[argyllcms] Re: Am I stupid or is it something else... my color management sucks.

  • From: Michel Joly de Lotbinière <michel@xxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Wed, 14 Apr 2010 19:06:53 -0400

I use a DTP94  colourimeter, and the only way to achieve neutral dark
grey tones on my notebook's decent but average display is to make a
Single Curve + Matrix profile: the RGB Curves + Matrix always have a
slight reddish cast in the RGB(0,0,0) to RGB(40,40,40) range of grey
tones, whether I use the Windows or LCMS colour management engines.
Using the 1xCurve+Matrix profile means tolerating deltaE errors of
something like 1 to 15 (most colours average around 3 or 4, but most
greys are within +-1 deltaE of neutral): as all I care about is a
tractable calibration curve and a convincing grey neutrality in the
display (which is a huge improvement to the uncorrected display), I
can live with that degree of inaccuracy. Obviously that is completely
unacceptable if you have a good quality display and want accurate

If I could figure out how all the black level offset, correction rate
and percentage adjustments actually work (e.g. does a higher numerical
correction rate imply that dark grey tones are pushed faster towards
the display's *native* colour temperature or towards the assigned
*target* colour temperature? Is anything done via the correction rate
if 0% correction percentage is specified, as is the default for
LCDs?), then I might be able to achieve better accuracy with a
3xCurve+Matrix profile.

The dispcal help text is really confusing here in terms of answering
the question: if the dark greys of a step wedge observed in a
colour-manged application using the final profile (perceptual intent)
produced by colprof are biased on the red/cyan axis when viewed on an
LCD display, but they are neutral in the calibration produced by
dispcal (as judged by observing a neutral step wedge in a non-colour
managed application), what adjustments can I make in dispcal to
attempt to correct that?

Maybe DTP94 (and Spyder3?) readings of dark colours are simply less
accurate than bright colours, and this skews the profile calculations,
even if the calibration LUT curve produces neutral dark greys.

Sorry not to help--but do try the single curve + matrix type of
profile, it may work for you as well, at least as a first

On Wed, Apr 14, 2010 at 4:49 PM, Magnus Berg <magnus@xxxxxxxxxxx> wrote:
> New try with a new Spyder 3, but still not satisfied.
> dispcalGUI run this:
> dispcal -v -d1 -c1 -yl -P0.474187380497,0.455830388693,1.0 -qh -t6500.0
> -b140.0 -gs -f0.0 -a13.8 -k0.0 -A4.0 -B0.5 colprof -v -qh -aX
> I got a perfect greyscale. From black to withe with all tones. But the
> calibration gave a red cast to some tones on the screen. The color #BEBEBE
> for instance. I got that color in my filemanager and then I take a
> screenshot it showed up perfect, as I can se it, in Gimp.
> Then I look at the vitpunkt.tif and svartpunkt.tif (Swedish for whitepoint
> and blackpoint - it shows neutral tones from tone 255 to 244 and tone 0 to
> 22 - download here http://www.profiler.nu/filer/Skarm.zip ) I see red casts
> in some of the tones. This occur both in color managed Gimp and in not color
> managed applications.
> And then I locket at pictures in Gimp and Geeqie they looked the same but in
> Firefox then look like in not color managed applications. I must say that in
> Gimp and Geeqie most of the color has disappeared, the colors looks out
> washed. My pictures have never looked so dull. But I suppose that it can be
> alright, and that it is something wrong with Firefox.
> I read the little discussion here about different profiles. I chosed to do a
> 'XYZ LUT + MATRIX' profile.
> Color management will soon drive me nuts. There are questions like can I
> trust the Spyder 3 and have I set up color management right in Gimp and
> Geegie. In Gimp I have done like this:
> Mode of operation: Color managed display
> RGB profile: None
> CMYK profile: None
> Monitor profile: None
> Try to use the system monitor profile = Yes
> Display rendering intent: Perceptual
> Print simulation profile: None
> Softproof redering intent: Perceptual
> Mark out of gamut colors (grey) = No
> File Open behaviour: Ask what to do
> Is that alright? And that about the Spyder 3, does it seems that it help me,
> or should I send it back and wait until I can afford a spectrometer, after
> that I first have payed my fancy but possibly wrong calibrated and therefore
> useless monitor? ;-)
> Now I will go to bed and cry myself to sleep...
> Magnus

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