4 ms·

Yeah, that is pretty wild. I recall a co-worker doing something related(?) for a kind of fun tech demo some ten years or so ago. If I recall it was shooting vi

Yeah, that is pretty wild. I recall a co-worker doing something related(?) for a kind of fun tech demo some ten years or so ago. If I recall it was shooting video while passing a slightly ajar office door. His code reconstructed the full image of the office from the "traveling slit". I think about that all the time when I find myself in a public bathroom stall.... :-/

Agree2468 2y ago
Line scan cameras operate on this principle, and are still used in various ways to this days. I'm especially partial to the surreal photos generated by them at the end of cycling races https://finishlynx.com/photo-finish-trentin-sagan-tour-de-france/ https://finishlynx.com/photo-finish-trentin-sagan-tour-de-fr...
- JKCalhoun 2y ago
  I was not aware of those. Reminds me of slit-scan as well. And of course rolling shutters.
- whycome 2y ago
  Similar to https://hackaday.com/2024/08/17/olympic-sprint-decided-by-40000-fps-photo-finish/ https://hackaday.com/2024/08/17/olympic-sprint-decided-by-40...
- hifikuno 2y ago
  I love line scan cameras. Wikipedia has an awesome photo of a tram taken with a line scan camera on the relevant wiki page[1]. I've just moved to a house with a train line track out front. I want to see if I can use a normal camera to emulate a line scan camera. I have tried with a few random YouTube videos I found [2]. I think the biggest issue I face is that there simply isn't the frame rate in most camera's to get a nicely detailed line scan effect. --- [1]: https://en.wikipedia.org/wiki/Line-scan_camera https://en.wikipedia.org/wiki/Line-scan_camera [2]: https://writing.leafs.quest/programming-fun/line-scanner https://writing.leafs.quest/programming-fun/line-scanner
  - mkl 2y ago
    A normal frame rate is probably enough if you do it with groups of columns rather than a single column of pixels. That's what https://trains.jo-m.ch/ https://trains.jo-m.ch/ does with a Raspberry Pi camera, posted in https://news.ycombinator.com/item?id=35738987 https://news.ycombinator.com/item?id=35738987 with lots of questions and answers.
    - hifikuno 2y ago
      Oh wow that's neat! I honestly didn't think of using chunks instead of a single line and the result looks pretty good. I love the fact the top (or first?) comment is by dllu, and looking on their webpage I saw the tram photo from Wikipedia! It's cool to see the photographer talking about their work. I think about that tram photo so much.
nkrisc 2y ago
> I think about that all the time when I find myself in a public bathroom stall.... :-/ Walk past a closed bathroom stall fast enough and you can essentially do that with your own eyes. Or stand there and quickly shift your head side to side. Just don't do it on one that's occupied, that's not cool.
- donatj 2y ago
  "Sir, why do you keep running back and forth in the bathroom?"
- altruios 2y ago
  The dither effect. Same as seeing through splayed fingers on a franticly oscillating hand.
  - Benjammer 2y ago
    This is the nerdiest way I've ever seen someone talk about John Cena
    - whycome 2y ago
      What's funny is that the described action didn't click until your comment.
- messe 2y ago
  > Walk past a closed bathroom stall fast enough and you can essentially do that with your own eyes Only in the US. The rest of the world has doors without a gap at the sides.
  - freddie_mercury 2y ago
    Doors in Vietnam are exactly the same as in the US. You clearly haven't traveled much so you should refrain from sweeping generalisations.
    - 2y ago
MisterTea 2y ago
> His code reconstructed the full image of the office from the "traveling slit". This method is commonly used in vision systems employing line scan cameras. They are useful in situations where the objects are moving, e.g. along conveyors.
- geerlingguy 2y ago
  Even today most cameras have some amount of rolling shutter—the readout on a high-megapixel sensor is too slow/can't hold the entire sensor in memory instantaneously, so you get a vertical shift to the lines as they're read from top to bottom. Global shutter sensors of similar resolution are usually a bit more expensive. With my old film cameras, at higher shutter speeds, instead of opening the entire frame, it would pass a slit of the front/rear shutter curtain over the film to just expose in a thousandth of a second or less time.
rosswilson 2y ago
This reminds me of https://github.com/jo-m/trainbot https://github.com/jo-m/trainbot, a neat example of stitching together frames of passing trains to form a panorama. This frontend presents them nicely: https://trains.jo-m.ch https://trains.jo-m.ch
- stevage 2y ago
  Surprised I've never come across this idea before
  - all2 2y ago
    For a long time I've wanted to install one of these to pull graffiti off of trains. As art goes, graffiti is one of the last 'free' expressions where it is essentially truly anonymous and definitely not for money. Being free of those constraints, I think, frees the mind to truly create. And I'd love an archive somewhere of some of the truly awesome train art I've seen.
    - jo-m 2y ago
      here you go... https://trains.jo-m.ch/#/trains/44010 https://trains.jo-m.ch/#/trains/44010
quietbritishjim 2y ago
Sorry if you're already aware, but in case not: The weird huge gap around the edge of cubical doors in pubic toilets is specific to the US. (For those that don't know, it's literally 1 or 2 cm.) In Europe you just get a toilet door that shuts properly and there's no slit to reconstruct. I remember my first visit to a toilet in the plush US office of a finance company and thinking WTF are they doing with their toilet cubicle? I only found out later that it's common there.
- stevage 2y ago
  It can be much more than 2cm. The US really hates people for some reason.
  - fc417fc802 2y ago
    I believe it started as an anti-drug thing more than 50 years ago but somehow it became pervasive even in fairly high end settings where you would never expect such measures. Cargo cult bathroom construction IMO. Luckily things seem to be gradually changing.
- nkrisc 2y ago
  I am aware, and of course this works for any gap you might be walking past. Plenty of newer bathroom stalls here do not have a gap.
nzach 2y ago
And if you "reverse" this idea you can make a "holographic(?) display"[0]. [0] - https://www.youtube.com/watch?v=ric-95ig5oE https://www.youtube.com/watch?v=ric-95ig5oE

Agree2468 2y ago

Line scan cameras operate on this principle, and are still used in various ways to this days. I'm especially partial to the surreal photos generated by them at the end of cycling races https://finishlynx.com/photo-finish-trentin-sagan-tour-de-france/ https://finishlynx.com/photo-finish-trentin-sagan-tour-de-fr...

JKCalhoun 2y ago
I was not aware of those. Reminds me of slit-scan as well. And of course rolling shutters.
whycome 2y ago
Similar to https://hackaday.com/2024/08/17/olympic-sprint-decided-by-40000-fps-photo-finish/ https://hackaday.com/2024/08/17/olympic-sprint-decided-by-40...
hifikuno 2y ago
I love line scan cameras. Wikipedia has an awesome photo of a tram taken with a line scan camera on the relevant wiki page[1]. I've just moved to a house with a train line track out front. I want to see if I can use a normal camera to emulate a line scan camera. I have tried with a few random YouTube videos I found [2]. I think the biggest issue I face is that there simply isn't the frame rate in most camera's to get a nicely detailed line scan effect. --- [1]: https://en.wikipedia.org/wiki/Line-scan_camera https://en.wikipedia.org/wiki/Line-scan_camera [2]: https://writing.leafs.quest/programming-fun/line-scanner https://writing.leafs.quest/programming-fun/line-scanner
- mkl 2y ago
  A normal frame rate is probably enough if you do it with groups of columns rather than a single column of pixels. That's what https://trains.jo-m.ch/ https://trains.jo-m.ch/ does with a Raspberry Pi camera, posted in https://news.ycombinator.com/item?id=35738987 https://news.ycombinator.com/item?id=35738987 with lots of questions and answers.
  - hifikuno 2y ago
    Oh wow that's neat! I honestly didn't think of using chunks instead of a single line and the result looks pretty good. I love the fact the top (or first?) comment is by dllu, and looking on their webpage I saw the tram photo from Wikipedia! It's cool to see the photographer talking about their work. I think about that tram photo so much.

nkrisc 2y ago

> I think about that all the time when I find myself in a public bathroom stall.... :-/ Walk past a closed bathroom stall fast enough and you can essentially do that with your own eyes. Or stand there and quickly shift your head side to side. Just don't do it on one that's occupied, that's not cool.

donatj 2y ago
"Sir, why do you keep running back and forth in the bathroom?"
altruios 2y ago
The dither effect. Same as seeing through splayed fingers on a franticly oscillating hand.
- Benjammer 2y ago
  This is the nerdiest way I've ever seen someone talk about John Cena
  - whycome 2y ago
    What's funny is that the described action didn't click until your comment.
messe 2y ago
> Walk past a closed bathroom stall fast enough and you can essentially do that with your own eyes Only in the US. The rest of the world has doors without a gap at the sides.
- freddie_mercury 2y ago
  Doors in Vietnam are exactly the same as in the US. You clearly haven't traveled much so you should refrain from sweeping generalisations.
  - 2y ago

MisterTea 2y ago

> His code reconstructed the full image of the office from the "traveling slit". This method is commonly used in vision systems employing line scan cameras. They are useful in situations where the objects are moving, e.g. along conveyors.

geerlingguy 2y ago
Even today most cameras have some amount of rolling shutter—the readout on a high-megapixel sensor is too slow/can't hold the entire sensor in memory instantaneously, so you get a vertical shift to the lines as they're read from top to bottom. Global shutter sensors of similar resolution are usually a bit more expensive. With my old film cameras, at higher shutter speeds, instead of opening the entire frame, it would pass a slit of the front/rear shutter curtain over the film to just expose in a thousandth of a second or less time.

rosswilson 2y ago

This reminds me of https://github.com/jo-m/trainbot https://github.com/jo-m/trainbot, a neat example of stitching together frames of passing trains to form a panorama. This frontend presents them nicely: https://trains.jo-m.ch https://trains.jo-m.ch

stevage 2y ago
Surprised I've never come across this idea before
- all2 2y ago
  For a long time I've wanted to install one of these to pull graffiti off of trains. As art goes, graffiti is one of the last 'free' expressions where it is essentially truly anonymous and definitely not for money. Being free of those constraints, I think, frees the mind to truly create. And I'd love an archive somewhere of some of the truly awesome train art I've seen.
  - jo-m 2y ago
    here you go... https://trains.jo-m.ch/#/trains/44010 https://trains.jo-m.ch/#/trains/44010

quietbritishjim 2y ago

Sorry if you're already aware, but in case not: The weird huge gap around the edge of cubical doors in pubic toilets is specific to the US. (For those that don't know, it's literally 1 or 2 cm.) In Europe you just get a toilet door that shuts properly and there's no slit to reconstruct. I remember my first visit to a toilet in the plush US office of a finance company and thinking WTF are they doing with their toilet cubicle? I only found out later that it's common there.

stevage 2y ago
It can be much more than 2cm. The US really hates people for some reason.
- fc417fc802 2y ago
  I believe it started as an anti-drug thing more than 50 years ago but somehow it became pervasive even in fairly high end settings where you would never expect such measures. Cargo cult bathroom construction IMO. Luckily things seem to be gradually changing.
nkrisc 2y ago
I am aware, and of course this works for any gap you might be walking past. Plenty of newer bathroom stalls here do not have a gap.

nzach 2y ago

And if you "reverse" this idea you can make a "holographic(?) display"[0]. [0] - https://www.youtube.com/watch?v=ric-95ig5oE https://www.youtube.com/watch?v=ric-95ig5oE