Optical Flow - Computerphile

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Pixel level movement in images - Dr Andy French takes us through the idea of Optic or Optical Flow.

More on Optic Flow: Coming Soon

This video was filmed and edited by Sean Riley.

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One of my instructors once said if someone is talking about some idea and lists the flaws in that, Its a great idea and they understand it very well. Im looking forward to see more of him

MrSigmaSharp

This guy is the reason why I subscribed to Computerphile :)

riyabanerjee

He never explained how you detect motion between images., only that it is "hard" for various reasons. How do you generate those vectors?

gorkyrojas

Just wondering. Modern video compression formats use vectors a lot already. Does it really take that much EXTRA calculation to detect stuff like a shaky image, or can you just use the existing video compression vectors to stabilise the image? If you want to record an image with stabilisation, would it be possible to do a kind of two-pass recording? Push it through the video compression circuitry once to get stabilisation data, then correct the image, and feed the corrected image through again for actual compression and saving?

ArumesYT

Doing essentially the same thing with lightness-independent colour channels as well (perhaps the a and b channels in the Lab colour space) seems like it could be very useful in many circumstances where the lighting varies. The amount of light reflected by a physical object might vary quite often, but the colour of most objects doesn't change as much. Still, you'd want to be able to detect a black ball moving against a white background, so *only* using colour information won't work because you'll miss some motion entirely. Given that you *do* detect motion in the colour channel though, I'd expect to have a higher confidence that something was actually moving as described, so it's kind of interesting to think about how you'd want to combine the results.

cgibbard

Speaking of optical and computers, Anynoe there at the UNI know anything reasonable on Optic CPUs ?

st_ProCactus

Your video really needs the Video Stabilization algorithm, which was made available by optical flow!

ericxu

what is optical flow good for? in a simple language

retfewte

You did him dirty with the thumbnail lol

zachwolf

Could your cameraman perhaps drink decaf instead of twelve cups of strong coffee before filming?

russell

Beautiful topic, thanks for making me more aware of it.

ashwanishahrawat

I would expect that the real processing should be much simpler, because otherwise it would need weeks of analysing every pixel in every frame. So you just look whether the whole image is rotated and how much, if the whole image is shifted up/down, left/right and the whole image is zoomed in or out. That's work enough for hirez images.

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