  Neural Radiance Fields employ simple volume rendering as a way to overcome
the challenges of differentiating through ray-triangle intersections by
leveraging a probabilistic notion of visibility. This is achieved by assuming
the scene is composed by a cloud of light-emitting particles whose density
changes in space. This technical report summarizes the derivations for
differentiable volume rendering. It is a condensed version of previous reports,
but rewritten in the context of NeRF, and adopting its commonly used notation.
