Questions on Form and Light

[OtherMuzz]

First off, this is a terrible image to study, it has way too much going on, is an extreme crop, and has multiple materials and textures in it. There is a reason why we study casts and statues instead of photos like this.



This photo is far more understandable to a student.

What you need to wrap your head around is the idea that a cast/core shadow exists any-time the form is 90deg or more from the light source, and everything else is lit. Within the lit area it is way more complicated, but the best way to explain it is that every angle will have a different value associated with it.

If it is perpendicular with the ray, it is fully lit, if it is at an angle, then it is partially lit. Lamberts cosine law is the mathematical equivalent of what you are trying to learn. The easiest way to express that is cos(angle) where the output is a percentage between 0-1.

I've found the best way to hammer these things into your brain is subdividing activities, like making a box out of value, and then subdividing it, using a fully opaque brush. Like this.