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

Till Kamppeter till.kamppeter at gmail.com
Mon May 31 15:03:17 UTC 2021


On 31/05/2021 15:24, Michael Sweet wrote:
> 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 not Cairo, Cairo does not appear as producer, but darktable itself.

If I print from gedit, I get Cairo-produced PDF which does not contain 
/CalRGB. Each page contains something like:

----------
34 0 obj
<< /Type /Page % 4
    /Parent 1 0 R
    /MediaBox [ 0 0 612 792 ]
    /Contents 36 0 R
    /Group <<
       /Type /Group
       /S /Transparency
       /I true
       /CS /DeviceRGB
    >>
    /Resources 35 0 R
 >>
endobj
----------

>> ...
>> 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...)

Do you know which Linux applications generate correct PDF files?

    Till




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