Hi Robert, thanks for your comments.

> This really sounds like you're using black as a spot color rather than
> going generic editing in CMYK space.

That was just an example. Another example could be just putting an image
in front of a gray gradient background.
In my experience, it's not that easy to find a printer that can convert
a RGB gray into a perfectly CMYK neutral grey.
Or isolating a photograph, putting it on a solid color layer and apply a
drop shadow of the isolated image on the color.
Why should I send an RGB file and see how my printer's RIP separates the
grays and the shadows when I could be specifying: I just want 100% black
over the color?
They are only real world examples. Probably there are excellent print
shops in Germany or USA that deliver excellent results from an RGB jpeg,
but that's not always the case.

> I question whether doing this in an image editing application is
> really the right thing to do.  If you're doing black text, you
> probably want the text to be vector rather than raster anyway --
> printing an image scaled to 240 DPI is fine, but the text won't look
> so good at that resolution.  In that case, you're better off using
> something like Scribus to do that kind of overlay, at least until GIMP
> has vector layers.

Again, that was just an example. It may be true in a brochure or a
magazine page, but what if you need to add a texture to a title,
breaking the borders of the characters with a "grunge" brush? or
something like that?

But let me show you a very simple example:
This image was created in Inkscape and exported as PNG. Then in Gimp the
yellow part got some texture and color work.

What if I want to put that image in a page of a magazine that I'm
creating in Scribus, and I want the black part of the image to be the
same black (100% black) than the text.
In that case I would have, according to your workflow, to:
-take the image to gimp, make the texture part, remove the black part,
save it, import in scribus the color blob and a black-only SVG version
of the drawing, make them match in size and alignment (ouch, I should
have imagined that I would need some bleed on the color shape to avoid
alignment errors), and export them as a CMYK PDF to send to the print

Or simply separate in GIMP to CMYK, remove the black part of the CMY
channels and tweak the black channel, save as TIFF and import in

Call me crazy but I choose the last one.

Of course there are alternative ways, but sometimes it's faster and more
direct, thus preferable, to do it with the image manipulation program
that using three or four separated applications for a simple task.

> Which again is a spot color kind of use case rather than a CMYK use
> case.

Yes, but we don't have spot channels either. At least having CMYK would
work as a viable temporal solution until we have spot channels.
I find it hard to imagine that GIMP will support spot channels if it
won't support CMYK channels. It wouldn't make much sense to add a spot
channel to an RGB image, would it?

> Does that indicate that separate+ is what needs to be enhanced, rather
> than the core application?

This discussion was about a PDF export plugin at the beginning.
I was trying to make evident that a PDF export plugin is probably
useless without CMYK/SPOT/VECTOR LAYERS, and improving and integrating
the Separate+ Plugin instead of focusing on a PDF exporter would make
sense and a big difference. 


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