[Openicc] CPD cannot disable all color transforms

[Chris Murphy]

We need a bit of a realization here that a CPD can disable color transforms ONLY in the print pipeline. If the application has already converted images internally, there's no way a setting in the CPD could change this. Therefore printing targets from a random application is NOT a good idea, and cannot ever be guaranteed to be workable.

If the target is untagged (and it should be), what is the correct assumption by some random application? Assume it's sRGB and immediately convert to Display RGB? That's probably not ideal but can the CPD no transform option (color management off) *guarantee* it does not happen? No. Therefore this is another non-starter.

Yes what should happen is the app should tag it as sRGB and not convert. And then when it prints, the CPD could be expected to cause the PDF spool file creation to drop the sRGB tag of the object to /DeviceRGB instead. But it cannot unwind conversions once they've happened. And once they've happened the target is USELESS regardless of the CPD settings.

An API is needed available to any application developer who wants to use it, including those who write apps that prematch content for printing, and don't need downstream color matching to occur. And we also need a reference utility for printing targets. I don't see a way around this. Even on Windows it's simply not a good idea to assume all applications are suitable for printing profile targets.


Chris Murphy