William F Pokorny <ano### [at] anonymousorg> wrote:
> 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.

Thank you for your reply, it was precious.
Only avoiding any gamma corrections I was able to validate the light fading.
BR
Motive17

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