On 08/31/2017 05:12 AM, Motive17 wrote:
> Good morning to all,
> my issue is relative to the validation of the light fading law applied by
> POV-Ray.
> 
> I want to verify it, then,
> 
> 

What you've posted for code looks quite off to me for how POV-Ray works.

If measuring other than some single image center point for itensity - if 
measuring all the values in a complete image - I'd start with a point 
light at the origin around which I'd place a hollow sphere with an 
inside texture having a white pigment and finish {diffuse 1.0 ambient 0.0}.

I'd use a spherical camera also at the origin. For light color I'd 
probably go with one of red, green or blue and measure only the color 
channel picked to avoid any issues with external grey scale conversions 
when measuring. Lastly, if measuring values in the resultant image you'd 
need to output linearly encoded images (the default is sRGB - 'web' 
compatible). There are ini file settings to do this I can't recall off 
the top of my head.

To make measurements at any given 'distance' from the point light vary 
the radius of the enclosing sphere around the origin, measure the image 
values - avoiding any external tool gamma corrections - for the r,g or b 
channel picked for your light source.

Note 1 : POV-Ray 3.71 / 3.8 added a quick inverse law light setting by 
using a fade_distance of 0 if I remember.

Note 2: POV-Ray doesn't search to infinity for ray-surface 
intersections, but rather - again if I'm remembering - to plus or minus 
1e7 units.

Bill P.

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