The goal of this paper is to present guidelines for interpreting soot natural luminosity images that are taken from within the combustion chamber of a single-cylinder research engine, which is fitted with a window in the piston-crown. In the experiments, fuel is injected near top-dead-center and luminosity from soot that forms as a result of the combustion process is imaged. Then, CFD simulations are run, from which soot luminosity and in-cylinder soot distributions are predicted. A luminosity to soot-distribution transfer function is developed from the CFD results and the transfer function is subsequently applied to the experimentally-obtained luminosity images in order to approximate soot distributions in the physical engine with improved accuracy. This method is applied to multiple operating conditions in order to develop the guidelines presented herein. Although this work builds on previous efforts, this is the authors’ first published work on this particular topic. In its essence is advancing a model that is written specifically to predict and visualize spatial distributions of soot luminosity from transient CFD results. Where CFD simulates the combustion and emissions formation processes, a separate model, the ‘line-of-sight’ model, is used to simulate the transport of soot radiation from initial emission in the cylinder, all the way to the radiation sensor in the imaging camera. Soot emission is predicted using Plank’s law. A well-established correlation is used to approximate soot emissivity. Radiation absorption by absorbing gases in the combustion chamber is also modeled. An empirical constant is used to estimate the reduction in radiation intensity between the piston crown and the imaging sensor. Renderings from this line-of-sight model are validated against the experimentally-obtained soot luminosity images and guidelines for interpreting the images, in terms of soot concentration distribution, are developed based on the aforementioned transfer function.