Don’t know that I’ll be able to describe this properly…
Every so often when I’m watching TV there will be a shot where there are no animate objects on the screen. It seems to me that I can tell the difference between when the shot is actually a live, filmed shot, and when it’s just a still image. What I can’t figure out is what the difference is that I’m seeing. Everything is motionless anyway, so I can’t see that it’s a lack of movement…
Does this make sense? Is there a simple explanation for what the difference is?
I’m not sure what you’re saying because there is no such thing as a moving picture. All film and all video is stills displayed in succession. I think perhaps what you are seeing is that when filmed, even a scene with no action will still usually show some “movement” even if it is nothing more than silghtly different exposures from frame to frame. If an actual still is inserted into the film or video at editing, it doesn’t show any variation at all from frame to frame and so that may be what you are noticing.
You may be talking about grain lock.
The emulsion grain that we’re usually not aware of is in constant “motion” from frame to frame. In a freeze frame the grain from the original frame, which is repeated over and over depending on how long the FF is, doesn’t “move”.
Agreeing with jimpatro. If you are watching a film, a freeze frame will have grain lock. The freeze frame may also have various other visual artifacts — a bit of dust here or there, a small scratch — that would normally go by too fast for you to take notice.