Yeah, not mentioning the filtering for high contrast makes this more confusing than it need be. Actually, the main link is worse than just not mentioning it...

Yeah, not mentioning the filtering for high contrast makes this more confusing than it need be. Actually, the main link is worse than just not mentioning it... it says "randomly choose 3-by-3 pixel patches" and leaves it at that. Saying "random" rather than "random then filtered" is worse then just saying nothing and letting the reader guess that maybe there is something going on in the choosing.