Green Screen: compression vs resolution

[Domenic Barbero]

Had a client rent one of my REDs and they shot some green screen. Instead of shooting 5k 7:1 on scarlet dragon or 6:1 on mini mags, they chose to shoot at 4k and do less compression. I'm curious is it better to have the extra resolution or compression when the compression numbers are so close to each other in terms of lowest comp for that resolution setting? Compression or resolution, what would yield the best result for keying?

Thanks

 

[Anton Shavlik]

I think resolution is more important especially if most of the image is a big, evenly lit and out of focus green field which should be easy to compress, leaving more data for the parts that don't get keyed out

 

[Ugo Del]

The scarlet dragon can benefit from mini mags? I didn't know.

 

[Nathan DuMoulin]

http://www.reduser.net/forum/showth...frame-rates-lower-ratios-VS-higher-resolution

Oddly enough, I posted a nearly identical question this morning.

 

[Stephen Williams]

Had a client rent one of my REDs and they shot some green screen. Instead of shooting 5k 7:1 on scarlet dragon or 6:1 on mini mags, they chose to shoot at 4k and do less compression. I'm curious is it better to have the extra resolution or compression when the compression numbers are so close to each other in terms of lowest comp for that resolution setting? Compression or resolution, what would yield the best result for keying?

Thanks

I did some tests 2 years ago & it's a close call.

At 75 FPS Alexa recording uncompressed raw was a better key than Dragon at 4k or 5k due to higher compression. At 25 FPS 6K Dragon was the best-

 

[Anton Shavlik]

The scarlet dragon can benefit from mini mags? I didn't know.

I don't think that it can.

 

[Björn Benckert]

Resolution is what you should strive for. So shoot FF.

 

[Gavin Greenwalt]

I pick compression over resolution up to about 4:1 or 5:1. R3D sacrifices chroma before luma and chroma key has chroma right in its name. Depends on what you're keying. If you can pull a good luma key then I would go with resolution. If you are planning on pulling a chroma key (say light skin on light green) then you need all the chroma you can get up to about 4:1 or 6:1 at which point you're mostly just getting light noise reduction. I still prefer compression to resolution though.

I shot a bunch of highspeed footage and we had to throw away footage which was too compressed at 12:1. 7:1 is a tough call.

 

[Tommy Kraft]

As someone who has worked with a friggin boatload of greenscreen footage, I have to say I was stunned the first time I went up from 2.5k raw to 4k raw. I made an entire feature on green screen, shot on the BMCC 2.5k EF, and as such got really good at compositing. Later I was working on a client gig shot 4k raw from a C500 and I just couldn't believe the extra latitude I had with those additional pixels.

I came to realize that things like color space/depth are much more important on lower resolution footage because you need all the help you can get to resolve small details. But when you're talking 4K and up, you just have so much more latitude to crush your mattes to hell and back and still get great results. Small details like hair are just so much easier to deal with because instead of a small hair being comprised of only 1 or 2 pixels in lower resolution footage, you may now have 4 or 5 or 6 pixels in your hair. These are just random numbers to make a point.

In my opinion, on green screen, resolution always matters more unless you're talking about compressing the image so much that you begin to lose your small details to the compression. If I was doing a client gig and they asked if I preferred 4K compressed or 2K raw, I'd almost always choose the 4K compressed.