@codinghorror you should also check out freeware app called http://www.irfanview.com and it’s plugins which include pngout etc. I have been using it for nearly 10yrs and really crunches PNG images down by alot !
I took your blog comic image and used irfanview to reduce a true colour 32bit version lossless version at 561KB and a 256bit colour optimised version down to 136KB - results at https://community.centminmod.com/threads/zopfli-optimization-literally-free-bandwidth.5516/ 
very useful for saving bandwidth 