NTSC versus PAL
in [Repair]
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From: Phil Allison on 5 Apr 2010 00:28 "isw" > stratus46(a)yahoo.com wrote: > > >> 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? > > 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
From: William Sommerwerck on 5 Apr 2010 08:56 >> 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). > 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: >> The user can adjust the color rendition to their personal (and usually incorrect) taste. * >> The user can correct for incorrect burst phase. 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.
From: Dave Plowman (News) on 5 Apr 2010 09:49 In article <hpcmlq$ltf$1(a)news.eternal-september.org>, William Sommerwerck <grizzledgeezer(a)comcast.net> wrote: > >> 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). > > 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. I've never seen a set designed for the PAL market with a hue control. Only ones modified from a basically NTSC design. > There are two reasons for having a manual hue control: > >> The user can adjust the color rendition to their personal (and > >> usually incorrect) taste. * > >> The user can correct for incorrect burst phase. > 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. 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. -- *I'm already visualizing the duct tape over your mouth Dave Plowman dave(a)davenoise.co.uk London SW To e-mail, change noise into sound.
From: Sylvia Else on 5 Apr 2010 09:51 On 5/04/2010 10:56 PM, William Sommerwerck wrote: >>> 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). > >> 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: > >>> The user can adjust the color rendition to their personal (and usually > incorrect) taste. * >>> The user can correct for incorrect burst phase. > > 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.
From: William Sommerwerck on 5 Apr 2010 10:53
>> 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. 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. |