How much information can you give about how to tell whether a PNG file will be recompressed based on a hypothetical JPEG version’s filesize?
I’m making a tool that allows users to optimize their art before uploading to twitter, by losslessly compressing it in optiPNG to see if it’ll come in small enough, and then offering to lossily compress it to 256-color in case that looks less bad than the eventual JPEG compression will.
But how are users supposed to know what approach to take? What good does an “if it’s smaller than the JPEG” clause do, if users don’t KNOW whether it’s going to be smaller than a JPEG whose settings we don’t know? The only way to learn what approach to take is to have already posted the image and seen what filesize it gave once it was online in front of everyone.
I know you said you don’t want to say in case the settings wind up changing, but I can tell you now, on February 11th I’m going to upload a test file, then look at the result in exiftool, and base my script on whatever it gives, and so will anyone else trying to deal with this vague rule that we’re depending on, so you may as well tell us what the initial settings are going to be, rather than making us scramble on the day the change goes live to find out the same information the hard way.