Imaging at a trillion frames per second | Ramesh Raskar

3,209,858 views ・ 2012-07-26

TED


Please double-click on the English subtitles below to play the video.

00:00
Translator: Joseph Geni Reviewer: Thu-Huong Ha
0
0
7000
00:16
Doc Edgerton inspired us with awe and curiosity
1
16162
5954
00:22
with this photo of a bullet piercing through an apple,
2
22140
5238
00:27
and exposure just a millionth of a second.
3
27402
3852
00:32
But now, 50 years later, we can go a million times faster
4
32921
6889
00:39
and see the world not at a million or a billion,
5
39834
4762
00:44
but one trillion frames per second.
6
44620
3053
00:49
I present to you a new type of photography,
7
49125
3664
00:52
femto-photography,
8
52813
2035
00:54
a new imaging technique so fast
9
54872
4576
00:59
that it can create slow motion videos of light in motion.
10
59472
4272
01:04
And with that, we can create cameras that can look around corners,
11
64673
4859
01:09
beyond line of sight,
12
69556
1973
01:11
or see inside our body without an x-ray,
13
71553
4856
01:16
and really challenge what we mean by a camera.
14
76433
3807
01:21
Now if I take a laser pointer and turn it on and off
15
81700
3134
01:24
in one trillionth of a second --
16
84858
2803
01:27
which is several femtoseconds --
17
87685
2787
01:30
I'll create a packet of photons barely a millimeter wide.
18
90496
3997
01:35
And that packet of photons, that bullet,
19
95620
2409
01:38
will travel at the speed of light,
20
98053
1926
01:40
and again, a million times faster than an ordinary bullet.
21
100003
3958
01:44
Now, if you take that bullet and take this packet of photons
22
104882
4511
01:49
and fire into this bottle,
23
109417
3332
01:52
how will those photons shatter into this bottle?
24
112773
3571
01:57
How does light look in slow motion?
25
117124
2588
01:59
[Light in Slow Motion ... 10 Billion x Slow]
26
119812
3000
02:21
Now, the whole event --
27
141301
1547
02:22
(Applause)
28
142872
6987
02:29
Now remember, the whole event is effectively taking place
29
149883
3501
02:33
in less than a nanosecond --
30
153408
1663
02:35
that's how much time it takes for light to travel.
31
155095
2401
02:37
But I'm slowing down in this video by a factor of 10 billion,
32
157520
4647
02:42
so you can see the light in motion.
33
162191
2548
02:44
(Laughter)
34
164763
1070
02:45
But Coca-Cola did not sponsor this research.
35
165857
2287
02:48
(Laughter)
36
168168
2102
02:50
Now, there's a lot going on in this movie,
37
170294
2023
02:52
so let me break this down and show you what's going on.
38
172341
2620
02:54
So the pulse enters the bottle, our bullet,
39
174985
2934
02:57
with a packet of photons that start traveling through
40
177943
2538
03:00
and that start scattering inside.
41
180505
1813
03:02
Some of the light leaks, goes on the table,
42
182342
2207
03:04
and you start seeing these ripples of waves.
43
184573
2612
03:07
Many of the photons eventually reach the cap
44
187209
3008
03:10
and then they explode in various directions.
45
190241
2890
03:13
As you can see, there's a bubble of air
46
193155
1888
03:15
and it's bouncing around inside.
47
195067
1642
03:16
Meanwhile, the ripples are traveling on the table,
48
196733
2450
03:19
and because of the reflections at the top,
49
199207
2000
03:21
you see at the back of the bottle, after several frames,
50
201231
3747
03:25
the reflections are focused.
51
205002
1699
03:28
Now, if you take an ordinary bullet
52
208470
5389
03:33
and let it go the same distance and slow down the video --
53
213883
3000
03:36
again, by a factor of 10 billion --
54
216907
2221
03:39
do you know how long you'll have to sit here to watch that movie?
55
219152
4393
03:43
(Laughter)
56
223569
1588
03:45
A day, a week? Actually, a whole year.
57
225181
3509
03:49
It'll be a very boring movie --
58
229569
2257
03:51
(Laughter)
59
231850
1391
03:53
of a slow, ordinary bullet in motion.
60
233265
3372
03:57
And what about some still-life photography?
61
237960
3357
04:08
You can watch the ripples, again, washing over the table,
62
248372
4986
04:13
the tomato and the wall in the back.
63
253382
2658
04:16
It's like throwing a stone in a pond of water.
64
256064
2790
04:22
I thought: this is how nature paints a photo,
65
262663
3660
04:26
one femto frame at a time,
66
266347
2563
04:28
but of course our eye sees an integral composite.
67
268934
4257
04:35
But if you look at this tomato one more time,
68
275183
2134
04:37
you will notice, as the light washes over the tomato,
69
277341
2745
04:40
it continues to glow.
70
280110
1664
04:41
It doesn't become dark. Why is that?
71
281798
2027
04:43
Because the tomato is actually ripe,
72
283849
2298
04:46
and the light is bouncing around inside the tomato,
73
286171
2389
04:48
and it comes out after several trillionths of a second.
74
288584
3420
04:52
So in the future, when this femto-camera is in your camera phone,
75
292974
4339
04:57
you might be able to go to a supermarket
76
297337
1954
04:59
and check if the fruit is ripe without actually touching it.
77
299315
3055
05:02
(Laughter)
78
302394
1686
05:04
So how did my team at MIT create this camera?
79
304104
3689
05:09
Now, as photographers, you know,
80
309166
1944
05:11
if you take a short exposure photo, you get very little light.
81
311134
3961
05:15
But we're going to go a billion times faster than your shortest exposure,
82
315119
3508
05:18
so you're going to get hardly any light.
83
318651
1929
05:20
So what we do is we send that bullet --
84
320604
1913
05:22
that packet of photons -- millions of times,
85
322541
2496
05:25
and record again and again with very clever synchronization,
86
325061
3083
05:28
and from the gigabytes of data,
87
328168
1939
05:30
we computationally weave together
88
330131
2220
05:32
to create those femto-videos I showed you.
89
332375
2899
05:36
And we can take all that raw data and treat it in very interesting ways.
90
336456
4150
05:41
So, Superman can fly.
91
341275
1817
05:43
Some other heroes can become invisible.
92
343116
2258
05:45
But what about a new power for a future superhero:
93
345870
4782
05:50
To see around corners.
94
350676
1861
05:53
The idea is that we could shine some light on the door,
95
353354
4469
05:57
it's going to bounce, go inside the room,
96
357847
2651
06:00
some of that is going to reflect back on the door,
97
360522
2406
06:02
and then back to the camera.
98
362952
1483
06:04
And we could exploit these multiple bounces of light.
99
364459
2997
06:07
And it's not science fiction. We have actually built it.
100
367947
2667
06:10
On the left, you see our femto-camera.
101
370638
2066
06:12
There's a mannequin hidden behind a wall,
102
372728
2355
06:15
and we're going to bounce light off the door.
103
375107
2505
06:18
So after our paper was published in Nature Communications,
104
378009
3493
06:21
it was highlighted by Nature.com,
105
381526
2142
06:23
and they created this animation.
106
383692
2476
06:26
(Music)
107
386192
1284
06:27
[A laser pulse is fired]
108
387500
2864
06:30
(Music)
109
390388
2872
06:33
Ramesh Raskar: We're going to fire those bullets of light,
110
393284
2867
06:36
and they're going to hit this wall,
111
396175
3376
06:39
and because of the packet of the photons,
112
399575
2631
06:42
they will scatter in all the directions,
113
402230
2110
06:44
and some of them will reach our hidden mannequin,
114
404364
2341
06:46
which in turn will again scatter that light,
115
406729
3382
06:50
and again in turn, the door will reflect some of that scattered light.
116
410135
4571
06:55
And a tiny fraction of the photons will actually come back to the camera,
117
415943
3496
06:59
but most interestingly,
118
419463
1151
07:00
they will all arrive at a slightly different time slot.
119
420638
3083
07:04
(Music)
120
424186
4833
07:09
And because we have a camera that can run so fast --
121
429043
2513
07:11
our femto-camera -- it has some unique abilities.
122
431580
3082
07:14
It has very good time resolution,
123
434686
2818
07:17
and it can look at the world at the speed of light.
124
437528
2895
07:21
And this way, we know the distances, of course to the door,
125
441374
3257
07:24
but also to the hidden objects,
126
444655
1777
07:26
but we don't know which point corresponds to which distance.
127
446456
3157
07:29
(Music)
128
449637
4045
07:33
By shining one laser, we can record one raw photo,
129
453706
3430
07:37
which, if you look on the screen, doesn't really make any sense.
130
457160
3024
07:40
But then we will take a lot of such pictures,
131
460208
2120
07:42
dozens of such pictures, put them together,
132
462352
2160
07:44
and try to analyze the multiple bounces of light,
133
464536
2458
07:47
and from that, can we see the hidden object?
134
467018
3451
07:50
Can we see it in full 3D?
135
470493
2134
07:53
So this is our reconstruction.
136
473373
1929
07:55
(Music)
137
475326
5130
08:00
(Applause)
138
480480
6976
08:08
Now, we have some ways to go
139
488051
1469
08:09
before we take this outside the lab on the road,
140
489544
3135
08:12
but in the future, we could create cars that avoid collisions
141
492703
3729
08:16
with what's around the bend.
142
496456
1481
08:18
Or we can look for survivors in hazardous conditions
143
498841
4087
08:22
by looking at light reflected through open windows.
144
502952
3224
08:26
Or we can build endoscopes that can see deep inside the body around occluders,
145
506864
5871
08:32
and also for cardioscopes.
146
512759
1700
08:34
But of course, because of tissue and blood,
147
514483
2366
08:36
this is quite challenging,
148
516873
1255
08:38
so this is really a call for scientists
149
518152
1935
08:40
to start thinking about femto-photography
150
520111
2307
08:42
as really a new imaging modality
151
522442
1881
08:44
to solve the next generation of health-imaging problems.
152
524347
3520
08:48
Now, like Doc Edgerton, a scientist himself,
153
528342
3857
08:52
science became art --
154
532223
2303
08:54
an art of ultra-fast photography.
155
534550
2662
08:58
And I realized
156
538140
1151
08:59
that all the gigabytes of data that we're collecting every time,
157
539315
3441
09:02
are not just for scientific imaging.
158
542780
2421
09:05
But we can also do a new form of computational photography,
159
545225
5539
09:10
with time-lapse and color coding.
160
550788
2532
09:14
And we look at those ripples.
161
554407
1469
09:15
Remember:
162
555900
1158
09:17
The time between each of those ripples is only a few trillionths of a second.
163
557082
5473
09:23
But there's also something funny going on here.
164
563862
2207
09:26
When you look at the ripples under the cap,
165
566093
2796
09:28
the ripples are moving away from us.
166
568913
2183
09:32
The ripples should be moving towards us.
167
572111
1914
09:34
What's going on here?
168
574049
1372
09:35
It turns out, because we're recording nearly at the speed of light,
169
575445
6790
09:42
we have strange effects,
170
582259
1889
09:44
and Einstein would have loved to see this picture.
171
584172
3261
09:47
(Laughter)
172
587457
1039
09:48
The order at which events take place in the world
173
588520
3047
09:51
appears in the camera sometimes in reversed order.
174
591591
3326
09:56
So by applying the corresponding space and time warp,
175
596306
3195
09:59
we can correct for this distortion.
176
599525
2367
10:03
So whether it's for photography around corners,
177
603866
4349
10:08
or creating the next generation of health imaging,
178
608239
3996
10:12
or creating new visualizations,
179
612259
2892
10:15
since our invention,
180
615175
1624
10:16
we have open-sourced all the data and details on our website,
181
616823
5125
10:21
and our hope is that the DIY, the creative and the research communities
182
621972
6953
10:28
will show us that we should stop obsessing about the megapixels in cameras --
183
628949
5505
10:34
(Laughter)
184
634478
1279
10:35
and start focusing on the next dimension in imaging.
185
635781
4388
10:40
It's about time.
186
640867
1310
10:42
Thank you.
187
642597
1152
10:43
(Applause)
188
643773
6870
About this website

This site will introduce you to YouTube videos that are useful for learning English. You will see English lessons taught by top-notch teachers from around the world. Double-click on the English subtitles displayed on each video page to play the video from there. The subtitles scroll in sync with the video playback. If you have any comments or requests, please contact us using this contact form.

https://forms.gle/WvT1wiN1qDtmnspy7