A lot of artists has made so-called rayographs, but Man Ray coined the term and
is perhaps most famous for making such images. The traditional process involves
lighting some objects on top of a sheet of photographic paper, then developing
the paper in the normal way. It's possible to mimic this process in POV-Ray by
using a light-source with negative strength and a glowing surface below
invisible objects. The light-source should theoretically have a strength of
-2.0, but a little more seems to be better. The plane below the objects should
have a finish with ambient and diffuse of 1.0, giving a glow. The objects on
the surface should have the no_image keyword to hide the object from view, but
keeping the shadow it casts. The negative light will eat away the glow from the
surface, but where the shadows are, the glow will show.

Following is the code and then some references to rayographs on the web.

Enjoy

H
--

// Persistence of Vision Ray Tracer Scene Description File
// File: rayograph.pov
// Vers: 3.6
// Desc: mimics rayographs in POV-Ray
// Date: 2008.07.13
// Auth: Helge Hansen
//
// Note: a square image format will show +/- 1.0 in x- and z-directions

#version 3.6;

global_settings { assumed_gamma 1.8 }

camera {
 location  <0, 3, 0> // position above plane
 direction 1.5*z
 right     x*image_width/image_height
 look_at   <0, 0, 0>
}

light_source {
 <1, 1, 1> // position
 color rgb <1, 1, 1> * (-2.5) // ! negative "colour", must be lower than -2.0
 area_light // area light gives more interesting shadows
 <0.75, 0, 0> <0, 0, 0.75> // light size
 5,5
 adaptive 1
 jitter
 //circular // for round light
}

#local Background = texture {
 pigment { color rgb <1,1,1> }
 finish { ambient 1 diffuse 1 } // glowing
}

#local Object = texture {
 pigment { color rgb <0,0,0> }
}

plane { y, 0 texture { Background } }

// objects:

union {
 cylinder { <-0.4, 0, -0.4>, <-0.4, 0.2, -0.4>, 0.1 }
 cylinder { <-0.4, 0,  0.4>, <-0.4, 0.2,  0.4>, 0.1 }
 cylinder { < 0.4, 0, -0.4>, < 0.4, 0.2, -0.4>, 0.1 }
 cylinder { < 0.4, 0,  0.4>, < 0.4, 0.2,  0.4>, 0.1 }

 no_image // ! hides the objects but keeps the shadows

 texture { Object }
}

--
On the web:

http://en.wikipedia.org/wiki/Man_Ray

http://en.wikipedia.org/wiki/Rayographs

http://www.manraytrust.com/

http://museum.icp.org/museum/exhibitions/man_ray/mr_bio.html

http://cs.nga.gov.au/IMAGES/LRG/88112.JPG
http://www.nga.gov/exhibitions/2006/dada/images/artwork/202-677-m.jpg

(or search for images in Google: man ray rayograph)

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