[Printing-architecture] Make use of extended color spaces on IPP printers

Michael Sweet msweet at msweet.org
Mon May 31 13:24:08 UTC 2021


Till,

> On May 31, 2021, at 7:26 AM, Till Kamppeter <till.kamppeter at canonical.com> wrote:
> ...
> PDF output when printing with darktable dos nowhere contain /calRGB, but it contains DeviceRGB at the beginning of a stream object:

So it isn't embedding the profile used for the image.  Does the file identify Cairo as the producer?

> ...
> This is a PDF generated on a Mac, containing CalRGB but not matching any of the examples you have mentioned:
> ...
> /Producer (Acrobat PDFWriter 3.0 for Power Macintosh)
> ...
> /DefaultGray 15 0 R
> /DefaultRGB  16 0 R
> >>
> endobj
> 15 0 obj
> [/CalGray
> <<
> /WhitePoint [0.9505 1 1.089 ]
> /Gamma 1.8
> >>
> ]
> endobj
> 16 0 obj
> [/CalRGB
> <<
> /WhitePoint [0.9505 1 1.089 ]
> /Gamma [1.8 1.8 1.8 ]
> /Matrix [0.4497 0.2446 0.0252 0.3163 0.672 0.1412 0.1845 0.0833 0.9227 ]
> >>
> ]

So this is a very old version of Acrobat, and the embedded (default/device) color spaces are for Apple's old monitors.

> Similar with a PDF generated on Windows:

Not sure at all what the default colorspace is here - the gamma is inverted in this file and I don't recognize the transform matrix.

> ...
> And this is generated by Ghostscript:

This looks like Apple's Generic RGB color space - similar to sRGB but with a 1.8 gamma.

> ...
> So does this mean that these 4 PDFs are neither sRGB nor AdobeRGB? For me it looks like that your method is rarely applicable.

These files are neither sRGB nor AdobeRGB.  And I'd say your sample size is far too small to make any kind of conclusions (but I suspect anything coming from Cairo on Linux will not be tagged correctly...)

________________________
Michael Sweet





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