[argyllcms] Re: Colorport CGATS to Argyll CTI3 conversion utility

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 10 Feb 2006 16:38:41 +1100

David R. Gangola wrote:

Was there an existing path from ColorPort to Argyll?

No. A couple of people have tried using ColorPort output, but I haven't received enough information (file format documentation, and/or example files) to be able to formulate a conversion utility along the lines of cb2cgats/kodak2cgats/logo2cgats.

One of the printers I've been profiling is a Canon iP8500 using after market inks and paper. The resulting colors are very good, but using the perceptual intent yields images with slightly lower than desired contrast. I've been using an abstract profile with "profile" to tweak the contrast. The abstract profile was created by adjusting 1024 patches in Photoshop with the "Curves" adjustment. The patch values extracted, (yet another utility) and converted to the abstract profile with refine.

Is there another, or easier way to do this?

Not at this time. Argyll isn't currently oriented towards manual color adjustment, most of the effort has gone into producing the "right" result based on the measured numbers. One method that has been used to manipulate the contrast to some degree is to override the viewing conditions parameters, particularly the adaptation luminance levels. e.g. using something like -d0 -da:1000 (substitute various luminance levels between (say) 1 and 5000 cd/m^2. La should be the ambient illuminance in Lux divided by 15.7). The source could also be manipulated with the opposite effect e.g. -c0 -ca:1000 etc. You should really check first if you are choosing appropriate viewing conditions for your situation, before artificially manipulating it this way.

The black ink I'm currently using (Lyson Fotonic) has a blue cast. The paper white reads as slightly blue as well. The default perceptual mapping places the gray axis between the white and black points, resulting in a blue cast to resulting images. I adjusted the gray mapping factor in "profile" to a value (0.4) which yielded a more pleasing result.

Again, is there another, easier way to do this?

The version 0.54 release I'm currently working on will change how the perceptual and saturation neutral axis are mapped, which will probably correct the effect you are seeing. I'm moving away from the assumption that "black point adaptation" exists, and instead preserving the source profiles neutral axis (adapted only for any change in white point.) Some trickiness is needed to do this while fully exploiting the full dynamic range of the destination colorspace, but it does seem to be a more reasonable result.

I hope this is of some help.

Graeme Gill.

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