how to NOT have calibre reduce pictures' resolution when converting from epub (or anything I guess) to MOBI

I’m selling art ebooks on KDP Amazon, and I need the pictures not be shrinked as they automatically are when passing from odt to mobi/epub.
But it would be easier if Amazon didn’t have to convert epub itself, time-wise to begin with, and also since there are errors here and there (rarely but still) and it just can’t do it sometimes. A hussle.
Now, I’m forced to make epub from libreoffice, then correct it a bit sometime with sigil, then provide it to Amazon. Too time-consuming.

Thanks.