In this photo from Oaxaca, two of the workers are in a shadow and two are in sunlight. The two in front separate from the background more obviously. If you were painting the scene, which variables would you adjust to show the difference? What if you wanted to exaggerate it? What could you do, then?
How much does the illusion of space in this image depend on edge quality working to separate the major shapes? Do you think it would be possible to make a reasonable version of this scene with no hard edges? Would there still be a feeling of space?
To practice making conscious choices about value, color, composition and wetness as tools for separating shapes in space, make a few quick studies where you adjust the variables differently. Be prepared to describe what you chose to do.