[argyllcms] Re: Applying calibration to sRGB profile
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Tue, 28 Jun 2011 12:35:02 +1000
Stephen T wrote:
colprof -v -D"Calibration plus sRGB" -qm -as 500patches
... Profile check complete, peak err = 1.679860, avg err = 0.527110, RMS =
0.580622
Because the default is cLut, and a cLut of the default resolution can't
perfectly represent
the gamma curve with straight section.
Increasing the number of patches or using -qh does not significantly reduce the
errors. Now, I
was expecting a near perfect fit with colprof option -as since the sRGB profile
seems to be a
shaper-matrix profile (which I inspected with iccdump). I don't know why, but
-ax or -aX gives a
near perfect fit:
Profile check complete, peak err = 0.121406, avg err = 0.020250, RMS = 0.026392
A general shaper + matrix model is a better fit to the sRGB gamma curve +
straight section + matrix characteristic than a cLut.
Graeme Gill.
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