31–40 of 115 posts
I thought his method of multiplexing the single channel was very smart. I guess it's more common on 2 channel or high end 4 channel scopes to have a dedicated trigger input, which I've checked this one doesn't have. That said, there're digital inputs that could've been used. Presumably from whatever was controlling the laser.
Earlier quoted context omitted.
They did the way more expensive version briefly mentioned towards the start of the video, having 12+ cameras with ridiculously fast shutters (as low as 10 nanoseconds) arranged to run in seqeunce.
That was probably not the more expensive version in that case.
He scans one line at a time with a mirror into a photomultiplier tube which can detect single photon events. This is captured continually at 2MSample/s (2 billion times per second: 2B FPS) with an oscilloscope and a clever hack.
The laser is actually pulsing at 30KHz, and the oscilloscope capture is synchronized to the laser pulse.
So we consider each 30KHz pulse a single event in a single pixel (even though the mirror is rotating continuously). So he runs the experiment 30,000 times per second, each one recording a single pixel at 2B FPS for a few microseconds. Each pixel-sized video is then tiled into a cohesive image
The triggering scheme is completely brilliant. One of those cases where not knowing too much made it possible, because someone who does analog debug would never do that (because they would have a 50k$ scope!.
Tl:dw for how this works: He scans one line at a time with a mirror into a photomultiplier tube which can detect single photon events. This is captured continually at 2MSample/s (2 billion times per second: 2B FPS) with an oscilloscope and a clever hack. The laser is actually pulsing at 30KHz, and the oscilloscope capture is synchronized to the laser pulse. So we consider each 30KHz pulse a single event in a single p…
Ah, two billion. The first several times I saw this it looked like "twenty eight", which didn't seem terribly interesting.
The video is definitely more interesting than 28 fps but it's also not really 2B fps. It captures two billion pixels per second. Essentially he captures the same scene several times (presumably 921,600 times to form a full 720 picture), watching a single pixel at a time, and composite all the captures together for form frames. I suppose that for entirely deterministic and repeatable scenes, where you also don't care…
As you say: It does capture two billion pixels per second. It does watch a single pixel at a time, 921,600 times. And these pixels [each individually recorded at 2B FPS] are ultimately used to create a composition that embodies a 1280x720 video.
That's all correct.
And your summary is also correct: It definitely does not really capture 2 billion frames per second.
Unless we're severely distorting the definition of a "video frame" to also include "one image in a series of images that can be as small as one pixel," then accomplishing 2B entire frames per second is madness with today's technology.
As stated at ~3:43 in the video: "Basically, if you want to record video at 2 billion frames per second, you pretty much can't. Not at any reasonable resolution, with any reasonably-accessible consumer technology, for any remotely reasonable price. Which is why setups like this kind of cheat."
You appear to be in complete agreement with AlphaPhoenix, the presenter of this very finely-produced video.
Earlier quoted context omitted.
The video is definitely more interesting than 28 fps but it's also not really 2B fps. It captures two billion pixels per second. Essentially he captures the same scene several times (presumably 921,600 times to form a full 720 picture), watching a single pixel at a time, and composite all the captures together for form frames. I suppose that for entirely deterministic and repeatable scenes, where you also don't care…
Others say that you're wrong, but I think you're describing it approximately perfectly. As you say: It does capture two billion pixels per second. It does watch a single pixel at a time, 921,600 times. And these pixels [each individually recorded at 2B FPS] are ultimately used to create a composition that embodies a 1280x720 video. That's all correct. And your summary is also correct: It definitely does not really ca…
What is your definition of "video frame" if not this?
> that can be as small as one pixel,"
Why would this be a criteria on the images? If it is, what is the minimum resolution to count as a video frame? Must I have at least two pixels for some reason? Four so that I have a grid? These seem like weird constraints to try and attach to the definition when they don't enable anything that the 1x1 camera doesn't - nor are the meaningfully harder to build devices that capture.
I agree the final result presented to the viewer is a composite... but it seems to me that it's a composite of a million videos.
Earlier quoted context omitted.
Others say that you're wrong, but I think you're describing it approximately perfectly. As you say: It does capture two billion pixels per second. It does watch a single pixel at a time, 921,600 times. And these pixels [each individually recorded at 2B FPS] are ultimately used to create a composition that embodies a 1280x720 video. That's all correct. And your summary is also correct: It definitely does not really ca…
> Unless we're severely distorting the definition of a "video frame" to also include "one image in a series of images What is your definition of "video frame" if not this? > that can be as small as one pixel," Why would this be a criteria on the images? If it is, what is the minimum resolution to count as a video frame? Must I have at least two pixels for some reason? Four so that I have a grid? These seem like weird…
That term is "pixel".