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Green screen - recording or post problem?

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Oliver Buckie
Green screen - recording or post problem?
on Feb 13, 2012 at 9:23:14 pm

We have shot some green screen for a e-learning video (1st frame below) - needs to be delievered in HD-quality:
http://www.eversys.de/downloads/creativecow/original.zip

Our post work in AE CS5 output the following (1st frame):
http://www.eversys.de/downloads/creativecow/post.zip

We are unhappy with the end result. Not really sure where the problem lays - with the original recording or the post work in AE.

Any comments welcome.


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Dave LaRonde
Re: Green screen - recording or post problem?
on Feb 13, 2012 at 11:32:41 pm

I see a couple of problems.

The green screen is lit with no hot spots, and that's good, but the background and the subject need to be lit separately. The subject is currently underexposed in relation to the background. Because you're using a single set of lights for both, you're not doing justice to the lighting on the subject

When you do a proper job with the lighting, it should automatically fix the second problem: the subject appears to be very close to the background, and should be six feet away from it at the very least. More would be better. Not only does this let you refine the lighting on the subject, but it will also reduce the amount of spill light falling on the subject. This makes a good-looking key easier to achieve.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Andrew Somers
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 8:15:18 am

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


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 12:11:18 pm

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: 1920x1080, 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: http://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 http://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!


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Steve Brame
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 2:47:26 pm

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

http://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


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 6:02:19 pm

@ 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.


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Steve Brame
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 2:56:21 am

"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


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 9:33:54 am

@ Steve Brame - I followed the tutorial step by step. With the downloaded files, no problem. With my video... see the results:

Auto-trace settings
Result pre auto-trace
Post auto-trace, 1st frame
Post auto-trace, 2 secs
Post auto-trace, 4 secs
Post auto-trace, 5 secs

Any idea?


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Dave LaRonde
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 5:16:30 pm

I can't access the PNG files, but if they're of the same shot originally posted, the shot isn't worth saving. It's worth re-shooting using proper lighting for chroma key. You've been misinformed about what constitutes good lighting.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 10:07:57 pm

@ Dave LaRonde - sorry, access to the images should now be OK.


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Dave LaRonde
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 3:39:42 pm

[Oliver de Morassé] "We do infact light the green screen and subject separately. The subject stands about 4-6 feet away from the screen"

That's good news. Your task them becomes a matter of re-lighting. There is a difference between flat lighting, which minimizes shadows and is ideal for a chroma key background, and lighting the subject unflatteringly, which is what you have at the moment. It doesn't hurt one bit to put natural-looking shadows on the subject, and to have a visible difference in key and fill lights.

I agree with Andrew both on the absence of back lighting -- you need some -- and the ratio of illumination between subject and background -- the background can be darker than it is currently.

I can't really speak to a camera model, but the crucial factor for me is the ability to record in 4-2-2 color resolution, aka color sampling. It contains more color information, which is a good thing when doing a color key.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Jon Bagge
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 5:07:43 pm

- 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: 1920x1080, 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.

--------------
http://www.jonbagge.net
Jon Bagge - Editor - London, UK
Avid - FCP - After Effects


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 6:13:12 pm

@ 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.


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 6:06:24 pm

@ 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.


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Dave LaRonde
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 6:12:23 pm

In your first example, the green screen is fine. It's a good example of flat lighting: no shadows or hot spots. It's the SUBJECT that needs better lighting; it's a train wreck.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Michael Szalapski
Re: Green screen - recording or post problem?
on Feb 14, 2012 at 4:47:57 pm

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.


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Andrew Somers
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 1:58:33 am

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.


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 12:38:12 pm

@ Andrew Somers - thanks for all your infos & tips ;O).

Been 'playing' with "levels" and "curves". Any particular settings for the "levels" effect - I have been adjusting the "Input black" setting? When the layer is duplicated, should this appear below the original layer? What do you mean with a "wider choke".

Thanks again.


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Andrew Somers
Re: Green screen - recording or post problem?
on Feb 15, 2012 at 5:29:07 pm

The additive layer needs to be above the normal layer.
"wider choke" means less shrinking.


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Oliver de Morassé
Re: Green screen - recording or post problem?
on Feb 29, 2012 at 9:35:44 am

Thanks for all of your feedback.

I have been 'playing' with camera settings and picture styles etc. and my tests can be found here: picture-styles.zip (original footage is 360MB - I can make smaller .zips if necessary).

I have used the following picture styles (shot with an ISO of 320 and aperture of 3.5). I have included a brief description of each style:

Faithful: 0, 0, 0, 0 (Sharpness, Contrast, Saturation, Color Tone)
- This Picture Style is for users who prefer to process images with their computer. When the subject is captured under a color temperature of 5200K, the color is adjusted colorimetrically to match the subject’s color. The image is dull and subdued.

Landscape: 4, 0, 0, 0
- For vivid blues and greens, and very sharp and crisp images. Effective for impressive landscapes

Neutral: 0, 0, 0, 0
- This Picture Style is for users who prefer to process images with their computer. For natural colors and subdued images.

Portrait: 2, 0, 0, 0
- For nice skin tones. The image looks softer. Effective for close-ups of women or children.

Standard: 3, 0, 0, 0
- The image looks vivid, sharp, and crisp. This is a general-purpose Picture Style suitable for most scenes.

Marvels Advanced 3.4: 0, -3, -2, 0

CineStyle: 0, -4, -2, 0

Marvels Cine 1.2: 3, -2, -1, 1

I would welcome your comments on which styles you think are the best to use.

When analysing the movies and looking at the red channel in the green screen element, a white line still appears around the subject, eventhough some of picture styles use NO SHARPNESS - any ideas why?

Also, I find the movies without any sharpness whatsoever, a little blurred. Yes I know - SHARPEN MUST BE OFF - but the end result doesn't look too nice. If the source material is bad, then one has little chance in the post - is it not a matter of "garbage in, garbage out"?!?!

Finally, do you think that investing in a camcorder (see post "Which camcorder for green screening full-HD e-learning DVDs") would help?

Thanks for your continued help in this matter.


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Dave LaRonde
Re: Green screen - recording or post problem?
on Feb 29, 2012 at 4:42:45 pm

[Oliver de Morassé] "When analysing the movies and looking at the red channel in the green screen element, a white line still appears around the subject, eventhough some of picture styles use NO SHARPNESS - any ideas why?"

It was the way it was recorded. Your description of what you shot is indicative of DSLR settings, and DSLRs typically record H.264-encoded video, which uses 4-2-0 color resolution, aka color sampling.

Think of an image having two components: a black & white image, with the image containing color information overlaid on it. In the compression process, all of the B&W image resolution is retained, but only a fraction of the color image resolution makes it.

When combined again for displaying the image, the reduced color resolution is stretched out to fill the image. It's enough to fool the human eye, but not a computer.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Andrew Somers
Re: Green screen - recording or post problem?
on Mar 12, 2012 at 3:00:18 am

If you must use a sharpen tool, it needs to be after you pull your key.

As for why you see the white line - since I don't use Canon dSLRs, I can't speak regarding how they may handle the compression in H264.

I did tests just now with my Nikon, using a dark and black objects in front of my green screen, and got no white line. The Nikon compresses into a 4:2:0 space as well.

But as you may recall, in a previous post I pointed out that your green screen is NOT sufficiently narrow band to get a good key (from what I can tell in the images you posted).


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