Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!ubc-cs!alberta!calgary!ctycal!ingoldsb
From: ingoldsb@ctycal.COM (Terry Ingoldsby)
Newsgroups: comp.graphics
Subject: Re: What's a hologram?
Summary: A hologram is
Message-ID: <453@ctycal.UUCP>
Date: 29 Aug 89 19:06:13 GMT
References: <4791@portia.Stanford.EDU> <1746@dover.sps.mot.com> <2330@ucsfcca.ucsf.edu>
Organization: The City of Calgary, Ab
Lines: 41

In article <2330@ucsfcca.ucsf.edu>, root@cca.ucsf.edu (Systems Staff) writes:
> 
> I see some quite different things being called "holograms" and
> would like to know what's what.
> 
> There are what I have understood to be holograms which are formed
> by beam splitting and interference pattern generation on a
> photographic medium. These are viewed with a matching coherent
> light source and form an image by diffraction effects.
...
IMHO a hologram, be it produced by a computer, using lasers with
reference beams or an Etch-A-Sketch must reproduce both the
amplitude (actually intensity) *AND* the phase (more precisely
the relative phase).  If either of the above are missing then
*I* don't consider it a hologram, though some things are closer
than others.
> Now, I've seen some things which are just multiple image prints
> with a surface molded to form a lens array to get some of the
> variable perspective image effects that a hologram as described
> above yields (but greatly inferior).
...
I doubt this is a hologram.
> Then I hear about "white light holograms" in contexts that suggest
> "genuine" holography but obviously involve a difference in process.
> 
By my definition, I'm not sure.  They sacrifice the 3D aspect in one
dimension in order to be able to use white light for reproduction.  A
professor of mine once said that they used the missing dimension (eg.
vertical 3D) to select a part of the white light to do the reprod-
uction.  White light holograms do appear in a sort of prism of light
effect.  I have said nothing about whether a hologram has to be 3D,
so (IMHO) that does not disqualify a white light hologram.  I doubt
they preserve phase explicitly, but it must be there implicitly.

Hmmm?


-- 
  Terry Ingoldsby                       ctycal!ingoldsb@calgary.UUCP
  Land Information Systems                           or
  The City of Calgary         ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb