Is there away to retrieve the number of photons/electrons from an image?

[Odotocodot]

Hello

I was wondering if it possible to retrieve the number of photons from an image.
I have been following this discussion #411 (comment), and have been using Film.develop(raw=True). However, im not sure what the values represent in the returned TensorXf for all channels.

I am using a specfilm with a thinlens sensor. My srf is only one band, with two wavelengths (500 to 501nm)

Any help is much appreciated!

[njroussel]

Hi @Odotocodot

You should have a 2-channel Tensor. The first channel is the weighted radiance of the band you're measuring, and the second is the weight channel. Although represented by a floating point value, in practice (with default settings) it should be the total number of "valid" ray paths for that position.

[Odotocodot]

Thanks for the reply.

I see, then can each valid ray then be thought of as a photon then? If so would the number of photons be calculated by multiplying by the previous channel? This value seems very small.

[njroussel]

I see, then can each valid ray then be thought of as a photon then?

Yes

If so would the number of photons be calculated by multiplying by the previous channel? This value seems very small.

I obviously don't know what you're rendering but in most cases it will be constant and equivalent to the spp value you pass to mi.render() or that is set in your scene description.