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OBS tutorial (video + written): chromakey greenscreen, but applied only on a specific part or region

Hi! This 6 minute tutorial will explain in depth (and from scratch) how to configure an OBS greenscreen scene setup, such that the greenscreen is only applied to certain preselected regions of the image.

See: (not monetized)

The whole thing explained in words below (and in the YT description too).

I don't know why OBS does not have a thing in video filter settings where you can just define a rectangle, or maybe even a polygon map, of areas where to apply filters.

There is a way to set it up, but for that you have to get a couple of things right, and in my opinion it's quite unintuitive to set it up for greenscreen n00bs such as myself. So once I figured it out, which took me a good chunk of my afternoon (and a lot of googling and experimenting), I decided to document my solution and record an extremely n00b-friendly tuturial, which would have helped me greatly :D

There are a few posts scattered around the internet about this, but they pretty much simply say "just use masking" and mostly just confused me even more.

Explained in words (please follow very literally, as slightly missing the details here kept me stumped for hours...):
1) Start a new scene
2) Insert your background source (like an image)
3) Create a new group (e.g. "group 1") as a layer above the background
4) Add your unfiltered camera input source to the group (meaning, do not apply ChromaKey to camera source!)
5) Apply the ChromaKey filter to the group (again, NOT to the camera source!)
6) Create another new group (e.g. "group 2") as a new layer above group 1
7) Add another instance of the same unfiltered camera source to that new group 2
8) Create a "masking image" (e.g. a PNG file in MS Paint will do fine) with the same size of your video. Paint white where you do NOT want your greenscreen to apply, paint black where you DO want your greenscreen to apply.
9) Apply the "Image Mask/Blend" filter to group 2 (again, not to the cam source) and select your masking image in the filter properties. Technically, you are telling the filter which parts of the video source that it applies to need to be visible (white) and which parts need to become transparent (black), i.e. where the background (the greenscreen layer) needs to shine through.

The layer order in the OBS 'sources' pane should now be:
1) group 2 (containing cam input) with masking filter
2) group 1 (also containing cam input) with chromakey filter
3) background source

And that should do it! A bit of a convoluted setup, but once it works, it works great!
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I think this type of help for others is terrific and appreciated. Specifying a region for the green screen offers considerable benefit when you want to position a graphic, such as a chart or diagram, as you explain research findings or a concept.

The next thing that needs to be understood is identifying a specific area of the image dropped into the green screen area as "active" in post-production. That means someone viewing it can touch or click on it and be taken to another piece of content, such as a description or added details. If possible, this is something I wish to understand as it will make the video dynamic for viewers and also tell me, as the producer, what people find most important or interesting for future content segments.