"PNG to PNG better" sounds like a search engine riddle. After all, why would you convert a PNG to a PNG? Isn't that like re-filling a glass of water that is already full?

In the world of digital imaging, converting a PNG to another PNG isn't about changing the file format. It is about —taking an existing PNG and creating a new PNG that is smaller, sharper, cleaner, or more compatible than the original.

zopflipng --lossless_8bit --iterations=25 step2.png final_better.png

A "better" PNG strips these out.