[argyllcms] Re: Perceptual intent in Display profiles?

  • From: Michel Joly de Lotbinière <michel@xxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Mon, 23 Nov 2009 02:06:51 -0500

Graeme, Roger,

Thanks for the advice and hints. Sorry for the delay in replying, I
really appreciate the response.

My earlier mistake was to even bother with the smaller targets and
medium quality option in the various programs. The medium quality
matrix/shaper profiles were just not very good, so I switched to LUT,
but with too small a target chart. This wasn't a good basis for
comparisons. The improved grayscale linearity, absence of
colour-casts, and separation in shadows/hightlights of these larger
ArgyllCMS lut profiles is really good now in colour managed

Yesterday I went through another calibration/profiling exercise and
used dispcalGUI (and Argyll 1.0.4 )to calibrate to the sRGB curve and
profile the LCD panel using the 512 patch "large" chart provided with
dispcalGUI, and finally specifying a plain LUT profile, another using
gamut-mapping options, with the sRGB profile included in the Argyll
1.1 RC1 archive as the source space (most of the photos I look are
already in the sRGB space), and finally with AdobeRGB as the gamut
source space: so colprof -S whatever.icc -cmt -dmt were the options

My simple idea was that a real perceptual conversion from working
space to monitor space would be an advantage in editing pictures,
since distinct colours outside the LCD gamut would be mapped
perceptually to distinct in-gamut LCD colors as far as possible,
instead of simply all mapped to the nearest colourimetric in-gamut
colour, thus losing gradations.

Using these various monitor profiles with a photo that had some pretty
intense out-of-sRGB-gamut colours, I've realized the whole idea is not
adapted to editing tasks: in effect, the gamut mapping means a visual
desaturation of the intense colours to show their gradations in the
working space data--the dull appearance of the AdobeRGB-->monitor
gamut mapping is really an artifact of the over-all dynamic range
compression that Graeme mentioned. The sRGB-->monitor profile had less
of an effect, but then what's the point? So this perceptual mapping in
a monitor profile is not very useful for accurate editing of what the
photos actually contain.

It's probably better to deal with any visible issues of out-of-gamut
colours in the conventional way, adjusting their luminosity &
saturation to suit the destination (using proofing, etc.).

Anyway, the upshot of all the weekend pixel-peeping and reading about
colour management is that is that I understand a little more of what's
going on, know what to expect--cf. Roger's remarks, and I'm going to
keep things simple from now on!


2009/11/19 Roger <graxx@xxxxxxxxxxxx>:
> Michel,
> Je pense que tu attends trop du profil, une fois la calibration appliquée,
> dans les ombres. Considères ton choix de gamma et le gamma "natif" de
> l'écran. Considère aussi que, pour obtenir le noir que tu demandes, il est
> possible que la calibration doive assombrir les ombres au-delà de ce que tu
> crois acceptable. Peut-être qu'en réalité ton écran montre trop de
> différentiation dans les ombres alors qu'il n'y en a pas vraiment.
> Bitte excuse my french / Roger

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