Yes Mackie lines! Here what I'm talking about. I first learned about it doing a project on solarization photography. It looks like edge or pencil light and I guess those could be..
In photographic science, a Mackie line is an adjacency or border effect created during development, at the border between areas of high and low densities.
During developing, developer remains relatively fresh in an area of low density as less developing takes place and consequently, developer oxidation product concentration remains relatively low. At the border between high and low density areas the relatively fresh developer diffuses laterally into the high density area and causes there a continuation of development. The result is an increased border density of the high density area.[1]
It is worth noting that Mackie heard many different theories to explain these lines (for over 30 years) and did NOT like any of them. Now that people observe these lines in the digital world, the chemical reasons for these lines may be only part of the story. There may also be quantum effects of light transmission involved, and people have developed different methods of scanning documents so as to minimize these effects in the digital world. Net: Mackie lines and different types of edge effects are far from a completely understood even today, and the level of the theory to apply may depend on the application at hand.
