Physically based light measurement

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Lummy
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Physically based light measurement

Post by Lummy » Thu May 07, 2020 8:54 pm

Hello, some time ago around the year 2015 I was using Luxrender to model and simulate an LED pointed at a flat diffuse target 1m away. Once the model was set up I push the render button, and a separate Luxrender window would open. The render would progress during which time I could choose a tonemapper. I was able to calibrate some multipliers in my LED+light model, and using the False colour tonemapper, I could read the Radiometric intensity by use of the tonemapper gradient, and also read values directly by hover my cursor over the image.

Fast forward to this year, and I am trying to get physically based measurement from LuxCoreRender .....
1) I dont need the mulitpliers I used previously, as the lights can now be set in watts, candelas, or lumens.
2) I can find a section where I can use a false colour tonemapper.

My questions are ...
1) How to I set the colours, banding and scales of the false colour tonemapper?
2) How may I make a physically based light measurement that falls on the target in for example watts per square meter?

I have most likely missed a tutorial and/or missed a section in blender; maybe I am not running the correct software even :-)
Thank you.
L.

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Dade
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Re: Physically based light measurement

Post by Dade » Thu May 07, 2020 11:24 pm

Lummy wrote:
Thu May 07, 2020 8:54 pm
My questions are ...
1) How to I set the colours, banding and scales of the false colour tonemapper?
LuxCore doesn't have false tone mapper so I'm wondering where you have found it ? Is it a Blender feature ?
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Lummy
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Re: Physically based light measurement

Post by Lummy » Fri May 08, 2020 1:00 am

Hi. Yes so I was confused between Blender colour management view transform, and the camera image pipeline tonemapper which I have just found.

Regardless of the view transform, I set the image pipeline tonemapper to linear, I enable the IRRADIANCE AOV, (and the Direct diffuse AOV ) and also enable the Irradiance contours line plugin.

All renders have a grid superimposed, which according to the bubble help means no irradiance info available.

I see nothing in the in either the irradiance or direct diffuse channels.

So my question 1 must be for blender not luxcore sorry.

My question 2 still remains... How do I get an Irrandiance channel either separately, or combined ?
Thank you
L

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B.Y.O.B.
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Re: Physically based light measurement

Post by B.Y.O.B. » Fri May 08, 2020 10:09 am

Open the render layer properties and enable the Irradiance AOV.

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Dade
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Re: Physically based light measurement

Post by Dade » Fri May 08, 2020 10:21 am

Check the attached test scene for an example:

Screenshot from 2020-05-08 12-18-00.png
Lummy wrote:
Fri May 08, 2020 1:00 am
My question 2 still remains... How do I get an Irrandiance channel either separately, or combined ?
Just save the AOV in .exr format than you can do whatever you want with the file :?:
Attachments
irradiance-test.zip
(89.6 KiB) Downloaded 5 times
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Lummy
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Re: Physically based light measurement

Post by Lummy » Tue May 12, 2020 9:34 pm

Thank you. My problem was that there is no irradiance contours available in the caustic part of the render.

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Dade
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Re: Physically based light measurement

Post by Dade » Tue May 12, 2020 10:09 pm

Lummy wrote:
Tue May 12, 2020 9:34 pm
Thank you. My problem was that there is no irradiance contours available in the caustic part of the render.
Yes, irradiance AOV uses only eye path samples (while light paths are the one most likely used to render caustics).
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