pngquant is a command-line utility and a library for lossy compression of PNG images. The conversion reduces file sizes significantly (often as much as 70%) and preserves full alpha transparency.
Install dependency, a library implementing an interface for reading and writing PNG (Portable Network Graphics) format files:
apt-get install libpng-dev
Download source code:
git clone git://github.com/pornel/pngquant.git
Go to directory:
cd pngquant
Build it:
make
Install it system-wide:
sudo make install
More info: http://pngquant.org/install.html, https://github.com/pornel/pngquant
Putokaz 