Hiding Images in Plain Sight: The Physics of Magic Windows

While the described window is not a hologram per se and I think the hologram-like effect can easily break for other images (i.e. it can not reliably represent depth), it should be noted that it has a certain relation to holograms. Holograms modify plane wave in a way which reproduces wavefront from a recorded scene. Usually it's done by capturing interference pattern, but alternatively hologram can introduce phase shifts by varying thickness (ideally it's worth to use both phase shift and absorption). I think it should be possible to create hologram with the same setup by changing optimization function. Although I am not sure if you will be able to perform precise enough carving with your setup for reproducing complex enough scenes. Try to start with representing several dots at different distance from hologram plane each radiating radial wave. Thinking about diverging lens as of hologram representing one such point should help with intuition.

Re: Hiding Images in Plain Sight: The Physics of Magic Windows

#5

Post by woko » Tue, Aug 24, 2021, 7:46 AM UTC

This is another amazing blog post by Matt Ferraro. You may remember his post last month about Poisson's Equation.

For the past 2 blog posts, see: https://news.ycombinator.com/from?site=mattferraro.dev

Re: Hiding Images in Plain Sight: The Physics of Magic Windows

#6

Post by tobr » Tue, Aug 24, 2021, 8:29 AM UTC

newpavlov wrote: post #4

While the described window is not a hologram per se and I think the hologram-like effect can easily break for other images (i.e. it can not reliably represent depth), it should be noted that it has a certain relation to holograms. Holograms modify plane wave in a way which reproduces wavefront from a recorded scene. Usually it's done by capturing interference pattern, but alternatively hologram can introduce phase sh…

That brings to mind this description of a technique for hand-engraved holograms[1].

> The required tools are so simple that ancient peoples could have drawn these images in hardened sooty resin pools with wooden tools, had they but known the trick.

1: http://amasci.com/amateur/holo1.html

Re: Hiding Images in Plain Sight: The Physics of Magic Windows

#7

Post by plutonorm » Tue, Aug 24, 2021, 8:59 AM UTC

newpavlov wrote: post #4

While the described window is not a hologram per se and I think the hologram-like effect can easily break for other images (i.e. it can not reliably represent depth), it should be noted that it has a certain relation to holograms. Holograms modify plane wave in a way which reproduces wavefront from a recorded scene. Usually it's done by capturing interference pattern, but alternatively hologram can introduce phase sh…

You can form this hologram trivially by considering each pixel as a source of rays in a variety of directions. You might then expect a series of hemispherical shapes on the surface, with areas of the dome missing where rays should not be fired. In this case you hit the age old problem of holograms - the sheer volume of information that needs to be encoded onto the surface for a hologram of reasonable resolution to be formed. Whether there is some more subtle surface that reproduces the light field but exploits its compressibility to reduce the surface complexity, I don’t know. Would be fun to try to optimise for it, but alas I have too many things to do already. How does one get grad students?

Re: Hiding Images in Plain Sight: The Physics of Magic Windows

#8

Post by enriquto » Tue, Aug 24, 2021, 9:04 AM UTC

tobr wrote: post #6

newpavlov wrote: post #4

While the described window is not a hologram per se and I think the hologram-like effect can easily break for other images (i.e. it can not reliably represent depth), it should be noted that it has a certain relation to holograms. Holograms modify plane wave in a way which reproduces wavefront from a recorded scene. Usually it's done by capturing interference pattern, but alternatively hologram can introduce phase sh…

That brings to mind this description of a technique for hand-engraved holograms[1]. > The required tools are so simple that ancient peoples could have drawn these images in hardened sooty resin pools with wooden tools, had they but known the trick. 1: http://amasci.com/amateur/holo1.html

This is incredibly awesome!

Re: Hiding Images in Plain Sight: The Physics of Magic Windows

#9

Post by 123pie123 » Tue, Aug 24, 2021, 9:16 AM UTC

tobr wrote: post #6

newpavlov wrote: post #4

While the described window is not a hologram per se and I think the hologram-like effect can easily break for other images (i.e. it can not reliably represent depth), it should be noted that it has a certain relation to holograms. Holograms modify plane wave in a way which reproduces wavefront from a recorded scene. Usually it's done by capturing interference pattern, but alternatively hologram can introduce phase sh…

That brings to mind this description of a technique for hand-engraved holograms[1]. > The required tools are so simple that ancient peoples could have drawn these images in hardened sooty resin pools with wooden tools, had they but known the trick. 1: http://amasci.com/amateur/holo1.html

many thanks for this great nugget of information

This could be used as a great art project, even young kids could do

Re: Hiding Images in Plain Sight: The Physics of Magic Windows

#10

Post by duffmancd » Tue, Aug 24, 2021, 12:47 PM UTC

constantform wrote: post #2

https://michaelberryphysics.files.wordpress.com/2013/07/berr...

For more information, the parent PDF describes a similar process using reflection discovered in China.

If you cast and polish a bronze mirror with raised letters/shapes on the back, the very slight deformations caused by polishing over the different thicknesses will create an image in the reflected caustics, despite the fact that the mirror appears smooth when using it as a mirror.