[argyllcms] Re: Perceptual intent

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 20 Dec 2014 12:18:48 +1100

robert@xxxxxxxxxxxxxxxxxx wrote:


> So the problem seems to be with my profile.  This is how I made it:
> colprof -v -A"Canon" -M"iPF6400" -D iPF6400-Canson-Baryta-310-Argyll-2584
> -qh -cmd -dpe -SBetaRGB.icc -O iPF6400-Canson-Baryta-310-Argyll-2584.icc
> iPF6400-Canson-Baryta-310-Argyll-2584

Right, it helps to have the details. You are applying a viewing environment
transform. This will affect the luminance scale reproduction. You are selecting
a destination viewing environment of Print evaluation environment, which is
quite bright. The source viewing environment you have selected is for a dark
environment, so the assumption is that the image looks right on the display
with a high gamma, or a darkened appearance. So the overall adaptation from
vey dark to a quite bright environment will involve significantly reducing
the gamma, or brightening of the image, raising the shadows.

[ The basic reason for this is that we tend to judge what is light and dark
  relative to the overall light level adaptation of our vision. So if we are
  adapted to bright, then a middle grey has to be lighter to look middle. If
  we are adapted to dark, then middle grey has to be darker to look middle. ]

To address this, try leaving out the -c and -d options for a start,
and evaluate this. More typical parameters would be -cmt and -dpp,
but if your display is a modern, very bright LCD display (ie. 300-400 cd/m^2),
this may not be right either, and -cmb -dpp may be more appropriate.

> So we're down to the viewing conditions, removing them:
> colprof -v -A"Canon" -M"iPF6400" -D iPF6400-Canson-Baryta-310-Argyll-2584
> -qm -SBetaRGB.icc -O iPF6400-Canson-Baryta-310-Argyll-2584.icc
> iPF6400-Canson-Baryta-310-Argyll-2584
> Gives this:
> 0.000000 0.000000 0.000000 [Lab] -> Lut -> 0.000000 0.000000 0.000000 [RGB]
> 5.000000 0.000000 0.000000 [Lab] -> Lut -> 0.042265 0.030243 0.034264 [RGB]
> 10.000000 0.000000 0.000000 [Lab] -> Lut -> 0.094410 0.081977 0.083767 [RGB]
> 15.000000 0.000000 0.000000 [Lab] -> Lut -> 0.148553 0.139288 0.138267 [RGB]
> 20.000000 0.000000 0.000000 [Lab] -> Lut -> 0.201001 0.194568 0.192339 [RGB]
> 25.000000 0.000000 0.000000 [Lab] -> Lut -> 0.252223 0.248458 0.245409 [RGB]
> So there you have it.  Either I should not have been using the -d/-c
> parameters, or I was using them incorrectly, or they aren't working as they
> should.

Right. See above.

> Which would indicate to me that -cmd (monitor darkened environment) and -dpe
> (Print evaluation environment (CIE 116-1995), whatever that is) are not
> unreasonable choices for someone who doesn't know the front end from the
> back end of color management.

I would draw a different lesson - one you will find that I tend to
preach a lot - if you're not sure why or what the parameter is for,
leave it out. The tute shows -cmt and -dpp, which should have a much less
pronounced effect than the ones you have chosen.

> Any chance of an ArgyllWiki for people like
> me??

It's not clear to me how it would add value, above the existing documentation.

If the existing documentation has mistakes or is lacking, I think it's
going to be far better to fix it or improve it, rather than wonder
if something, somewhere in a Wiki that's not kept up to date with
software releases, could help.

Graeme Gill.

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