By that definition, all formats are lossy, because any preprocessing could be lossy, and the word loses all meaning … which is why we don't use that definition.
replyBy what definition? I didn’t say anything was lossy; I said you couldn’t be sure that the image was lossless just from the extension. Of course, it might still be, and you might have other reasons to know it to be.
replyThe word doesn't lose definition, it has different definitions for codecs and images.
replyIf you reencode a jpeg to a png, you used a lossless format but your image is very lossy.
It's not the PNG encoding that causes the loss. The optimisers are literally creating a different image and then losslessly encoding it as PNG.
replyBut it's also a valid point.