[argyllcms] Re: printer profiles - how to get max black

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 07 Dec 2006 17:54:24 +1100

Mike Russell wrote:
It says Digital Swatchbook on the top. I'd be glad to try out the software.

Hopefully I'll have it finished by the next release.

One remaining problem - the profiles I create are satisfactory, but
> for one of my printers the PCS value for black, Lab(0,0,0), yields an
> RGB value of RGB(13,8,2).  This is very close to black, but measures
> as a slightly lower density than a max black.  The profile is probably
> attempting to compensate for the rather cool black of this printer by
> adding red-orange.  Is there a way that I can specify that black should
> map to RGB(0,0,0)?

Looking at the gamut shape, my general reaction is that it's not
the best separation I've seen from an Epson (is it an older model ?
Are there any firmware updates for those things ?).

It's not shaped much like a printer gamut, which means that you're
not getting everything the colorants are capable of giving, and the
black separation has the distinctive "cone" shape that hints at
a poor black generation algorithm. Not much you can do about all
that though.

The black point is rather far from neutral, which perhaps hints
why there are issues.

The explanation is that for out of gamut colors the closest color
is measured in appearance space (CIECAM02 Jab space), and it's view
of the closest point is a little different to L*a*b* space
(that's the point of using it, so that things like blue don't
go purple), and from a CAM02 perspective, the black point
returned is very slightly closer to the target L*a*b* = 0,0,0
than RGB = 0,0,0.

You can fudge this particular case by altering the viewing conditions
slightly, ie. add -cf:4 (after any -c flag used), and it should
improve things a little.

Graeme Gill.

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