[argyllcms] Re: Dispcal - Inverting Jacobian failed?
- From: "Alastair M. Robinson" <profiling@xxxxxxxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 22 May 2009 16:42:23 +0100
Hi,
Gerhard Fuernkranz wrote:
There is obviously a "clipping knee" at about 97% RGB (with a flat
region beyond the knee), but even more interesting is the negative
dX/dRGB gradient in the non-clipped region. I'm indeed wondering how
this can happen - maybe by applying a matrix (with nagative entries) to
non-linear or already clipped RGB numbers.
Well, I shall investigate further as and when time allows - as I said
the "brightness" control on this monitor appears to apply some kind of
gamma curve - and that in combination with the RGB controls gives some
interesting hue shifts in places - it's possible the particular
combination of settings I was using for that test were interacting in
"interesting" ways.
Btw, also conspicuous is the excellent repeatability of this instrument
(in the flat region, readings #7...#12) - I don't get such low noise
with my i1 Display on repeated white measurements [RMS delta E 0.021
versus 0.13 - nearly too good to be true...]
Hmmmm, interesting. Could this be due to quantization? Maybe the i1
trades repeatability for finer granularity?
All the best,
--
Alastair M. Robinson
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