@Eidetic_Paarthurnax Yo, I'm so sorry! I was writing up a response like a week ago and then got distracted and forgot to post it. Better late than never, I guess!
So, that credits page from chapter 22 that was like 21 MB was corrupted and literally about 60% metadata when I opened it up in a hex editor (seriously, like 12 MB of pure ASCII text in the form of XML tags like
Code:
<rdf:li>xmp.id:02801174072068118C14AE862C7C4ED1</rdf:li>
). For comparison, when I took the exact same PNG, fixed the corruption by converting it, and exported it from GIMP, it got down to 1.5 MB without doing anything special. I see that you're using Photoshop CC 2015, and this seems to be
a known issue with Photoshop--looks like you can solve it by just exporting without metadata, which you should be doing anyway to minimize filesize.
That'll fix most of your problems, but I also recommend using
ECT (Efficient Compression Tool) to (as the name implies) efficiently compress your PNGs after exporting them. There's a ton of lossless PNG optimizers out there, but I've found that ECT usually gets the best results while also being significantly faster than similar tools--about three times faster than the ones I was using before. There's no GUI, but it's really straightforward--just run
on the files you need to compress (or just
in the folder where you have your PNGs to batch process) and let it do its thing.
Here's my final result after optimizing with ECT, weighing in at a svelte 1.35 MB without any loss in quality.
Hope that helps! Let me know if you need a more detailed explanation and I'll see what I can do. Also, while ECT is (IMO) your best option, if you'd really rather avoid the command line I can try to recommend a GUI alternative.