Path: utzoo!utgpu!water!watmath!clyde!rutgers!uwvax!oddjob!hao!ames!sdcsvax!ucsdhub!hp-sdd!hplabs!hpcea!hpfcdc!hpfcdq!wanger
From: wanger@hpfcdq.HP.COM (Leonard Wanger)
Newsgroups: comp.graphics
Subject: Re: ray tracing 3d holograms
Message-ID: <390006@hpfcdq.HP.COM>
Date: 17 Dec 87 16:08:00 GMT
References: <1987Dec15.152944.3586@mntgfx.mentor.com>
Organization: Hewlett-Packard - Fort Collins, CO
Lines: 25


	Last year I visited the Media Lab at MIT. The way they were
creating the computer generated holograms was to expose a thin
vertical strip of the film to an image. Then a new image (rotated
by a small amount) and the vertical strip next to the last one was
exposed. Repeating this process for the whole piece of film allowed
a cylindrical hologram to be produced. This method is a little
expensive for ray-tracing considering the number of images to be
produced (over a thousand per hologram if I remember!). Also,
although the result was impressive, you only can see the three
dimensionality in the horizontal direction. Normally a hologram
allows you to look around objects (an example is one I made with
a magnifying glass in it that allows you to look at the object
through the glass or under normal magnification around the side)
but since the holograms are created in vertical strips, you can
not look over and under objects (normally every point in a hologram
has the complete image, in this case all the points in the vertical
strips contain the image). 

	Has anyone heard about a computer generated hologram created
in squares (opposed to strips)? This would square the number of
images needed, but would give the true 3-dimensional effect (in
the vertical and horizontal).

	Len Wanger -- Hewlett Packard Graphics Technology Division