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Photo finishes are typically done with a line scan camera. It only captures a single column of pixels at a time. So the horizontal axis in the image is actually
by porphyra 2y ago
Photo finishes are typically done with a line scan camera. It only captures a single column of pixels at a time. So the horizontal axis in the image is actually time, not space. Super cool stuff.
- SoftTalker 2y agoAh I was wondering why you can't actually see the finish line in the image. This wasn't really described well. Are the shadows of the runners artificial then?
- jetrink 2y ago> Are the shadows of the runners artificial then? As the runners' shadows cross the finish line, they are recorded by the camera in the same way that the runners are.
- wiredfool 2y agoYou can, it's the white bit. It just doesn't move. The shadows are what's projected on the line from the stadium lights, and the shape is how they changed in time.
- SoftTalker 2y agoOh I see, it's the entire "track" that is rendered in the image. Again, not well explained in the article.
- wanderingstan 2y agoBecause this is a line camera, the entire image is the finish line. That is, each vertical column of pixels is what was on the finish line at that particular point in time. That’s also the reason for the distortions. It’s not a single frame taken at one time.
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- laweijfmvo 2y agoshouldn’t the runners be facing left then?
- bonzini 2y agoTime goes backwards on the x axis.
- jasode 2y ago>This wasn't really described well. This short video might be a better explanation of the "line camera" concept of multiple photos of a single line being stretched out over the x-axis : https://www.youtube.com/watch?v=Ut0nKdLCAEo&t=0m23s https://www.youtube.com/watch?v=Ut0nKdLCAEo&t=0m23s
- xnorswap 2y agoIs the advertising board behind faked then? Shouldn't that be static relative to the finish line, and therefore not really show up?
- wanderingstan 2y agoAccording to Reddit thread on this, the led board behind is specifically animated with the right timing so the content shows up correctly in the line camera.
- jonahhorowitz 2y agoThere is a special advertising board that only the camera can see.
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- wtallis 2y agoThere's a narrow display behind the finish line with a quickly-scrolling banner ad.
- LeoPanthera 2y agoI was there at the time, and I could clearly see how the advertising board works. It's a vertical line of LEDs that constantly rotates through the columns of the logo. To the naked eye it just seems to be flickering randomly.
- iainmerrick 2y agoI was curious what the advertising board would have looked like to the athletes -- it must be a bit distracting to see a display scrolling at ~10m/s! You can see it here at 9m50s: https://youtu.be/7Xnr805bm4E?feature=shared&t=590 https://youtu.be/7Xnr805bm4E?feature=shared&t=590 It's just a single animated strip, one pixel wide. I assume the camera array is on the opposite side.
- adolph 2y agoWhen I read "line scan camera" I thought of "rolling shutter" which in digital cameras works out to be a horizontal line at a time, which causes interesting artifacts with quick moving objects like propellers or windshield wipers. Questions that came to mind and answers as far as I can tell: Q: Are the scan lines parallel to the plane of completion? A: There is only one scan line and it is parallel to the plane of completion. "In track, the cameras are only focused on the 5 mm near the finish line." [0] Q: If yes, is the sequence of lines scanned in the same direction as the competitor movement? A: There is only one scan line. 0. https://www.axios.com/2024/08/05/noah-lyles-wins-gold-track-camera-omega https://www.axios.com/2024/08/05/noah-lyles-wins-gold-track-... Also interesting: https://www.hodinkee.com/articles/olympics-2024-mens-100m-photo-finish https://www.hodinkee.com/articles/olympics-2024-mens-100m-ph...
- jasomill 2y agoNote that the rolling shutter effect is not limited to digital photography: it also affects physical focal plane shutters at high shutter speeds due to the time it takes for shutter curtains to move across the frame. This effect is the origin of the "fast race car slants forward" trope: https://about.usps.com/news/national-releases/2011/images/pr11_054.jpg https://about.usps.com/news/national-releases/2011/images/pr... https://imsmuseum.org/adoptable_car/1911-winner/ https://imsmuseum.org/adoptable_car/1911-winner/
- ortusdux 2y agoI find line scan cameras and strip photography fascinating. https://en.wikipedia.org/wiki/Strip_photography https://en.wikipedia.org/wiki/Strip_photography Early film versions used a highspeed spinning slit aperture to film fast objects. This paper from 1931 shows some very impressive results for ballistics, including the shockwave: https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1931.0095 https://royalsocietypublishing.org/doi/pdf/10.1098/rspa.1931... Outside sports, digital line scan cameras are used in various quality control applications (objects on conveyer belts, vehicle mounted road/rail scanners, etc). This unit can film an 8k px strip at a rate of 80khz. https://www.youtube.com/watch?v=OXUwJOJ7fMk https://www.youtube.com/watch?v=OXUwJOJ7fMk
- dllu 2y agoOh yeah I took that picture on the Wikipedia article! I have a couple more on my website [1]. One of these days I want to go to Atherton station with my line scan camera to scan some Caltrains. [1] https://daniel.lawrence.lu/photos/ https://daniel.lawrence.lu/photos/
- fouronnes3 2y agoFun fact! This is actually how many earth observation satellites work too! Except the motion comes not from the subject, but the satellite orbit itself. It's called a pushbroom camera.
- imoverclocked 2y agoHiRISE in MRO is a pushbroom imager too… so we have sent the tech beyond Earth’s orbit :)
- mhb 2y agoYes. And this is a terribly uninformative article which says nothing interesting about any of that.
- ghayes 2y agoShouldn’t the screen (Olympics logo) in the background be a constant blur then?
- Tuna-Fish 2y agoIt's also 1 pixel wide, and varies over time. https://youtu.be/7Xnr805bm4E?feature=shared&t=417 https://youtu.be/7Xnr805bm4E?feature=shared&t=417
- hn_throwaway_99 2y agoAgreed. Better article IMO: https://www.hodinkee.com/articles/olympics-2024-mens-100m-photo-finish https://www.hodinkee.com/articles/olympics-2024-mens-100m-ph... To the question of the Omega logo and Olympic rings asked below, this article states "In fact, the entire photo is literally the finish line viewed one pixel at a time (the Omega and Olympic branding is added at the top)."
- ortusdux 2y agoIIRC, they have a single pixel wide display that strobes the logos, similar to a persistence of vision display.
- xanderlewis 2y agoIt’s slightly misleading to say it’s time rather than space, though, because of course the subjects are moving and so each column does correspond to a different position (with respect to each one). With respect to the track, however, moving horizontally is obviously just moving in time. Another weird (until you think about it) thing that’s true: every pixel in the image is at the finish line.
- mannykannot 2y agoThe 'vertical' axis is spatial, representing position across the track, but I would argue that if we take your final sentence and append "...at sequential time intervals" to it, we end up making the case that the horizontal axis in the image is actually time, not space. Each column is the finish line at a different time, and perhaps counter-intuitively (given the usual convention), the right-most column is the earliest. This is clearer, I think, from considering how the banner is made: as others have pointed out, it is produce by having a single row of LEDs in line with the finish line, each one being turned on and off in a sequence which results in the banner shown in the picture.
- hasoleju 2y agoFirst I was wondering why there are ad banners visible in the image. With a line scan camera the background which is standing still should actually only have horizontal stripes. But since the company Omega produced this photo it actually makes sense to artificially add their logo next to the Olympic rings.
- jaffa2 2y agoi read that that actually a led screen that basically is synced to the camera so it appears as a 2d banner when in actuallity its a 1d banner that changes over time which when displayed like it is looks like a 2d banner. kinda neat. In a weird way similar to the the adverts painted on the pitch or trackside that look like 2d on screen dogs but only look that way from a certain camera angle
- mmmmmbop 2y agoThis is genius, thanks for pointing that out!
- Tuna-Fish 2y agoYou can see it flash in the video of the event: https://youtu.be/7Xnr805bm4E?feature=shared&t=417 https://youtu.be/7Xnr805bm4E?feature=shared&t=417
- hasoleju 2y agoThanks for the link! This is so great so actually see how the line camera and this line screen work together to create an ad in the finish line photo.
- tuyiown 2y agoI had to combine Tuna-Fish comments and yours to understand what's going on. > And the Omega/Olympics flag "banner" behind the runners is not a banner, it is a led screen, one pixel wide. So the one pixel wide scan line camera outputs and image that has time as horizontal axis, and the one pixel screen that draws the omega banner is a 40kfps single line video that does marketing one the photo finish that likely serves as a clock sync check.