When I upload an Image with Joomla the .jpg has a much bigger filesize on the server than it had when it was on my harddrive. It usually is about 2-3 times bigger, although the dimensions are the same or smaller. Of course this is not good for the performance of the website. I could imagine that some library changes the compression of the image but I don't know where to start looking.
I use Joomla 3 and PHP 5.4 on an Apache Webserver.
Thanks for your help!