NTSC versus PAL

[William Sommerwerck]

If we were building an analogue colour TV transmission infrastructure

NTSC? No delay line? Moron. The luminance data had to be delayed to
allow time to process the Chroma data. An open delay line in a NTSC
video display caused a very dark image with moving blotches of color. I
found and replaced several, in NTSC TVs and Video Monitors.

She's talking about phase averaging (or whatever it's called -- I don't know
the term).

The delay line /you're/ talking about is required in NTSC and PAL receivers,
because the narrower-band color signal(s) have greater group delay, and the
luminance has to be "slowed down" to match.

 

[William Sommerwerck]

If the transmission network has constant group delay,

It's not clear to me why that wasn't the case anyway. Whatever
phase error was introduced to the colour signal by the transmission
system would also affect the colour burst. If the problem could be
addressed by means of a tint control with a setting that remained
stable even over the duration of a program, it rather seems to imply
that a phase error between the colour burst and the colour subcarrier
was built into the signal at the studio.

We're talking about non-linear group delay. This is not a simple phase error
in the burst, but a non-time-constant delay across the bandwidth of the
chroma signal. Any such non-linear delay will introduce varying color errors
that cannot be corrected with a single hue setting.

 

[Phil Allison]

"William Sommerwanker FUCKING TROLL "

Phil Allison

That's really going too far.

** Really ??????????????

Which laws of nature have changed since 1953 ?

Please give all relevant details.


Or I will **** you right off usenet for ever -

you vile, stinking, pile of sub human autistic SHIT !!






...... Phil

 

[Phil Allison]

"William Sommerwanker LYING TROLL "

NTSC has always "performed well".

** MASSIVE LIE .

Poor NTSC image quality was always due to
bad studio practice.

** Another MASSIVE LIE.



..... Phil

 

[Phil Allison]

"William Sommerwanker LYING FUCKWIT TROLL "

NTSC has always "performed well".

** MASSIVE LIE .

Poor NTSC image quality was always due to
bad studio practice.

** Another MASSIVE LIE.

FOAD you stupid old **** !!



..... Phil

 

[Phil Allison]

"William Sommerwanker LYING TROLL "

NTSC has always "performed well".

** MASSIVE LIE .

Poor NTSC image quality was always due to
bad studio practice.

** Another MASSIVE LIE.

FOAD you stupid old AUTISTIC **** !!



..... Phil

 

[Sylvia Else]

We're talking about non-linear group delay. This is not a simple phase error
in the burst, but a non-time-constant delay across the bandwidth of the
chroma signal. Any such non-linear delay will introduce varying color errors
that cannot be corrected with a single hue setting.

But, as you say, that kind of problem cannot be corrected with a single
hue setting, so no amount of fiddling with the tint control would have
produced an acceptable picture, even over a short timescale.

I understand that prior to the expiry of the Telefunken PAL patent, Sony
Trinitron sets for the PAL market actually threw away the chrominance
signal on alternate scan lines, thus landing themselves back in NTSC
territory. Those sets had a tint control, and I know from personal
experience that they produced a perfectly satisfactory result (I only
learnt the other day why they had a tint control).

So even if non-linear delay was a theoretical problem, it appears not to
have been one in practice. At least, not in the UK.

Sylvia.

 

[David Nebenzahl]

That's really going too far. Is there any way to permanently block Mr.
Allison?

You're not serious, are you? I mean, I'm sure you already know the
answer to that question.

My suggestion: enjoy the Phil Allison Ride while it's running. Wheee!

 

[Phil Allison]

They still do some composite D-2 editing at CBS network. Or don't they
count as broadcast?

** Hey fuckwit.

In relation to television transmission - where does one find the "
broadcast signal " ???

Don't strain you tiny brain thinking too hard.

What the heck has the transmitter got to do with it?


** I made no mention of any " transmitter"

- you FUCKING ILLITERATE MORON !!!


The fuckwit still no idea where a " broadcast signal" is to be found.

Cos obviously, this asinine cunthead has no clue why engineers were
motivated to develop PAL in the first place.




...... Phil

 

[Phil Allison]

"isw"

You are evidently not aware that a poorly designed or operated
transmitter can introduce all sorts of distortions to the signal. Talk
to the engineers who designed or operated them sometime.

** Maybe you can tell this utter imbecile what the phrase " broadcast signal
" refers to ??




...... Phil

 

[William Sommerwerck]

I understand that prior to the expiry of the Telefunken PAL patent,

Depends on what you mean by "satisfactory". Passable, maybe.

When you discuss something at length, you become aware of those things you
thought you understood, but didn't. (Well, I do, anyway.)

I'd always read that one could construct a PAL receiver in such a way that
eliminated the need for a manual hue control. I never questioned this, but
now it makes little sense.

There are two reasons for having a manual hue control:

That seems to be "it". As we've seen, these errors can be corrected by
adjusting the hue control, whereas the other error -- differential phase
shift -- cannot be so-corrected, because the timing errors are not linear.

Here's where I get confused. The line-to-line polarity reversal ** causes
the differential phase errors to be equal and opposite, and thus cancel out
when added (at the cost of desaturation -- but that's another issue).

However... If the burst phase is wrong, then there is no cancellation of
errors, because there are no "errors" /in the signal itself/. (Right? (???))
Therefore, I don't see how line averaging can be used to eliminate the need
for a manual hue control.

If anyone knows of a reference with a non-tautological explanation, I'd
appreciate a pointer to it. Thanks.

* Left to their own devices, the average user generally sets the color for
greenish skin tones. I wonder if Vulcan viewers tended towards a pinkish
error.

** It's actually line-to-line+2, because the image is interlaced.

 

[Sylvia Else]

When you discuss something at length, you become aware of those things you
thought you understood, but didn't. (Well, I do, anyway.)

I'd always read that one could construct a PAL receiver in such a way that
eliminated the need for a manual hue control. I never questioned this, but
now it makes little sense.

There are two reasons for having a manual hue control:


That seems to be "it". As we've seen, these errors can be corrected by
adjusting the hue control, whereas the other error -- differential phase
shift -- cannot be so-corrected, because the timing errors are not linear.

Here's where I get confused. The line-to-line polarity reversal ** causes
the differential phase errors to be equal and opposite, and thus cancel out
when added (at the cost of desaturation -- but that's another issue).

However... If the burst phase is wrong, then there is no cancellation of
errors, because there are no "errors" /in the signal itself/. (Right? (???))
Therefore, I don't see how line averaging can be used to eliminate the need
for a manual hue control.

Think of the chroma signal as a vector with its y coordinate equal the
red difference component, and the x coordinate equal to the blue
difference component. A phase error rotates that vector about the z
axis. Effectively, the blue difference component receives a bit of the
red difference component, and vice versa.

On alternate lines the phase of the red difference component *only* is
inverted. In our view, this has the effect of reflecting the vector in
the x axis - what was a positive y value becomes negative.

The same phase error causes this vector to rotate in the same direction
about the z axis, but because of the reflection, the mixing of the
components has the opposite sign.

If you then negate the resulting red difference component of the second
line, and average with the red difference component of the first line,
the parts received from the blue difference component cancel out,
leaving a red different component that equals the original, multiplied
by the cosine of the phase error. The same applies to the blue
component. The result is that the hues are correct, but not as saturated
as they shoud have been.

Sylvia.

 

[William Sommerwerck]

However... If the burst phase is wrong, then there is no cancellation of

Think of the chroma signal as a vector with its y coordinate equal the
red difference component, and the x coordinate equal to the blue
difference component. A phase error rotates that vector about the z
axis. Effectively, the blue difference component receives a bit of the
red difference component, and vice versa.

On alternate lines the phase of the red difference component *only* is
inverted. In our view, this has the effect of reflecting the vector in
the x axis - what was a positive y value becomes negative.

The same phase error causes this vector to rotate in the same direction
about the z axis, but because of the reflection, the mixing of the
components has the opposite sign.

If you then negate the resulting red difference component of the second
line, and average with the red difference component of the first line,
the parts received from the blue difference component cancel out,
leaving a red different component that equals the original, multiplied
by the cosine of the phase error. The same applies to the blue
component. The result is that the hues are correct, but not as saturated
as they shoud have been.

No argument. That's always been my understanding. But...

If the burst phase gets screwed up somewhere along the line, no amount of
line averaging will fix the problem, because there's nothing "wrong" with
the subcarrier to fix.

Granted, this problem hardly ever happens. But the argument that a fully
implemented PAL set is inherently immune to color errors is hard for me to
swallow.

 

[Geoffrey S. Mendelson]

If you then negate the resulting red difference component of the second
line, and average with the red difference component of the first line,
the parts received from the blue difference component cancel out,
leaving a red different component that equals the original, multiplied
by the cosine of the phase error. The same applies to the blue
component. The result is that the hues are correct, but not as saturated
as they shoud have been.

Since PAL TV sets have a saturation (color level) control, isn't that
a "non-problem". If it matters, you just adjust it to compensate.

My experience is that people set the color saturation too high, if I hold
my hand up to the screen my skin looks pale in comparison to everyone
on it.

Geoff.

 

[Geoffrey S. Mendelson]

Especially CSI. ;-)

That's funny, I was thinking of last Thursday night's episode of CSI
when I wrote that.

Geoff.

 

[Sylvia Else]

No argument. That's always been my understanding. But...

If the burst phase gets screwed up somewhere along the line, no amount of
line averaging will fix the problem, because there's nothing "wrong" with
the subcarrier to fix.

If the burst has a random phase relationship to the colour subcarrier on
each line, then my analysis falls apart because the vectors would have
random orientations. In such a situation a PAL receiver would do no
better than NTSC, and they'd both perform awfully.

If the burst just has a fixed phase offset from the true colour
subcarrier, then the averaging will work.

Indeed it will work if the colour subcarrier drifts in a consistent way
relative to the burst - or if the receiver's oscillator similarly
drifts. The effect of such a drift on an NSTC picture would be a
variation of tint from left to right. However, a tint control wouldn't
be able to address that problem - it would simply move the horizontal
position on the screen where the colours are accurate - suggesting that
it doesn't occur in practice except in equipment that is recognisably
broken.

Granted, this problem hardly ever happens. But the argument that a fully
implemented PAL set is inherently immune to color errors is hard for me to
swallow.

I don't think there's a claim that it is inherently immune to all colour
errors, only those caused by consistent differences between the phase of
the subcarrier and the burst.

Sylvia.

 

[Sylvia Else]

Since PAL TV sets have a saturation (color level) control, isn't that
a "non-problem". If it matters, you just adjust it to compensate.

If it's a fixed phase error, yes. If the phase error is changing slowly
over time the the picture will have a saturation that varies over time
which would be annoying if the effect were high enough.

However, I've never noticed such an effect.

Sylvia.

 

[William Sommerwerck]

If the burst just has a fixed phase offset from the true colour

subcarrier, then the averaging will work.

Right. I missed that.

I don't think there's a claim that [PAL] is inherently immune to
all colour errors, only those caused by consistent differences
between the phase of the subcarrier and the burst.

 

[William Sommerwerck]

Many years back, Bush in the UK produced a colour decoder which was

'revolutionary' compared to other manufacturers' efforts, in that the
subcarrier was regenerated in the decoder directly from the burst, rather
than being a free-running oscillator just locked to the burst with a PLL.
They did this by deriving a phase-adjustable pulse from the H-flyback, and
using this to 'notch out' the burst from the back porch period. The 10
cycles of burst thus recovered, were then applied directly to the 4.43MHz
crystal, which caused it to ring at exactly the same frequency and in
exactly the same phase as the original subcarrier. Always seemed to work
pretty well, and they continued to use this system over a period of
probably 10 years or more, covering three chassis designs / revisions.

This was first done by GE, circa 1966, in the Portacolor set, mostly because
it was cheaper.

Another way of looking at this system is that the crystal was an extremely
narrow-band filter that removed the "Fourier sidebands" around the
subcarrier frequency created by transmitting the 10-cycle burst only once on
each scanning line.

 

[Sylvia Else]

Many years back, Bush in the UK produced a colour decoder which was
'revolutionary' compared to other manufacturers' efforts, in that the
subcarrier was regenerated in the decoder directly from the burst, rather
than being a free-running oscillator just locked to the burst with a PLL.
They did this by deriving a phase-adjustable pulse from the H-flyback, and
using this to 'notch out' the burst from the back porch period. The 10
cycles of burst thus recovered, were then applied directly to the 4.43MHz
crystal, which caused it to ring at exactly the same frequency and in
exactly the same phase as the original subcarrier. Always seemed to work
pretty well, and they continued to use this system over a period of probably
10 years or more, covering three chassis designs / revisions.

Arfa

I'm left wondering what exactly was the *real* problem that PAL was
intended to fix. It appears that the NTSC tint control could only
address a fixed phase offset between the colour burst and the
subcarrier, with both transmitters and TV sets able to maintain that
offset sufficiently closely that the hue wouldn't vary from left to
right of the picture.

Other issues, such as non-linear phase shift would have been a problem
for NTSC viewers, regardless of the tint control.

So were NTSC viewers tolerating colour pictures that couldn't be set
right even with the tint control? Or is there something else that I've
missed?

Sylvia.