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List:       graphicsmagick-help
Subject:    Re: [GM-help] cmyk+spot psd reader might display the spots inverted
From:       James Cloos <cloos () jhcloos ! com>
Date:       2012-05-26 20:00:56
Message-ID: m3ipfipv8v.fsf () carbon ! jhcloos ! org
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>>>>> "BF" == Bob Friesenhahn <bfriesen@simple.dallas.tx.us> writes:

BF> This does not seem like a direct download link.  Is it part of one of 
BF> the download package options?

The zip file on that page has the test pdfs.  Ghostscript has the suite
in its svn; you can grab the individual spot color pdfs from:

http://svn.ghostscript.com/ghostscript/tests/Ghent_V3.0/080_DeviceN-Support_6c_x3.pdf
http://svn.ghostscript.com/ghostscript/tests/Ghent_V3.0/081_DeviceN-Support_5c_x3.pdf
http://svn.ghostscript.com/ghostscript/tests/Ghent_V3.0/082_DeviceN-Support_4c_x3.pdf

Conversion to cmyk psd can then be done with:

 gs -sDEVICE=psdcmyk -dBATCH -dNOPAUSE -r300 -sOutputFile=081.psd 081_DeviceN-Support_5c_x3.pdf

and the like.

It is the resulting psd that is of interest here, and how gm display
renders them.

Unlike imagemagick, gm knows to reverse the polarity of the cmyk samples
in the psd file (full ink is 0x00, no ink is 0xFF, for an 8-bit cmyk psd).

But although it gets that right for the CMYK planes, when it uses the
spot color's CMYK fallback data to add the spot color planes it either
reverses twice or not at all, and shows the 'GWG Green' spot as magenta.

I discovered this while testing my changes to gs to support 16 bit/color
psd file generation.  gm and im were the only software I had to test the
resulting cmyk psd files.

Thanks for that.  And for getting the four color cmyk correct!

-JimC
-- 
James Cloos <cloos@jhcloos.com>         OpenPGP: 1024D/ED7DAEA6

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