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wobbly edges green screen
Hi all,
it is my first post.I have just started to make some experiments of footages on green screen where the subject makes some movements with the hands. I use adobe after effect cs6.
My biggest problem is the edges. Sometimes they look wobbly.
How can I fix the problem in after effect cs6? (I know I have to lit evenly the screen….the subject has to be 2 feets away from the screen….etc….)
In addition could you kindly suggest me a really advanced tutorial on green screen processing in after effects? I saw several tutorials on the internet but I don’t know which one is the best.
Thanks in advance
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13 Replies
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One softbox CFL light is to illuminate the screen and two softboxes CFL to illuminate the subjects ( I know I should illuminate the screen with another softbox)
Here you are the screenshots
Footage
Footage keyed
thanks
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The culprit is almost certainly camera noise. Look at each of your channels separately and it is probable that one will show a lot of noise and will be the source of your edge chatter.
Simon Ubsdell
tokyo productions
hawaiki -
There will be many (including highly experienced camera people) who will tell you that the exposure of your green screen backing is just fine.
But they are wrong.
It is considerably underexposed from an optimal point of view.
However, your screen grabs don’t help to explain what you mean by “wobbly edges”.
Simon Ubsdell
tokyo productions
hawaiki -
[Alex Sporanox] “the subject has to be 2 feets away from the screen”
Whoever told you this is very much mistaken. Try something closer to ten feet!
Simon Ubsdell
tokyo productions
hawaiki -
Thanks everybody.
– Ok 10 feet (2 feet was a mistake, sorry)
-Right, screenshots don’t help me to show you “wobbly edges”. I mean that looking at video the edges seem “live”….like THIN SNAKES that move forward and backward along the edge line while the subject moves….that you can easily conclude it is a keyed video (i.e. poor keyed video).
-You say the culprit is one noisy channel….once found it, what can I do?
I’ll try to rise the exposure of the green screen……what else?
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[Alex Sporanox] “- Ok 10 feet (2 feet was a mistake, sorry)”
In the example you posted, the subject is far too close to the backing. As a result, the fine hairs on the arm are nearly twice as green as they are red (the next highest channel). This is because of the spill from the backing resulting from the proximity, and it means the keyer won’t be able to interpret them as (semi-transparent) foreground and they will simply disappear. Preserving edge transparency is the main reason for keeping the subject at a good distance from the backing. (Spill itself, i.e. green contamination of the foreground where it is meant to be solid and not semi-transparent, is mostly taken care of by your keyer’s despill options and is less of a problem.)
[Alex Sporanox] “-You say the culprit is one noisy channel….once found it, what can I do?”
I suspect that if you look closely at your red channel you will see blocky compression artefacts which could well be the cause of your problem. Better lighting of the backing could help, but it might be that the only option is to use a better camera.
[Alex Sporanox] “what else?”
Make sure that any in-camera sharpening is turned off. This is absolutely crucial. Sharpening will make a serious mess of your keying before you’ve even started. It is a process that deliberately introduces edge artefacts which might make your picture look “sharper” but which you really don’t want anywhere near your image if you are shooting green screen.
Simon Ubsdell
tokyo productions
hawaiki -
Simon, thanks a lot!
Next weekend I’ll try to put into practice your advise. -
[Alex Sporanox] “Simon, thanks a lot!
Next weekend I’ll try to put into practice your advise.”Simon has given a lot of good guidance on the post side, and he’s completely right about your exposure. To add on to his comments, It’s best practice to light the backdrop and the subject separately; light the green screen, then put your subject on their mark, they should be completely silhouetted against the backdrop. Take care to ensure that there is as little spill on the subject as possible. Turn the lights off, then light your subject, the backdrop should be VERY dark with as little illumination from the main lights as possible. If you’ve done your job correctly, you should be able to turn all the lights on and shoot without having to re-adjust exposure. You should also try to get rid of the wrinkles on you green screen. ☺ BTW, which camera are you shooting with, and which codec are you capturing to?
Shawn
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thanks Shawn…other useful advice!
Percorso file: ..\P3190243.MOV
Tipo: Filmato di QuickTime
Dimensioni file: 48.0 MB
Dimensioni immagine: 1920 x 1080
Frequenza fotogrammi: 25.00
Formato audio sorgente: 48000 Hz – 16 bit – Stereo
Formato audio del progetto: 48000 Hz – virgola mobile a 32 bit – Stereo
Durata complessiva: 00:00:13:11
Proporzioni pixel: 1.0I need to export in photojpeg.
I have 3 skoftbox 60×90. One of them is a softbox boom.
How I have to set the lights?
Softbox boom for subject and the other softbox (left and right) for the screen…..orSoftbox boom for screen and and the other softbox (left and right) for the subject??
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[Alex Sporanox] “How I have to set the lights?
Softbox boom for subject and the other softbox (left and right) for the screen…..orSoftbox boom for screen and and the other softbox (left and right) for the subject??”
Ideally, you would have a five light setup, two for the backdrop and three for your subject. If you only have three lights to work with, you might consider using two for the backdrop and reserving the softbox for your subject. If you have a reflector, you could use that for fill.
Shawn
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