Hi Jeff, I’m worried by this part:
Yes, it is technically possible to produce strange “lossy” PNG images, but I think that’s counter to the spirit of PNG which is designed for lossless images. If you want lossy images, go with JPG or another lossy format.
You’re getting hung up on categories that aren’t the best categories to get hung up on. To not use lossy optimizations on PNGs is a huge waste of bandwidth, since we know that lossy – but visually lossless – optimizations can drastically reduce the size of PNG images. To not do that because it’s “counter to the spirit of PNG” is to basically light your money on fire (and waste energy, increase page load time, etc.) Image formats have no spirit, just bytes.
PNG is designed for graphics. You wouldn’t want to use JPEG or JPEG-2000 for graphics just to adhere to the spirit of different formats. When you’re dealing with images like your cartoon example, PNG by default is going to waste a lot of space describing fairly simple patterns of shape and color. For that kind of image you can use a good lossy optimizer like PNG Quant and what they do at TinyPNG.com, and reduce the file size by more than 50% with no visual difference.
Here’s the proof: Imgur: The magic of the Internet
Can you tell the difference between yours and this 163 KB version? (It was produced by TinyPNG.com)
Note that these kinds of savings are common in lossy PNG optimization of crude images – by crude I mean cartoons, graphics, and so forth where the math of PNG is extremely inefficient in describing the visual manifestation of the image. webp gets similar results, and the new “near-lossless” mode of webp is pretty good too.