Is wordpress compressing my images? if so, how to prevent it?

A nice explanation is at WPMUdev: http://premium.wpmudev.org/blog/how-to-change-jpeg-compression-in-wordpress/

According to their tutorial, you’d need to add the following to your functions.php

add_filter( 'jpeg_quality', create_function( '', 'return 100;' ) );

They also suggest regenerating your thumbnails once the change is made so previously uploaded images will be affected by the quality change.

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