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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

I don't think there are any phase effects in the parent attached? Or are there?

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gpderetta

3 days ago

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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).

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CyberDildonics

3 days ago

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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.

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gpderetta

2 days ago

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The video shows that it projects a 3D surface as if it was storing volumetric information.

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CyberDildonics

2 days ago

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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/Papas...

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.

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mkmk

4 days ago

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

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dang

4 days ago

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Thanks! Macroexpanded:

Hiding Images in Plain Sight: The Physics of Magic Windows - 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 - Aug 2021 (1 comment)

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shiko11pin

3 days ago

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

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isoprophlex

3 days ago

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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

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LarsDu88

3 days ago

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That's so cool!