Flattens alpha, removes ghosts, optimized.
A lot of digital artists either do not flatten their opaque images before publishing, or paint directly on transparent backgrounds, which leave very small amounts of semi-transparent pixels in an image designed to be fully opaque.
Optipng is a good tool for automatically optimizing images, but it doesn't ever reduce available data. Specifically, if an image has even one pixel with a different alpha, the entire image will keep the alpha layer, wasting space.
Fargo attempts to remedy this by ignoring the alpha layer, unless there is a large amount of alpha pixels. This saves a lot of data (15% to 20% normally!), with no human visible quality loss.
Requires ImageMagick 6 or 7.
git clone https://github.com/DaemonLee/fargo
cd fargo
make
sudo make install