Green screen – recording or post problem?

[Andrew Somers]

I agree with Dave in that this does not seem particularly well lit, though you seem to have other issues too.

Footage notes:

I’m not sure if this is your camera, of if this happened wen you created the frame for posting here – but there is sharpening going on!! BAD! If you look at the red channel in your green screen element, you will see a white line around your subject. This indicates that you are using some type of sharpening. This will prevent you from getting a clean edge.

Can you upload a bit of the camera original, that has NOT been transcoded – i.e. something straight out of your camera, for analysis?

Look at the RED channel of the image – this is with no keying or any other effect:

Since you used no rim light, there should not be this white line around the subject. This is consistent with an artifact of sharpening.

Lighting Notes:

1) A green screen can be as much as two stops UNDER key. In other words, it does not have to be “bright” – it just needs to be as evenly lit as possible, and you can make it two stops darker than your subject. Keep in mind that we are looking for saturation of green here – as you increase brightness/exposure, you tend to decrease saturation. Under-expose your screen relative to the subject.

2) If you place your subject farther from the screen, three good things happen:

a) It is easier to keep subject light off the screen.
b) It is easier to make the screen softer/out of focus.
c) You will find it easier to reduce spill on the subject.

3) Have as little green in FRONT of the subject as possible. If necessary, lay down duvetyne (black cloth) in front of the subject. This will reduce spill on the first of the subject. Alternately lay down highly reflective mylar on the floor, instead of green on the floor – here, the background green will be reflected in the mylar on the floor, but the mylar will not cause spill on the subject. However, you will have to roto out the subject’s reflection if it is in frame, and you lose natural shadows if you want them.

4) I don’t know what you are planning on comping this over, but that is a factor – in some cases you might want to add a rim light, but not in others. Knowing what this is intended to be comped onto will guide some of these choices.

On Keying:

Despite the problems, I was able to pull a reasonable key using Keylight, thought it’s hard to say for certain with a still frame as some artifacts rear their head more in motion.

In looking at your “keyed” clip, it looks like you are “pushing too hard”.

TIPS:

1) Turn off all color correction for the layer, and make sure any adjustments layers with CC are turned off, as we want to make sure we sample only the original image color. (Also, any color correction on a layer with Keylight should be AFTER the keylight plug in).

2) When you use the eye dropped to select the screen color, click on an area of the green screen that is darker. Don’t use the brightest portions of the screen for sampling. I sampled in an area of shadow behind her feet camera right. (Tip: look at the red channel alone, and find an area of the screen where the red channel is the blackest, then turn all channels back on and sample that point).

3) Use a bit of black clip, so you don’t have to crank GAIN too high – but be careful of clipping too much.

4) Adjust gain/clip in “status” mode so that solid areas are white, edges and transparencies are grey, and screen is black.

5) Use a garbage matte, so that you only have to worry about the area around the subject, and ignore the screen areas that may be uneven.

6) Use the “shrink” to hide the edge, and avoid too much screen “blur”.

7) Because the images seems to have sharpening turned on, I cranked up pre-blur a bit

[Oliver De morassé]

Many thanks to you both for your quick replies.

@ Dave – We do infact light the green screen and subject separately. The subject stands about 4-6 feet away from the screen. We use the following lighting.

– For the green screen: 2 x Daylight lightbanks with mirrored barndoors. 4x55w equ. 1300w. 5400K

– For the subject’s head/body: 2 x Softbox diffusers 60x60cm. 5x24w bulbs. 5000-5400K.

– For the subject’s feet: 2 x Softbox diffusers 40x60cm 1x50w bulb. 5400K.

– Backlight for hair: 4W LED 230v Bulb. 3000K.

– We have been told to shot a very ‘flat’ image for better post-work. We use a Canon EOS 550d with the Magic Lantern firmware. Settings are:

Movie rec. size: 1920×1080, 25 frames
Auto Lighting Optimizer: Disable
Picture Style – CineStyle
– Sharpness: 3 (scale 0 to +7)
– Contrast: -3 (scale -4 to +4)
– Saturation: 0 (scale -4 to +4)
– Colour tone: 0 (scale -4 to +4)
ISO: 320
Apeture: f/4.5
Shutter: 1/48
WhiteBalance: 6500k
Bit Rate:
– Mode: CBR
– CBR Factore: 1.4x
– QScale factor: -12

…could this be our problem – the camera settings? We have also tried to shot with a more ‘friendly’ picture style. See:

@ Andrew Somers – Here a sample from the camera: https://www.edv-sorglos.de/downloads/creativecow/original2.zip

The screenshot you made, is that from the original or post? Yes, we used sharpening both on the camera side and post side – the customers wanted more ‘crisp’ and well defined edges. Should I have no sharpening from the camera side – a neutral picture style with no sharpening? What about contrast, saturation and colour tone?

Sorry, but I’m not sure how to view the red channel in my green screen video within AE?

Regarding keying – we follow this workflow:
1) Effect > Color Key – turn tolerance up to 20, turn feather up a little bit;
2) repeat Color Key 3-4 times at least, each with a tolerance of 20;
3) Effect > Simple Choker. Turn up easy choker slightly (negative value);
4) Keylight > turn up keylight, eliminating all green adjusting clip blacks and clip whites.

Regarding your tips – great, thanks.
1) Yes, our color correction comes after keylight.
2) How do I look at the red channel alone?
3) I don’t understand what you mean here?
4) 5) Yes, we do this.
6) What screen shrink setting did you use?
7) Should sharpning come before or after keylight?
I would be interested in any other AE settings you used to get a good output.

Finally, we are thinking about upgrading our DSLR camera to a camcorder – check post https://forums.creativecow.net/thread/54/860836 – what do you think… would this give us better results?

Once again – thank you both for all your input!

[Steve Brame]

Do yourself a favor and preface each keying expedition with this fairly simple technique which will greatly improve your results.

https://library.creativecow.net/articles/rabinowitz_aharon/junk_mattes.php

This technique reduces the amount of green screen for your keyer to worry about, down to about a 25 pixel band surrounding your actor.

Steve Brame
creative illusions Productions

[Michael Szalapski]

Never use in-camera sharpening.

And never never never never never never use in-camera sharpening when shooting green screen.

– The Great Szalam
(The ‘Great’ stands for ‘Not So Great, in fact, Extremely Humble’)

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.

[Jon Bagge]

– We have been told to shot a very ‘flat’ image for better post-work. We use a Canon EOS 550d with the Magic Lantern firmware. Settings are:

Movie rec. size: 1920×1080, 25 frames
Auto Lighting Optimizer: Disable
Picture Style – CineStyle
– Sharpness: 3 (scale 0 to +7)
– Contrast: -3 (scale -4 to +4)
– Saturation: 0 (scale -4 to +4)
– Colour tone: 0 (scale -4 to +4)
ISO: 320
Apeture: f/4.5
Shutter: 1/48
WhiteBalance: 6500k
Bit Rate:
– Mode: CBR
– CBR Factore: 1.4x
– QScale factor: -12

Shooting on a camera that uses very heavy compression is never going to give you good results for keying. But you’ve made it worse by using these settings. You should always use ‘neutral’ shooting style when shooting with these cameras, especially for keying. But I’d use it for everything, since it stops the camera from doing too much processing. You want to add contrast/sharpening in post.
Also shooting on anything other than 100 ISO when you want to do keying is probably also bad.

I don’t know what lens you’ve used, but my general advice would be to not shoot with the aperture wide open, and not zooming all the way in or out. Then at least the lens isn’t giving you more trouble.

————–
https://www.jonbagge.net
Jon Bagge – Editor – London, UK
Avid – FCP – After Effects

[Oliver De morassé]

@ Steve Brame – We do mask our persons before keying. I have already looked at this video on junk mattes but was unable to get it to work with my footage. Not sure what I am doing wrong, but only the 1st frame got correctly masked – the auto tracing did not work correctly for the rest.

[Oliver De morassé]

@ Dave LaRonde – what do you mean about lighting the green screen more flat? I will also try to shot some green screen with a Camcorder and let you see the results.

[Oliver De morassé]

@ Jon Bagge – OK, I will try a neutral picture style. Would you leave all settings for Sharpness, Contrast, Saturation and Colour tone at 0?

I thought I read in the Magic Lantern docs that best quality video needs to use ISOs in increments of 160 (160, 320, 480)?

As for lens, we use the normal EF-S 18-55mm f/3.5-5.6 IS Lens.

[Andrew Somers]

Oliver: “The screenshot you made, is that from the original or post? Yes, we used sharpening both on the camera side and post side – the customers wanted more ‘crisp’ and well defined edges. Should I have no sharpening from the camera side – a neutral picture style with no sharpening? What about contrast, saturation and colour tone?”

From the original. To look at independent channels in AE (i.e. see red only) click on the red/green/blue dot icon on the bottom of the VIEWER window.

And yes, to reiterate, set SHARPEN to ZERO in the camera. Do not use sharpen, nor any color correction, at any time before the keying plug in.

SHARPEN MUST BE OFF.

Also, use no color filters on the camera (I once worked on a film where the DP put a *yellow* filter on the camera while shooting green screen making a key impossible. Huh. Can you say “manual roto”? lol).

Since you are shooting to an 8 bit H264, I won’t say that you have to totally neutralize the image, though you may find that shooting lower contrast and then boosting contrast in post is helpful. I don’t suggest lowering saturation, since saturation is important for the key. Also, it tends to be easier to reduce saturation later, as opposed to attempting to increase it.

Mainly turn sharpen OFF, keep the highlights in range so you don’t lose detail, and try not to crush your blacks.

Oliver: “regarding keying – we follow this workflow:
1) Effect > Color Key – turn tolerance up to 20, turn feather up a little bit;
2) repeat Color Key 3-4…..

Okay, I’d suggest that you don’t use the “Color Key” plug in *at all*. Simplify your effects stack. Use KEYLIGHT only. Or use Primatte. (I would say use Ultimatte Advantedge, but it is no longer supported).

Here are a couple down and dirty keys I puled from your footage, on two different backgrounds (and two different settings). There is one instance of Keylight and then one instance of levels below it. The layer is then duplicated (with keylight) and the keylight settings are very different (much wider choke), with ADD transfer mode for that layer.

Example

Even so, there are still problems due to having to fight the sharpening effect, such as the bits under her arms. And if doing this for real, we’d probably want to paint out that flyaway hair, lol.

Oliver:
3) I don’t understand what you mean here?
6) What screen shrink setting did you use?
7) Should sharpning come before or after keylight?”

3) In keylight adjust the black clip to clean up the BG screen noise, in conjunction with GAIN, instead of trying to get a clean screen with gain alone.

6) It depends on the material, but basically just enough to hide the edge.

7) Sharpening should always be after any keying or comping operations, and in fact in most cases it should be last. “Sharpen” does not sharpen the image – it just highlights the edges by increasing edge contrast.. Ypu may find that you can help apparent sharpness by adjusting contrast, using levels or curves, and I suggest trying this before using the sharpen filter.

Hope this was helpful – I think you’ll find that you’ll get an easy key if you:

CLIFF’S NOTES:

1) Turn off sharpen.

2) Expose your subject a stop or two brighter than the screen. As a rule of thumb, the green screen should never be brighter than an 18% grey card. In fact, if you took all the red and all the blue of of a grey card, leaving only green, it would be roughly equal to a 7% grey card, which is roughly one and a half stops darker than the 18% grey, and this is about where you want your green screen exposed – 1 1/2 stops under subject’s meter.

3) Consider a back-light/rim light if it will work with your comp background.

[Steve Brame]

“Not sure what I am doing wrong, but only the 1st frame got correctly masked – the auto tracing did not work correctly for the rest.”

Make sure that under the ‘Time Span’ heading of the ‘Auto-trace’ dialog you select ‘Work Area’ instead of ‘Current Frame’. Also make sure that your entire length of the comp is selected as the ‘Work Area’.

Steve Brame
creative illusions Productions