[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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