Reducing noise

[Tudor “ted” jelescu]

Keylight should enable you to tweak the key and get rid of some of that noise, however, in some instances, black or dark clothing will still have a lot of noise. Using Neat Video or Remove Grain can help. You can either use roto garbage masks to apply them over the problem areas without affecting the skin, or try to pull a second color range key o separate these areas. Of course you need to do that by duplicating the layer and applying the effects on the top one.

Tudor “Ted” Jelescu
Senior VFX Artist

[Frank Brown]

DenoiserII from Red Giant Software is very cool and smart plugin for removing noise.
https://www.redgiantsoftware.com/blog/2012/02/28/magic-bullet-denoiser-ii-is-here/

It is removing only noise, not making smooth and blurry image such as Neat Video plugin.

[Oliver De morassé]

@ Frank – thanks for Denoiser II tip from Red Giant… currently testing. Is it best to use the plugin before or after Keylight?

[Oliver De morassé]

Sorry Dave, not really sure what you mean by using the noisy key as an alfa matte – but sounds good ;O)

[Jim Bachalo]

I’ve heard from others that Neat video is THE best noise reduction solution for video. have you tried tweaking the settings?

Local is the new global

[Frank Brown]

jim
I`ve tried both in different situations. IMHO Denoiser is the best solution, because of its smart filter.

Oliver
I didn`t compare KeyLight and Denoiser on green screen footages, but if the problem only noise, Denoiser should fit you.

[Benjamin Ausmith]

I believe Dave means using Keylight to generate basically a cookie-cutter layer– not for the color correction. Sometimes keylight can produce noisy artifacts. So if you use keylight to generate just the alpha layer– that is, the layer that says whether video is transparent or opaque– then combine that layer with your original footage by using Track Matte > Alpha Matte. Keylight will cut out the shape that you want, but you’ll be able to preserve your original color because we’ll actually be seeing your original footage without Keylight’s noisy processing.

[Andrew Somers]

I’m assuming we are talking about the same shot of the blonde in a tux.?

To address the noise in the first place, as I indicated in the earlier threads, your “greenscreen” is not a good narrow band of green – it contains a lot of blue, at least as you are shooting it.

As a result, you are making the keyer (Keylight, what have you) work harder, and when you make it work harder, you may then be causing noise to become more obvious.

Since you also have the “white line” in the red channel issue, this could be an artifact of the debayering or the compression algorithm due to the excessive blue in the green screen you are using.

NOTE: how are you white balancing your camera? It is VERY important when shooting green/blue screen that you NEVER EVER use AUTO WHITE BALANCE.

White balance to a neutral grey card that is lit with the same color temperature lighting used on the green screen (and use that same color temperature lighting for the subject).

This is critically important especially when shooting to an 8 bit compressed format like in a dSLR.

If you ARE properly white balanced, try this:

https://www.rosco.com/us/scenic/ultimatte.cfm

[Oliver De morassé]

I use both a DSLR camera & camcorder dependent on the shooting. My lights use a Color Temperature of approx. 5400K. I have experiemented with the white balance settings… I think I shot around 4900k.

Should I be using a 18% grey card for setting my white balance manually?

[Andrew Somers]

Oliver said: “My lights use a Color Temperature of approx. 5400K. I have experiemented with the white balance settings… I think I shot around 4900k.”

Don’t do that.

With lighting at 5400K, setting WB to 4900K will fill the green screen with BLUE. If you were shooting RAW, you could fix it later, but because you are shooing to an 8 bit format, with 4:2:0 color and highly compressed H264 – you must white balance your camera such that the green screen is ending up in the green channel, and not the red or blue.

Oliver said: “Should I be using a 18% grey card for setting my white balance manually?
“

Yes.

You want to WB your camera to your lighting, ESPECIALLY the lighting on the green screen. You want your camera to give you a file that has that green screen in the G channel, and NOT in the R or B.

This is ESPECIALLY critical in 8-bit, 4:2:0, DCT compressed files.

If you bring your footage into After effects, in LINEAR 32-bit space (which you should always be using for compositing), and you eyedropper the GREEN screen, your numbers should look like one of these examples:

Your screen does not look like that, here are values for the file you gave me last month:

This is not good. Your blue channel has barely a stop difference from the green channel.

Again, if you were shooting RAW, it could be corrected – but shooting in 8Bit, your camera is having to debayer this wacked white balanced footage,, then cram it into a 4:2:0 H264 container. And then you’re stuck.

RAW does not have a whitebalance – your white balance is what guides the camera in how to debayer, gamma encode, and YUV encode the file. If your white balance is wrong, so will be your shot.

LET’S GET BACK TO BASICS:

1) Use a green that is *very narrow band* (nearly florescent, or Ultimatte, etc.).

2) Light it evenly, and keep it at meter and no more than 2 stops UNDER meter. Overexposing will hurt you, so err on the side of exposing it darker. I normally aim for one stop under meter for green screen exposure.

3) Whitebalance the camera to the light source, and make sure that the Green Screen is mainly in the G channel, and not in the R or B. There should be about 3 stops (or more) difference between the G and the next brightest channel.

4) Never use sharpening in camera.

5) Never use filters on the camera, except ND or polarizers.

6) Be careful what “picture style” you use in a Canon dSLR. I can’t say if Cinestyle is the right choice, but it might work great. I don’t use Canon, so I can’t experiment here.

7) A camera that shoots RAW like the Red Epic or Scarlett is IDEAL for green screen.

PECKING ORDER OF MOST PREFERRED, TO MOST AVOIDED, CAMERA/FILE TYPES
For Green/blue screen.

BEST: RAW.

SECOND BEST: After “RAW”, the next preferred solution is RGB or 4:4:4 YUV in 10 bit or 12 bit.

THIRD BEST: 4:2:2 in 10 bit or 12 bit with moderate compression or uncompressed.

FOURTH BEST/AVOID if possible: 4:2:2 and 4:2:0 in 8 bit. 422 8-bit is better than 420, but 420 is not that much worse that 422 8 bit.

420 is not the end of the world – it is useable if shot and handled correctly. Some formats like HDV do much worse – but HDV is not bad just because of the 420 – it’s bad because it also uses non-square pixels that have to be stretched, and it uses severe compression. Some say that HDV is bad for greenscreen because it uses 420 – but in reality HDV is bad for greenscreen because HDV is overall a very low fidelity format.

So don’t use HDV. Having said that, I’ve pulled plenty of good keys using 420 dSLR video.

DO NOT USE: 4:1:1 or 3:1:1 for green/blue screen work. Just don’t. (unless you are a masochist.) Unlike 420 that has equal color res both vertical and horizontal )1/2 res vertical and 1/2 res horizontal), 411 has 1/4 the horizontal res, making it nearly useless. Similar issue for 311.

And having said that, I’ve pulled “useable” keys from 411 and 311. But I wasn’t very happy about being in that situation.

8) Keep your subject as far away from the green screen as possible – among other things this allows keeping the green screen as out of focus as possible.

I’ll add some more tips later, dinner time… 🙂