How to convert PNG to 8-bit PNG using PHP GD library

Question

I want to write a routine which takes PNG image path as parameter and convert that image into 8-bit PNG image. I need to use PHP GD library for this.

Answer 1

Instead of GD library I strongly recommend using pngquant 1.5+ commandline using exec() or popen() functions.

GD library has very poor-quality palette generation code.

Same image as in the other answer, same file size as GD library, but converted using pngquant to merely 100 colors (not even 256):

pngquant supports alpha transparency very well.