Emission node problems

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Egert_Kanep
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Emission node problems

Post by Egert_Kanep » Wed Oct 09, 2019 1:14 pm

I am experiencing weird behavior when using emission nodes. I have attached a small test scene. Maybe I am doing something wrong.

Problem is that different kind of node setups disable the effect of other nodes parameters. There might be more cases like this, but for now these 2 caught my eye.

Also there is a slight brightness difference when using only one channel from remap node or using combine rgb to make it 3 channels.
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emission_problems.blend
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Re: Emission node problems

Post by B.Y.O.B. » Thu Oct 10, 2019 8:28 am

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Re: Emission node problems

Post by marcatore » Thu Oct 10, 2019 12:18 pm

Just to avoid to create another thread and trying to stay on topic.
Before report another issue, could @Dade say me how emission on material is calculated? I mean, what's the relation bt gain, power and efficacy?

thanks

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Re: Emission node problems

Post by Dade » Thu Oct 10, 2019 1:00 pm

marcatore wrote:
Thu Oct 10, 2019 12:18 pm
Just to avoid to create another thread and trying to stay on topic.
Before report another issue, could @Dade say me how emission on material is calculated? I mean, what's the relation bt gain, power and efficacy?
The emitted light is:

Code: Select all

<Material gain> * <Material power> * <Material efficiency>
-----------------------------------------------------------------------
                             <Triangle area>
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Re: Emission node problems

Post by marcatore » Fri Oct 11, 2019 7:06 am

Thank you.

So, I can't say if it's an issue of Blender addon, anyway I have this
Everything with 0
blender_2019-10-11_08-52-32.png
Just Gain with 1
blender_2019-10-11_08-52-46.png

Another "strange thing"
Without a blackbody temperature node attached
blender_2019-10-11_09-03-22.png
With
blender_2019-10-11_09-03-31.png
With blackbody attached with 1 on all the settings (gain, power, efficacy)
blender_2019-10-11_09-05-11.png

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Re: Emission node problems

Post by Dade » Fri Oct 11, 2019 8:10 am

marcatore wrote:
Fri Oct 11, 2019 7:06 am
Just Gain with 1
blender_2019-10-11_08-52-46.png
This is the expected behavior: you are supposed to use "gain" (i.e. artistic tool) or "power" and "efficiency" (i.e. like in a real light bulb), not both ways at they same time. If "power" and/or "efficiency" are 0.0, only "gain" is used; this is explaining what you are observing.
marcatore wrote:
Fri Oct 11, 2019 7:06 am
Another "strange thing"
Without a blackbody temperature node attached
blender_2019-10-11_09-03-22.png

With
blender_2019-10-11_09-03-31.png

With blackbody attached with 1 on all the settings (gain, power, efficacy)
blender_2019-10-11_09-05-11.png
I'm unable to replicate this problem here, can you post the scene ?
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Re: Emission node problems

Post by marcatore » Fri Oct 11, 2019 9:40 am

Dade wrote:
Fri Oct 11, 2019 8:10 am
This is the expected behavior: you are supposed to use "gain" (i.e. artistic tool) or "power" and "efficiency" (i.e. like in a real light bulb), not both ways at they same time. If "power" and/or "efficiency" are 0.0, only "gain" is used; this is explaining what you are observing.
Ok, understood. So, now a request for BYOB: is it possible to have a checkbox that enables and shows the "power&efficacy" settings, because now, is not so clear that power&efficacy are not needed if you don't want.
Dade wrote:
Fri Oct 11, 2019 8:10 am
I'm unable to replicate this problem here, can you post the scene ?
Sure!!
test_Emission.zip
(122.26 KiB) Downloaded 4 times

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Re: Emission node problems

Post by B.Y.O.B. » Fri Oct 11, 2019 12:05 pm

marcatore wrote:
Fri Oct 11, 2019 9:40 am
Ok, understood. So, now a request for BYOB: is it possible to have a checkbox that enables and shows the "power&efficacy" settings, because now, is not so clear that power&efficacy are not needed if you don't want.
Sure, add it to my todo list (github issues).
It's actually something I have considered doing since a while, but never got around to it.
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Re: Emission node problems

Post by marcatore » Fri Oct 11, 2019 1:00 pm

done!

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Re: Emission node problems

Post by Dade » Fri Oct 11, 2019 3:18 pm

marcatore wrote:
Fri Oct 11, 2019 9:40 am
Dade wrote:
Fri Oct 11, 2019 8:10 am
I'm unable to replicate this problem here, can you post the scene ?
Sure!!
test_Emission.zip
Ok, you can find an explanation of how black body works here http://www.westinghouselighting.com/col ... ature.aspx and a more technical explanation here: http://www.techmind.org/colour/coltemp.html

Image

You need to adjust your camera exposure or material emission gain. You seems to assume blackbody texture return values between 0. and 1.0; it doesn't, for instance:

- BlacBody(1000) = RGBColor[9581.77, 0, 0.000183105] (Red-ish)
- BlacBody(6500) = RGBColor[66523.2, 63735.1, 67380.9] (White-ish)
- BlacBody(10000) = RGBColor[32116.3, 37786.2, 54656.2] (Blue-ish)

So you need to scale the values if you want an [0.0, 1.0] range, You can change the camera exposure or use scale node or use the emission gain, for instance with a value of (1/65000, 1/65000, 1/65000) = (0.000015385, 0.000015385, 0.000015385).
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