One more thing: After finalizing your PNG, send it to https://tinypng.com/, where it will be compressed without visible quality loss.
Your file is 68kb large and afterwards only 15kb. This can make a huge difference in experience for your readers, particular when you use larger images in PNG format. I do that for all of my PNGs.
Cheers for the tip, I wasn't aware that there is much compression going on with png, thought that was only true for jpeg mostly :P
I'll upload there in a minute and will edit the photos afterwards, let's see if it does something for the quality :)
Is there any noticable difference now?