Green screen tracking

Help/How To
1

Is there a way to track a green screen within a video where the camera pans across a room and the green screen portion within that room moves across the frame?

Theres a funny video clip that has a crowded bar of people and they are all staring at a giant screen (which has been green screened). Then they go crazy cheering. The camera pans the crowd so the giant screen in the bar moves out of frame. I want to put my podcast logo on the green screen in the bar to make it look like the crowd cheers when they see it, funny right? I have a basic understanding of chroma keying but how do i get that image on the screen in the bar to stay in that place as the camera pans the room?

2

I’m thinking I must have to use the “Size-Position-Rotate” filter and its keyframes function to move the image with many keyframe points as the camera pans?

3

It depends. If the shape of the TV screen changes (because of the perspective) while the camera pans the bar, you’ll probably need to use the Corner Pin filter.

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This filter will allow you to control the 4 corners of your logo image and make its perspective match the one of the TV as the camera pans the room.

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But it will be a lot of work. You’ll probably need to use a keyframe on each frame of the clip.

Can you share your bar scene clip?

4

Try this link Fans at Ashton Gate Stadium, Bristol, celebrate England winner against Wales at Euro 2016 - YouTube

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To have the greenscreen area move, with perspective will as far as I know require 3D perspective transforms, or ‘Homography’.

Try this for the greenscreened version: Bar Crowd Scene Cheer Green Screen Video Download - YouTube

In Adobe After-Effects and Blender, they have Wall perspective replacement areas like this.

I’d welcome the introduction of OpenCV Homography examples using OpenCV Homography ( Python / C ++ ) | (learnopencv.com) filters that would allow this to happen.

5

Natron also have a multi-point tracking feature.
I experimented with it a couple of years ago. It works quite well.

Learning how to use it is not super easy, but there are some tutorials available.

6

Thank you for hour help. The bar scene is the one shared by david.lyon in this thread below. It would be so great if this worked.

7

That is the exact clip, yes! Thank uou for your suggestions.

8

I also found a ‘How to’ for After-Effects and the very same video with a sample Project File for AE included

Just including the link for inspiration and education rather than anything else. It proves at least that it can be made easy.

9

Thanks so much. Ill see what i can do. I really do appreciate it.

10

Thanks for using the term “Multi-point” - that helped quite a lot.

I upgraded my experiment to track with 4-points. I now just draw a greenscreen on the area.

The next step to do is to paste the inserted video on the greenscreen area.

Experimental status only

1 Like
11

Looks promising David :+1:

1 Like
12

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