Re: Black Generation
Re: Black Generation
- Subject: Re: Black Generation
- From: Darrin Southern <email@hidden>
- Date: Tue, 13 Feb 2001 11:51:50 +1100
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> The problem is the black, which seems to print a very large dot for the
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> lighter shades. This becomes an issue when lighter colors are needed to be
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> proofed, and this output I have mentioned before on the digest as the 'dodgy
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> black stiple'.
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> ...and this only seemed to reduce the Black Generation, not
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> remove it.
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> Should I be ... profiling in RGB ?
>
>
An inkjet has a larger elementary spot size than a press. Offset
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printing is a contact sport, inkjet printing isn't. The jet of ink
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travels a short distance and the spot is oversized to allow for error
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in the placement. This is why the black spots are more visible in
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inkjet prints.
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When you do a proof, you do a CMYK-to-CMYK conversion via three
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channel CIELab. This means that the original offset or newsprint
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black is lost. It also means you get a black generation which is
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optimized for your inkjet.
I have never really read a clear definition of the color space process for
printing 'proofing' from a layout program like Quark Xpress, to the BEST
rip, and then to the Epson inkjet Range of printers, particularly at what
stage (LW Driver, BEST rip or Epson printer) the light magenta and light
cyan.
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The relation between gamut volume, total area coverage and black
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generation is roughly speaking like so: The goal is to get the pure
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colors because they define the gamut volume which means keeping the
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total area coverage up. Then substitute K for CMY in the shadows to
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avoid soaking.
There needs to be a clear definition of 'pure colors' as the final result
requested from the BEST rip and the Epson printer is to 'simulate' the
requested output - ie the analog proof or printing press.
The process of setting up the BEST rip is to BaseLine (set the ink densities
for each of the CYMK seperately) then set the total ink limit (based on a
visual check of a test file). Then to profile, which my thoughts have been
to set maximum total ink and maximum black ink, as the RIP has already
defined the printer's ink limitation.
BTW The Mach1 Rip leaves all the density and total inks to the profile.
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If you're using PrintOpen 4 for PC, there are presets for inkjet proofers.
This really gets interesting when the PC version of PrintOpen forces the
user to read the calibration strip before talking to the DTP41, when Xrite
states on their website that this feature does not work.
http://www.xrite.com/helpdesk/3PDetail.asp?id=21&VendorNr=466
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> I hope that this is not the only benefit of PrintOpen 4.0 (Black Generation
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> is a feature of the upgrade mentioned at their website),
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>
PO4 just has other black generation algorithms than PO3. You can use
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heavier GCR now, but you don't want to do that for profiling inkjets
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as GCR replaces CMY with K in skintones, for instance.
This is the 'dodgy black stiple' issue, when the GCR takes place, and the
Black is also introduced to pastel colors, as well as skin tones.
Darrin.