What a great plugin!

Hi Helen-kh.

The Resized Image Quality plugin only works on JPEG images.

GIF and PNG images can’t be compressed by WordPress’ internal code. There are ways to compress them using server-side tools (you need to be a server admin/root to install these) or a 3rd-party service. Taks a look at these plugins, but note that they can be hard to support & setup:

* https://www.ads-software.com/plugins/wp-smushit/
* https://www.ads-software.com/plugins/ewww-image-optimizer/

It does all image extensions for Imagick and for GD only JPEG yet but there is a ticket for PNG. The problem is that Imagick ins’t widely supported.