I wanted to measure visual information content of a page, and yes, PNG is maybe not the best to do that. JPEGs are smaller, but it introduces another problem of visible artifacts around text.
If anybody knows a better way to measure visual information content, please suggest.
19.5 / 10 = 1.95. (assuming the PNG is 10 MB for simplicity).
You could be fancy and use exponent.
But I doubt there's a good mechanical way to do this. Whether an image is bloat or valuable content requires sophisticated judgment and understanding of what the purpose of the page is.
I completely agree with that. Quick check is to replace all images on a page with placeholder images—if that doesn't reduce functionality of the page then maybe you don't need that images at all.
By the way, your calculator seems to include prefetched pages in the calculation. (link rel="prefetch".) Not sure if that's deliberate or not.