On Tuesday, May 5, 2015 at 3:53:28 PM UTC-7, John-Del wrote:
On Tuesday, May 5, 2015 at 5:39:42 PM UTC-4, wrote:
VIR had a preset amplitude and phase (hue) subcarrier riding on a defined amplitude pedestal

It was a bit more than that. It wasn't a preset value; the broadcaster would set the saturation and phase, even changing it to compensate for different film systems or video tape variances from program to program.


....riding on a defined amplitude pedestal to set brightness, contrast hue and saturation and nothing more.

My recollection is that it did not adjust brightness or picture (contrast)

Keep in mind that this does NOTHING about bias and gain on the display (back then CRT) device. How your TV was aligned was up to you and your repair tech.

That's true, but grey scale and black level were amazingly close from sample to sample. I would say that the grey scale adjustment of the average GE from that era was quite close to perfect. The Japanese TVs of that era were shipped above 9000 k.



From Wikipedia. I know this is correct because I used to maintain this equipment at the CBS affiliate in Madison WI, WISC TV 3.

VIR (or Vertical interval reference), widely adopted in the 1980s, attempts to correct some of the color problems with NTSC video by adding studio-inserted reference data for luminance and chrominance levels on line 19.[25] Suitably equipped television sets could then employ these data in order to adjust the display to a closer match of the original studio image. The actual VIR signal contains three sections, the first having 70 percent luminance and the same chrominance as the color burst signal, and the other two having 50 percent and 7.5 percent luminance respectively.[26]

The signal was NOT altered by the local broadcaster. It was intended to correct black level, gain, phase (hue) and saturation errors that may occur during transmission. In Channel 3s case, a Tektronix 1440 (?) video corrector processed the incoming CBS network feed to maintain those parameters. At the time network came via terrestrial microwave and was extremely consistent even without the corrector.

IF your TV referenced VIR, all it did was those 4 parameters. Any bias (black level) and gain adjustments AFTER the VIR processing may or may not be calibrated correctly. What it DID ensure was that it would be consistent. That's all.

G²