Hey, it's me, Matt. Welcome back to standupmaths.
Now, rolling shutters. A recap if you've not been on YouTube for the past week or so.
Digital cameras, like while I'm filming on now, expose the top row of pixels
before they expose the bottom row.
The exposure kind of rolls across the sensor, which means if you've got anything
moving within that frame on the same speed or faster than the rate at which the shutter is rolling,
you get these all kind of
It also means you get photos like one of my favorite photos here,
where someone was shooting a water balloon
with an air rifle, and the shadow balloon has burst before the real balloon, and that's because with a rolling shutter
the bottom of the frame is newer than the old.
The old bit at the top-- the top is the past; the bottom is the future.
SmarterEveryDay, a fantastic
science and curiosity YouTube channel (I assume you're all already subscribed)
did a video about the rolling shutter effect and all the
science YouTubers collectively wet themselves over how good this explanation was
and I'll be honest it was very good,
but I have two issues with Destin's explanation.
First of all, he beat me to it.
Like him, I had also been collecting examples of rolling shutter whenever I saw it.
So when I was in Australia recently and I was flying on a prop plane between Sydney and Canberra,
I took this footage where you can see the propellers do weird things,
and as you rotate the phone, the weird, distorted, fragmented bits of propellers go in different directions.
And so I was gradually accumulating this footage thinking I'll do a video and he beat me to it,
admittedly with a fantastic explanation.
So if you haven't seen his video watch it now or watch it after this.
It is a very good way of looking at the effect.
My second and perhaps only genuine
problem with the SmarterEveryDay video is that Destin put in too much effort.
Yes, he came up with a turbo-awesome way of showing the rolling shutter effect
by getting a slow-motion camera and
filming the propellers on a plane and then recreating it in After Effects afterwards.
But he didn't have to go to all that effort for something to be so stinkin' cool.
I've just bought a propeller.
It cost me less than ten pounds, and I could do exactly the same thing with this
for a fraction of the cost and effort.
So the propellers on the planes Destin was using will be spinning about 2,000 RPM (revolutions per minute).
He wanted to look like they were spinning a lot slower, and so he filmed it with a high-speed camera,
let's say at 10,000 frames per second,
he plays it back at 30 frames per second,
and his footage makes it look like the propellers were spinning at about 6 RPM,
about once every 10 seconds, and that he can use for his special effects.
But why not just film the propellers rotating at 6 RPM?
Because if I rotate this at 6 RPM
and I film it at 30 frames and play it back at 30 frames,
it looks like it's going at 6 RPM.
If you film a fast-moving thing with a slow-motion camera,
it makes it look like the same thing moving slowly.
Just move that thing slowly.
So I have got a drill. I have attached two of these on the thing to get kind of four props.
I have some-- I've put some gardening wire on the trigger.
That's probably not a good idea as far as safety is concerned.
But what I want to be able to do is line this up, there we go, right in front of the camera.
And-- you know, also he use big propellers.
Big propellers a long way from a camera look exactly the same size as small propellers right near the camera.
So if I get this going…
That in shot there. Haha!
See? That is exactly the same.
Okay, enough of that.
It's probably not very good for the drill, but now we've got our footage,
we can do a little bit of processing.
Okay, so Destin took Henry away from making fantastic
physics videos for Minute Physics and Minute Earth,
I recommend checking them out, very good channels,
to do some After Effects effects to get the rolling shutter effect to work.
All I'm doing here is I'm writing a few lines of Python code that takes the top row of one frame,
pastes at the top, takes a second row from the second frame, third row from the third frame, and so on.
Once I export that back into a video, I now just line up a wipe effect, which is synchronized with a
horizontal green line, add some emotional music, and… we're done.
Wait-- wait-- wait-- wait-- branding! There we are.
Let's see you steal that and turn it into a gif or whatever you kids do.
So there you are. You don't need an expensive slow-mo camera, trip across the Australian outback,
and a prop plane, and, you know, complicated After Effects.
You just need a toy propeller and a few lines of Python code.
I achieved the same thing for under 10 pounds.
Assuming my time is worthless.
If you want to try this yourself, I will put the Python code in the description below.
If you improve what I've done or make it more user friendly, please do share it as well.
But there's an even easier way, which Destin was so close to doing.
You can actually just print out some propellers, which I've done here,
you stick them onto a circle of cardboard,
you put that onto a scanner, and now, while you're scanning it,
you just rotate it at as constant a rate as you can manage, which I'm doing terribly.
And… it's not perfect 'cause you're doing it by hand, but still,
for just printing something out and putting on a scanner, that's pretty cool.
In fact, I've even got here, I wouldn't normally show this, this is my
original prototype when I was first just testing out if this idea would work,
and even that was…
I mean, it was terrible, right?
But it's a proof of concept.
So I will have a link to this down below as well.
Print it out yourself, put on a scanner.
And a scanner genuinely is a fantastic way to play with the rolling shutter effect.
Pro tip: if you want to change the speed at which it's moving,
change the resolution it's scanning at.
So a quick scan at 100 DPI, a slow scan at 600 or greater.
In conclusion, Destin does make amazing videos;
he sets the standard for what you can do with science videos on YouTube.
You absolutely should subscribe to SmarterEveryDay if you haven't already.
But, when you watch his videos, always be thinking
could you try this yourself at home a lot easier and a lot cheaper?
So, thank you very much for watching my video about his video.
I hope you have a good, which is equal to or greater than one.