I didn’t know about the OS X command sips and now I’m super happy about it. With it, I converted a bunch of PNGs to GIFs and I didn’t have to wrestle with anything at all.
mkdir gifs sips -s format gif ./*.PNG --out gifs
Holy cow — it’ll let me resize things too and retain proportions. Woah, love this one:
#Resize a batch of images to 250px (largest side) sips -Z 250 *
Note that it will modify your files “without apologies” — but thanks, sips!
For a one-off file, you need to specify the –out like this:
sips -s format gif back.PNG --out back.gif
Or you can just do this:
sips -s format gif back.PNG --out .
And it’ll name the image properly to the specified suffix.