I am not understanding the difference between 4D light field and 2D photograph? In a 2D photograph, we are sampling one vertical column on the grid to the right for a single pixel. What are we doing in 4D light field photography that is different?
As I understand it, we get more detail from looking at light as a 4d function, and carving out 2d slices from it can give new perspectives on the scene because light can be more accurately represented as a 4d function than a 2d function.
I think this slide is also alluding to how cameras capture images imperfectly, and how getting a "perfect" capture of a scene (if such a thing is even possible) would entail an immense amount of data.