My school bought a Panasonic 4K camcorder (which I don't remember exactly which model) pointed at a green screen and this got me thinking.

If it's a HC-X1000 with it's tiny sized sensor and 8 Bit 4:2:0 (In HDMI output too!) it probably means it won't record green screen and subject transition nicely.

So what I wonder is. Is 4:2:0 really enough for chroma key? I have heard even 4:2:2 has problems when it comes to chroma key so I am worried and would like some clarification

Also, If I downscale 4k 4:2:0 to 1080p somehow will it mean it will become 4:2:2 footage? I have thought about trying to do this then doing some recent "Artificial Intelligence Supersampling" wizardry to push it back to 4k

  • 2
    4:2:0 subsampled to 1080p is absolutely 4:2:2. Scaling it back up using AI is probably going to introduce a metric sh!t ton of artefacts and weirdness though. What are you delivering? Unless you're delivering to cinema most people are going to be watching in HD. – stib Oct 21 at 11:00
  • @stib I honestly don't know. I am an intern at a TV station and I am pretty sure my teachers will ask for help sooner or later. – Delta Oscar Uniform Oct 21 at 11:33
  • Hah, in my country broadcast TV is almost all 720p, not even 1080p. – stib Oct 22 at 10:22

"Good enough"? Sure. I wouldn't love to work with subsampled footage for keying, though. You want to maximise resolution, minimise or avoid subsampling and avoid spill. If your screen is well lit, you got the best circumstances.

So yeah, on paper, a chromatically subsampled file will give you more artefacts and jagged edges in your matte compared to a prores4444 or raw-recording. It is still a workable compression, though. Just try to optimise everything else I mentioned.

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