As hinted in my comment to @Mark Storer, it turns out that forcing a gray print only on the K plate in CMYK, may not be so trivial ... I guess it depends much on what is being used as "preflight" preview device - for Linux, the only thing I can find is ghostscript with tiffsep, which is what I use for 'sanity check' regarding CMYK separations.
Anyways, I got a lot of help in this thread on comp.lang.postscript:
... and one workflow that works for me is:
- Convert PDF to PS using
ghostscript's ps2write
- Use
ghostscript to convert this PS back to PDF, while executing replacement functions in HackRGB-cmyk-inv.ps
- Use
ghostscript's tiffsep to check actual separations
In respect to, say, this PDF generated by OpenOffice: blah-slide.pdf, the command lines would be:
# PDF to PS using `ps2write` device of `ghostscript`
gs \
-dNOPAUSE \
-dBATCH \
-sDEVICE=ps2write \
-sOutputFile=./blah-slide-gsps2w.ps \
./blah-slide.pdf
# PS to PDF using replacement function in HackRGB-cmyk-inv.ps
gs \
-dNOPAUSE \
-dBATCH \
-sDEVICE=pdfwrite \
-sOutputFile=./blah-slide-hackRGB-cmyk-inv.pdf \
./HackRGB-cmyk-inv.ps \
./blah-slide-gsps2w.ps
# check separations
gs \
-dNOPAUSE \
-dBATCH \
-dSAFER \
-sDEVICE=tiffsep \
-dFirstPage=1 \
-dLastPage=1 \
-sOutputFile=p%02d.tif \
blah-slide-hackRGB-cmyk-inv.pdf \
\
&& eog p01.tif 2>/dev/null
This should only work on RGB values where R=G=B (and hopefully grayscale values), and only on text colors, and it also flattens text information - but it should be possible to confirm via tiffsep that the text indeed ends up only on the K plate.
As mentioned in the newsgroup post, this is not extensively tested, but looks promising so far...
Cheers!
