[libreoffice-users] Re: How does 4.4 compress PDFs so well? Is there a quality problem?

V Stuart Foote wrote
> Hey that was fun to track down.  You were spot on...
>
> Looks like a long present issue of JPEGs being exported to PDF were not
> retaining their JPEG compression…

Thanks for that, Stuart.

I have tested further using GIF, JPG and PNG images, opening PDFs in
LibreOffice Draw and exporting the graphics (right-click > Save Graphic…).

Comparing the files to the originals, the story seems complicated.

Sometimes, the original images are stored without change, and sometimes with
change (always larger and as PNG, even if the original is PNG). But I cannot
find a pattern. It doesn't matter if the images are large or small, embedded
or linked, resized within the document or at their original sizes.
Furthermore, sometimes 4.3.4.1 does save the images as the original. Again,
I can discern no pattern.

It seems entirely random to me.

The link that you gave is, unfortunately, too technical for me, so I can't
use that to figure out why it sometimes stores the images as their original
and sometimes not.

At least the new PDF files are significantly smaller, without losing
resolution.

Perhaps someone with technical understanding can weigh in to explain when
4.4 saves an image in its original format and when it converts to PNG
(sometimes already PNG, just made larger) — and why? What is behind the
decision to *sometimes* change the format to PNG or, when already PNG, to
make it larger?



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