For a website I control that sells consumer goods, fast page performance is important, especially for potential customers on mobile devices. Therefore, we want our images to be as small as possible without showing any noticeable degradation of image quality. Because of that, we use PNG files when providing graphic content such as infographics on how a product helps a customer.
TinyPNG.com compresses PNG files by stripping metadata and converting from 24 bit to 8 bit depth, so we are using this site to compress PNGs served up from our site. I found that you can run it repeatedly on the same file and it keeps getting smaller. Why would the file keep getting smaller and will the result be noticeable? Do you just get fewer and fewer colors?