Render post effect: false color

hi all,
I wonder on what basis is calculated the distribution of tones when converting to false colors. Is it based on the decomposition of the 10 zones that Ansel Adams calls the “Zone System”?
Do you have any documentation on the subject, thank you.
This images from Iray render but the same question with another plug-in.

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I believe @johnc is the person to answer your question.

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Hi @fr.petitjean,

The false color code I originally wrote was very simple and not based on any published algorithm. Since then it has been rewritten to run on the GPU and I don’t know what algorithm that uses. But @DavidEranen might be able to help.



hi @johnc
thanks for the reply, i’m just trying to get an idea of ​​how the colors are converted.



Hi @fr.petitjean,

As mentioned, I converted @johnc’s code to run on the GPU. The logic for how to get the colors is the following:

Calculate the luminance of the rendered pixel. Then mix pairs of colors depending on the luminance value. Here are the colors:

White, Red, Orange, Yellow, Green, Cyan, Light blue, Blue, Dark Blue, Black.

If the luminance is >= 1, then it’s White. If luminance is 0.0, then it’s Black. For the values in between, we mix the colors in the order I gave them above.

Does that help? If you need an even more specific description, let me know.


hi @DavidEranen
thank you
I have just discovered this processing station option and I wanted to try to find out how this conversion was calculated. Because I use the Iray plug-in to achieve beautiful renderings but this false color option could be an additional element for understanding and comparing different materials.
There is Grassehopper and Honey bee but I want to find a fast and coherent way to explain sizes and not precise and / or regulatory values.
The concern that I see is that the gradation of the colors must be different with the sunlight and an interior environment lit by lights.
an RGB 240 white with light from the sky will not have the same intensity as an RGB 240 white with spot lights for example.

I found software to read, measure and convert HDR images from RADIANCE. I rendered an HDR image with Iray in rhino but the values ​​are very low, I am probably setting the software incorrectly.

what would be really nice is to have the conversion parameters accessible to vary them depending on like for Radiance and Honey bee.

Hi @fr.petitjean,

I’ve filed your feature request here:


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bonjour @DavidEranen

merci beaucoup :slight_smile: