09-14-2014, 04:24 PM
It's most easily done is Aseprite. Put your sprite into a new file, then hit F4 and click the + on the corner of the window that pops up. A selection of new buttons will appear. Click on "Quantize" to have the program count the colors and generate a palette. Save the image as a GIF, then as a JPG. Reopen the GIF and the JPG separately (the one you left open before may not autocorrect pasted images, so close it and reopen just in case), and paste the JPG into the GIF. It will correct itself to match the GIF's palette while remaining grainy, then all you have to do is clean up any stray pixels that end up outside the sprite. Hope that helps.