Pngout is not enabled by default because it is resource intensive. Optipng is the preferred PNG optimizer if you have resource (CPU) constraints. Pngout is also not open-source for those who care about such things, but the command-line version is free.
- Use the "override" to enable PNGOUT--set the EWWW_IMAGE_OPTIMIZER_DISABLE_PNGOUT constant to false.
- Visit the setting page, and look for the Optimization Score near the top. Click the View Recommendations link, and then click the "automatically" link for the PNGOUT recommendation. The plugin will download the pngout archive, unpack it, and install the appropriate version for your server.
- Adjust the pngout level according to your needs (again, using the overrides). Level 0 gives the best results, but can take up to a minute or more on a single image.
To manually install pngout:
- Click the Manual link in the tooltip that appears when you hover over the Compress gauge.
- Download the version of pngout that matches your webserver (NOT your desktop/laptop). Always use the -static downloads for Linux and FreeBSD. If you don't know if you have a linux server, or Mac, or whether it is 32-bit vs 64-bit, ask your webhost, or turn on debugging and send the debug information with your support request.
- If you have Windows on your personal computer, you may need to install 7-zip or something similar to extract the .tar.gz files. Linux and Mac OS X systems should have built-in support for gzipped files.
- For Linux and FreeBSD pngout downloads, you will see an i686 folder and x86_64. The first is for 32-bit the latter is for 64-bit. Upload the pngout-static file (pngout for Mac, pngout.exe for Windows) to the wp-content/ewww/ folder on your web server.
- Make sure the permissions are set correctly. It is recommended to use 755 or rwxr-xr-x, which is read, write, execute for the owner, read/execute for the group, and read/execute for everyone else.
- If pngout still is not working, you can download older versions, but do not go further back than the 20130221 release: http://static.jonof.id.au/dl/kenutils/