EXIF orientation info in PNGs isn't used for image-orientation: from-image

I personally like the status quo that PNGs don't encode orientation. I can dump PNGs when I'm debugging and I know I'm looking at the bits the same way up as the code is!

PNG now does - and they've been as vague as they could be in the spec about whether any exif data should affect the image display or not. The spec says:

"It is recommended that unless a decoder has independent knowledge of the validity of the Exif data, the data should be considered to be of historical value only."

Instead of either saying: "yes you must rotate it" or "no you shall not rotate it" to make everyone do the same thing. And if it were yes, they should also have made this a mandatory chunk since now they made it optional to read.

That’s pretty typical in technical standards. It’s so that existing software isn’t forced to choose between the Scylla of not being able to claim conformance to the updated standard and the Charybdis of breaking backwards compatibility.