[Octave-bug-tracker] [bug #65959] qt backend: should print with -rNUM set dpi related metadata for png, jpeg, etc.?

[b3nmore]

URL:
  <https://savannah.gnu.org/bugs/?65959>

                 Summary: qt backend: should print with -rNUM set dpi related
metadata for png, jpeg, etc.?
                   Group: GNU Octave
               Submitter: b3nmore
               Submitted: Sat 06 Jul 2024 09:09:53 AM UTC
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: None
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
                 Release: 9.2.0
         Discussion Lock: Any
        Operating System: Any
           Fixed Release: None
         Planned Release: None


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Follow-up Comments:


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Date: Sat 06 Jul 2024 09:09:53 AM UTC By: b3nmore <b3nmore>
I recently switched from the fltk to the qt graphics-toolkit and noticed, that
the dpi related metadata is handled quite differently when printing to
jpeg/png files with the resolution option "-rNUM".

Here are may findings:
* the image size is calculated correctly by both backends
* fltk backend: 'X Resolution'/'Y Resolution' (jpeg) and 'Pixels Per Unit
X/Y', 'Pixel Units' (png) are set correctly
* qt backend: jpeg: 'X Resolution'/'Y Resolutions' is always set to 72 dpi.
png: no dpi related metadata is written at all

Not sure what would be the right approach (setting dpi related metadata
explicitly or omitting it), but imo it should be handled consistently for all
raster image files (at least where applicable).

Thanks







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