NTSC versus PAL

PAL doesn't /require/ a delay line.

NTSC has always "performed well". Poor NTSC image quality was always due to bad studio practice.

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.

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.

"William Sommerwanker LYING TROLL "

.... Phil

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.

=A0"

What the heck has the transmitter got to do with it? Anything that is right or wrong with an NTSC signal is equally right or wrong BEFORE the transmitter. The transmitter is just a way to get the signal to lots of folks at once. Or does that confuse YOU?

G=B2

Depends on what you mean by 'satisfacory'. Passable, maybe.

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.

Isaac

..... Phil

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:

incorrect) taste. *

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.

I've never seen a set designed for the PAL market with a hue control. Only ones modified from a basically NTSC design.

You simply don't get hue errors on PAL sets - unless the grey scale is set incorrectly. Of course some sets also used the incorrect phosphors to provide a brighter picture - but a hue control couldn't compensate for that.

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.

(???))

need

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.

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.

Especially CSI. ;-)

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

Geoff.

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.

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.

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.

Right. I missed that.