[Openicc] [Gimp-print-devel] [Printing-architecture] Colour

[Michael Sweet]

On Nov 14, 2009, at 1:03 PM, Hal V. Engel wrote:
> ...
> on the new pdftoraster filter to add CM support shouldn't it be capable of 
> doing DeviceN separations if it is supplied a DeviceN output ptofile?

CUPS raster currently does not define DeviceN color spaces, so there is no way to send DeviceN data to the driver if N > 4.  Adding DeviceN to CUPS raster isn't hard, but so far there has been no need for it.

> ...
> prematched using a DeviceN profile.  What happens now if CUPS gets a PDF spool 
> file that has been prematched to DeviceN?  Does it fail even if the device 
> supports DeviceN and the separations are correct for that device?  Or does it 
> convert it to some other format like CMYK?

That depends on the PDF filter you use.  For Mac OS X, CoreGraphics can't do more than 4 color channels, so I'm not sure what you'd get if you provided a 6 channel color in a PDF file.

>>> I'm dubious of sRGB-only command sets for inkjet printers.  It
>>> artificially restricts the available gamut, and doesn't work if you
>>> use a medium other than that specified by the manufacturer.
>> 
>> Like it or not, you're going to see more sRGB/AdobeRGB-only devices in the
>> future, even from Epson. Only the high-end printers will support a DeviceN
>> mode that can be used by third-parties...
> 
> Again almost no one here is using the hardware vendor supplied drivers.

I'm not talking about drivers, I'm talking about hardware.  Most of the HP Deskjet/Photosmart/OfficeJet printers and many of the low-end HP DesignJet printers only support printing using PCL3GUI, which is an sRGB raster pipe. No CMYK or DeviceN path exists for these devices - legacy PCL CMYK data, when supported, is converted to sRGB for printing.  I'm seeing similar paths being taken by recent Canon and Epson printers.

So, even if you wanted to write your own DeviceN driver for these printers there would be no way to get the data to the printer since they only take sRGB.

___________________________________________________
Michael Sweet, Senior Printing System Engineer



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