[reportlab-users] CMYK overprinting (colour-separated PDF output)
haktom at gmail.com
Thu Jul 1 07:00:50 EDT 2010
Am 30.06.2010 um 14:18 schrieb Robin Becker:
> the problem here may be that non-separating overprint is not controllable by the pdf definitions; it is a function of the output device.
> from the 1.7 manual
>> If the overprint parameter is true and the output device supports overprinting, no such erasing actions are performed; anything previously painted in other colorants
>> is left undisturbed. Consequently, the color at a given position on the page may be a combined result of several painting operations in different colorants. The effect produced by such overprinting is device-dependent and is not defined by the PDF language.
>> Note: Not all devices support overprinting. Furthermore, many PostScript printers support it only when separations are being produced, and not for composite output. If overprinting is not supported, the value of the overprint parameter is ignored.
> I looked inside the PDF produced by the example and there is only one setting of the overprint control (effectively we set /op true). After that I don't see any restore states that affect the simple CMYK drawing; I think we're not doing anything wrong. So it could be that the acrobat tools just decide not to show this overprint as a colour mix for this case.
> That being said there is an additional parameter that affects process cmyk overprinting that is the opm value. We don't control that parameter currently. According to the manual when OP is true OPM controls the interpretation of zero tint values.
> Have you tried printing any of this output with a CMYK capable printer?
> Robin Becker
No, i dont really have the oportunity to try out printings. I am delivering PDFs to different printshops, and it would be great, if reportlab could generate files, which are showing correctly in the overprint preview.
i generated 2 pdfs from one Illustrator file and compared them with, and without checking the "overfill print" attribute in illustrator.
here is one line i copied out of the diff, which seems to be the interesting part (and the only occurence of /op):
7 0 obj
<</AIS false/BM/Normal/CA 1.0/OP true/OPM 1/SA true/SMask/None/Type/ExtGState/ca 1.0/op true>>
10 0 obj
<</AIS false/BM/Normal/CA 1.0/OP false/OPM 1/SA true/SMask/None/Type/ExtGState/ca 1.0/op false>>
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