[argyllcms] Re: Dispcal - Inverting Jacobian failed?

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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