Eyes are good at generating the signal or we wouldn't have much use for the vision they do provide us.
On a somewhat related note, due to a head injury I suffered now many years ago, I started developing small-ish blind spots "once in a while" that remain anywhere from a few minutes up to a few months.
The spots are very noticeable when they first appear, grabbing the attention all the time. The ones that persist long tend to "disappear" when my brain filters out the broken (?) signal of where the blind spot appeared, and the spot mainly becomes noticeable again if it hides or interrupts a known pattern that I'm looking at.
It's as if the brain fills the spot with the average color around it (blue sky - blue spot, white wall - white spot etc), which works well for single color surfaces and such but not great for repeating and predictable patterns. And the hiding "lags" which means if I quickly shift between colors then the spot will momentarily be visible as the old color shows up on the new color.
So the brain does "imagine" things, but when it does, it isn't perfect.
