One picture is worth 1000 words:

Every photon in the image was simulated through the ab initio physics in PhoSim using its Monte Carlo methods. We performed 3 simulations using the Rubin (LSST) observatory PhoSim configuration for 15 second exposures using the y, i, and u filters. This 3-color image was produced by combining three images in the RGB channels corresponding with the y, i, and u filters (respectively). The images were corrected for basic calibration (gain, offset) and the overall levels were set to make the color of stars close to the Sun. The overall intensity is scaled using an inverse hyperbolic sine function (Lupton, Gunn, & Szalay 1999). We just show the top portion of a single chip, so the field covers roughly 13 by 6 arcminutes. The background was not subtracted, but some under-subtraction was performed in the blue and red channels to make the overall background have a grey color. No other corrections or calibrations were performed--intentionally in order to highlight the details.  There are many physics details inside of PhoSim that are not directly observable without performing a detailed analysis on the image with sophisticated algorithms. On the other hand, there are many details that are visible by to the human eye, so here we show some of the detailed observable features in the image: