Internal Program Version: pngquant  2.18

pngquant is a command-line utility and a library for lossy
compression of PNG images.

The conversion reduces file sizes by converting images to 1/2/4/8-bit
paletted PNG format with alpha channel (often 60-80% smaller than
24/32-bit PNG files). Generated images are compatible with all modern
web browsers, and have better fallback in IE6 than 24-bit PNGs.

https://pngquant.org