OK, let me expand on my thought.... There are a number of dynamics at work here. You have the light, the subject and the instrument used to take the picture(s). All these dynamics MUST be taken into consideration. In the example I tried to mimic you have the Sun light, the room, the subject and the camera. The subject leans over into shadow and the photographer has to adjust the camera's exposure settings to properly capture the image. If the subject stands up straight, her face will be in direct sunlight and thus force the photographer to re-adjust the camera's exposure settings accordingly. What has changed between leaning over and standing up straight? The amount of sunlight entering the room remains constant. The light bouncing around that room remains constant. The subject (for the most part) remains constant. What has changed is the amount of light relected into the camera. The photographer MUST adjust the exposure settings (ie: f-stop, shutter speed) inorder to deal with changes in the amount of light entering the lens. The dynamic of "camera settings and exposure levels" is VERY important with regard to the examples you have given. The VSS process does not deal with the dynamics of light intensity, it does not deal with the dynamics camera exposure - it deals, mostly, with how light bounces/reflects off the subject matter. (...continued next post)