Re: [libreoffice-users] Writer's A4 page pixel dimensions

Hi Mark,

On 20/03/16 02:07, libreoffice-ml.mbourne@spamgourmet.com wrote:
> Dave Koelmeyer wrote:
> > Hi All,
> >
> > I'm creating full A4-sized page background images in GIMP to insert into
> > A4-format Writer documents. I've noticed that when these images are
> > added to Writer and anchored to page, things are not perfectly flush as
> > I would expect.
> >
> > After a bit of tinkering I believe this is because Writer doesn't treat
> > an A4-format page as having exactly 2480x3508 pixel dimensions (at
> > 300 DPI).
> >
> > For example, my GIMP working files use the A4 300 DPI preset, which is
> > 2480x3508 pixels. If I create a new blank Writer document using A4 page
> > size, then export this blank document as a PNG and set the export DPI
> > setting to 300, Writer instead displays this as 2481x3507 pixels. I see
> > similar ever-so-slightly different results when attempting to import an
> > A4 PDF exported from Writer into GIMP at 300 DPI, again off by a matter
> > of pixels.
> >
> > Everything I've read points to 2480x3508 definitely being the dimensions
> > for A4 (e.g. http://www.a4papersize.org/a4-paper-size-in-pixels.php).
> > Can someone please help me understand why there is a difference in
> > Writer?
>
> Probably differences in rounding. An A4 page isn't exactly 2480 x 3508
> pixels at 300 dpi. A4 is 210mm x 297mm.
>   210mm / 25.4mm/in * 300dpi ~= 2480.3 pixels
>   297mm / 25.4mm/in * 300dpi ~= 3507.9 pixels
> Rounding that to 2481 x 3507 does seem a bit odd, but it looks like
> there may be some intermediate rounding in the calculation:
>   210mm / 25.4mm/in ~=  8.27in;  8.27in * 300dpi = 2481 pixels
>   297mm / 25.4mm/in ~= 11.69in; 11.69in * 300dpi = 3507 pixels
>
> How are you determining the pixel sizes that LibreOffice is using for
> your image anyway? Image sizes are specified in terms of the printed
> size (mm, inches, etc.) rather than in pixels. Unless your display is
> 300dpi, the image on screen will be scaled anyway.
>
> If you're finding that the size in the image properties can't be set
> to 210mm x 297mm because of the slight difference in pixel aspect
> ratio, you could try unticking the "keep ratio" box so that the size
> can be set to 210mm x 297mm.
>
> If you've got LibreOffice set to work in inches, you might setting it
> to cm or mm when using ISO paper sizes avoids the intermediate
> rounding. Tools > Options > LibreOffice Writer > General > Measurement
> unit.

A belated thanks for your very useful information (I have only just
found time to look at this in more detail). I think your observation of
intermediate rounding does indeed explain this. I can confirm that I see
this behaviour when Writer's measurement units are set to inches. When
the same image 2480x3508 resolution image is inserted as a full page
background with centimetre or millimetre measurement units set as you've
suggested, it then does appear to be flush.

Thanks again! :)

Cheers
Dave

-- 
Dave Koelmeyer
http://blog.davekoelmeyer.co.nz
GPG Key ID: 0x238BFF87


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