To combine two photos or movies, a blending mode is employed. It’s best thought of as a mathematical operation performed on the two RGBA values of both images/videos. Screen, add, multiply, overlay, divide, and difference are just a few examples.
Most effects are shot against black, white, mid-grey, green, or blue backgrounds, which must be removed using blending mode or keying.
​Some assets are pre-keyed, which means they already have an alpha channel and are ready to use.
We made a composted scene using blending modes.
I decided to go with a space theme where there are space ships flying through space.
Final thing: