This is a sequence of image of indices. The background wall in the physical world does not change its intensity. However, in image of indices it receives lower ranking (i.e., "darker" values) when the scene is predominantly filled with brighter surfaces (e.g., face).  When the darker surfaces enter the scene (e.g., subjects hair), the wall receives comparatively higher indices (i.e., "brighter" values).  The sensor automatically adapts to the scene content

*The sorting sensor is a 21x26-pixel prototype.