[Openicc] Is CUPS the right place... Flat color documents vs. ICCbased objects

[Chris Murphy]

On Feb 8, 2011, at 4:59 AM, Jan-Peter Homann wrote:
> 
> Cairo is already dealing with transparencies between individual objects. The concept of attaching a document color space to a Cairo session, allows the use the current rendering workflow in Cairo and apply the color transformation to the output device, after the Cairo document has been rendered to an image for the monitor or for the printer.
> Using this strategy would it make much easier to introduce also CMYK as a native colorspace in Cairo including handling of transparencies in a CMYK blending space.

Any application using Cairo to support the creation of CMYK documents needs to tread very carefully when producing Exported PDFs for the world. It is perfectly legitimate to either tag those objects as ICCBased in order for color appearance to be best preserved because an OutputIntent is not reliably honored except in PDF/X workflows. So I would not make PDF/X a requirement, but rather an option. And a good option at that. So there are choices the user will have to make: ICCBased CMYK objects, no OutputIntent, or one of the PDF/X standards which would allow /DeviceCMYK and an OutputIntent.

For the PDF print spool file, the objects would still be ICCBased CMYK because the OutputIntent is the local printer profile or display profile.

> The alternative for Cairo to introduce ICCbased colorspaces on object level including transparencies between such objects increases the complexity of the internal rendering to another galaxy.
> At least, we would need to do live rendering from Cairo via the GhostScript Graphics API to the monitor, which is far from being trivial in terms of speed.

If you're going to enable transparency effects in Cairo applications, for best quality they need to be included in the PDF as live transparency, regardless of the color space issues. You could certainly produce /DeviceCMYK with live transparency either as PDF/X or not.

If Cairo applications are going to enable transparency effects and flatten them before the creation of the PDF (print spool or export) then you have an inherently lower quality PDF as well as large in size.

So as long as this is understood...


Chris