[argyllcms] Re: colprof
- From: Gerhard Fuernkranz <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 3 Feb 2020 00:03:11 +0100
Am 02.02.20 um 23:22 schrieb graxx@xxxxxxxxxxxx:
Gerard,
The outFile300 -> XYZ Lux + Matrix profile ‘stats’ are as follows :
> peak err = 0.888202, avg err = 0.244000, RMS = 0.285845
This is way better than the ‘-as’ Matrix+shaper profile stats:
> peak err = 2.220396, avg err = 0.642870, RMS = 0.747308
CLUT models can adapt even more "flexiby" to the data than matrix/shaper
profiles, having a typical number of 50...200 effective parameters, depending on the
chosen amount of smoothing (just a rough number from my experience). So 300 points may
still be too low in order to achive a significant overdetermination.
One comment…
A quick look at the TRC tags reveals an important difference in the -ag
compared to the -as encoding.
The -ag encoding starts at 0 where the -as encoding does not. That’s an
important difference.
A power function y=x^gamma always passes through the point (0,0). The display's black
level may not be zero, though. A potential idea to might be to fit a gamma+offset model,
and record the resulting TRC as 1D LUT (but I think this would need to be implemented
first, and I can't say in advance whether it would provide the expected value). Generally
it is always a good idea to use the "stiffest" model (with the fewest number of
parameters) which can describe the (noise-free) device characteristics accurately enough.
Regards,
Gerhard
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