5. HDRI lighting

An HDR (high dynamic range) image or lightprobe simulates a more natural 
environment. The lighting, but also the reflections, will be more realistic. You
can download a few free lightprobes from www.debevec.org.

First, remove all the lights that are in the scene. Then, change the skysphere 
definition from 

	sky_sphere {
	  pigment {
	    gradient -y
	    color_map {
	      [ 1 rgb 1 ]
	    }
	  }
	}

to this:

	sphere {
	  <0,0,0>,10000          
	  pigment {
	    image_map { hdr "lightprobe.hdr" once interpolate 2 map_type 7 }
	  }
	  finish { ambient 1 diffuse 0 }
	  hollow  
	}

Again, play around with the settings. I'm using a sphere here, because the 
version of MegaPOV that I'm using doesn't accept hdr-images as textures for a 
skysphere. That may change in a future version.

The map_type depends on what kind of hdr-image you're using. There are different
kinds of projections that can be used to make one. Read more about it at 
www.debevec.org. Map_type 7 is used for a spherical lightprobe, like the ones 
that can be downloaded from there.

The ambient value defines how bright the hdr is.

<tutorial_chapter05a.png>: looks nice already, doesn't it?