Comment by bee_rider

English is my native tongue, but it doesn’t really help analyze this type of thing. Titles often use terms-of-art and shortened phrases.

But, fwiw, to my eyeballs “Physics based rendering techniques,” because it uses the word Physics, as in the whole big field of study, looks like it is a Physics text that happens to include a bit of rendering.

“Physically based rendering techniques” seems like it is a work about rendering techniques, which will draw a lot from physics.