Space-Time Warping Imaging at 1T fps - Ramesh Raskar

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Discussion Overview

The discussion revolves around the phenomenon of imaging at a trillion frames per second as presented by Ramesh Raskar. Participants explore the implications of capturing events at such high speeds, particularly regarding the observation of light and the potential reversal of events in the recorded images.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why there is a perceived reversal in events when photographing at speeds approaching that of light, referencing Raskar's comments on time distortion.
  • Another participant clarifies that a photo captures light reaching the camera at a specific moment, rather than all light emitted at a specific time, which is significant in high-speed imaging.
  • It is noted that the time taken for light to travel from the emitter to the camera can lead to effects in the images, although this does not necessarily imply a reversal of events.
  • A participant expresses a realization that they may have overthought the process, suggesting a potential misunderstanding of the explanation provided.

Areas of Agreement / Disagreement

Participants exhibit some agreement on the nature of light capture in high-speed imaging, but there remains uncertainty regarding the implications of this on the perception of events, particularly the notion of reversal. The discussion does not reach a consensus on the interpretation of these effects.

Contextual Notes

Participants acknowledge the complexity of the timing and distances involved in high-speed imaging, but specific assumptions and definitions regarding the reversal of events and time distortion remain unresolved.

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Imaging at a Trillion Frame Per Second - Ramesh Raskar

http://www.ted.com/talks/ramesh_raskar_a_camera_that_takes_one_trillion_frames_per_second.html

Although this video is extremely interesting, The part I'm most interested in occurs at about the 9:30 mark.


Ramesh Raskar says,

"But there is also something funny going on here .. the ripple are moving away from the camera towards the cap of the bottle when we know that light should be moving from cap to the camera?
Well Einstein would have loved to see this femto-photo.
It turns out that because we are recording nearly at the speed of light, there is reversal in how we observe events in the world. After a correct mathematical space-time warp, we can correct for this time distortion."

So my question is, why do we observe a reversal in the events when photographing at almost the speed of light? I may be overthinking, but I'm curious and was wondering if anybody had an explantation. Thanks in advance for any responses!
 
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A photo is the collection of all light that reaches the camera at a specific point (better: very short interval) in time. It is not a collection of all light emitted at a specific time.

For regular photos, this does not make a difference, as the time needed from emitter to camera is negligible. For those high-speed videos, the effect is relevant. To determine the frame where the camera will see light somewhere, you have to add the length between light source and this point and the length between this point and the camera.

This does not have to lead to a "reversal", but it leads to significant effects on the images.
 
mfb said:
For regular photos, this does not make a difference, as the time needed from emitter to camera is negligible. For those high-speed videos, the effect is relevant. To determine the frame where the camera will see light somewhere, you have to add the length between light source and this point and the length between this point and the camera.

Ahh that makes more sense now. I was definitely overthinking the process. Thanks
 
dsmikk said:
I was definitely overthinking the process. Thanks
Or the guy was over-explaining the issue.
 

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