The .config file for anti-aliasing defaults to 30. This is ok, but not great. The best is 0 and final rendering should always be 0. So you must edit this file every so often (before opening Im) or build a front end on the work bench (requires programming knowledge, though). BTW, the anti-aliasing is EDLE in .config file.
(for those unfamiliar with the term jaggies - they refer to the way lines drawn by computers tend to haved a jagged or stair stepped appearance, instead of a smooth continuous line. This is usually found more in low resolution images.)