Irradiance Contour

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JuandeLara
Posts: 17
Joined: Wed Oct 28, 2020 2:39 pm

Irradiance Contour

Post by JuandeLara »

Hello all,

I have been looking into trying to visually represent lux measurements on a Luxcore render.

I understand from Dade, that one way to do it is with false colour setting, and trying to match each colour to the real-world values using a photometer. I think this could work, but I would need to test it at some point.

For a more reliable approach I though of working with the values for the Irradiance contour lines (see this post: viewtopic.php?f=4&t=2142). Here I found the Irradiance test.blend, but I cannot replicate the same effect.

The main difference is I am using a sun value at 1.0 gain. And there are a number of values in the camera irradiance feature, which I cannot understand mathematically, namely:
  • Scale
    Range
    Steps
    Grid size
I have been playing around with these values, but since I don't fully understand them, particularly when applied to a sun I am getting something like this: https://bit.ly/2YoGN39

Would really appreciate any input on this workflow and figuring out the best setup for the Irradiance paths.
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Dade
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Re: Irradiance Contour

Post by Dade »

The sun is a LOOOOOT more powerful than artificial light sources so you need to increase the range of the contour plugin by a looooot.

With the following parameters:

Code: Select all

film.imagepipelines.000.3.type = "CONTOUR_LINES"
film.imagepipelines.000.3.range = 3500000
film.imagepipelines.000.3.scale = 179
film.imagepipelines.000.3.steps = 32
film.imagepipelines.000.3.zerogridsize = 16
you obtain this result:

cont.jpg

Note: producing the above result takes quite some time due to noise. At the start, the lines are all mixed but the will clean over time.

There also a couple of stuff you should disable because they are not useful for your task (or may introduce artifacts in your results): bloom and denoiser.

You can save the plain rendering in EXR format and than check the pixel values to have an idea of the range of values.
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JuandeLara
Posts: 17
Joined: Wed Oct 28, 2020 2:39 pm

Re: Irradiance Contour

Post by JuandeLara »

Thanks Dade,

It does work, you are right, it just takes a lot of time.

If I change the steps from 32 to say 128, does it mean I will get more of the contour lines? I mean at a shorter interval on the image?

I am quite curious to understand which function is the one you used to obtain the scale as 179, and range 3,500,000.
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Dade
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Re: Irradiance Contour

Post by Dade »

JuandeLara wrote: Tue Oct 05, 2021 8:13 am If I change the steps from 32 to say 128, does it mean I will get more of the contour lines? I mean at a shorter interval on the image?
Yes.
JuandeLara wrote: Tue Oct 05, 2021 8:13 am I am quite curious to understand which function is the one you used to obtain the scale as 179, and range 3,500,000.
It is conversion factor to match Radiance results: https://github.com/LuxCoreRender/LuxCor ... es.cpp#L36
// Scale should be set to 179.0: the value of 179 lm/w is the standard luminous
// efficacy of equal energy white light that is defined and used by Radiance. It
// can be used here to produce the same output of Radiance.
//
// More information here: http://www.radiance-online.org/pipermai ... 03616.html
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JuandeLara
Posts: 17
Joined: Wed Oct 28, 2020 2:39 pm

Re: Irradiance Contour

Post by JuandeLara »

Great thank you Dade!
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