The ngx_pngquant module is a filter for lossy compression of PNG images.

server {

    set $store_path /tmp/pngquant;

    root /var/www;

    location ~ \.png$ {
        root $store_path;
        try_files $uri @pngquant;
    }

    location @pngquant {
        pngquant on;

        pngquant_buffer_size 1M;
        pngquant_colors 256;
        pngquant_dither on;
        pngquant_speed 1;

        pngquant_store $store_path$uri;
        pngquant_store_access user:rw group:rw all:r;
    }
}

Install module dependencies:

Ubuntu or Debian

sudo apt-get install build-essential libgd-dev

RedHat, CentOS, or Fedora

sudo yum install gcc-c++ gd-devel pcre-devel make

Download ngx_pngquant and install libimagequant submodule:

cd
git clone https://github.com/x25/ngx_pngquant
cd ngx_pngquant
git submodule update --init

Download and build nginx/openresty/tengine with support for ngx_pngquant:

cd
# check http://nginx.org/en/download.html for the latest version
wget http://nginx.org/download/nginx-1.6.2.tar.gz
tar -xvzf nginx-1.6.2.tar.gz
cd nginx-1.6.2/
./configure --prefix=/tmp/nginx --add-module=$HOME/ngx_pngquant
make
sudo make install

If you want to have debug logs available:

./configure --prefix=/tmp/nginx --add-module=$HOME/ngx_pngquant --with-debug

Start nginx with pngquant module:

/tmp/nginx/sbin/nginx -c /path/to/nginx.conf

Turns on/off module processing in a surrounding location.

Sets the maximum size of the buffer used for reading images. When the size is exceeded the server returns error 415 (Unsupported Media Type).

Sets the maximum number of palette entries in images.

If dither is set, the image will be dithered to approximate colors better, at the expense of some obvious "speckling."

Speed is from 1 (highest quality) to 10 (fastest). Speed 0 selects library-specific default (recommended).

Enables saving of processed images to a disk. The file name can be set explicitly using the string with variables:

pngquant_store /data/www$uri;

An example of caching:

server {
    root /var/www;

    location ~ \.png$ {
        root /tmp/pngquant;
        try_files $uri @pngquant;
    }

    location @pngquant {
        pngquant on;
        pngquant_store /tmp/pngquant$uri;
    }
}

Sets temporary area where files are stored before they are moved to pngquant_store area.

Sets access permissions for newly created files and directories, e.g.:

pngquant_store_access user:rw group:rw all:r;

If any group or all access permissions are specified then user permissions may be omitted:

pngquant_store_access group:rw all:r;

This module is experimental and it's compatible with following web servers:

• nginx 1.6.x (tested with 1.6.2).

• nginx 1.7.x (tested with 1.7.9).

• openresty 1.7.x (tested with 1.7.7.1).

• tengine 2.1.x (tested with 2.1.0).