1. So, in Atlas I create a map and use one of the 'Special' terrains, such as purple, cyan, or green as the default terrain. These colors are easy to select and cut out in your image editing software (Photoshop, Gimp, Photopea, whatever) and just like when filming FX for movies, the right (contrasting) background color can ensure that you get a clean mask. Very important to turn off distance fog and bloom. I also turn off anti-aliasing, so that you get a nice crisp edge when selecting the backgr