Andrew Coppin <orp### [at] btinternetcom> wrote:

> OK, on reflection maybe I was a little unclear. (Reflection, get it? Hehe...
> eh... heh... oh never mind! :-P) What I ment was... can I put a hologram
> into a POV-Ray scene?

(Sorry for late response. I have not checked posts for a while.)

This is a very interesting problem I have been thinking about for a
while. I am actually what you would call a "holographer", but relatively
new to povray. My interest is to "preview" a hologram before I make one.
So I like to see if there are any distortions of the image when I move
relative to the hologram. For example, this happens when you change the
wavelength of the reconstruction beam to that of recording. For an
example of what I mean, you can look at 

http://www.bazargan.org/Swing.mp4

This is an animation done with povray, using the (forward) ray tracing
equations for obtaining a holographic image. The beauty of povray is
that it is an excellent language for putting in math formulae, and then
it renders and animates it for you!

Here is a more complex example:

http://www.bazargan.org/dispersion-comp.mp4

Here the 'object' is a horizontal line of spheres. The hologram is
viewed with polychromatic light, but the light has first been dispersed
with a diffraction grating, so that the final images are all in line.

Of course the animation you see is just a geometric grid, not what you
would "see". For instance the image is only visible by the observer (the
eyeball) when it is looking through the hologram itself, but it does
show the "swing" of a holographic image. This is already very useful for
looking at distortions, multiple-wavelength playback, etc.

The next challenge is to show a 'photorealistic' image of a hologram in
a scene. For example, you have a hologram hanging on a wall, illuminated
by a white light above it. I think we can apply the same ray tracing
formulae, but this time in a 'backward' or computer graphics sense. So
the hologram becomes a 'special' surface. When a scene is rendered, the
color of each pixel on the hologram can be calculated by taking into
account the recording geometry, the original wavelength, the final
reconstruction wavelength (or band of wavelengths) and the object. 

I am not really clear about how to do this, but I have in mind some kind
of 'function' for the hologram surface. I hope this can be done in a
single pass in povray. 

A very useful tool has been the Lightsys 3 macros:

http://www.ignorancia.org

which draw in a color approximating to the wavelength chosen.

-- 
Kaveh

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