[Radiance-general] Images too bright with gendaylit

[Joe]

Hi,

I am quite new to Radiance and have not used the exposure setting so 
far.
So far I had expected to get a "well illuminated" scene with some 
shadows
cast.
I have to read a bit on how exposure works.

Does it work like an ambient light to sort of adjust the overall 
brightness
of the image?

 From what I understand so far exposure only affects
the view of the rendered image, not the actual physical properties
like illuminance, radiance and irradiance.
And if rtrace is used to "view" the image instead of rvu the
illumination would be consistent.

Is that correct?

Kind regards,
Joe


Am 08.08.2017 10:01 schrieb Jan Wienold:
> Hi Joe,
> 
> why do you think it is too bright? Is the luminance to high? I guess
> you just have to adapt your exposure setting for the image.
> 
> The physics for gendaylit and your parameters is correct:
> 
> 1. test of luminance of the sun (ray in sun direction):
> 
> gendaylit -ang 90 0 -W 900 200 >sky.rad
> oconv -f sky.rad >sky.oct
> 
> echo  0 0 0 -0.000000 -0.052336 0.998630 |rtrace -h sky.oct | rcalc -e
> '$1=47.4*$1+120*$2+11.6*$3'
> result: 1.356104e+09 cd/m2
> 
> This value looks reasonable - the max is about 1.6 e9 cd/m2
> 
> 2. test of irradiance (sensor also looks towards sun):
> 
> gendaylit -ang 90 0 -O 1  -W 900 200 >sky_irr.rad
> oconv -f sky_irr.rad >sky_irr.oct
> echo  0 0 0 -0.000000 -0.052336 0.998630 |rtrace -h -I+ sky_irr.oct
> result : 8.998834e+02   W/m2
> 
> Equals the direct irradiance which was "put" into the model (the sky
> is ignored, as in your example).
> 
> cheers
> 
> Jan
> 
> 
> On 08.08.17 09:17, Joe wrote:
>> Hello,
>> 
>> when I use gendaylit to create a sun my images are too bright.
>> 
>> The command used is
>> 
>> gendaylit -ang 90 0 -W 900 200
>> 
>> 
>> void light solar
>> 0
>> 0
>> 3 7.576e+006 7.576e+006 7.576e+006
>> 
>> solar source sun
>> 0
>> 0
>> 4 -0.000000 -0.052336 0.998630 0.533000
>> 
>> This will put the sun to the zenith with reasonable values
>> for direct normal and diffuse irradiance in W/m^2.
>> 
>> Correct so far?
>> 
>> I removed the skyfunc, just the sun source is active.
>> 
>> I put together a simple scene:
>> - plastic cylinders as coordinate origin,
>> - large brown ground plate
>> - dielectric spheres (I just love those :)
>> 
>> Here is an image with renderings of different sun settings:
>> 
>> http://imgur.com/hOqCpmY
>> 
>> When I use the sun as stated above the image on the right
>> side is rendered. Much too bright.
>> 
>> Reducing the parameters of void light solar:
>> 
>> middle image (7.576e+005 7.576e+005 7.576e+005 )
>> left image (7.576e+004 7.576e+004 7.576e+004)
>> 
>> Viewed with default parameters of rvu.
>> 
>> Do you have an idea what I am doing wrong
>> or might have missed?
>> 
>> Kind regards,
>> Joe
>> 
>> 
>> 
>> 
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