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bacula8630 Yep! Rotoscoping historically implies doing it by hand (the process of painting out the background manually) but it can refer to the act of cutting out elements in general. Depending on the footage and the tools available there are many different ways to achieve it, like chroma key (greenscreen/bluescreen), depth matte (an algorithm looks at the focus/sharpness to determine an element's distance from the lens...not perfect, but amazing advancement in the last couple years), difference matte (the program compares a "clean plate" — the shot with the background only — to the same shot with the performer in frame and cuts out any pixels that are identical, so only the performer remains...often has issues because of camera sensor noise, background elements moving a little, that kind of thing). There are even tools now like Magic Mask in Davinci Resolve that use machine learning to recognize a body, or even a body part like selecting a face, or hair, or clothes. It's all pretty incredible.
Usually an effective matte requires some combination of tools to get the right polish. You also have to consider things like matching light direction and color temperature.
Then, a final color grade and application of film grain/digital noise can help tie it all together and hide the seams.