"it only applies for low-contrast backgrounds, like in these examples, for high-contrast backgrounds it doesn't necessarily make scanning harder" Not sure what

"it only applies for low-contrast backgrounds, like in these examples, for high-contrast backgrounds it doesn't necessarily make scanning harder" Not sure what you mean... It seems like these examples are very high contrast, no? There are multiple places where a pixel is (255,255,255) and an adjacent pixel is about (63,63,63), for example.