Ah! Ok, I get this now. This is the relationship between frequency and resolution. Higher frequency creates a finer pattern of bright and dark samples, which means more detail. And a complex image is made of a combination of different patterns. I think I get it now without learning too deep about Fourier transforms. BTW,
this video is awesome! I think I understand the concept now.
So, there is a "cloud" of frequencies around the carrier representing a complex pattern. This cloud changes every 1/60 of a second for interlaced video. Well, actually it changes constantly, as analog video is just one big string of samples. I guess my attempts to imagine how it would look like in static are pointless, because frequency by definition presumes something happening over time.
I am not sure this helps me understand the relationship between the pattern onscreen and some of its parts being brighter or darker.