NTSC versus PAL
in [Repair]
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From: isw on 6 Apr 2010 22:54 In article <4bbbee16$0$24357$c3e8da3(a)news.astraweb.com>, Sylvia Else <sylvia(a)not.at.this.address> wrote: --snippety-snip-- > I'm left wondering what exactly was the *real* problem that PAL was > intended to fix. Political. The Europeans didn't want US companies selling sets there. Isaac
From: Dave Plowman (News) on 7 Apr 2010 04:27 In article <isw-55C6A6.19545706042010@[216.168.3.50]>, isw <isw(a)witzend.com> wrote: > In article <4bbbee16$0$24357$c3e8da3(a)news.astraweb.com>, > Sylvia Else <sylvia(a)not.at.this.address> wrote: > --snippety-snip-- > > I'm left wondering what exactly was the *real* problem that PAL was > > intended to fix. > Political. The Europeans didn't want US companies selling sets there. Didn't stop the Japanese, etc. But US companies would have to do other mods to their products for European sales anyway. Like mains voltage and frequency. Most couldn't be bothered - even when that's all which had to be changed. -- *Letting a cat out of the bag is easier than putting it back in * Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound.
From: William Sommerwerck on 7 Apr 2010 08:12 > 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. Correct. > Other issues, such as non-linear phase shift would have been > a problem for NTSC viewers, regardless of the tint control. Also correct. > 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? You /have/ missed something, which I explained "long ago and far away". <grin> The US TV-distribution system DID NOT generally suffer from non-linear group-delay problems, whereas the European system DID. That's it. Even without the extra delay line, there is some degree of visual color averaging, which tends to mitigate the phase error.
From: William Sommerwerck on 7 Apr 2010 08:14 >> Political. The Europeans didn't want US companies selling >> sets there. > Didn't stop the Japanese, etc. But US companies would have > to do other mods to their products for European sales anyway. > Like mains voltage and frequency. Most couldn't be bothered -- > even when that's all which had to be changed. I don't buy that. US sets would have been fairly expensive in Europe, even in the mid-60s. Not to mention the strong competition from Thomson, Philips, etc.
From: PeterD on 7 Apr 2010 08:40
On Wed, 07 Apr 2010 12:29:40 +1000, Sylvia Else <sylvia(a)not.at.this.address> wrote: >On 7/04/2010 10:08 AM, Arfa Daily wrote: >> "Sylvia Else"<sylvia(a)not.at.this.address> wrote in message >> news:4bba994c$0$15459$c3e8da3(a)news.astraweb.com... >>> On 6/04/2010 12:53 AM, William Sommerwerck wrote: >>>>>> 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. >>>> >>>> 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. >>> >> >> 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. > Part of the difficulity in understanding is that perhaps you don't have experience with early American color televisions... I certainly remember how in the 60s we had to adjust the tint control on a regular (show by show) basis, because of lack of consistancy. Today, with predominatly digital systems, it has been so long since I've touched a tint control, that I wonder if they still exist! Anyone who had one of those old, tube (valve) color sets, with the 21" round color CRT, will remember seeing green skies, and blue grass while having skin colors set to the proper shade. Get the sky blue, and the skin turned red, or blue, or green! |