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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,
1.I have set an ortographic camera.
2.I am considering only a white light without other effects (I hope it).
I tried with the default fading light law of POV-Ray (setting fade_power and
fade_distance) and also introducing a new simple law like this:
#declare dist = vlength (Light_Location - Wall_Center);
#declare LightFactor = 1/dist;
light_source {
Light_Location
color rgb 1 * LightFactor
fade_distance 1
fade_power 0
media_interaction off
}
3.Light hits an "infinite" black wall with this characteristics:
finish {
ambient 0
diffuse 0
specular 1
roughness 1
brilliance 0
reflection {1}
}
and positioned at different distances from the emission light.
I am post-processing the images (result of several runs relative to different
distances) evaluating the white mean value in the images by an image editor
software.
It seems that light fading law set in POV-Ray is different from the image
results.
Do you suggest an other method for verifying the light fading?
Is it possible that POV-Ray is not accurate in this tool?
Thank you
Regards
Motive17
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On 8/31/2017 5:12 AM, Motive17 wrote:
> Do you suggest an other method for verifying the light fading?
> Is it possible that POV-Ray is not accurate in this tool?
have you had a look at:
http://wiki.povray.org/content/Reference:Light_Source#Light_Fading
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Jim Holsenback <spa### [at] nothanks net> wrote:
> On 8/31/2017 5:12 AM, Motive17 wrote:
> > Do you suggest an other method for verifying the light fading?
> > Is it possible that POV-Ray is not accurate in this tool?
>
> have you had a look at:
> http://wiki.povray.org/content/Reference:Light_Source#Light_Fading
Thank you for the answer.
Yes, I did. I know quite well the documentation on this topic.
What I am trying to do is verifying the fading light laws applied by POV-Ray.
BR
Motive17
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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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Le 17-08-31 à 05:12, Motive17 a écrit :
> Good morning to all,
> my issue is relative to the validation of the light fading law applied by
> POV-Ray.
>
To get acurate results, you need to use assumed_gamma 1.
The value that you measure in your graphic/paint/image editing programm
are affected by your system gamma setting, and it's handling quality.
In
light_source {
Light_Location
color rgb 1 * LightFactor
fade_distance 1
fade_power 0
media_interaction off
}
and change
#declare LightFactor = 1/dist;
to
#declare LightFactor = dist;
you should use rgb pow(LightFactor, 2) and fade_power 2
Using fade_power gives you a non-fading light. It's the same as if you
did not use fade_distance and fade_power at all.
Using fade_power 1 would simulate fading in a 2D space.
fade_power 2 gives realistic fading relative to the distance from the
light source.
For your plane, in this case, reflection is meaningless as ther is
nothing to reflect. specular is used to simulate the reflection of the
actual light_source.
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William F Pokorny <ano### [at] anonymousorg> wrote:
>
> 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}.
>
If using v3.7xx, the finish should be {diffuse 1.0 ambient 0.0 emission 0.0}--
because emission also has a default, I believe (of 0.1?), although I can't
recall where I saw that in the documentation.
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Alain <kua### [at] videotronca> wrote:
>
> you should use rgb pow(LightFactor, 2) and fade_power 2
> Using fade_power gives you a non-fading light. It's the same as if you
> did not use fade_distance and fade_power at all.
You probably meant to say "Using fade_power 0 gives you a non-fading light." ;-)
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Am 31.08.2017 um 19:56 schrieb Kenneth:
> If using v3.7xx, the finish should be {diffuse 1.0 ambient 0.0 emission 0.0}--
> because emission also has a default, I believe (of 0.1?), although I can't
> recall where I saw that in the documentation.
`emission` defaults to 0.0.
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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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Thank you all for the replies.
They were precious.
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