RE: Jeri videoboard gfxconv

From: Richard Atkinson (
Date: 2001-05-26 13:00:36

On Fri, 25 May 2001, William Levak wrote:

> > I think here you're referring to the NTSC automatic hue control of some US
> > televisions; this only applies to more modern NTSC sets. PAL sets do not
> > have (or need) such circuits at all.
> I was referring to the color response curve, which is not directly
> proportional to the signal.  The region for flesh tones is stretched out
> and the adjacent color regions are compressed.  This prevents images of
> people looking greenish when the signal is slightly off.

Right. This only happens on modern NTSC sets and on no other TV system's
sets. The reason is that only NTSC has colour signals that can make people
look green.

The alternative would be to have a proper colour space and a "hue" or
"tint" control, but this potentially requires you to adjust the control
every time you change channel. I think the response curve William
describes is a nasty hack to reduce the need for this control, although I
think such sets do still have the control. The one in my apartment in
Austin had an automatic hue (on/off) control; perhaps that switched the
modified response in and out of the signal path.


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