Figure 1b is diffuse because it's from a very big source. Note that edges be-tween light and shade can't be defined, so visual emphasis here is on the actual form and texture of objects in the scene. Figures 2a, 2b. Total contrast and local contrast. Local contrast is mostly altered by the light's direction, and its specular or diffuse nature.
Visual emphasis is on pattern.
Visual emphasis is on form and texture. Figures 3a, 3b. High and low brightness key. The brightness quality of real scenes and objects are seldom duplicated literally on film, even a transparency. Photography interprets brightness.