[HN Gopher] A camera that shoots 40k FPS decided the 100-meter s...
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A camera that shoots 40k FPS decided the 100-meter sprint final
Author : wallflower
Score : 124 points
Date : 2024-08-11 12:11 UTC (1 days ago)
(HTM) web link (petapixel.com)
(TXT) w3m dump (petapixel.com)
| formerly_proven wrote:
| (It's a line scan camera)
| porphyra wrote:
| 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 wrote:
| Ah 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?
| wiredfool wrote:
| You 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 wrote:
| Oh I see, it's the entire "track" that is rendered in the
| image.
|
| Again, not well explained in the article.
| wanderingstan wrote:
| Because 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.
| jetrink wrote:
| > 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.
| jasode wrote:
| _> 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
| xnorswap wrote:
| Is the advertising board behind faked then? Shouldn't that be
| static relative to the finish line, and therefore not really
| show up?
| wanderingstan wrote:
| According 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 wrote:
| There is a special advertising board that only the camera can
| see.
| wtallis wrote:
| There's a narrow display behind the finish line with a
| quickly-scrolling banner ad.
| LeoPanthera wrote:
| I 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 wrote:
| I 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
|
| It's just a single animated strip, one pixel wide. I assume
| the camera array is on the opposite side.
| ninju wrote:
| Video no longer available :-(
| ceejayoz wrote:
| NBC is _very_ quick to DMCA Olympics clips.
| ipsum2 wrote:
| NBC isn't DMCA-ing the official Olympics channel.
| reaperducer wrote:
| _NBC is very quick to DMCA Olympics clips._
|
| Writing a check for $12,000,000,000.00 will do that to
| you.
|
| https://marketrealist.com/p/how-much-did-nbc-pay-for-the-
| oly...
| ipsum2 wrote:
| Region blocked from the US.
| chch wrote:
| Thanks for pointing that out! This video doesn't seem to be
| available in the US, so you can also see it in the slow
| motion footage here, right on the finish line:
|
| https://www.youtube.com/watch?v=tcxyXnPIF4o#t=2m45s
|
| (You can see it in normal speed too, but I can feel the
| formation of shapes better in the slow-mo, instead of it
| just feeling like blinking)
| iainmerrick wrote:
| Ha, and that video isn't visible outside the US!
|
| I guess pick one or the other depending on your country
| (or if neither works, search for one that does).
| ipython wrote:
| This makes total sense as a way to quickly validate the
| cameras calibration visually. "Does the ad look correct?"
|
| Clever.
| adolph wrote:
| When 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-...
|
| Also interesting:
| https://www.hodinkee.com/articles/olympics-2024-mens-100m-ph...
| jasomill wrote:
| Note that the rolling shutter effect is not limited to
| digital photography: it also affects physical focal plane
| shutters at high shutter speeds where the time it takes for
| shutter curtains to move across the frame is a significant
| fraction of exposure time.
|
| This effect is the origin of the "race cars going fast slant
| forward" trope:
|
| https://imsmuseum.org/adoptable_car/1911-winner/
|
| https://about.usps.com/news/national-
| releases/2011/images/pr...
| ortusdux wrote:
| I find line scan cameras and strip photography fascinating.
|
| 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...
|
| 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
| dllu wrote:
| Oh 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/
| ortusdux wrote:
| Small world! You took some amazing images. Can I ask - what
| hardware did you use?
| dllu wrote:
| Alkeria Necta N4K2-7C
| ortusdux wrote:
| Very cool. Have you thought about filming a rocket
| launch? The smooth acceleration should cause very a
| interesting distortion.
| brbcoding wrote:
| Very cool photos! Just as an FYI, the link to the full
| sized "Victorian house in San Francisco, CA, 2020" image
| 404s for me.
| dllu wrote:
| Weird, I'll fix that later but meanwhile you can also
| find it here: https://commons.wikimedia.org/wiki/File:Vic
| torian_house_on_W...
| justsomehnguy wrote:
| Long train is long!
|
| It's actually hilarious what you really need to scroll it
| to see it on your Wiki page.
| fouronnes3 wrote:
| Fun 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 wrote:
| HiRISE in MRO is a pushbroom imager too... so we have sent
| the tech beyond Earth's orbit :)
| mhb wrote:
| Yes. And this is a terribly uninformative article which says
| nothing interesting about any of that.
| ghayes wrote:
| Shouldn't the screen (Olympics logo) in the background be a
| constant blur then?
| hn_throwaway_99 wrote:
| Agreed. Better article IMO: 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 wrote:
| IIRC, they have a single pixel wide display that strobes
| the logos, similar to a persistence of vision display.
| voytec wrote:
| Ok, what's the underlying storage?
| jsheard wrote:
| High speed cameras usually record into RAM and then dump the
| recording out to an SSD in slower-than-realtime when it ends.
| Since the recording duration is limited by RAM capacity they
| have rolling modes which record continuously into a ring buffer
| and then store the current contents when the shutter is
| pressed, so that unpredictable events can be captured after
| they happen.
| freedomben wrote:
| Is RAM even fast enough? I remember reading somewhere that
| the high speed cameras have special cache-like memory on or
| near the processor that is faster write than RAM. I can't
| find it now though so I'm taking it with a grain of salt.
| jsheard wrote:
| Maybe in specialty cameras with ultra low maximum recording
| durations but it's usually just a bunch of DRAM, take this
| Phantom camera as an example.
|
| https://www.phantomhighspeed.com/products/cameras/tmx/7510
|
| The spec sheet lists up to 512GB of RAM depending on
| configuration. There's no way you're scaling cache-like
| SRAM up to those numbers.
| Denvercoder9 wrote:
| The necessary data rate for these photo finish cameras
| isn't actually that high, because every "frame" is only 1
| pixel wide. If the photo is 10000 pixels high, you need a
| datarate of about 10 Gbit/s at 40000 fps and 24 bits/pixel.
| RAM is plenty fast enough for that.
|
| Regular high-speed cameras that shoot a video are a whole
| other story, though.
| johndhi wrote:
| Hmm -- call me crazy, but I feel like the positioning of the
| camera might have wrongly decided the race for Lyles. The first
| torso to cross the line wins.
|
| If you look at the still image in the article, Lyles' right
| shoulder is leaning forward and visible to the camera, positioned
| to his right.
|
| But Thompson's left shoulder seem to be leaning forward, but is
| hidden in the camera by his head and neck. It's possible
| Thompson's left shoulder is ahead of Lyles' right shoulder, but
| the image doesn't seem sufficient evidence to conclude on that.
|
| What do other think?
| wanderingstan wrote:
| According to this Reddit thread, the camera actually _is_ the
| finish line:
|
| > According to UCI regulations, the camera is the finish line.
|
| > The painted line on the road or track is placed there as a
| visual reference for riders and spectators, and obviously
| organizers try to align the painted line with the photo finish
| camera as best as possible. But that's all it is - a visual
| reference. The finish line is officially defined as the plane
| of the photo finish camera, not the painted finish line.
|
| https://www.reddit.com/r/bicycling/comments/1emivk1/dont_if_...
| johndhi wrote:
| Woah! Helpful. I guess Thompson should learn to dive forward
| with his right shoulder next time!
| swasheck wrote:
| commentators tangentially referenced this when they
| mentioned that lyles had "learned" how to make a good
| finishing lunge, but it was also heavily implied that they
| were talking about the timing of the lunge and not the
| mechanics.
| deanCommie wrote:
| Yeah, keep in mind at athletics competition, a "false
| start" is deemed to be anything within 100m of the actual
| firing gun - because that is deemed to be below the level
| of human perception, and therefore someone "bet" or
| "guessed".
|
| So I can't imagine a human can take a conscious step to
| get a FIVE millisecond advantage over another.
| f5ve wrote:
| Your comment just made me realize something. The 5
| milliseconds which Lyles won by is shorter than the time
| it takes sound to travel between his lane and Thompson's.
| If the starting gun were on the outside of the track
| (it's not), then Thompson would have actually run the
| race faster, if measured from the time he perceived the
| sound.
|
| In reality the gun is usually on the inside of the track,
| so it would be Lyles overcoming this (negligible)
| advantage.
| yuliyp wrote:
| There's a speaker behind each runner in the starting
| blocks to avoid that being a factor.
| smallpipe wrote:
| Of course you can. A good drummer will not deviate from
| beat by that much.
| amluto wrote:
| This doesn't really answer the question. The camera can only
| see the non-occluded portions of the plane. Since Thompson's
| left shoulder is not visible in the image, we know that his
| shoulder crossed the image plane at a time at which it was
| occluded by his head. But without extrapolation, it's not
| clear to me that we know when his shoulder crossed the line.
| johndhi wrote:
| Good point. I guess if you're occluded to the camera, I was
| assuming the presumption is you haven't crossed the line.
| But it could still be arguable that he did cross the
| camera's finish line, it was just occluded.
| gamblor956 wrote:
| It doesn't matter when Thompson's shoulder crossed the
| finish line, since the shoulder is not part of the torso.
|
| The torso was chosen as the body part for determining when
| a runner crosses the finish line precisely because torsos
| were easy to identify/distinguish and there is no ambiguity
| as to a runner's torso.
| johndhi wrote:
| you don't think shoulder is part of torso?
| adolph wrote:
| _The exact location of the border line between the upper
| arm / shoulder and the "torso" would vary depending on
| the development of the upper body of an individual
| athlete and would not therefore be totally consistent.
| Based on anatomy, we can say that the endpoint of the
| torso is the outer end / articulation of the collarbone
| (clavicle)._
|
| _Although the pelvic area is anatomically part of the
| torso, for consistency in photo finish judging, it is
| more practical to define the lower end of the torso as
| the horizontal cross section of the body through the hip
| line . . ._
|
| IAAF Photo Finish Guidelines (June 2015): https://worldat
| hletics.org/download/download?filename=4423f7...
| 1-more wrote:
| >> UCI regulations, the camera is the finish line
|
| UCI is Union Cycliste Internationale, i.e. the biggest
| international governing body of cycling events. Not athletics
| (i.e. track and field). I checked out the C1.1 & C2.1
| rulebook from the IAAF and I'm not seeing an equivalent rule.
| Just a lot of rules for how to place the camera and mark the
| lane lines and finish line in 19.13
|
| index of all IAAF rulebooks https://worldathletics.org/about-
| iaaf/documents/book-of-rule...
|
| direct PDF link to the English version of the 17 JAN 2024
| C1.1 & C2.1 - Competition Rules & Technical Rules rules (2.5
| MB PDF) https://worldathletics.org/download/download?filename
| =675a00...
| adolph wrote:
| I think it might be more fair if the camera was above the
| participants.
| amluto wrote:
| That sounds fine for the Olympics but rather awkward for a
| lower profile race at which someone just wants to roll a
| camera out to the track.
|
| The same problem could also be addressed by having two
| cameras, one on each side of the track, synchronized and
| recording the same plane.
|
| One could align the cameras into the same plane by putting a
| vertical array of distinctive marks (e.g. rapidly blinking
| LEDs) on each camera, above and below the optics and in line
| with it, such that each camera would see the other's marks
| when correctly aligned.
| Denvercoder9 wrote:
| > a vertical array of distinctive marks (e.g. rapidly
| blinking LEDs)
|
| This doesn't work, as light beams diverge. Even taking a
| high-quality laser beam with a divergence of 0.1
| milliradian (for comparison, a typical laser pointer is
| about 1-2 mrad), after crossing the 11 meters width of a
| 9-lane athletics track, you end up with a beam diameter of
| 2.2 millimeters. At the 10 m/s speed of the athletes and a
| 40000 fps framerate, they travel 250 micrometers between
| each frame.
| amluto wrote:
| I'm not sure what the issue you're describing is. If I
| have two devices, each with a camera and a line of marks,
| if they can each see each other's marks, then they are
| aligned to within the horizontal spread of the camera
| pixels. There are no lasers involved -- the marks can be
| paint, stickers, blinking wide-angle LEDs, etc. -- my
| suggestion to use blinking LEDs is just so that's it's
| more obvious when one is in the field of view of the
| camera.
| Denvercoder9 wrote:
| You don't just need the cameras to see each other, you
| need them to be perfectly parallel to each other as well,
| as otherwise they're photographing along a different
| plane, which may give conflicting results.
| amluto wrote:
| Suppose camera A has line L_A on the camera. A's optics
| and marks are both on L_A, so A's image plane contains
| L_A and camera B's image plane _also_ contains L_A (you
| know the latter because you've aligned the cameras so
| camera B sees L_A). And vice versa: camera A sees L_B. In
| 3D Euclidean space, two distinct lines define a plane,
| and both camera's are photographing planes that contain
| L_A and L_B, so both cameras are photographing the same
| plane.
|
| More concretely, if the cameras are photographing along
| different but parallel planes, then they won't see each
| other.
| Denvercoder9 wrote:
| Your solution works in a geometric world, where light
| propagates in a perfect straight line of infinitesimally
| small width. That's not true in reality, where light
| propagates in an ever-expanding cone.
|
| More concretely, you can have two cameras photographing
| along different but parallel planes that do see each
| other.
| fragmede wrote:
| it's a line scan camera so there is no angle. that picture is a
| composite.
| dist-epoch wrote:
| I'm pretty sure the arbiters at the most important race at the
| most important sport event know what they are doing :)
|
| Not to mention there was no controversy afterwards.
| JoblessWonder wrote:
| My knee-jerk internet reaction was "YOU ARE CRAZY" but then I
| took a breath and looked at the photo and I can see your
| argument. There is no point in a runner learning with their
| left shoulder forward since it will be difficult to place the
| exact spot behind their heads.
| johndhi wrote:
| Thanks! Usually nutty conspiracy theorists online don't
| preface their statements with "call me crazy" but I was
| worried about that, ha.
| jhayward wrote:
| In Olympic track and field at least two cameras, mounted on
| opposite sides of the finish line, are required to be used. So
| the judges had available for their use both perspectives.
| ck2 wrote:
| Even elite marathons now are almost always ending in sprint
| finishes which is a bit dumb but an obvious problem. The women's
| olympic marathon was won by less than 3 second after more than 26
| miles?
|
| Photos no matter how fast still require human objectivity in
| evaluation.
|
| Instead there should be some digital signal or laser reflection
| that is precise?
|
| I don't like the rule where it's any part of the athlete's body
| first to cross the line, it should be the first athlete to
| ENTIRELY cross the line, no part of them still remains before the
| line, not even their trailing foot.
| semitones wrote:
| > I don't like the rule where it's any part of the athlete's
| body first to cross the line, it should be the first athlete to
| ENTIRELY cross the line, no part of them still remains before
| the line, not even their trailing foot.
|
| What's the difference?
| iainmerrick wrote:
| _it should be the first athlete to ENTIRELY cross the line_
|
| a) Why entirely across, and not just the first to touch the
| line?
|
| b) I get that basing it on the whole body feels a bit more
| objective, but it would probably also lead to people diving
| over the line to gain a few milliseconds. As well as looking a
| bit silly it could be dangerous. The lean through a (now
| virtual) tape at chest height is traditional.
| grogenaut wrote:
| I could see bigger people at a disadvantage so is it fair?
| Please show your work in the form of a myth busters episode,
| and figure out how to work some form of explosion in.
| p1mrx wrote:
| > any part of the athlete's body
|
| I think it's any part of the athlete's _torso_ , which
| corresponds to the red lines on the image.
|
| Though I wonder if a runner could gain an advantage using very
| long breast implants?
| croes wrote:
| Digital signals and lasers aren't any better. There are lots of
| errors that can be made that change the measurements.
|
| Photo finish is one of the best methods.
|
| Where is the difference between first body part crosses the
| line vs the whole person?
|
| It's still hard to know who has won in a photo finish.
| crazygringo wrote:
| > _it should be the first athlete to ENTIRELY cross the line_
|
| No, because then you'd be changing the distance of the race.
|
| Runners start _behind_ the starting line. So for consistency,
| they finish when the first part of their torso passes the
| finish line.
|
| Your suggestion would only make sense if they started with e.g.
| their trailing foot touching the starting line and the rest of
| their body in front of it. But that's not how they start.
|
| Also, if you based it on foot position rather than torso
| position you'd be introducing a rather random element, since it
| would change based on what part of their stride they were in.
| Torso position is much more continuous, and therefore is a far
| more accurate assessment of athletic ability.
| GuB-42 wrote:
| > Instead there should be some digital signal or laser
| reflection that is precise?
|
| These photo finishes are really precise. 40k FPS, that's 25
| microseconds, or about a quarter of a millimeter in distance
| (at 10m/s running speed). If you look at it, with the lines
| drawn, it is very obvious who's won.
|
| The organizers took some time to double check everything since
| it wasn't obvious from the naked eye, but with the photo finish
| there is absolutely no ambiguity. In fact, the photo finish is
| 400x more precise than what is required here.
|
| > I don't like the rule where it's any part of the athlete's
| body first to cross the line.
|
| It is not the case, the article says the torso matters, not
| "any part". Also, the athletes stand completely behind the
| starting line, it makes sense that the race ends just as soon
| as they touch the finish line, otherwise it wouldn't be 100m
| but 100m + one body length.
| laweijfmvo wrote:
| would have liked to have seen a better explanation of the red
| lines in the image. it sounds like those are added by humans to
| outline the runners' chests; how do they ensure the lines are
| drawn on the frame exactly at the finish line?
| grogenaut wrote:
| If you read the other comments and the article the camera is
| one pixel wide, each vertical column in the image IS a frame.
| It's ensured with physics. It's a bit subtle but makes sense
| once you grok that. So each pixel left is 1/40,000 later
| iainmerrick wrote:
| Does it matter if they're off by +-1 pixel? It's pretty easy to
| eyeball the rightmost part of each athlete's torso and the
| frame rate is high enough that there's plenty of space between
| them.
|
| It looks plenty reliable as long as the camera was positioned
| and calibrated correctly (which I assume was carefully tested
| beforehand).
| dist-epoch wrote:
| There could be two sets of line, one line assigned exactly when
| each runner crosses to get his time, and another set assigned
| when the first runner crosses, and this picture is distributed.
| jhayward wrote:
| > how do they ensure the lines are drawn on the frame exactly
| at the finish line?
|
| They don't.
|
| The horizontal axis is time. The red lines mark the _time_ each
| runner 's torso was counted as crossing the finish line.
| syspec wrote:
| In the top image, where exactly is the "finish" line?
| stavros wrote:
| Nowhere, the camera takes an image of a single line in time
| (and what the camera sees _is_ the canonical finish line). The
| visual finish line isn 't where that camera is looking, so it's
| never captured. The left and right of that camera isn't space,
| it's time (right is earlier, left is later).
| jarboot wrote:
| The entire photo is the finish line. Look at the color of the
| ground -- it's cream, the color of the lines on the track,
| while the track is blue. Each vertical line of the photo is
| taken in the same position on that finish line.
|
| The first "line photo" is the right-most column of pixels on
| that photo. The next photo is the second-to-the-right column,
| etc. This way the winner can be determined as the line first
| photo that has the contestant's torso in it.
| vitaflo wrote:
| Also every runner in this photo is showing them at the finish
| line even tho they appear in the photo to be at different
| places. It's why all the runners are leaning forward because
| they are all crossing the finish line.
| kzrdude wrote:
| And to add, every placement can be decided from this one
| "photo", right?
| system2 wrote:
| Why is it so difficult for these articles to insert the photo or
| place the correct link for it?
|
| Here is the image of the camera:
|
| https://www.swatchgroup.com/sites/default/files/inline-image...
| setgree wrote:
| There was controversy in 2012 at the U.S. Olympic Trials when
| Allyson Felix & Jeneba Tarmoh finished neck and neck -- basically
| the cameras at the time couldn't make out the difference [0]. I
| think that was pretty hard on the athletes, so I'm glad to see
| we've made some progress.
|
| [0] https://www.theguardian.com/sport/2012/jul/02/jeneba-
| tarmoh-...
| nunorbatista wrote:
| As someone who worked closely to the Omega / Swisstiming
| operations at the Olympics, this is super cool stuff.
| Congratulations to all involved in being able to deliver when it
| mattered.
|
| The team also makes really interesting stuff on other sports,
| such as Beach Volley. Worth checking how it's done.
| oulipo wrote:
| I think it's totally ridiculous that we give gold, silver,
| bronze (and we totally "forget" about the other athletes) when
| they basically have THE EXACT SAME SPEED
|
| If it takes 30s for judges to determine who wins with a 40k FPS
| camera... it means the athletes have the EXACT SAME SKILL
|
| We should celebrate their common performance, rather than
| trying to "order" and "hierarchize" them...
|
| Capitalism truly fucked up the humanity
| tqi wrote:
| Is there a 1-pixel wide display at the finish line that is
| showing the Omega / Olympic Rings banners?
| michaelt wrote:
| It's more like an inch wide, but yes:
| https://www.youtube.com/watch?v=7Xnr805bm4E&t=590s
|
| There have been times in the past when photo finish cameras
| have been installed crooked relative to the finish line painted
| on the ground [1] and while I have no great love for yet-more-
| advertising, this does serve to confirm that the camera was
| pointed in the right direction :)
|
| [1] https://news.ycombinator.com/item?id=26970854
| urda wrote:
| I used to be a big time operator of FinishLynx equipment
| stateside, which is the same idea here used by the Omega, it's a
| finish line camera.
| munchler wrote:
| Since this camera scans 1D lines, rather than 2D frames, I don't
| think FPS is the right unit of measure. Perhaps 40,000 lines per
| second is correct?
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