[argyllcms] Re: RGB Printer profiling and ColorSavvy CM2C
- From: "Alastair M. Robinson" <blackfive@xxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Mon, 01 Aug 2005 00:20:05 +0100
Hi Graeme - thanks for the response :)
Graeme Gill wrote:
The randomization is there for a number of reasons, including
averaging out device non-uniformity, recognizing strips, and making
sure there is enough contrast between patches in a strip for
the instrument to recognize the patch boundaries. It can be
turned of by using the -r flag to printtarg.
OK - that makes sense...
It's not really set up to do that kind of thing easily, since I was
aiming at strip or XY instruments rather than one patch at a time
type instruments. Don Bone had a interesting approach to that kind
of thing, generating new test patches based on previously read
patches, but it's not something I've pursued.
Sounds interesting. For now, however, I don't want to do multi-pass
work if I can help it - though it might be an interesting thing to
explore in future. What I intended was to get Argyll to generate a
basic patch set and then augment it manually before printing a single
target.
I think the areas where colour inaccuracy is most objectionable - at
least for photo printing - are grey-balance, skin tones and skies, so it
makes sense to me to concentrate profiling effort on those areas...
It could be anything really. Check your source profile (is it really
accurate for the material you are printing ?), intent (are you
creating a gamut mapped perceptual intent table and using it ?) and
viewing conditions (are they appropriate ?).
Source profile is sRGB. I used the LCMS monitor profiling tool to do a
rough calibration on my monitors (semi-decent 17" TFT and very nice
Iiyama VMPro 410 CRT), but since display profiles aren't easily used
under Linux ATM, I set the screen with the grey-patch / stipple matching
trick to the sRGB standard sRGB gamma of 2.2, then adjusted the monitor
itself to match - so I'm fairly confident that the source data is
reasonably well characterised.
For producing the profile itself I used the instructions on your typical
usage scenarios page almost to the letter (apart of course from the
number of patches!)
As a source profile for the gamut calculations I used USWebCoatedSWOP.
For a profile that's primarily intended for printing RGB photos to an
RGB printer is this a good choice, or would an RGB space with a wider
gamut be better?
Viewing conditions... well I certainly don't have access to a D50
viewing booth! I've viewed the print under bright (but admittedly
fluorescent) room lighting, and daylight. The print looks rather good -
both hue and saturation are excellent overall - it's just a bit darker
than it should be. Like I said, Colour Confidence Print Profiler's
profile exhibits the same behaviour, but Profile Prism's doesn't - at
least not to the same extent. I'm going to do another Argyll profile
with different print settings, and when I've done that, I'll stick a
testcard in my webspace, transformed with all three profiles, and post
the URLs here...
BTW - how do the problems caused by fluorescent whitening agents
generally manifest themselves?
All the best,
--
Alastair M. Robinson
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