is fooled into detecting
them as actual colour signals. For a high frequency of this kind to
find its way into the black and white signal, the picture must include
fine vertical lines, such as those found on certain clothing.
And there you have it !
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| User: "THE_ONE" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 05:01:24 PM |
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Hello dummies.
You are not listening.
When it comes to TV signals, the colour info is separated from the
Black and White.
Way back when, all we had was the original Black and White TV. Because
of this, we all we had was a simple black and white baseband Video
signal.
Then came the new colour image breakthrough. But the trick was to add
color to the original Black and White signal, and do so in a manner
that would not distort the picture if still viewed on an old Black and
white TV.
That was when they decided to add a colour carrier signal that would be
added on top on the Back and White Video signal. The carrier signal
is different for PAL than it is for NTSC. But a colour carrier it
still is.
As I said, your TV must then extract this colour carrier from the
signal, and then add it to the underlying black and white signal which
has now been broken down into the three RGB signals that are fed to
your TV's picture tube.
However, if the black and white signal includes frequencies that are
close to colour carrier frequency, then the TV is fooled into detecting
them as actual colour signals. For a high frequency of this kind to
find its way into the black and white signal, the picture must include
fine vertical lines, such as those found on certain clothing.
And there you have it !
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
12 Dec 2006 06:24:24 PM |
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"THE_ONE" <floppy01@idirect.com> wrote in message =
news:1165964484.810350.89350@l12g2000cwl.googlegroups.com...
| Hello dummies.
|=20
| You are not listening.
|=20
| When it comes to TV signals, the colour info is separated from the
| Black and White.
|=20
| Way back when, all we had was the original Black and White TV. =
Because
| of this, we all we had was a simple black and white baseband Video
| signal.
|=20
| Then came the new colour image breakthrough. But the trick was to add
| color to the original Black and White signal, and do so in a manner
| that would not distort the picture if still viewed on an old Black and
| white TV.
|=20
| That was when they decided to add a colour carrier signal that would =
be
| added on top on the Back and White Video signal. The carrier signal
| is different for PAL than it is for NTSC. But a colour carrier it
| still is.
|=20
| As I said, your TV must then extract this colour carrier from the
| signal, and then add it to the underlying black and white signal which
| has now been broken down into the three RGB signals that are fed to
| your TV's picture tube.
|=20
| However, if the black and white signal includes frequencies that are
| close to colour carrier frequency, then the TV is fooled into =
detecting
| them as actual colour signals. For a high frequency of this kind to
| find its way into the black and white signal, the picture must include
| fine vertical lines, such as those found on certain clothing.
|=20
| And there you have it !
|
Well put.
.
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| User: "Edward Green" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 08:17:50 AM |
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Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two kinds of answers possible. One is "well, the clothes
have periodic patterns, and the capture/transmission/playback system
has periodic patterns, and you will get some interesting effect by
their interaction". The second one is to attempt a detailed technical
analysis of the first.
Several posters have mentioned "moire patterns". That is a buzz word
equivalent to the first kind of answer, with the tacit implication that
they _could_ give the second kind of answer if they wanted to, but are
just too busy right now. ;-)
I'm not even sure if this precaution isn't historical: I can picture
very easily old black and white video with strange effects regarding
guest's clothing (it was always the guests... the hosts definitely
would know better), but not modern shows. Better clothing
pre-screening, or better equipment?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of
the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
I kind of understand the principle of interlacing and I read about the
artifacts called 'interline twitter', but I cannot find the exact origin
of this artifact.
You are striving for the second kind of answer.
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| User: "Sorcerer" |
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| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 08:22:56 AM |
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"Edward Green" <spamspamspam3@netzero.com> wrote in message =
news:1165587470.400094.314010@n67g2000cwd.googlegroups.com...
| Bert Harleman wrote:
|=20
| > This is a question in a popular Dutch science quiz:
| >
| > When people appear on television they are asked not to wear clothes =
with
| > a detailed line-pattern. Why is that?
|=20
| There are two kinds of answers possible. One is "well, the clothes
| have periodic patterns, and the capture/transmission/playback system
| has periodic patterns, and you will get some interesting effect by
| their interaction". The second one is to attempt a detailed technical
| analysis of the first.
|=20
| Several posters have mentioned "moire patterns". That is a buzz word
| equivalent to the first kind of answer, with the tacit implication =
that
| they _could_ give the second kind of answer if they wanted to, but are
| just too busy right now. ;-)
|=20
| I'm not even sure if this precaution isn't historical: I can picture
| very easily old black and white video with strange effects regarding
| guest's clothing (it was always the guests... the hosts definitely
| would know better), but not modern shows. Better clothing
| pre-screening, or better equipment?
|=20
| > There are two options between which I can choose:
| > A. The detailed pattern causes interference with the scan frequency =
of
| > the camera's
| > B. The detailed pattern causes 'false colours' on the analog tv at =
home
| >
| > I kind of understand the principle of interlacing and I read about =
the
| > artifacts called 'interline twitter', but I cannot find the exact =
origin
| > of this artifact.
|=20
| You are striving for the second kind of answer.
The tacit implication being that Green could NOT give the second kind of
answer if he wanted to, but pretends he is just too busy right now. ;-)
.
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| User: "Edward Green" |
|
| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 09:15:52 AM |
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|
Sorcerer wrote:
"Edward Green" <spamspamspam3@netzero.com> wrote in message news:1165587470.400094.314010@n67g2000cwd.googlegroups.com...
| Bert Harleman wrote:
|
| > This is a question in a popular Dutch science quiz:
| >
| > When people appear on television they are asked not to wear clothes with
| > a detailed line-pattern. Why is that?
|
| There are two kinds of answers possible.
<...>
| You are striving for the second kind of answer.
The tacit implication being that Green could NOT give the second kind of
answer if he wanted to, but pretends he is just too busy right now. ;-)
Of course I can't.
.
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|
|
| User: "Sorcerer" |
|
| Title: Re: Why not wear clothes with detailed patterns on tv? |
08 Dec 2006 01:21:26 PM |
|
|
"Edward Green" <spamspamspam3@netzero.com> wrote in message =
news:1165590952.324108.228940@16g2000cwy.googlegroups.com...
|=20
| Sorcerer wrote:
| > "Edward Green" <spamspamspam3@netzero.com> wrote in message =
news:1165587470.400094.314010@n67g2000cwd.googlegroups.com...
| > | Bert Harleman wrote:
| > |
| > | > This is a question in a popular Dutch science quiz:
| > | >
| > | > When people appear on television they are asked not to wear =
clothes with
| > | > a detailed line-pattern. Why is that?
| > |
| > | There are two kinds of answers possible.
| <...>
|=20
| > | You are striving for the second kind of answer.
| >
| > The tacit implication being that Green could NOT give the second =
kind of
| > answer if he wanted to, but pretends he is just too busy right now. =
;-)
|=20
| Of course I can't.
I can.
=
http://www.mediacollege.com/video/test-patterns/television/bbc-f1997.jpg
http://www.cogsci.ed.ac.uk/~richard/tcf.png
(second image by courtesy of Richard Tobin)
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| User: "Sam Wormley" |
|
| Title: Re: Why not wear clothes with detailed patterns on tv? |
07 Dec 2006 06:36:17 PM |
|
|
Bert Harleman wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
Moiré patterns
.
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|
|
| User: "THE_ONE" |
|
| Title: Re: Why not wear clothes with detailed patterns on tv? |
07 Dec 2006 08:22:07 PM |
|
|
Sam Wormley wrote:
This is a question in a popular Dutch science quiz:
When people appear on television they are asked not to wear clothes with
a detailed line-pattern. Why is that?
There are two options between which I can choose:
A. The detailed pattern causes interference with the scan frequency of the camera's
B. The detailed pattern causes 'false colours' on the analog tv at home
Yes, this brings back memories.
The video signal is limited to a certain bandwidth. The video image
signal is composed of the Black and White image that is converted into
variation of voltage, and the higher the voltage the brighter the
picture will be on the TV. Riding on top of the Black and White image
signal, is a color carrier of 3.58Mhz. The Black and White image info
is therefore limited to less than the 3.58Mhz, such that it does not
interfere with the color carrier.
Phase shifting of the color carrier, determines what color will be
added to the Black and White image at the TV. The amplitude of the
color carrier will determine the intensity of that color.
If however, the original image has fine line like details within it,
the color carrier detector present within the your TV, may lock onto
these stripes as well, if the frequency of these fine lines is very
close to the actual color carrier frequency of 3.58Mhz, or is perhaps
exactly one half of the 3.58Mhz color carrier frequency . Hence the
strips function as a false but strong high amplitude color carrier, and
color suddenly appears on the screen even though the fine stripes may
have been black and white to begin with.
The_One
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