Good day, Nikolay!
Thank you for your quick response! I'll check it, but I see that using typical
Canson or Inkpress profiles as pre-conditioning produces few light patches.
I've made one-step profiling with 840 patches without -V and -p keys and
pre-conditioning, but this had the same result with significant red cast for
D65. I've also made profile for better printer and canvas and it was generally
good, but with slight red cast too. Perceptual intent enhaces blacks with some
tint but doesn't enhace lights. Does Argyll have ability to embed blacks
compensation in a printer profile? Some people also note red tint of
Argyll-made profiles, what is the cause here?
With regards,
Aleksei
Четверг, 21 февраля 2019, 13:20 +05:00 от Nikolay Pokhilchenko
<dmarc-noreply@xxxxxxxxxxxxx>:
Hi, Алексей. Forget about RGB linearization for printers. It is useless.
When you're linearizing true CMYK output device in CMYK mode, it have a sence.
Using the linearization you can keep printing process precision without of
re-profiling. But when there is RGB-driven CMYK device, the conversion between
RGB to CMYK is hided from you. And when there is a need to re-calibrate, this
hided conversion doesn't allow you to calibrate device channels behavior. You
had to perform full re-profiling anyway. That is why nobody uses RGB
linearization for an output device.
To deal with highly non-linear RGB devices, where you had, for example, a lack
of dark patches, use preconditioning profile. Make first, "bad" profile by
standard ArgyllCMS workflow. You may use targen -V option at this stage, a
demphasis to dark region, at the target generation stage. Do not use standard
targets like IT8 in your quite extreme case. This is useless, at least at
printer profiling stage.
Having preliminary profile, perform main profiling. Use targen with -c
"Pre-profile.name" parameter. Targen will generate target with most
appropriate patches densities across the volume. And your problem with a lack
of patches at the dark regions will gone. You need not to use -V targen option
when you have preliminary profile. For future profiling use last valid profile
as pre-conditioning for targen.
Mention must be noted: If your printer black point has significant color cast,
the resulting profile produced by default colprof and collink utilities will
be bad. You will got color cast in darks because of output adaptation to
actually bad black point in perceptual and saturation (and similar) gamut
mapping modes. You need to disable black point adaptation or use the intents
which doesn't perform it. I had to disable black point adaptation in sources
and re-compile the ArgullCMS to get best profiles for such a bad cases.
HTH. Good luck!
четверг, 21 февраля 2019г., 10:02 +03:00 от Алексей Коробов
dmarc-noreply@xxxxxxxxxxxxx :
Dear Argyll team,
I use last version of Argyll together with LittleArgyll tool and manually
inserted arguments under Windows 10 64-bit Home. And I find that Argyll makes
RGB targets for Windows printer inproperly, especially for calibration.
Manual pages describe that RGB is transformed to CMY here, i.e. without K.
Right, I get graded CMY target for calibration. But if I add K patches, this
doesn't influence on calibration curves as the algorythm doesn't use K
channel here. The result is uneven K ramp on final IT8 print: dark areas are
totally black, white is grey enough. Of course, this happens with third-party
inks on cheap enough photo paper, but I get out more of this paper after
manual settings tuning. It's an obvious thing that for RGB printer colors
should be converted to full CMYK using some law, maybe using some
pre-conditioning profile like FOGRA ones. And then make upside down step for
drawing calibration curves. But now I find that Argyll doesn't have right
tool to make it properly, so I ask you to do it. I also note that target
generation for RGB printer is always uneven, it lacks of many dark patches by
default and it is difficult to correct the spread with arguments.
With regards,
Aleksei Korobov,
Yekaterinburg, Russia
