CGI has made a few huge strides these last few years by making some great new lighting plugins.
This is huge because before this the artists had to guess and CGI would stand out more simply because the color wasn't right or the lights and shadows behaved different compared to the light and shadows of the real enviroment.
Basically they scan the environment with a 360 degrees camera so the 3d program knows where all the light in the scene is coming from and perfectly simulates it for the render.
I know they 'promised' to go old school with this flick and I applaud them for it, but when they actually do use CGI it will probably look fantastic.
Corridor Crew has a nice video about it with Spiderman as an example:https://youtu.be/4b2Jm2WWUl4
Start at 08:19 for the info, but that whole video is awesome.
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