On 1/2/2013 11:13 AM, Le_Forgeron wrote:
> Le 02/01/2013 19:53, handos nous fit lire :
>> Hi everyone,
>>
>> I am wondering if it possible to quantify the lighting in the POVRay scene in
>> lumens? Is there a variable in the scene I can access or is it just the average
>> Irradiance values observed at the pixels? Could someone send pointers to that
>> please?
>
> You would want a gamma of 1.0; And probably diffuse 1, ambient 0 on your
> target surface. (which might rules out any complex scene with reflection)
>
> Notice that there is no notion of distance for one pov unit. (can be
> meter, kilometer, millimeter, miles, yards or what ever).
>
> You would need to adjust the light_source to have fade_distance &
> fade_power.
> Spherical light source are easy, as well as far far away sun... but
> conical ones are more difficult. Also read in details:
>
>> http://wiki.povray.org/content/Documentation:Light_Source
>
>
Yeah, this is something that kind of makes things more annoying than 
usual, on occasion. lol But, it should be calculable anyway, if someone 
bothered, right? Say, you set a variable, using meters as the default, 
Assumed_Unit = 0.01 (i.e., a centimeter), then your calculations are 
going to be based on, "X is pure white, at Y units, when Assumed_Unit = 
1 meter", and all you need to do is scale your lighting by the fact that 
you are using a centimeter, instead of a meter.

The real trick being that you need to figure out what the correct 
settings, for a light, to get that result, with a specific falloff 
(which, I don't think changes much, other than with lumins, in the real 
world, right?), then work out where the correct Y is, for your "default" 
1 meter distance. After that, you just tweak the variables, including 
falloff, to work out what the change is, over different scales.

Bound to be hard, but not impossible. It just means, when you need/want 
to use that lighting model, you have to have a defined 1 unit = X 
meters, to work from, during the entire process. And, frankly, we do 
that anyway, when building, to get everything scaled properly (unless 
your someone that just builds things, then scales them after, until they 
look right, or something...)

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