Radiance map extraction


Does anyone know of a way to extract a radiance or illuminance map from a render?
I’m trying to extract photon flux values from cycles that I then want to feed to a custom sensor simulation.
Has this been done before? Any tips on where to look in the source code?


I’m not sure Cycles is the rendering engine you want for this kind of thing. While Cycles can use physical units for light brightness, albedo, etc. it is by no means geared towards scientific measurement. To get a really accurate luminous flux values, you may want to consider a spectral rendering engine: those can path trace at arbitrary frequencies of light, while Cycles only traces at red, green and blue wavelengths.

If you just want a plausible linear monochrome output, you can do that in compositing fairly simply. Just make sure you set your color space to linear and export to OpenEXR (or some other floating point image format).

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Thanks for the reply!

Do you know of any open spectral rendering engine that can run in Blender?

Wouldn’t you know it, also Cycles!

…But it’s still experimental and in development. I’m not sure if it would be of any use to you here.

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Mitsuba 2 seems to have spectral and even polarization support; it is a much more scientifically targeted rendering engine, and may require you to compile it yourself though.