[argyllcms] Re: Absolute colorimetric - dark saturated colours excessively light
- From: Gerhard Fuernkranz <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sat, 04 Feb 2006 19:24:07 +0100
Graeme Gill wrote:
Some folks currently think that things are overly light, and under
saturated (e.g. blues and greens).
Graeme,
actually this is my subjective impression as well - strongly saturated
out-of-gamut colors are IMO rendered by Argyll's gamut clipping
subjectively too ligh and not saturated enough, particularly in
comparison to profiles from other profilers which seem to render them
darker (resulting in a higher apparent saturation).
Notice that Saturation is not the same as Chroma. According to "Color
Appearance Models, 2nd Edition" by Mark Fairchild, Saturation is the
"Colorfulness of an area judged in proportion to its Brightness". As a
rule of thumb, Fairchild specifies Saturation=Colorfulness/Brightness
(chapter 4.8). The various color appearance models eventually use more
specific formulas, but most of them do define a Saturation correlate in
addition to Chroma (in CIELAB space, no Saturation correlate is
officially defined, but only Lightness, Chroma and Hue).
This implies, that Saturation can be increased by increasing Chroma (at
constant Lightness), but also by decreasing Lightness (at constant
Chroma). So I could imagine that the CUSP point of a gamut hull (in JCh
space) for a given Hue angle (i.e. the point with the largest
reproducable Chroma at the given hue angle) is not necessarily the most
_saturated_ color which can be reproduced at this hue angle (but I have
never verified this for real printer gamuts).
Regards,
Gerhard
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