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  #1  
Old 09-24-2016, 08:35 AM
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Could NTSC VIR = PAL

Was wondering if VIR, implemented to its full potential, have eliminated the Tint control?
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Old 09-24-2016, 01:18 PM
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That (as well as saturation control) was the idea.

It was not at all the same system as PAL, in which the red-minus-white (R-Y) switched with each horizontal scanning line. In NTSC with VIR, every line of the actual picture was transmitted exactly as had been done for the coverage of the 1954 Tournament of Roses Parade. The difference was one line in the vertical retrace interval, a consistent reference signal the a TV set would use to automatically set the hue and saturation perfectly - to the Vertical Interval Reference - VIR.

I really don't know why it didn't catch on. I can only wonder if its promotor wanted too much money for the patent royalty? was the inventor an outsider? (see interval windshield wipers), did TV manufacturers believe their products produced fine color anyway?, was NTSC color reliable enough by the time VIR came around that setting the dials just once was enough to assure good color? Did the entertainment industry want any improvement in picture quality to be tied to selective availability and copy blocking?

Last edited by Robert Grant; 09-24-2016 at 01:49 PM.
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Old 09-24-2016, 11:42 PM
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Quote:
Originally Posted by Robert Grant View Post
...

I really don't know why it didn't catch on. ...
The reason it didn't catch on is that the local stations started using it to close the loop on their transmitter adjustments by inserting it locally. Of course, when they did that, it no longer bore any fixed relation to the original video, just as the locally re-inserted color burst didn't either. So, set manufacturers decided not to use it, as it often made the color worse instead of better. It could have succeeded if GE had managed to get the FCC to mandate its correct use.

EDit: By the way, GE was the inventor and promoter.
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Old 09-25-2016, 12:19 PM
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Originally Posted by old_tv_nut View Post
The reason it didn't catch on is that the local stations started using it to close the loop on their transmitter adjustments by inserting it locally. Of course, when they did that, it no longer bore any fixed relation to the original video, just as the locally re-inserted color burst didn't either. So, set manufacturers decided not to use it, as it often made the color worse instead of better. It could have succeeded if GE had managed to get the FCC to mandate its correct use.

Do you mean they (stations) used the actual VIR format for transmitter monitoring, or just snatched the assigned lines for similar test signals?
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Old 09-25-2016, 01:27 PM
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Do you mean they (stations) used the actual VIR format for transmitter monitoring, or just snatched the assigned lines for similar test signals?
Yes, they used the actual VIR format, newly inserted. They had to, for material that didn't contain it originally, and then just did it for all material.
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Old 09-25-2016, 10:41 PM
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Originally Posted by old_tv_nut View Post
...when they did that, it no longer bore any fixed relation to the original video, just as the locally re-inserted color burst didn't either.
Though I'm no expert on VIR, wouldn't locally regenerated (network sourced for instance) burst have precise phase lock to the original and, by extension, the VIR (regenerated?) bursts.

So I'm guessing from this the networks used VIR with their feeds?
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Old 09-25-2016, 11:11 PM
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Though I'm no expert on VIR, wouldn't locally regenerated (network sourced for instance) burst have precise phase lock to the original and, by extension, the VIR (regenerated?) bursts.

So I'm guessing from this the networks used VIR with their feeds?
Not sure if I understand your question completely.

The local burst must be reinserted to standard amplitude and clean waveform per FCC rules. Therefore, it at least loses its relation to the chroma amplitude, which may have changed due to analog transmission distortion over the network. In practice, the reinserted phase is also adjustable and therefore can be misadjusted. If there is significant phase distortion of the chroma over the network, the phase of the incoming burst may also vary over its width, making it difficult to know where to set the phase of the re-inserted burst. The VIR reference had a much wider burst of chroma during the active line, which was supposed to fix this by ignoring edge distortions. Unlike NTSC, the PAL burst, by alternating phase sequence from line to line, should average out to the correct phase even when phase distortion is present.

The whole idea of VIR was to insert it at the originating studio and not replace it anywhere along the chain, not even at network central control; but not every program had it inserted.

I would note that VIR, occurring once per field, had a much slower control action than color burst, and could not possibly compensate for fast signal variations like airplane flutter.
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Old 09-29-2016, 12:55 AM
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=old_tv_nut;3170654
The local burst must be reinserted to standard amplitude and clean waveform per FCC rules. Therefore, it at least loses its relation to the chroma amplitude, which may have changed due to analog transmission distortion over the network. In practice, the reinserted phase is also adjustable and therefore can be misadjusted. If there is significant phase distortion of the chroma over the network, the phase of the incoming burst may also vary over its width, making it difficult to know where to set the phase of the re-inserted burst. The VIR reference had a much wider burst of chroma during the active line, which was supposed to fix this by ignoring edge distortions. ..
The whole idea of VIR was to insert it at the originating studio and not replace it anywhere along the chain, not even at network central control; but not every program had it inserted...
Some great info there!
Brilliant of General Electric to have a wider burst in active line - and at a luminance level of a typical flesh tone!

So, to me, the "problems" would have been easily avoidable with good broadcasting practice:
For example source material with VIR needed to be first reclaibrated thru a professional VIR processor
that also regenerated burst & VIR (with exact phase similitude) to the gated line 19 sample).
Was there such an instrument?

Last edited by NewVista; 09-29-2016 at 12:59 AM.
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Old 09-29-2016, 10:51 PM
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Originally Posted by old_tv_nut View Post
.. If there is significant phase distortion of the chroma over the network, the phase of the incoming burst may also vary over its width, making it difficult to know where to set the phase of the re-inserted burst. The VIR reference had a much wider burst of chroma during the active line, which was supposed to fix this by ignoring edge distortions. .
Didn't know of this problem of burst phase distortion , nevertheless the burst must be the reference for regeneration I would think and not the higher level VIR chroma which may have phase shift wrt the burst?

To eliminate any guesswork, just have color bars on another vert interval line!
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Old 09-25-2016, 11:26 PM
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Another note regarding the mismatch of re-inserted burst to chroma amplitude distorted by network transmission:

The two major US TV makers, Zenith and RCA, had different philosophies in this regard.
Zenith used the burst as automatic color level reference, as this took out the final transmission variations due to ghosts, airplane flutter, etc. However, this ignored the network distortions. RCA's auto color mode worked on the average chroma level of the picture. They felt this was an overall improvement, although it meant the color level could be affected adversely by overcompensating for scenes either with large areas of bright colors or with no saturated colors. The general public seemed to be accepting of these "subject errors." They bothered me, though, and I always preferred to run the RCA sets with auto color off for this reason. Unfortunately, this meant also losing RCA's superior auto hue ("tint") correction, which actually had been invented by a colleague of mine at Motorola and was licensed to RCA. It worked only on hues near flesh tone, and didn't destroy greens and purples the way other makers' auto tint did. Motorola, by the way, never used their own invention.
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Old 09-27-2016, 12:53 PM
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..RCA's superior auto hue ("tint") correction, ...worked only on hues near flesh tones.
How on earth did this work?
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  #12  
Old 09-27-2016, 01:20 PM
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How on earth did this work?
The usual auto tint worked by changing the angles, and possibly the gains, of the color demodulators. The result was a reduction in saturation of greens and magentas, plus colors that were near orange or cyan had any green or magenta component reduced. If you picture a circular color wheel (or a gated-rainbow test pattern), the circle got compressed into an ellipse.
Thus, all colors were distorted to be closer to flesh tone or cyan, or at least a weaker green or purple.

The RCA circuit worked on the phase of the oscillator output going to the demodulators. The nearer the chroma phase was to flesh tone, the more strongly it was pulled towards flesh phase (hue). If it was already a flesh hue, this made no difference. If it was close, it was pulled strongly towards flesh. If it was further away, it was pulled less. So, yellows were made a bit more orange, but greens weren't significantly changed. Similarly, reds were pulled toward orange-red, magentas were pulled a bit towards red, but purples were changed even less if at all. Since this change was phase only, it didn't affect the saturation of greens, purples, or any color, for that matter.
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Old 09-26-2016, 06:25 PM
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It was originally required by the FCC for remote controlled transmitter stations. The studio had a Tektronix 147 inserter which stripped anything that was already on line 19 and insert the vir. The output fed the STL. At the transmitter there was a Tektronix 1440 which looked at the inserted vir and controlled luma, color and phase.
I remember there was a non-remote station that never had anything in the vertical interval. They even stripped the network vits.
We later upgraded the studio to the Tektronix 1910 which had GCR. We got calls from cable companies if the GCR was malfunctioning.
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Old 09-27-2016, 05:58 PM
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That is interesting how it worked.
Instead of all that effort, they should have - like you said - lobbied to mandate VIR for all transmissions as VIR decoder no more complex - and much better - than Auto Color?

That year did Auto Color appear?
What year did networks abandon VIR?
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  #15  
Old 09-28-2016, 08:57 AM
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VIR was required till the end of analog transmission. The ONLY set I ever remember that utilized it was a 19 inch GE that was installed at a station I worked at in '77 in SC.
And I remember seeing a Sylvania that used the GCR in the 90's.
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