On 26-2-2018 1:03, Alain wrote:
> Le 18-02-25 à 02:53, Thomas de Groot a écrit :
>> On 24-2-2018 17:07, Mike Horvath wrote:
>>> On 2/23/2018 8:18 AM, Alain wrote:
>>>> The 3 lumen looks a little to bright.
>>>> Can you post the 1 lumen image?
>>>>
>>>> Also, the sun position is not the same for the two images. It mover 
>>>> by around 40°.
>>>
>>> Here it is with RGB instead of SRGB, and 1 lumens.
>>>
>>> https://i.imgur.com/AcGBbla.jpg
>>>
>>> As you can see, it is pretty dim and lifeless.
>>>
>>
>> On my screen it looks right.
>>
>> I often use CIE.inc myself, maybe in a little different way than you 
>> do. This is an example of how I define my sunlight in a scene:
>>
>> //start code -----------------------------------
>> #include "CIE.inc"
>> #if (Fog)
>>    #local Intensity    = 5;
>> #else
>>    #local Intensity    = 3;
>> #end
>> //Sun's temperature (Kelvin): 2800=red; 7500=blue white
>> #declare SunColor     = Blackbody(6500)*Intensity;
>> #declare SunPosition  = <0, 0, -2>*10e4;
>> #declare SunDis       = vlength(SunPosition)*2/215;
>> #declare Sun_alt      = 60;
>> #declare Sun_azm      = -115;
>>
>> #if (Area)
>>    #debug "\nUsing an area_light for the Sun.\n"
>>    light_source{
>>      <0, 0, 0>
>>      color SunColor
>>      area_light
>>      SunDis*x, SunDis*z, // lights spread out (x * z)
> 
> A better, more descriptive, name would be "SunDiam"
> 
>>      4, 4                // total lights in grid (4x*4z = 16
lights)
> 
> This will actually use a 5 by 5 array...
> 
>>      adaptive 1          // 0,1,2,3...
> 
> ...and start with a 3 by 3 one.
> With adaptive, you can use a much larger value, like 17 or 33 without 
> increasing the render time much.
> adaptive 0 DON'T turn the feature off, but start with a 2 by 2 array.
> 
>>      area_illumination on  // full area diffuse and specular
>>      jitter              // adds random softening of light
> 
> Makes the penumbra grainy if using a sparse array.
> 
>>      circular            // make the shape of the light circular
>>      orient              // orient light
>>      translate SunPosition
>>      rotate Sun_alt*x
>>      rotate Sun_azm*y
>>      parallel
>>      point_at <0, 0, 0>
>>      media_interaction on
>>      media_attenuation off
>>    }
>> #else
>>    light_source {
>>      <0, 0, 0>
>>      color rgb SunColor
>>      translate SunPosition
>>      rotate Sun_alt*x
>>      rotate Sun_azm*y
>>      parallel
>>      point_at <0, 0, 0>
>>      media_interaction on
>>      media_attenuation off
>>    }
>> #end
>> //end code -----------------------------------
>>
>>
> 
> Using adaptive, you need larger arrays to get all the benefit. Some 
> suggested sizes in relation with the adaptive steps values :
> adaptive 0 (0 initial subdivisions)  at least 5 by 5 (2 steps)
> adaptive 1 (1 initial subdivisions)  at least 9 by 9 (3 steps)
> adaptive 2 (2 initial subdivisions)  at least 17 by 17 (4 steps)
> adaptive 3 (3 initial subdivisions)  at least 33 by 33 (5 steps)
> 
> You can always use larger arrays to get smoother results.

Thanks Alain, well spotted indeed. I always unthinkingly use the set up 
as is. ;-)

-- 
Thomas

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