5 ms·

The Physics of Magic Windows (2021)

178 points by mhb 2y ago

deleted 2y ago
[deleted]
mkmk 2y ago
Some nice comments on this previous discussion of the same link: https://news.ycombinator.com/item?id=28283411 https://news.ycombinator.com/item?id=28283411
- dang 2y ago
  Thanks! Macroexpanded: Hiding Images in Plain Sight: The Physics of Magic Windows - https://news.ycombinator.com/item?id=28283411 https://news.ycombinator.com/item?id=28283411 - Aug 2021 (24 comments) Hiding Images in Plain Sight: The Physics of Magic Windows - https://news.ycombinator.com/item?id=28220376 https://news.ycombinator.com/item?id=28220376 - Aug 2021 (1 comment)
LarsDu88 2y ago
That's so cool!
shiko11pin 2y ago
Similar to "Pixel Window" link: https://x.com/Hakusi_Katei/status/1807591865132466324 https://x.com/Hakusi_Katei/status/1807591865132466324
rawgabbit 2y ago
Reminds me of magic mirrors of Japan and China. https://www.cnn.com/style/article/magic-mirror-cincinnati-art-museum-scn/index.html https://www.cnn.com/style/article/magic-mirror-cincinnati-ar... https://www.greenshinto.com/2014/02/16/magic-mirrors/ https://www.greenshinto.com/2014/02/16/magic-mirrors/
injidup 2y ago
Not to take away the brilliance of what is achieved but I think hologram is the wrong word. This is purely about caustics. Amplitude engineering rather than phase. The calculations are just assuming light as particle, not light as wave. A true hologram uses diffraction grating effects and the phase difference from light. There was a very nice explanation on three-blue-brown recently. https://www.youtube.com/watch?v=EmKQsSDlaa4 https://www.youtube.com/watch?v=EmKQsSDlaa4 I don't think there are any phase effects in the parent attached? Or are there?
- gpderetta 2y ago
  Depends if we consider holograms only the specific technique of using phases to encode the information or any general technique that can encode 3D information on a 2D surface. This solution relies on a physicals height map (in the author's word, a 2.5D surface), whether that counts as a 2D surface I don't know. (and yes, I also saw the great explanation from 3blue1brown).
  - deleted 2y ago
    [deleted]
  - deleted 2y ago
    [deleted]
  - CyberDildonics 2y ago
    any general technique that can encode 3D information on a 2D surface This isn't 3D information on a 2D surface. If anything it is 2D information on a 3D surface.
    - gpderetta 2y ago
      The video shows that it projects a 3D surface as if it was storing volumetric information.
      - CyberDildonics 2y ago
        It isn't projecting a 3D surface (I'm not sure that even makes sense in this context) and it isn't storing volumetric information. It is just using refraction to make brighter and darker areas in its shadow/caustics to make an image. The paper is 10 years old at this point and linked by this article. https://rgl.s3.eu-central-1.amazonaws.com/media/papers/Papas2011Goal.pdf https://rgl.s3.eu-central-1.amazonaws.com/media/papers/Papas... https://nishitalab.org/user/egaku/tog14/yue-continuous-caustics-lens.pdf https://nishitalab.org/user/egaku/tog14/yue-continuous-caust... I think once you read the papers you will realize that the only thing 3D is the surface of the lens and that is only so it can get curves and angles for the refraction.
isoprophlex 2y ago
Quite curious that the backside of the lens is modeled as a mesh of quads with varying (x, y). I could imagine that a fixed grid of points with only varying height would be easier to model, am I missing something crucial? You can probably build an end-to-end model of a grid of heights (constrained to be h=0 at the edges), a simulated ray exiting the slab (surface normals modified by whatever Snell's law tells you), and the eventual light intensity on the target plane... and immediately optimize the entire thing with backprop? I'm probably massively oversimplifying this and ignoring half of the physics

178 points by mhb 2y ago

deleted 2y ago

[deleted]

mkmk 2y ago

Some nice comments on this previous discussion of the same link: https://news.ycombinator.com/item?id=28283411 https://news.ycombinator.com/item?id=28283411

dang 2y ago
Thanks! Macroexpanded: Hiding Images in Plain Sight: The Physics of Magic Windows - https://news.ycombinator.com/item?id=28283411 https://news.ycombinator.com/item?id=28283411 - Aug 2021 (24 comments) Hiding Images in Plain Sight: The Physics of Magic Windows - https://news.ycombinator.com/item?id=28220376 https://news.ycombinator.com/item?id=28220376 - Aug 2021 (1 comment)

LarsDu88 2y ago

That's so cool!

shiko11pin 2y ago

Similar to "Pixel Window" link: https://x.com/Hakusi_Katei/status/1807591865132466324 https://x.com/Hakusi_Katei/status/1807591865132466324

rawgabbit 2y ago

Reminds me of magic mirrors of Japan and China. https://www.cnn.com/style/article/magic-mirror-cincinnati-art-museum-scn/index.html https://www.cnn.com/style/article/magic-mirror-cincinnati-ar... https://www.greenshinto.com/2014/02/16/magic-mirrors/ https://www.greenshinto.com/2014/02/16/magic-mirrors/

injidup 2y ago

Not to take away the brilliance of what is achieved but I think hologram is the wrong word. This is purely about caustics. Amplitude engineering rather than phase. The calculations are just assuming light as particle, not light as wave. A true hologram uses diffraction grating effects and the phase difference from light. There was a very nice explanation on three-blue-brown recently. https://www.youtube.com/watch?v=EmKQsSDlaa4 https://www.youtube.com/watch?v=EmKQsSDlaa4 I don't think there are any phase effects in the parent attached? Or are there?

gpderetta 2y ago
Depends if we consider holograms only the specific technique of using phases to encode the information or any general technique that can encode 3D information on a 2D surface. This solution relies on a physicals height map (in the author's word, a 2.5D surface), whether that counts as a 2D surface I don't know. (and yes, I also saw the great explanation from 3blue1brown).
- deleted 2y ago
  [deleted]
- deleted 2y ago
  [deleted]
- CyberDildonics 2y ago
  any general technique that can encode 3D information on a 2D surface This isn't 3D information on a 2D surface. If anything it is 2D information on a 3D surface.
  - gpderetta 2y ago
    The video shows that it projects a 3D surface as if it was storing volumetric information.
    - CyberDildonics 2y ago
      It isn't projecting a 3D surface (I'm not sure that even makes sense in this context) and it isn't storing volumetric information. It is just using refraction to make brighter and darker areas in its shadow/caustics to make an image. The paper is 10 years old at this point and linked by this article. https://rgl.s3.eu-central-1.amazonaws.com/media/papers/Papas2011Goal.pdf https://rgl.s3.eu-central-1.amazonaws.com/media/papers/Papas... https://nishitalab.org/user/egaku/tog14/yue-continuous-caustics-lens.pdf https://nishitalab.org/user/egaku/tog14/yue-continuous-caust... I think once you read the papers you will realize that the only thing 3D is the surface of the lens and that is only so it can get curves and angles for the refraction.

isoprophlex 2y ago

Quite curious that the backside of the lens is modeled as a mesh of quads with varying (x, y). I could imagine that a fixed grid of points with only varying height would be easier to model, am I missing something crucial? You can probably build an end-to-end model of a grid of heights (constrained to be h=0 at the edges), a simulated ray exiting the slab (surface normals modified by whatever Snell's law tells you), and the eventual light intensity on the target plane... and immediately optimize the entire thing with backprop? I'm probably massively oversimplifying this and ignoring half of the physics