Sample CSV output from image-report (a responsive images efficiency tester) imports nicely into a Google docs chart.
You want the match to be as close to 0% as possible. Go over and you’re loading extra pixels you don’t need. Go under it’s blurry.
Trying to get the sample output for image-report to be a little clearer! Here’s the next iteration. It should be ready for release here in the next day or two!