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2006.12.05 15:52 "Grayscale, or is it?", by Joris Van Damme
2006.12.05 17:18 "Re: Grayscale, or is it?", by Bob Friesenhahn
2006.12.05 17:34 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.05 17:45 "Re: Grayscale, or is it?", by Bob Friesenhahn
2006.12.05 18:44 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.05 22:10 "Re: Grayscale, or is it?", by Frank Warmerdam
2006.12.05 20:37 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.05 21:16 "Re: Grayscale, or is it?", by Edward Lam
2006.12.05 21:30 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.05 22:28 "Re: Grayscale, or is it?", by Edward Lam
2006.12.05 22:41 "Re: Grayscale, or is it?", by Jean-yves Le Ridant
2006.12.05 23:13 "Re: Grayscale, or is it?", by Bob Friesenhahn
2006.12.05 23:29 "Re: Grayscale, or is it?", by Phillip Crews
2006.12.06 02:05 "Re: Grayscale, or is it?", by Graeme Gill
2006.12.05 22:56 "Re: Grayscale, or is it?", by Glenn Widener
2006.12.05 23:26 "Re: Grayscale, or is it?", by Toby Thain
2006.12.06 01:58 "Re: Grayscale, or is it?", by Graeme Gill
2006.12.06 04:45 "Re: Grayscale, or is it?", by Edward Lam
2006.12.06 20:56 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.06 22:19 "Re: Grayscale, or is it?", by Graeme Gill
2006.12.06 23:30 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.07 01:28 "Re: Grayscale, or is it?", by Graeme Gill
2006.12.07 07:45 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.06 20:56 "Re: Grayscale, or is it?", by Joris Van Damme
2006.12.06 21:57 "Re: Grayscale, or is it?", by Graeme Gill

2006.12.06 22:19 "Re: Grayscale, or is it?", by Graeme Gill

Joris wrote:
>
> If you colour model goes as far as to be based on actual physical
> properties of light, it's extremely complicated to convert RGB to
> "greyscale". You'll have to dig into spectra and whatnot, for all I
> know.

I can't agree with you on this. Taking the weighted sum
of an RGB output in linear light is not an approximation,
it's actually correct, equivalent to CIE Y value if the
right weightings are used. The weightings simply depend
on the primary locations and the white point.

This is because any additive space is a 3x3 transform from
CIE XYZ space, so it only takes one row of the inverse
matrix to compute Y again.

See <http://www.brucelindbloom.com/index.html?Eqn_RGB_XYZ_Matrix.html>

Graeme Gill.