fargo - Removes unseeable or ghost channels from PNG images, optimized.
fargo [-h -v -c -s] -i image.png -o output.png
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.
-h Display a short help text.
-i <image> The input image to optimize. This flag is required.
-o <output> The output image. This flag is optional.
-f <factor> A number between 0 and 1 that changes the threshold of what is considered a "dirty" alpha. Higher is safer. Defaults to 0.975.
-v Enable verbose mode.
-c Enable clobber mode. Ignores output. Will automatically overwrite dirty alphas! DANGEROUS!
-s Run in a simulated mode. Won't automatically overwrite empty alphas. Safe!
Daemon Lee Schmidt, with small contributions from Zach Mertes