I was surprised that it is possible to apply simple(?) signal processing techniques to extract subtle signals from a video, e.g. somebody's heartbeat.
Surprise levels:
1) I never thought of that (that there could be useful hidden signals in standard video). Their paper references a few other attempts at this.
2) If I had thought of it, or someone had mentioned the idea, I would have guessed that those signals are not strong enough to
be extracted by any method.
3) And, even if there were a signal, I would have thought it would take very powerful techniques and many assumptions (like manually annotating where you expect to see the heartbeat, etc.) to make it work.
This is required less than I'd expect. From the paper:
we auto- matically select, and then amplify, a band of temporal frequencies that includes plausible human heart rates.
The same way we could obtain details from an astronomy video. One hour of a video of a distant planet might be worth of a big telescope, The long exposition time was the first step in this direction, long ago.
The current exo planet detection is another, bigger.
We simply don't yet use every information we have.
I recently flipped through the "Cartoon Guide to Physics", expecting an easy-to-understand rehash of ideas I was long familiar with; and that's what I got - right up to the last few pages, where I was presented with a fairly fundamental concept that's been absent from the popular science media I've enjoyed over the years. (Specifically, that the uncertainty principle, when expressed as linking energy and time, explains what electromagnetic fields actually /are/, as the propensity for virtual photons of various strengths to happen.) I find myself happy to try to integrate this new understanding - and at least mildly disturbed that I'd been missing it for so long, and with an increased curiosity about how I might find any other such gaps in my understanding of how the universe works.
So: what's the biggest, or most surprising, or most interesting concept /you/ have learned of, after you'd already gotten a handle on the basics?