Could NTSC VIR = PAL

[old_tv_nut]

Originally Posted by NewVista

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.