question about early color tv

[old_tv_nut]

Originally Posted by Robert Grant

Years ago I was adjusting the color balance on a modern CRT computer monitor.

I had made a wallpaper in MS Paint of a color bar test pattern mimicking the NTSC pattern.

I found that when I turned the green and blue channels to zero, that the red no longer looked red, rather an orange with a sepia cast.

Since then, I've wondered if CRT color TV sets abt computer monitors was delivered with a very blue color balance (9300K versus about 5500K of daylight illumination) because the "orange-sepia" yttrium red phosphor looks red against such a bluish image (comments most welcome).

Some of that is true. However, the "9300K + 27MPCD" is just a sneaky way of saying the picture doesn't have enough red drive to make D65 (6500K, the standard for TV white point [or the original illuminant "C," which was slightly magenta compared to D65]). Besides the increase in R-Y gain to make up for the sulfide yellowish green, running at 9300 made flesh tones look unacceptably cyan unless the color gain was turned up even more. The original reason for this was to keep the beam current ratios somewhat reasonable to prevent red blooming on the highlights; however, it was a disaster for color rendering and for the stability of color with transmission variations. Zenith at one time (after rare-earth reds came into use) used a different white point, between 9300 and D65, which still gave some additional contrast between white and red and reasonable current ratios, but improved the apparent stability of color rendition. Best color, of course, is with white point set to D65 so it matches studio use, but then the current ratios may actually require more current in green than red, depending on the phosphor efficiencies in a particular tube model.

Unequal currents are always a problem due to possible blooming of the spot size of the most heavily driven gun on highlights, putting a color halo around small bright details. Before rare-earth reds, the 9300K was a compromise to get acceptable beam ratios. After rare earth reds appeared, 9300 was still used in some sets apparently because people were used to it, even though it wasn't necessary. Mitsubishi used a very cyan white point in their rear projos for a long time, and I personally think whoever made that decision should have been fired and replaced with someone who had a clue.