title: How to detect the compression level of a PNG file?
body: <p>Services like Google PageSpeed tell me that I can save file space, by compressing PNG files. I haven't found a (Linux) tool that would give me such information, unless I actually compress the file. </p>
  
  <p>Is there a (fast) way to detect the compression level of a PNG file, without actually compressing it? Any hint is appreciated!</p>