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# Radiance confusion

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Hi

I´m trying to implement a Stochastic Path tracer using the pseudo code described in the book Advanced Global Illumination by Dutré, Bala and Bekaert. I´m doing it in c++. I think I understand the algorithm but the whole thing about radiance makes me a bit confused.

Right now I have implemented basicly everything to get started with the actual tracing. I have a scene with objects like spheres and planes. These I can calculate intersection and give material proerpties. I also have a vector class wich handles the linear algebra.

My scene description looks like the one in this tutorial: link, where I can set diffuse, and reflection constants and the color of objects.

Now to my question: the pseudo code in the book uses radiance. How do I calculate the radiance in for example: radiance leaving the light source, Le? Is my scene description wrong if I want to use radiance? In the tutorial they dont seem to use radiance at all. Is radiance same as (r,g,b)?

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In the case of graphics, our definition of "radiance" is typically just the amount of light being emitted by a particular surface in a particular direction. So if you're just working with RGB colors (and doing spectral rendering), then we're really just talking about a triplet of RGB values. So yeah, usually for your light sources you just need to define R, G, and B values representing the intensity of the light being emitted.

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So when when the pseudo code says this for direct illumination with a single light source: estimatedRadiance += Le * BRDF * G(x,y) * V(x,y) / pdf(k), I just replace the Le with the color of the light source? Where does the color of the object that is intersected go? Or should I put the color of the lightsource * the color of the object hit = Le?

If I want to do the computation with radiance instead of the actual color values how would my scene description look like then? And how do I convert the radiance values to (r,g,b) so I can display the image on my computer?

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