I'm disappointed the article and all the comments here ignored Mach banding...
On top of all the mechanism that would distribute the solids in a bit of a ring, we also have a perceptual distortion that would enhance the contrast a bit, making it look like a stronger gradient than it actually is.
On top of all the mechanism that would distribute the solids in a bit of a ring, we also have a perceptual distortion that would enhance the contrast a bit, making it look like a stronger gradient than it actually is.