[cairo] Subtractive API, part 0

Jon Cruz jon at joncruz.org
Thu Feb 4 22:34:37 PST 2010

On Feb 4, 2010, at 3:57 PM, ecir hana wrote:

> On Sat, Jan 30, 2010 at 9:07 PM, Chris Murphy <lists at colorremedies.com> wrote:
>> On Jan 29, 2010, at 4:32 PM, ecir hana wrote:
>>> For printing, even with untagged cmyk, nothing stops the application
>>> or CMS to supply correct cmyk values to Cairo. Those values would get
>>> baked-in into the pdf, making them possibly unusable on another device
>>> - so what? Do you print a poster on two different printers?
>> Absolutely, all the time. Movie posters will be printed on dozens of printers, perhaps in multiple geographic locations.
> I'm  still trying to connect the dots and struggling with this one:
> I read your post above as if you were suggesting that the better
> alternative to untagged CMYK PDF would be tagged one because the
> printer at the other location could easily just swap the profile and
> print it on different paper, say.
> But that means going to LAB again, and back to CMYK again. And I just
> did a small experiment, trying to convert 40% 30% 30% 100% CMYK SWOP
> to Euroscale Coated and it completely messed-up the colors. And from
> the little I read about ICC profiles it seems (?) that there is no
> official way (intent) of how to preserve such blacks.

No, I think you are misunderstanding things there. It does not really require going to LAB at all. All a particular print-house needs to do is have a straight "SWOP CMYK" to "printer in bay two CMYK" one-way conversion. Additionally if you do a CMYK->L'a'b'->CMYK2 conversion (with LAB in the middle), you pretty much are guaranteed that you will get color loss/corruption as far as professional print jobs go.

>> Untagged CMYK in a PDF is OK, but I would then require that an outputintent is set for the PDF, so that we know what the intended CMYK output condition is, in case the PDF needs to be repurposed.
> So wouldn't it better solution to just use untagged PDF and then name
> the file something like "new_movie-poster_final-cmyk_uncoated.pdf"
> (that's only because I'm not yet familiar with PDF specs on
> "outputintent", yet)?

Not really. That's like sending digital frames off to a film printer that have random RGB values that were tuned to match some random monitor on a single random artist's random desktop PC, none of which have been calibrated and all of which have aged, even during the project itself.

That's where "old school" to avoid such lighting problems, etc. Ray Harryhausen used to stay up all night working on a sequence of stop motion since just the act of shutting down and starting up again the next day would change the color of his lighting and cause frames not to match.

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