Bride Of Slenderman

November 14, 2012 6:55 AM

While slit-scan photography is most well known for the "stargate" sequence in 2001: A Space Odyssey, advances in technology now allow it to be applied to moving objects in 3D. (via)
posted by The Whelk (35 comments total)

Can someone PLEASE explain how slit-scan works as if I am a small child? I've read the Wikipedia entry, other MeFi discussions, random websites and even played around with Processing code that works w/ webcam input and I still do not understand what is going on.
posted by griphus at 6:59 AM on November 14, 2012 [2 favorites]

I very much like the briefly glimpsed passerby at around 2:45: while the man and the woman in the foreground are twirling around each other, some random pedestrian is walking through the park on a fall afternoon, unaware that her gait has been turned into a Seussian galumph.
posted by ricochet biscuit at 7:05 AM on November 14, 2012 [1 favorite]

griphus: Break the video signal up into horizontal lines. Delay each line slightly more than the one above it. That's all there is to it.

Golan Levin maintains the best linkdump of all things slitscan.
posted by phrontist at 7:08 AM on November 14, 2012 [1 favorite]

Memo Akten has been experimenting on how to use slit-scan in actual 3d with the Kinect and come up with some pretty cool results.
posted by skullbee at 7:09 AM on November 14, 2012

Break the video signal up into horizontal lines. Delay each line slightly more than the one above it.

Nope. Draw a picture because this still makes no sense.
posted by DU at 7:13 AM on November 14, 2012

griphus, if you've an iPhone then grab the free version of "Slit-Scan". You will quickly get it.

Basically, instead of a camera that captures a 2D image at a single moment, you have one that captures a 1D image (a vertical line) over a series of moments. Each of these 1D slices of time is placed alongside the slice one prior to it, so in the finished image the passage of time is represented horizontally across the image.

Animated slit-scans are a bit more complex.
posted by phl at 7:16 AM on November 14, 2012

While slit-scan photography is most well known for the "stargate" sequence in 2001: A Space Odyssey

Don't forget the rather iconic 1970s openings to Doctor Who!
posted by RonButNotStupid at 7:18 AM on November 14, 2012 [1 favorite]

Okay, I have a better idea of what is happening in the linked video, but how are the 2001/Doctor Who sequences made? Or, rather, what is the base video of?
posted by griphus at 7:19 AM on November 14, 2012

I understand about taking slit photographs and reassembling them and THAT this will warp time and space. But what continues to be elided in all explanations I've ever found is exactly HOW that occurs. What is moving relative to what in what direction and with what speed so as to get a wavy line vs a straight one.
posted by DU at 7:24 AM on November 14, 2012

Whoops. The first Doctor Who title link is someone's (very faithful) recreation. Here's the actual example.
posted by RonButNotStupid at 7:26 AM on November 14, 2012

Okay, so:

When you record a video image, you are recording a whole bunch of individual rows of image data. In 1080p HD, for example, the 1080 is how many rows of pixels are stacked top to bottom to make the image: one thousand and eighty.

In normal video, when you record each frame, you're recording those thousand and eighty lines with the expectation that they'll all be displayed again during the same 30th (or in this case 60th) of a second: the picture recorded is the picture played back.

What this does is push back the moment when each row of pixels is displayed proportional to how far down the frame it is. So, let's say the first row of pixels from frame 1 of the recording plays on frame 1 of playback. But the second row plays on frame 2 of playback; the third on frame 3; and so on. What this means practically is that a movement that starts in frame 1 of the original recording will start happening at the top of the video on frame 1 of playback but will not start happening at the bottom of the video until many, many frames later. And so that movement ripples downward through the video.

So when someone does a pirouette, in reality they've turned their whole body around at once over the period of about a second, let's say. But in the processed video, their head starts turning right away, their neck a little bit later, their shoulders a bit later, then their torso, hips, thighs, knees, feet. The slow downward wiping delay creates this timewarp effect where what happens at the top of the video is always a second or two ahead of what happens at the bottom. It's a simple trick, but it creates a pretty wonderful little jellyfish effect as a result.

(The funny thing is that this is actually just an intentional exaggeration of what is a basic, built-in problem with a lot of video scanning hardware; you can see slight echoes of this sort of weird distortion when someone films a fast moving object or makes fast camera moves with a Canon 7D or 5D mkII because the camera scanning the video sensor many times a second still start scanning the image a fraction of a second at the top of the frame before it finishes scanning it at the bottom.)
posted by cortex at 7:26 AM on November 14, 2012 [6 favorites]

This is nifty.
posted by weapons-grade pandemonium at 7:28 AM on November 14, 2012 [1 favorite]

What is moving relative to what in what direction and with what speed so as to get a wavy line vs a straight one.

I think constant velocity will get you the straight lines, but when the images accelerate they create curvy lines. Check out the guy when he first enters the frame, he's pretty straight on the way in.
posted by grog at 7:28 AM on November 14, 2012

griphus, a Clever Person has actually reversed engineered the stargate sequence and reconstructed the original images.

Essentially it's stop-motion sequence of slit-scan photos. Take a slit-scan frame, move the camera a bit, do another one - so you get that impression of flying past/through the image. Also the individual stargate frames are done by moving the camera toward the subject image as well as across it, so the slit-scan is smeared in perspective instead of just flat across the frame.
posted by phl at 7:30 AM on November 14, 2012 [3 favorites]

Oh, so that's how they did that bit in the Look Away Lucifer video (about the 3 minute mark).
posted by edheil at 7:32 AM on November 14, 2012

Hooray for MetaFilter! I now kinda sorta grasp it. Thanks y'all.
posted by griphus at 7:33 AM on November 14, 2012

OK, so the explanation in the FPP link is just BS then?

The camera views the world through an unmoving vertical slit, taking successive shots over time. The left side of the image here corresponds to the earlier shots and the last sliver on the far right is the most recent. It's a time-panorama. The background didn't move, so is smeared out, but the farmer and his buffalos passed by. If the farmer had stopped for a while in front of the slit he would appear elongated; had he raced past the camera, he would appear compacted.

No wait, I get it. The problem with this explanation is the words "smeared out". Nothing is smeared out. That would imply motion of something (camera, slit or scenery).

The background that isn't moving only ever gets a single slice photo taken of it, so that's all we see repeated across the screen. The yak or whatever moves past at exactly the right speed so we take a bunch of slice photos of it and when stacked together we can see the whole thing.
posted by DU at 7:35 AM on November 14, 2012 [1 favorite]

I understand about taking slit photographs and reassembling them and THAT this will warp time and space. But what continues to be elided in all explanations I've ever found is exactly HOW that occurs. What is moving relative to what in what direction and with what speed so as to get a wavy line vs a straight one.
posted by DU at 7:24 AM

You have access to a photocopier, right? OK. Take a photograph of, say Einstein, and put it on the photocopier. When you press the copy button, move the photo on the glass. If you move it the same direction as the light bar is moving, Einstein will be stretched. If you move it the opposite way, he will be compacted. If you move it up and down as the light bar moves across, Einstein will be wavy. Relativity.
posted by weapons-grade pandemonium at 7:39 AM on November 14, 2012 [4 favorites]

Caveat: Your boss will wonder why the volume of photocopies has doubled in a month.
Tell her it has something to do with relativity.
posted by weapons-grade pandemonium at 7:41 AM on November 14, 2012 [1 favorite]

I think lifehacker used a terrible image to illustrate the idea. I get intuitively how the vimeo works; I don't get at all how the lifehacker image could have been put together with a stationary camera as an example of slit-scan photography. The photographer would have to have been moving parallel to the buffalo, and at the same speed.
posted by postcommunism at 8:06 AM on November 14, 2012

That's a great explanation, weapons-grade, I never occurred to me that photocopiers produce slit-scan images. Same is true of scanners too, of course.

In fact, if the original subject of MeFi's first ever post was still online, you'd be able to see some slit-scanned cats, and what happens when the cats move relative to the slit.
posted by phl at 8:07 AM on November 14, 2012 [1 favorite]

If?
posted by cortex at 8:14 AM on November 14, 2012

Just recently I discovered/realized that Cat-Scan was made by Cliff Bleszinski. Kind of blew my mind.
posted by zsazsa at 8:21 AM on November 14, 2012 [1 favorite]

holy crap really

Am I being so gullible right now?
posted by postcommunism at 8:41 AM on November 14, 2012

There are several 'web-apps' that allow your webcam to do this effect right at home.

This is one, a cool one, seemingly built by the person behind 'star wars uncut' (I was on another one recently, but the link is eluding me right now), this is another one, with links to other webcam effects.
Oh, awesome, "An Informal Catalogue of Slit-Scan Video Artworks and Research"

Slitscan imaging techniques are used to create static images of time-based phenomena. In traditional film photography, slit scan images are created by exposing film as it slides past a slit-shaped aperture. In the digital realm, thin slices are extracted from a sequence of video frames, and concatenated into a new image.

cool post, btw.
posted by infinite intimation at 8:43 AM on November 14, 2012

The inevitable pornography will be disturbing.
posted by Curious Artificer at 8:56 AM on November 14, 2012

disturbingly hot.
posted by The Whelk at 9:01 AM on November 14, 2012 [1 favorite]

postcommunism: really!
posted by zsazsa at 9:13 AM on November 14, 2012 [1 favorite]

woah, the "better light" imager is neat (shooting the waves, intentional misuse).

This page sort of helps comprehend what slit scan is all about, but let the "informal catalogue of slit scannerism" fully load, there are lots of informative and cool links (like to the liquid time art installation).

inevitable (1988)?
posted by infinite intimation at 9:18 AM on November 14, 2012

The inevitable pornography will be disturbing.

Huh, I am thinking about this and you'd probably have to rotate the camera to match the direction of the motion to have it be a workable effect.
posted by griphus at 10:23 AM on November 14, 2012

Also, assuming there are women in it, titling the film Slit Scan is the most perfect thing I can think of.
posted by griphus at 10:24 AM on November 14, 2012

weapons-grade pandemonium: "You have access to a photocopier, right? OK. Take a photograph of, say Einstein, and put it on the photocopier. When you press the copy button, move the photo on the glass. If you move it the same direction as the light bar is moving, Einstein will be stretched. If you move it the opposite way, he will be compacted. If you move it up and down as the light bar moves across, Einstein will be wavy. Relativity."

I have no idea how these people got their Einsteins wedged into their photocopiers, or why.
posted by radwolf76 at 11:35 AM on November 14, 2012

The inevitable pornography will be disturbing
Slit Scan is the most perfect thing I can think of.

I believe you overlooked "Slit Scan Sluts".
The only thing more disturbing would be trying to say that five times fast.
posted by weapons-grade pandemonium at 12:14 PM on November 14, 2012

Her hair swinging; I'll be in my bunk.
posted by humboldt32 at 1:14 PM on November 14, 2012

1) Man, this is cool. Took a while to get my head around, though.
2) Holy shit, Cliffy B made cat-scan.com?!
posted by Bugbread at 8:02 PM on November 14, 2012