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List:       gimp-print-devel
Subject:    [Gimp-print-devel] Generating a profile - a quick HowTo
From:       "Alastair M. Robinson" <blackfive () fakenhamweb ! co ! uk>
Date:       2009-04-05 10:14:03
Message-ID: 49D8846B.205 () fakenhamweb ! co ! uk
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Hi Robert,

Since you're experimenting with the i1 for the first time, it occurred 
that it might be helpful for you to see some "instantly gratifying" 
results from it!  Jumping straight into GPLin, which is extremely 
experimental and half-baked at present, possibly isn't the best 
introduction to what the instrument can do!  Generating a printer 
profile may be a better introduction - and others may find this useful 
too, so:

What you need:

* ArgyllCMS

* A colorimeter or preferably a spectrophotometer, supported by Argyll.

* An ICC profile describing the typical images you'll be printing with 
this profile.  Usually sRGB, but could be AdobeRGB or even a wide gamut 
profile.  For now, use sRGB.  If you don't have the sRGB profile you can 
find it here: http://littlecms.com/downloads.htm in the "Utility 
Profiles" download.

* A program capable of printing out a 16-bit TIFF RGB image with no 
scaling - PhotoPrint in "Manual Size" layout mode is ideal.

* Some way of applying the profile when printing images.  PhotoPrint is 
probably the easiest option - but you can also do this manually using 
the LCMS tifficc utility or the Argyll cctiff utility.


 From the command line, perform the following steps:

targen -d3 -f462 TestProfile
(A .ti1 file will be generated with 462 patches.  The -d3 means use RGB 
rather than CMYK or one of the other combinations Argyll supports.)

printtarg -ii1 -PLetter -T TestProfile
(A .ti2 file will be generated, along with a 16-bit TIFF, as requested 
by our use of the -T flag.  -t instead gives an 8-bit tiff.  Without 
either flag, the target is generated in PostScript format instead.  The 
-ii1 parameter tells targen to print a target suitable for an i1, as 
opposed to the other supported instruments - each requires its own layout.)

Print out the TIFF, ensuring that (a) any existing colour correction is 
disabled, that Gutenprint's Colour Correction is set to Uncorrected, and 
if using PhotoPrint that the Print Profile is disabled in the Colour 
Management dialog, (b) that you're using the exact same print settings 
you'll use later when using the profile, and (c) that you're printing 
the image with no scaling.

Allow the print to dry.  Note that the colours can drift quite 
significantly in the few hours after printing, so it's best to wait a 
while before the next step.

Read in the printed chart with:
chartread TestProfile

Having read the chart you should now have a .ti3 file.  From that, we 
can build a profile, like so:

colprof -v -cmd -dpp -S/path/to/sourceprofile_probably_srgb -D"My First 
Profile" TestProfile

This takes a few minutes to complete.  The -cmd -dpp parameters mean 
"Monitor in Dim Surround" and "Practical Reflection Print", respectively 
- there are other options that can be used here - which will give best 
results for you will depend on the characteristics of your monitor, your 
room lighting, which source profile you chose, and personal preference!

You should now have a file called TestProfile.icc  Set this as the 
Printer Profile in PhotoPrint's Colour Management dialog and you should 
now be able to print using the profile.

(Please note, 462 patches isn't many for generating a high-quality 
profile - what Argyll achieves with small number of patches is 
remarkable, but you may see errors in the grey axis in particular, 
because Argyll's RGB targets do seem to somewhat under-represent the 
greys.  It's perfectly possible to augment a target using a spreadsheet 
to add extra patches in "weak spots" - but that's beyond the scope of 
this mini-howto.)

Anyhow, hope someones finds this useful! :)

All the best,
--
Alastair M. Robinson

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