[argyllcms] Re: Optimizing profiles to match Pantone colours
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 27 Sep 2017 11:29:03 +1000
Tony Mah wrote:
I am trying to proof to an RGB printer and I have already profiled it and
profile is
good for pictures but a few logo solids are off. I want to print from a pdf
file that
will send the Pantone colors to the driver and convert it to CMYK.
Well, if the PDF reader or printer driver is converting Named (Pantone) colors
to
printer device values, then to change this you need some access to the read or
driver mechanism that does this. Sounds like it might be a hard problem though
(i.e. no standard file formats or API's that I know of, and if the
reader/driver was
using Named spot color libraries and ICC profiles properly in the first place,
you wouldn't have a problem - it would just work).
So if you want to take control, then it's perhaps best not to use Named colors
in
your PDF.
I am not exactly sure how
*xicclu works. Will it add that color to the profile?
It lets you convert values though a profile.
Wondering if I am satisfied with
a profile if I can spot correct a few colors inside the profile?* * * *The
other way I
thought about was reprofiling the printer and adding the logo colors at the
end of the
test chart but it is not clear how to do this. I would have to generate a
patch set
with lab values and print a tiff with a lab profile or convert lab colors to
prophoto
rgb and print that. I don’t want to try this unless you say it will work. *
Sounds "iffy".
The way that it is done now that works for sure is to open the pdf in
indesign and
manually key in the values. 1. Print color 2. Measure the color on the pantone
reference swatch with i1 Pro 3. Calculate the CMYK value within the printer
profile 4.
Key in those colors into Adobe indesign and print.
If indesign lets you specify device values (i.e. Non-Color managed values), then
put in the ones that you get from xicclu.
The real life example is that at the front desk in our office we have a sign
that has
people’s names and where they are in the building. It is full of 1 inch x 14
inch
plastic strips. We normally paid a commercial printer to print these strips
but I
offered to print them to save money. The receptionist complained that the
colors don’t
match. So I am trying to fix it.
The only sure-fire method I can describe is to render your PDF to a device
colorspace
raster file using a RIP, GhostScript etc., and then edit the raster file,
substituting
the Absolute Colorimetric converted L*a*b* values you got from xicclu into the
spot color areas, and then print the raster file out without color management
to the
printer.
You could also investigate what facilities GhostScript has for controlling
color conversions. I know that internally it has full color capability, but I'm
not sure what external controls are available (ICC profile settings for source
spaces,
destination spaces), and whether it takes something like an ICC Named color
library to
determine its Named Color conversions. [This hints that it does:
<
https://www.ghostscript.com/doc/9.06/Use.htm#ICC_color_parameters>]
If so, then perhaps it could be setup to RIP the file properly, if you
can supply your Pantone lookups in an ICC named color profile.
Cheers,
Graeme Gill.
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