[cairo] Spot colors (and CMYK)

[ecir hana]

On Sat, Feb 20, 2010 at 9:17 PM, Chris Murphy <lists at colorremedies.com> wrote:
>
> On Feb 20, 2010, at 4:19 AM, ecir hana wrote:
>
> Both RGB and CMYK and spot values are meaningless without being tagged. You may specify CMYK values directly, rather than needing a CMS to produce them, however those CMYK values should be tagged with a profile so that their color meaning is usable downstream: for display, for proofing, and for preflight purposes to confirm the proper printing conditions are applied.

Ok, lets see what would happen with tagged and untagged workflows:

Tagged - I have CMYK SWOP 0, 0, 0, 100. If I print on coated paper in
US, no big deal. If I print in Europe on uncoated paper, they just
convert from SWOP to FOGRA (?). Now, how does my CMYK look like?
Definitely not 0, 0, 0, 100 - there would be no zeros anymore and no
100, i.e. no solid, just 4 rasters - *this* is something I don't want.
But then you say, that's because you didn't use device link - sure
thing, but where can I get it?

Untagged - 0, 0, 0, 100. I print in US - 0, 0, 0, 100. I print in
Europe - 0, 0, 0, 100.

What's so difficult to understand about this?

> Metadata describing "black text" rather than "this generic object is C0M0Y0K100" is superior. Because how black text should be handled is different depending on the output process. For a printing press, it would need to be 100K only. But for a billboard, you'd print rich black because 100K is often a dark gray, and its perfect register makes rich black text feasible. Leaving devicedependent data floating around in the world is a pretty bad idea. Even for printing to known destinations, the PDF/X-1a model should be chosen, which is to tag all CMYK content.

1. this 'metadata describing "black text"' is new to me, please, do
you have more info? Is it in PDF specs?

2. If they would print "my black" as CMYK 0, 0, 0, 100 first time, and
as CMYK 40, 30, 30, 100 second time, I would ..... not like them.

3. PDF/X-1a is the best thing since sliced bread. Really, if Cairo
could output PDF/X-1a I would throw away Acrobat. PDF/X-1a has
everything I need, it's in fact that good. (One tiny side note: I
don't have the specs, as it is not freely available. But from what I
read it does not require profiles for spot colors, just for its
fallbacks - there is just one global tagged CMYK space, defined in
print intend. If this is truly the case, then this is just what I
want. If it is not, I apologize for the confusion and welcome any more
precise description).

I, for one, don't understand what's so bad about untagged content - if
you know what you are doing, it simplifies a few things.