Did RCA use WB IQ after the CTC2/Bs.

[old_tv_nut]

Originally Posted by amptramp

For what it's worth, Hoffman had a wideband system which used R-Y and B-Y detectors but after a chrominance channel where the high bandwidth chroma signal was delayed while the narrowband was not. This is a bizarre method and was used briefly (around 1955, I think), but I would prefer I, Q demod. The NTSC spent a lot of effort to determine the resolution and criticality of the eye for various colours and I think I, Q demod would be as good as HDTV because the eye does not see large bandwidth in blue or yellow.

It is usually stated that the I axis was chosen to match the axis of maximum color resolution of the eye. But if that is true, the eye can't see if the small details are somewhat off in hue, so the axes chosen by NTSC actually could have been R-Y (wideband) and B-Y (narrowband). Actually, it is probable that using B-Y as the narrow axis would be better in terms of color detail than using Q, that is choosing the axes so the narrowband one falls on the lowest color resolution axis and not worrying if the high res one is slightly off. However, there are other more important reasons to use I and Q. One is that I is very close to flesh tones, so if there is a transient effect on the edge of a face, it doesn't look the wrong hue. This is probably the most important practical result of using the I axis in particular. Another is that the roll-off in color resolution is not abrupt, and you can't force people to sit far enough away to guarantee they won't see edge effects. A further reason is that pictures made of I axis colors often look plausible, while pictures made of only Q axis colors often do not. Most of the automatic tint circuits developed later were based on this. Another reason is that much of the test material was color slides scanned by unmatrixed cameras, both facts which tended to suppress greens, so the test material was notably lacking in strong Q axis colors. So, if you picked the axes to provide the best overall results with a random selection of color transitions, you might have ended up with something different; but the choice of I and Q actually catered to the statistics of the color palette of common source materials and important image elements (faces), which meant it was well suited for general use.

Summary: the choice of I and Q was optimum, but not purely for the reason of resolution that is usually stated.