I'm trying to improve my chroma key setup. I'm struggling with a green contour, mainly around my hair. This is puzzling me because I use blue screen as background. (I want to use blue because I've greenish eyes, I don't wear blue cloths and I want to background to be blue-ish anyhow). In the first image you see the bare setup. The lighting setup consists of two lamps for the foreground (me) and three for the background. It could still be a bit better, but I'd expect this to be good enough (right?)

vMix Capture 22 april 2021 09-46-10.jpg (107kb) downloaded 13 time(s).

The second image shows my problem in a very exaggerated way. I've selected the backround with the Chroma Key colour picker but set the Chroma Key Filter slider to zero. Where does this green color come from?? I'd understand if it would be blue. Apparently this is something in the chroma key algorithm. Do I miss something?

vMix Capture 22 april 2021 09-47-56.jpg (168kb) downloaded 2 time(s).

Chroma Key Filter slider to 40%. Still exaggerated, but shows the actual problem best. If the green halo would be sam colour as my background, it would already be more acceptable

vMix Capture 22 april 2021 09-48-44.jpg (225kb) downloaded 0 time(s).

Chroma Key Filter slider to 80% This is the best I get without anti aliasing. Not REALLY bad, but if one is critical there are too many artifacts: this is eating into my contours, in my righ sleeve the chair is shining through and there is still some green contour. Moreover, this setting is a critical comprimise. With a slight change in lighting conditions or clothing, it already shifts.

vMix Capture 22 april 2021 09-50-49.jpg (227kb) downloaded 2 time(s).


A bit better wrt the contour is Chroma Key Filter slider to 80% + medium Anti aliasing. However, the anti- aliasing only masks the green and it adds other artifacts.


vMix Capture 22 april 2021 09-51-31.jpg (222kb) downloaded 1 time(s).

My questions to you:

1. Where does the green halo come from? Can I change it to colour of the background?
   
2. Is this the best result I can expect in vMix? If not, would could I do more to improve it?
   
3. Is there an option to add a possibly more advanced (more refined, more robust) chroma key solution in the system (for a reasonable budget)?
   
4. Am I unrealistically critical for this budget?
   

Thanks in advance!

Joost

Thanks for your reply and suggestions. Space is very tight unfortunately. At least for now, I have to deal with a distance of 1-1.5m between me and the background. The lighting setup is a 5 point one: 2 foreground (left/right) + 3 background (left/right/top-middle). If you say "lighting issue", I can think of two different improvement directions:

1. further improving the background lighting: more even, brighter
   
2. adding a separation light (lighting the head and shoulders from the back) to separate hair and background better
   

Frankly, I've avoided the separation light so far as, to my feeling this would also be unnatural for informal the living room feel that I like to achieve. But perhaps I just have to. That would also give more room to brighten the background and not interfer with the hair. I don't notice much spill, so that is not my main consideration for now.

What is likely to give the most contribution? Or do I really have to do all?

i agree that the lighting setup is not bad at all given the physical constraints of the space you're in.



Brighter is not necessarily better. If anything a slightly underexposed, evenly-lit chroma backdrop is easier to key than an overexposed one, as hotspots wash out the colour. You can use the RGB parade view, or the zebra function in a video camera, to check for lighter areas on your bluescreen. Don't worry about vignetting as you can crop stuff near the edges, but try to get even exposure around your subject.



A backlight often helps reduce colour fringing around the edges. I'd be tempted to see if you can get away with just 2 lights on your backdrop, and use the top one - which is currently creating a little hotspot above you - as a rim light on your hair and shoulders. And, if your replacement background image of the living room had a table lamp in there behind you, it would be coherent with the lighting setup and not look strange.

It's been years since I used a blue screen, and green screen dominates chroma setups to the extent that I do wonder if some keying algorithms make assumptions about key colour & spill correction, which might explain the green fringe you're seeing. If you've ever used something like the Keylight plug-in for post-production keying, there are a lot of parameters to tweak in order to pull a nice key, so a real-time key with only 2 sliders is going to have to compromise somewhere. I'm not aware of anything in the same price range as vMix that offers a real-time tweakable chroma key. An external software keyer will cost you some latency (at best a roundtrip via NDI), and hardware keyers were traditionally very expensive, although the Blackmagic Atem switchers include a keyer, but I've never tried it.

Thanks for the confirmation and further suggestions.




I'm planning an experiment. The suggestion of the fake table lamp is a nice one. Although for day-time streams (I use this for live telco's and webinars) it could be still a bit weird. But it's worth a try.



That's a fair comment. I reached out to Martin to get his input on this.




Actually, your comment plus some searching pointed me to the BM ATEM mini. Price point (under 300$) would be acceptable to me, if it really solves this issue. I've found some nice demo's, unfortunately from guys with either a cap or a sleeker hairdo then mine ;). Worth some further research.

Thnx!!!!!

Anyone here with handson experience with the Black Magic ATEM mini????

I have sent an email, but also will reply here for the benefit of others.

Take a look at the blue screens colours in a photo editing app (I am using Paint.Net as an example).
Use the eye dropper tool to pick a colour and look at the RGB values.

Note the green is very high, almost as high as the blue at some points.
This means it is not really a blue screen at all, due to camera white balance, lighting, the screen or simply
because blue is not a very good colour for keying with digital video cameras.

Green screens have a much easier colour separation due to how camera sensors work and should pretty much always be used
unless it is critical to have something green in the scene.

Regards,

Martin
vMix

If you're running a GeForce RTX series GPU (I think they opened it up for GTX too, but it may be too intensive), you may want to consider trying the free NVIDIA Broadcast App and see how it handles background removal. It's AI based.

I've only tried it once for a remote shot where their chroma key lighting wasn't up to par. It did a great job with the hairline... Although it left a border on the sharp-edged stuff.

It's worth a look for at least a comparison.

One thing you could try to get a purer blue - which, as Martin suggests, might help the key - is to change the camera white balance settings and/or lighting on the backdrop, and see if that helps reduce the colour fringe you were seeing. If your camera allows you to dial in the colour temperature while you watch the scopes, that might be better than the built-in white balance function, which can vary quite a bit between camera manufacturers, I find.

Of course, that will probably throw off the colour on your face, but some lighting gels on the foreground light could compensate (if the shot becomes colder once you balance for the background, some CTO to warm up your face, for example) and, if necessary, some final colour correction in vMix after you pull the key.