Imaging at a trillion frames per second | Ramesh Raskar

3,209,014 views ・ 2012-07-26

TED


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Translator: Joseph Geni Reviewer: Thu-Huong Ha
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Doc Edgerton inspired us with awe and curiosity
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with this photo of a bullet piercing through an apple,
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and exposure just a millionth of a second.
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But now, 50 years later, we can go a million times faster
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and see the world not at a million or a billion,
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but one trillion frames per second.
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I present to you a new type of photography,
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femto-photography,
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a new imaging technique so fast
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that it can create slow motion videos of light in motion.
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And with that, we can create cameras that can look around corners,
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beyond line of sight,
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or see inside our body without an x-ray,
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and really challenge what we mean by a camera.
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Now if I take a laser pointer and turn it on and off
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in one trillionth of a second --
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which is several femtoseconds --
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I'll create a packet of photons barely a millimeter wide.
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And that packet of photons, that bullet,
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will travel at the speed of light,
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and again, a million times faster than an ordinary bullet.
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Now, if you take that bullet and take this packet of photons
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and fire into this bottle,
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how will those photons shatter into this bottle?
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How does light look in slow motion?
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[Light in Slow Motion ... 10 Billion x Slow]
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Now, the whole event --
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(Applause)
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Now remember, the whole event is effectively taking place
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in less than a nanosecond --
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that's how much time it takes for light to travel.
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But I'm slowing down in this video by a factor of 10 billion,
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so you can see the light in motion.
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(Laughter)
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But Coca-Cola did not sponsor this research.
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(Laughter)
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Now, there's a lot going on in this movie,
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so let me break this down and show you what's going on.
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So the pulse enters the bottle, our bullet,
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with a packet of photons that start traveling through
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and that start scattering inside.
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Some of the light leaks, goes on the table,
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and you start seeing these ripples of waves.
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Many of the photons eventually reach the cap
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and then they explode in various directions.
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As you can see, there's a bubble of air
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and it's bouncing around inside.
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Meanwhile, the ripples are traveling on the table,
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and because of the reflections at the top,
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you see at the back of the bottle, after several frames,
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the reflections are focused.
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Now, if you take an ordinary bullet
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and let it go the same distance and slow down the video --
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again, by a factor of 10 billion --
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do you know how long you'll have to sit here to watch that movie?
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(Laughter)
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A day, a week? Actually, a whole year.
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It'll be a very boring movie --
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(Laughter)
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of a slow, ordinary bullet in motion.
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And what about some still-life photography?
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You can watch the ripples, again, washing over the table,
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the tomato and the wall in the back.
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It's like throwing a stone in a pond of water.
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I thought: this is how nature paints a photo,
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one femto frame at a time,
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but of course our eye sees an integral composite.
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But if you look at this tomato one more time,
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you will notice, as the light washes over the tomato,
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it continues to glow.
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It doesn't become dark. Why is that?
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Because the tomato is actually ripe,
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and the light is bouncing around inside the tomato,
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and it comes out after several trillionths of a second.
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So in the future, when this femto-camera is in your camera phone,
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you might be able to go to a supermarket
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and check if the fruit is ripe without actually touching it.
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(Laughter)
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So how did my team at MIT create this camera?
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Now, as photographers, you know,
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if you take a short exposure photo, you get very little light.
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But we're going to go a billion times faster than your shortest exposure,
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so you're going to get hardly any light.
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So what we do is we send that bullet --
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that packet of photons -- millions of times,
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and record again and again with very clever synchronization,
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and from the gigabytes of data,
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we computationally weave together
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to create those femto-videos I showed you.
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And we can take all that raw data and treat it in very interesting ways.
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So, Superman can fly.
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Some other heroes can become invisible.
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But what about a new power for a future superhero:
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To see around corners.
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The idea is that we could shine some light on the door,
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it's going to bounce, go inside the room,
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some of that is going to reflect back on the door,
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and then back to the camera.
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And we could exploit these multiple bounces of light.
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And it's not science fiction. We have actually built it.
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On the left, you see our femto-camera.
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There's a mannequin hidden behind a wall,
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and we're going to bounce light off the door.
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So after our paper was published in Nature Communications,
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it was highlighted by Nature.com,
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and they created this animation.
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(Music)
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[A laser pulse is fired]
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(Music)
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Ramesh Raskar: We're going to fire those bullets of light,
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and they're going to hit this wall,
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and because of the packet of the photons,
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they will scatter in all the directions,
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and some of them will reach our hidden mannequin,
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which in turn will again scatter that light,
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and again in turn, the door will reflect some of that scattered light.
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And a tiny fraction of the photons will actually come back to the camera,
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but most interestingly,
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they will all arrive at a slightly different time slot.
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(Music)
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And because we have a camera that can run so fast --
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our femto-camera -- it has some unique abilities.
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It has very good time resolution,
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and it can look at the world at the speed of light.
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And this way, we know the distances, of course to the door,
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but also to the hidden objects,
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but we don't know which point corresponds to which distance.
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(Music)
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By shining one laser, we can record one raw photo,
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which, if you look on the screen, doesn't really make any sense.
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But then we will take a lot of such pictures,
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dozens of such pictures, put them together,
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and try to analyze the multiple bounces of light,
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and from that, can we see the hidden object?
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Can we see it in full 3D?
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So this is our reconstruction.
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(Music)
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(Applause)
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Now, we have some ways to go
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before we take this outside the lab on the road,
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but in the future, we could create cars that avoid collisions
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with what's around the bend.
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Or we can look for survivors in hazardous conditions
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by looking at light reflected through open windows.
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Or we can build endoscopes that can see deep inside the body around occluders,
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and also for cardioscopes.
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But of course, because of tissue and blood,
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this is quite challenging,
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so this is really a call for scientists
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to start thinking about femto-photography
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as really a new imaging modality
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to solve the next generation of health-imaging problems.
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Now, like Doc Edgerton, a scientist himself,
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science became art --
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an art of ultra-fast photography.
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And I realized
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that all the gigabytes of data that we're collecting every time,
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are not just for scientific imaging.
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But we can also do a new form of computational photography,
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with time-lapse and color coding.
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And we look at those ripples.
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Remember:
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The time between each of those ripples is only a few trillionths of a second.
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But there's also something funny going on here.
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When you look at the ripples under the cap,
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the ripples are moving away from us.
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The ripples should be moving towards us.
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What's going on here?
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It turns out, because we're recording nearly at the speed of light,
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we have strange effects,
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and Einstein would have loved to see this picture.
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(Laughter)
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The order at which events take place in the world
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appears in the camera sometimes in reversed order.
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So by applying the corresponding space and time warp,
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we can correct for this distortion.
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So whether it's for photography around corners,
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or creating the next generation of health imaging,
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or creating new visualizations,
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since our invention,
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we have open-sourced all the data and details on our website,
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and our hope is that the DIY, the creative and the research communities
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will show us that we should stop obsessing about the megapixels in cameras --
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(Laughter)
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and start focusing on the next dimension in imaging.
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It's about time.
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Thank you.
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(Applause)
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