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Anchor text: Theory and practical implementation of Global Illumination using Monte Carlo Path Tracing.

Wikipedia: Global illumination

Anchor text: Introduction to Shading.

Wikipedia: Shading

Anchor text: An intuitive introduction to the concept of reflection model and BRDF.

Wikipedia: Bidirectional reflectance distribution function

Anchor text: Light Transport in Tissue as an Example of Monte Carlo Simulation (with C++ source code).

Wikipedia: Monte Carlo method for photon transport