A question about holograms

Discussion in 'Rendering Technology and APIs' started by MfA, Mar 2, 2009.

  1. MfA

    MfA
    Legend

    Joined:
    Feb 6, 2002
    Messages:
    7,008
    Likes Received:
    535
    I've been reading a bit about Computer Generated Holograms and I came upon the paper A Framework for Holographic
    Scene Representation and Image Synthesis
    .

    What amazes me is how detailed their reconstructions are considering they are only computing 1024^2 samples per hologram, whereas photographically created holograms use films which can resolve sub-micron features. Can someone explain to me why this can work inside the computer but not inside physical reality? (Physical reconstructions from such low resolution holograms look like crap.)

    PS. hey Simon, I guess pre-filtering is possible after all :p
     
    #1 MfA, Mar 2, 2009
    Last edited by a moderator: Mar 3, 2009
  2. GourdFreeMan

    Newcomer

    Joined:
    Feb 1, 2009
    Messages:
    3
    Likes Received:
    0
    For many of the same reasons an amateur 35mm photograph of a computer screen usually looks worse than a screen capture converted to a JPEG... namely imperfect optics, imperfect media, environmental factors (we don't live in an isothermic 0K perfect vacuum), human error, etc. The theoretical resolution of the media is simply not an issue given the budget and technical expertise you are talking about. We also don't use idealized pinhole cameras in the creation and viewing of holograms, nor do we usually view holograms from exactly the reverse direction of their illumination direction to 64 bits of floating point precision. Really without starting or ending with something physical their technique is little more than a sophisticated encoding of color and Z data of a single 3D frame.
     
  3. MfA

    MfA
    Legend

    Joined:
    Feb 6, 2002
    Messages:
    7,008
    Likes Received:
    535
    Not quite enough to explain multiple orders of magnitude (the best holograms would have around 4 orders of magnitude higher dpi than a 1024x1024 pixel image on a decent monitor).
    Either the information is in there or it isn't.
    Neither did they, they used virtual apertures in the reconstruction (there are no cameras at all, virtual or physical, in hologram creation though).
    Now this is important, I didn't immediately realise they never did any off axis reconstructions.
    No, it's a limited resolution encoding of the object wave (a pure 2D representation I might add). There are some nice animations showing off axis viewing angles and varying apertures on his site.
     
    #3 MfA, Mar 3, 2009
    Last edited by a moderator: Mar 4, 2009
  4. GourdFreeMan

    Newcomer

    Joined:
    Feb 1, 2009
    Messages:
    3
    Likes Received:
    0
    Let me amend that to "depth" rather than "Z", as it isn't simply depth from camera to object, but rather an approximation of depth from camera to object to simulated emitter being encoded through simulation of wave propagation in the technique described in the paper.


    ---
    beyond3d lies technical marketing
     
  5. MfA

    MfA
    Legend

    Joined:
    Feb 6, 2002
    Messages:
    7,008
    Likes Received:
    535
    Actually they don't simulate wave propagation, that's just to explain how holograms work. They use a FFT based technique to compute the interference patterns for individual textured polygons.

    PS. well they simulate it on reconstruction, obviously ...
     
    #5 MfA, Mar 3, 2009
    Last edited by a moderator: Mar 3, 2009
  6. MfA

    MfA
    Legend

    Joined:
    Feb 6, 2002
    Messages:
    7,008
    Likes Received:
    535
    Oh hey I'm an idiot ... this is why it works for them :
    So you can get really nice detail in physical holograms too with only 1024x1024 samples ... they just have to be tiny.
     
Loading...

Share This Page

  • About Us

    Beyond3D has been around for over a decade and prides itself on being the best place on the web for in-depth, technically-driven discussion and analysis of 3D graphics hardware. If you love pixels and transistors, you've come to the right place!

    Beyond3D is proudly published by GPU Tools Ltd.
Loading...