Thanks, Graeme. Wow...there is a lot of information that comes up from a search for "Color Appearance Models" by Mark Fairchild! I'm looking for the "lite version" for the lay person and will look around to see what I can find. Even if I don't understand it all, especially the math, hopefully I will gain a better understanding of how it all works (according to the model, anyway). Regards, Lou

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Message: 4 Date: Tue, 20 Aug 2013 00:38:16 +1000 From: Graeme Gill <graeme2@argyllcms.com> To: ColorSync <colorsync-users@lists.apple.com> Subject: Re: WB, Gray Cards and Cloudy Days Message-ID: <52122DD8.80408@argyllcms.com> Content-Type: text/plain; charset=ISO-8859-1

Louis Dina wrote:

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I'd like feedback on this topic, especially if there are any hard color science and studies to back it up. I'm also interested in general opinions and observations, even if not backed up by science.

Hi, there is an awful lot of literature about chromatic adaptation out there, if you go looking for it. One summary close to hand for me was "Color Appearance Models" by Mark Fairchild.

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If I use a spectrally neutral gray card on a heavily overcast day, and use it to set WB in my Raw Converter, I usually find that my images end up being much warmer than the scene I perceived.

This may not be too hard to explain. Chromatic adaptation to a display screen is typically close to complete, since often there are many white or grey samples in your field of view. In general though, chromatic adaptation may not be complete, and is the product of many visual and cognitive mechanisms. If the prevailing color of a heavily overcast day is towards blue, and especially if it is off the blackbody or daylight illuminant locus (I'm not sure if that can be the case - it would be interesting to measure it), then perhaps you don't fully chromatically adapt to that color, so the overall appearance is cold - ie. your visual white point reference is in a slightly warm direction from the scene illuminant. If you normalise (ie. "chromatically adapt") your photo fully to the illuminant color, then naturally it will look warmer than your partially chromatically adapted visual impression of the real scene.

Graeme Gill.