after effects remove still background

Question

I have a movie in the after effects that dosent have a KEY color of background, but a still background.

I want to detect the motion of 2 persons walking in front of this still background and bring them to the front, so I can create effects on the background.

Is that possible to do? Witch Effect do I use?

Presurmise

Answer 1

This works with a technique called difference matting. It never works well even if you have a solid clean plate. your best bet is to rotobrush or just mask them out manually. if you want to try difference matting you can set the footage layer with the people in it to difference blending mode and put a clean plate below it.

Brew

Answer 2

you can use the rotobtush that allows to separate elements from a static background. Works better if:

• you have a clean background
• good quality videos
• front object needs to be cutted as big as possible

Tobietobin

This isn't available in AE 2021 – Nuncle

Answer 3

This method works well with a locked down camera. Depending upon how active people are and how still the background - you can remove the people by cutting and assemble pieces of the background to create a background layer without the people... Once you have a clean plate - then use a difference matte to subtract the background from your clip which will leave anything that moves (read people). This will work well if the hue/values between the background and the people are different.

Doing this in conjuncture with animated masks gives good results and can give you a jump on your rotobrushing to improve your edges.

If all else fails the Mocha plug works well as long as you break your masks up into lots of parts to follow the planes of your actors.

I have never found doing this is a single tool solution.

Stumpf

Answer 4

It is not impossible, but I don't think it could give you the best result. Anyway, you should mask them out manually. but not keyframe by keyframe. there is a technic for it. for setting the mask keyframes, first, you should set 3 keyframes in first, middle and end of your footage. after masking three one, you do it the same for first keyframe and the middle one. it means between the first keyframe and the middle keyframe, you should set a key. Do the same for middle and end key. this technic could save your time and make masking with less fault. by the way, you can use Mocha pro as well for tracking the persons.

Mendelevium