Green screen: How can I make sure my image is large enough?
October 30, 2024 9:53 AM Subscribe
I'm looking at green screen backgrounds now, using iMovie for iOS, and I'm seeing that some of the backgrounds take up the whole screen, whereas others are too small --- they have a black border around them.
How do you make sure that the green screen picture is at least as large as the screen size so there is no black border? Is there some formula for that?
[yes, I asked a related question yesterday, that was actually a follow-up to a more basic green screen question, but nobody's looking at it anymore, so...]
How do you make sure that the green screen picture is at least as large as the screen size so there is no black border? Is there some formula for that?
[yes, I asked a related question yesterday, that was actually a follow-up to a more basic green screen question, but nobody's looking at it anymore, so...]
While your background clip is selected, you can tap the zoom button (magnifying glass icon) in the viewer, then “pinch” with two fingers in the viewer area to resize the image however you want.
posted by mbrubeck at 10:09 AM on October 30
posted by mbrubeck at 10:09 AM on October 30
Best answer: Simpler still is just making sure to use background video clips with the same pixel dimensions as the foreground one.
Green screen compositing works pixel by pixel, testing the colour of each pixel from the foreground frame to work out whether or not to replace that pixel with one from the same position in the background frame. If the foreground and background frames are not the same size then there isn't a corresponding background pixel for every foreground pixel, and the compositor will need to crop, scale and/or pad the background frame to make them the same size before doing the actual compositing.
So if your foreground video was shot at 1920x1080, so should your background video or images be. If you're shooting your foreground in 4K, shoot the background in 4K as well. And so on.
posted by flabdablet at 10:28 AM on October 30 [2 favorites]
Green screen compositing works pixel by pixel, testing the colour of each pixel from the foreground frame to work out whether or not to replace that pixel with one from the same position in the background frame. If the foreground and background frames are not the same size then there isn't a corresponding background pixel for every foreground pixel, and the compositor will need to crop, scale and/or pad the background frame to make them the same size before doing the actual compositing.
So if your foreground video was shot at 1920x1080, so should your background video or images be. If you're shooting your foreground in 4K, shoot the background in 4K as well. And so on.
posted by flabdablet at 10:28 AM on October 30 [2 favorites]
Best answer: mbrubeck has already provided you a useful answer, and I don't know iMovie (I'm on a PC) but there are some standard ratios/sizes to keep in mind depending on what the output from your camera is and/or the composition size of the project on your computer
Most standard right now is probably HD (1920x1080) - 1920 pixels wide by 1080 pixels high
If you are shooting in 4k it would be 3840 × 2160
Wikipedia has a full list
Yes you can scale but it's helpful to know what aspect ratio you would be scaling to when you're looking for backgrounds to use, and whether you're downloading or designing images it's good to know what size you have to hit so that they don't look degraded/blurry
posted by matcha action at 10:30 AM on October 30
Most standard right now is probably HD (1920x1080) - 1920 pixels wide by 1080 pixels high
If you are shooting in 4k it would be 3840 × 2160
Wikipedia has a full list
Yes you can scale but it's helpful to know what aspect ratio you would be scaling to when you're looking for backgrounds to use, and whether you're downloading or designing images it's good to know what size you have to hit so that they don't look degraded/blurry
posted by matcha action at 10:30 AM on October 30
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posted by DMelanogaster at 9:58 AM on October 30