Green screen and grain

[Gaspar Matheron]

Hi everyone !

I juste shoot some stuff on a green screen, and I think that there is a little bit much grain that it suppose to be ...
maybe I haven't setup the camera the right way, maybe it's a blackshade problem, I don't know, but first I want
to have your opinion on the amount of grain, and if you think that there is too much grain, what is the solution ???


Have you some other advice about the camera settings to shoot green screen ?

I was shooting 4K 120fps at 11:1 (I think)
(the pictures below are not the full frame, this is juste a crop of the shot at 100%)

Thanks,

Gaspar Matheron


http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN01.jpg
http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN02.jpg
http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN03.jpg
http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN04.jpg

 

[paulcurtis]

That is quite noisy, but those are JPG images and so could be looking worse with that extra layer of JPEG compression. The blockiness in the colour channels does look like compression artefacts for sure.

There is a checkbox in RedCine for DEB (i think) and if you check that it can really reduce colour noise, that is worth looking at.

I've keyed much much worse though!

cheers
Paul

 

[Robert Berger]

Hi everyone !

I juste shoot some stuff on a green screen, and I think that there is a little bit much grain that it suppose to be ...
maybe I haven't setup the camera the right way, maybe it's a blackshade problem, I don't know, but first I want
to have your opinion on the amount of grain, and if you think that there is too much grain, what is the solution ???


Have you some other advice about the camera settings to shoot green screen ?

I was shooting 4K 120fps at 11:1 (I think)
(the pictures below are not the full frame, this is juste a crop of the shot at 100%)

Thanks,

Gaspar Matheron


http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN01.jpg
http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN02.jpg
http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN03.jpg
http://gasparmatheron.com/wp-content/uploads/2017/04/GRAIN04.jpg

Hi Gasper,

I shoot a lot of greenscreen. I always go to the lowest compression, shoot at least in your case a 1/400 shutterspeed, go to a lower iso as normal 800 and go to 320 in case of slomotion. You are already cropping so your grain wil be bigger. So you have to do more than normal speed to lower the grain as i wrote above. Best luck Robert

 

[paulcurtis]

Hi Gasper,

I shoot a lot of greenscreen. I always go to the lowest compression, shoot at least in your case a 1/400 shutterspeed, go to a lower iso as normal 800 and go to 320 in case of slomotion. You are already cropping so your grain wil be bigger. So you have to do more than normal speed to lower the grain as i wrote above. Best luck Robert

Good advice but why 1/400th?

Also Gasper has a Raven, i think that's the lowest compression he can get at 120fps and at 4K.

I assume you need 120fps? An alternative would be shoot 60fps (can go to 7:1) and the in post slow down the footage by half using optical flow. Depending on what you're actually shooting it could work well. Test first, but 7:1 would probably give you a much better image. (and slow down after keying!)

Also if you're not using the whole frame for the subject matter don't dismiss framing something like 2.4:1 and even turning the camera vertically, that would squeeze some extra headroom potentially.


cheers
Paul

 

[James Falco]

Good advice but why 1/400th?


Paul

Most common mistake DP's make when shooting green screen is shoot at 180º shutter.

Motion blur is one of the boggiest problems to deal when keying. You can add post motion blur but not remove it.

An a side note, avoid green on your subject when shooting green screen, like the great ornaments on santa's hat.

///

 

[Gaspar Matheron]

That is quite noisy, but those are JPG images and so could be looking worse with that extra layer of JPEG compression. The blockiness in the colour channels does look like compression artefacts for sure.

There is a checkbox in RedCine for DEB (i think) and if you check that it can really reduce colour noise, that is worth looking at.

I've keyed much much worse though!

cheers
Paul

Yes I know for the JPEG compression, this is not the best way to show you the problem but it's showing pretty good the result I have in reality !
I'm gonna try the DEB in redcine. I also Keyed way much worse but as I am doing the shoot and the post production I want to improve as much
as I can

Hi Gasper,

I shoot a lot of greenscreen. I always go to the lowest compression, shoot at least in your case a 1/400 shutterspeed, go to a lower iso as normal 800 and go to 320 in case of slomotion. You are already cropping so your grain wil be bigger. So you have to do more than normal speed to lower the grain as i wrote above. Best luck Robert

It's the lowest compression I can go with the raven, I was at 800iso so next time I will go to 320, and I was at 1/200 or 1/250 so same, I will go to 1/400 next time. I don't really crop, I use all the
frame but I just screenshotted a crop at 100% to show you well the grain ! Thanks for the tips

Good advice but why 1/400th?

Also Gasper has a Raven, i think that's the lowest compression he can get at 120fps and at 4K.

I assume you need 120fps? An alternative would be shoot 60fps (can go to 7:1) and the in post slow down the footage by half using optical flow. Depending on what you're actually shooting it could work well. Test first, but 7:1 would probably give you a much better image. (and slow down after keying!)

Also if you're not using the whole frame for the subject matter don't dismiss framing something like 2.4:1 and even turning the camera vertically, that would squeeze some extra headroom potentially.


cheers
Paul

In fact yes, I need 120fps (or 100fps, I said in the post I was at 120 but I think I was at 100fps) and I can't use 60fps and post production solution because there is a lot of details in clothes, accessories etc...
And I already shoot in vertical, but thanks for your answer.



Thanks all three for the tips, as I have say, the result is not so bad, but since there is a lot of little problem on this production, green clothes, reflective clothes, transparent accessories etc etc ... (this
is not negociable, we're doing the same thing than a big photoshoot next to us and creation is the most important thing for the campaign)
I just want to enhance as much as I can


Thanks again

Gaspar Matheron

ps: Sorry for my English, as you will have noticed, this is not my native langage

 

[James Falco]

I did quick test with your screen shot and the file keys fine.

 

[paulcurtis]

Most common mistake DP's make when shooting green screen is shoot at 180º shutter.

Motion blur is one of the boggiest problems to deal when keying. You can add post motion blur but not remove it.

An a side note, avoid green on your subject when shooting green screen, like the great ornaments on santa's hat.

///

Actually as someone that works in vfx for a living i'd disagree with that. IMHO of course.

Keying is a science and an art, it's difficult to do right and there are no shortcuts. Blur is just part of the game, whether it's motion blur or DOF or even fine detail.

You cannot add perfect motion blur afterwards either, i deal with optical flow techniques all the time and sometimes it can work well, but on a complicated scene with objects crossing at different parallax in different directions that's a recipe for odd artefacts leading to a lot of paint work and roto. I suggest it as a fallback because we're looking for better compression and this particular scene might work with a simple doubling of frames.

What i would recommend is talking to whoever is doing the keying. We all have our preferences and pipelines.

For example the degree of lighting on the screen: sometimes one of the most difficult tasks is matching background luminance - if your new background is super dark and you're keying off a super bright screen the need to balance luma and despill can be quite difficult - in those cases i'd rather a lower luma screen so long as separation is possible. A lot of time these days, especially the higher end don't bother with screens or use black or white - both very useful approaches.

Or the lenses can be very painful, those vintage lenses that diffract RGB light differently around the edges. Total nightmare. Or lenses with variable distortion and chroma issues...

Which just highlights - talk to post. ask them what they prefer.

But your subject matter is still your subject and so should be shot how you want it to be.

cheers
Paul

 

[Gavin Greenwalt]

Not noise, just overly compressed. If you need to shoot highspeed greenscreen, you'll save money overall by renting an Epic or Weapon.

Since that opportunity is passed.... my advice would be to copy the red channel into the blue channel (which is probably by far the most choppy) and then key from that. And then use the alpha from that key over your regular RGB image.

 

[Jarek Zabczynski]

It's the compression. But either way, that should key fine, I've keyed WAY WAY worse than this just fine.