Feature request/enquiry: Overprint support

[Bernard Gray]

Hi David,
Thankyou for your informative reply!

On Tue, 30 May 2023 at 05:49, Laura David Hurka <david.hurka at mailbox.org> wrote:
>
> Hi Bernard,
>
> I don’t know exactly what overprinting is, or what your requirements are.
> I understand it as a feature similar to PDF layers.

I'm afraid I don't exactly understand it either, but from the link I
posted in the original email[1] it seems to be tied to (some) physical
printers and the way the PDF defines the separation of CMYK toners for
certain elements.
The problem is that the screen viewers (okular, et al) don't render
this to the screen correctly, creating the multi-layered, unclear font
in the example I sent


> Okular has a side panel for layers, you can try it with the last page of what
> a quick internet search gave me:
>
> https://www.edcfiresafe.org/wp-content/uploads/2015/12/Using-Layerd-PDFs-with-Sample-Map.pdf

Great, that was useful to see how okular implements layers, however it
does not recognise the Overprint features in the PDF as layers (there
was no layers tab appearing in the sidebar of okular in my example
PDF[2])


> I assume your requirement is to display the document correctly, only on your
> screen of your local desktop computer.

Correct


> My conclusion is that Poppler (the PDF library normally used by Okular) will
> need to support “overprinting”.

I don't really understand how the library would interact with the
viewer in this case, but I am happy to pose the question to the
poppler team separately
Do you have any recommendation on how best to contact them/frame the request?

> If a user interface is necessary, that should be a sensible addition to
> Okular, similar to how layers already have a user interface.


This is the user interface implemented in AdobeReader 9 - Via the
program preferences, setting "Use Overprint Preview: [Always |
Automatic]" displays the PDF correctly
https://drive.google.com/file/d/1ix9ZPtq8LD4EosaKZXFF5aRCVnEQv_bM/view?usp=sharing

> Cheers, David


[1]: https://pdfa.org/understanding-overprint/
[2]: https://drive.google.com/file/d/1WGlly-EvzQl1Jhj39R9hvJ16CIgVZD5j/view?usp=share_link

>
> > Hi everyone,
> >
> > We are currently supporting a very old version of 32 bit adobe reader on
> > our ubuntu 22.04/kde desktops, due to the requirement for support for a PDF
> > feature called "Overprint" which is used by our label printing supplier (I
> > work for an Australian winery)
> >
> > [...]
> >
> > Is this feature something Okular would be interested in developing?