[OJFord]

Surely anything other than duplicating each pixel x times both horizontally and vertically (so 1 turns into 4, or 9, or 16, ...) adds information?

(This submission is going to have me reaching for my old textbooks.. about time really!)

[geon]

No. Nearest neighbor, bilinear bicubic etc. is just encoding the same information in different ways.

You could add noise, or generate new details with an ai upscaler. That would create new information.

[OJFord]

Ah, right, anything that's a function purely of what's in the image - no randomness, no external context/'knowledge' to interpret it semantically, is as you say 'encoding the same information in different ways'?

If it can be computed (deterministically) from the image alone, then it was already there.