[argyllcms] Re: paper profile (RGB)

  • From: Yves Gauvreau <gauvreau-yves@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 15 Feb 2020 07:34:00 -0500


Yes. The end result won't be as smooth though due to multiple cLUT transforms, and
there is a lot more to go wrong when you actually use the profile (i.e source profile
needs to be consistent so that the source gamut is what the profile was setup for,
you need to remember to select perceptual, not use BPC etc.)

Maybe not my best option then. right?

from "Creating a printer profile" scenario:

"Where the resulting profile will be used conventionally (ie. using collink -s, or cctiff or most other "dumb" CMMs) it is important to specify that gamut mapping should be computed for the output (B2A) perceptual and saturation tables. This is done by specifying a device profile as the parameter to the colprof -S flag. When you intend to create a "general use" profile, it can be a good technique to specify the source gamut as the opposite type of profile to that being created, i.e. if a printer profile is being created, specify a display profile (e.g. sRGB) as the source gamut. If a display profile is being created, then specify a printer profile as the source (e.g. Figra, SWOP etc.).  When linking to the profile you have created this way as the output profile, then use perceptual intent if the source is the opposite type, and relative colorimetric if it is the same type."

Here I'm trying to create an output profile for a specific paper (Hahnemuehle Fine Art Pearl or Canson Platine Fiber Rag, both large gamut papers) , (pigment) ink and a RGB printer (PRO-1000) combination and for specific images. Many (mostly flower macro) of my image present a lot of out of gamut colors even for those papers so I always use ProPhoto RGB as working space and to save my original, I can add I always save all these in tif 16 bit as well. I also always use the 16 bit driver for my printer.

When it come time to print those kind of images, since I already know if I use a colorimetric intent I'll crush, clip and or squash a lot of colors I prefer to use the perceptual intent but as Graeme writes "using large gamut colorspaces as the source gamut for gamut mapping is generally a bad idea...". Thus I would think a situation like mine would need the use of the image gamut for "optimal" mapping.

"The correct approach is to use a source gamut that represents the gamut of the images themselves."

Now for a device link profile the doc suggest this:

tiffgamut -f80 -pj -cmt ProPhoto.icm image.tif
collink -v -qh -G image.gam -ip -cmt -dpp ProPhoto.icm RGBDestinationProfile.icm Source2Destination.icm
cctiff Source2Destination.icm image.tif printfile.tif

Here we see the intent used is perceptual, then my question is: "Do we need to build the 'RGBDestinationProfile.icm' profile in a special manner? For example do I use the -S flag and if I so, do I use ProPhoto or something else? Can I use black point compensation? Just to be sure, this is not a typical scenario, I understand that and I would probably never use this destination profile alone, I would name it so I don't forget to use it only to create a device link profile.

In others words to use my destination profile always in this image dependent gamut mapping scenario, do I need to use the S flag and if so what would be the preferred source profile to use? Another way to put this maybe is that this "gamut mapping" stuff when done via collink as above doesn't use the perceptual table in the destination profile so I could use whatever I want and even use the profile in other scenario, is this how it works?

Yves








I understand if this give essentially the same result, one would need to have the data (.ti3) for each paper which make this approach less flexible I would believe, right?

But how is that different to any other situation ?

To make a profile for a specific printer/media/ink/setting, you need to
measure that specific printer/media/ink/setting.

My other question in this same line of thinking (image dependent...), what would be a good choice for the profile given to colprof when you intend to create a device link profile for each image you want to print via this method.

It's not clear which profile you are talking about - the source or the destination
profile ?

In other words, I would create a  profile for the systematic use of the image dependent gamut mapping scenario via device link profile.

I'm not sure what you mean by that.

Cheers,
    Graeme Gill.


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