> Let's suppose the aim of the article was indeed to learn PBR from first principles, what would it look like?

Well given the title I at least expected the article to explain or derive things like why and how metals and their alloys have the color (wavelenght-dependent complex index of refraction) that they do, why and how say quartz crystals have different colors, birefringence, fluorescence (makes T-shirts appear extra bright) etc.

And there is no mention of the recording process. Are we simulating good old film with its silver crystals of various sizes? Different film stock is known to have very different looks due to their chemistry.

Or a digital camera sensor with its quantum and thermal noise, bayer filter and a rolling shutter causing those funny-looking propeller pictures?

Not knocking the article, but given the title it fell well short of my expectations going in. That is, I was wondering how on earth anyone had managed to do all that.

Yes I didn't have time to write a chapter about camera sensors, the human retina, and the whole image formation process. I'll definitely expand on this later on.