Re: [libreoffice-users] Compress images

> The odt file is a compressed zip archive. Compressing the contained
> pictures would hardly reduce the file size.


That's not true. The point was (if I remember this thread correctly) that
when designing the document, you have high-definition pictures, say
1200dpi, and those takes a lot of space. Now, if you want to output this
for a projector you'll only need pictures at 90dpi, or for printing with a
medium quality you only need 150dpi, and doing a poster you'll need the
whole 1200dpi.


Sending the same file with the original 1200dpi pictures to everyone sure
is a solution, but you'll see the waste of space. It doesn't have anything
to do with odt file being compressed; there's juste *more* informations
with bigger images. Other (impractical) solutions could be to maintain
multiple version of the same file, or keep the images linked to multiple
folder, and swap them outside of LibreOffice. Not good when you manipulate
large documents.

Now, what would be nice is a way to take an odt with such large pictures,
and produce different versions suited for different needs. You keep the
"original", and with the press of a button, produce a separate odt file
where the pictures are scaled down appropriately (like the option in PDF
export). From the discussion, it looks like MS Word have something like
this, and while mimicking Word is not a necessity, I clearly see the need
for such an option for LibreOffice power users.

2014-11-02 22:36 GMT+01:00 Tom Davies <tomcecf@gmail.com>:

> Cley seems to have created something like an Extension or maybe
> independent program to automatically re-scale the byte-size of all images
> in a document and i'd forgotten all about it.


​It was (is? I probably left it online) a separate tool. You could feed it
an ODT, and produce a (hopefully) smaller ODT where all pictures are scaled
to a given dpi.
It was only a proof of concept: I didn't read the whole ODT spec or
something. It works by looking in the XML for pictures links, and retrieve
their "printing" size (in centimeters). It then scale down all linked
images in the ODT archive, so that their size in pixels exactly meet their
printing size for the specified DPI.

For example, if you have a document with a picture set to 10x10cm, and the
picture source is 4700x4700 pixels, the image is roughly at 1200dpi. When
modified for printing at 150dpi, the picture would be scaled back to
590x590 pixels, drastically reducing the file size while keeping the
expected output quality.

(this also depend on scaling methods and other things, but it was the
general idea).

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