Is it possible to Chroma key this out?

[Grant Swanson]

Hi Blahtor,

It’s possible to take multiple passes on a shot like this. If I were you, I would try to move as little as possible during the shot, that way you can roto out the shadow areas, so you can save yourself some work.

You can also create an “inverse–junk matte” very tightly around the inside of your body, and then key out the light and dark green separately. Something like that is probably too dark for a keyer like Keylight, so you’d need to use a luma–keyer like Extract.

Hope this helps!

Grant Swanson
Visual Effects Supervisor
Video Apex – Minneapolis, MN
videoapex.net

[Brendan Coots]

I’m less optimistic than Grant. No keyer will successfully, cleanly key that plate out, so your only real option (if you want a clean result) will be frame by frame rotoscoping.

It’s the shadows that are killing you most. If you can re-shoot, try placing the light much higher up so your shadows fall lower down, and hopefully out of frame.

You might want to also consider shooting at the highest speed your camera offers, even if it means using an interlaced option. Low frame rates (like 24p) result in motion blur on moving objects, which is great for live shots but a nightmare for keying. The motion blur on CineAlta frames can make keying tough, so it definitely will on any camera of lesser quality than that.

Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com

[Grant Swanson]

Brendan–

What I said was to rotoscope out the shadow areas, and use Keylight to key out the green that is not covered in shadow. I also mentioned that since Keylight would be unable to key out the shadows, try using a luma-keyer such as Extract, combined with a garbage mask around the inside of the character.

Blahtor–

I would recommend not shooting at a higher frame rate; even a jump from something like 24 fps to 60 fps will result in a noticeable loss in light, and from what you say, you can’t afford that. To deal with motion blur, my previous advice holds: try to move as little as possible during the shot.

Grant Swanson
Visual Effects Supervisor
Video Apex – Minneapolis, MN
videoapex.net

[Blahtor Magnus]

OK, seems that it is impossible to key out shadows from the green screen.
I read about plugins that can do that but I am pretty sceptical about this whole miracle thing.
Not to mention that those plugins cost a fortune (I am talking about Ultimatte Advantedge)
I will try to SOMEHOW place an additional light AND a white screen that makes it diffuse.

At present I am able to make the shadow behind the actors blurry and not noticeable by moving the white screen away from the light, but this also kills the light. So, I guess that one more light with another screen insfront of it will help me have a blurred out shadow and good light at the same time.

_

About frame rate: Is it OK to shoot at a higher frame rate if I manage to arrange a good light setup?
Or should I stay to a lower bitrate anyways?

Also: does video resolution affect the light in the shot?
I am using a crappy pocket HD camera (Aiptec A-HD+) and it has the following resolution settings:

1. CIF 30f (WEB)
2. D1 60f (DVD)
3. HD 30f (720P)
4. HD 60f (720P)
5. HD 30f (1080)

–

[Grant Swanson]

Blahtor-

It is certainly okay to shoot at a higher frame rate-if you can get some decent lighting. If I were you, I would try to get at least one more light, put it behind the actor, and aim it at the green screen. And of course keep the light you already have aiming at the actor.

Then shoot at the 1080 30fps your camera offers. I wouldn’t sacrifice video resolution for a higher frame rate. HD 1080p/i will give you more room to work with when pulling the key and it will make your job a lot easier. Not to mention you’ll have more detail to work with when you do rotoscope work (which will be minimalized if you use the advice above).

Grant Swanson
Visual Effects Supervisor
Video Apex – Minneapolis, MN
videoapex.net

[Blahtor Magnus]

Thanks, I will take your advice and shoot in the highest resolution possible..
By the way, I did a test.
I placed my only light on the side of the green screen and placed the actor infront of it.
Even though I am using a light diffuser, the light creates a hot spot and makes the green screen white.
I guess I just need more room for this kind of setup.

_

[Brendan Coots]

Grant,

Sorry to disagree with you again, but shooting in HD, especially with a consumer-grade camera, won’t necessarily translate into a better key.

Problem 1 – Sure you technically have more pixels to work with, but almost all consumer/prosumer HD cameras, including the Panasonic HVX200, use tiny sensors with a native shooting size of 960×540 (barely larger than standard definition). The camera internally uses scaling tricks to get that size up to 960×720, resulting in the first level of stretching. You can pretty much double the scaling required for 1080p.

Problem 2 – Virtually all consumer/prosumer cameras use the 1.33 aspect ratio to get the “true” HD width of 1920 or 1280 from their starting point of 1440 or 960. This is your second level of stretching used to arrive at “HD” sizes.

Problem 3 – All consumer/prosumer HD cameras have notoriously hideous low-light response when shooting in HD mode. Wild pixelation in the shadow areas is common unless you use several thousand watts of lighting, allowing the DP to stop down substantially.

Problem 4 – Consumer/prosumer HD tends to compress using HDV or similar, which has the same 25Mbps datarate as mini-DV. How a 1920×1080 image can contain only the same amount of data as 720×480 DV and not fall apart in front of your eyes is a miracle, but it certainly tells you what to expect if you try to do any color correction to the footage to match it into your background plate. There just isn’t enough data there to push or pull color values around without severe damage to the image.

In the end, you have a camera pushing, pulling, scaling and stretching your pixels like mad, and when you throw in the motion blur you will get from 24p (or even 30p) you end up with a softer, grainier image with poor edge detail. It may be larger, but the problems this format introduces almost offsets any gains to be had from the larger physical size of HD. I would rather have a DVCPRO50 (4:2:2) 30p file to key than a consumer HD file any day.

—-

I should add that not many of these issues matter as they relate to shooting live footage in consumer HD. These problems are usually fairly buried away in those cases and imagery can look quite nice. It is with keying that you start zooming in very close and examining edge detail, and you start to see real problems.

Brendan Coots
Splitvision Digital
http://www.splitvisiondigital.com

[Graham Quince]

We set up a tiny greenscreen studio at home, and though we shoot on a Panasonic 3CCD comsumer camcorder our setup might help you.

We bought a large (5″) 100W+ pearl sphere bulb for the ceiling lamp (I also took off the lamp shade) and three flexible-neck desk lamps. We place one directly behind the subject pointing up and towards them. The ceiling light provides general illumation and I use the other two lamps to migtigate the shadows by placing them parallel with the subject pointing at the wall. We use pearl bulbs in each lamp.

Hot spots do occur, but with a lot of tweaking you can get enough clean wall to shoot.

The biggest problem is the camcorder you’re using though. I’ve never got anything useful from 1-CCD, even rotoscoping can be awkward.

Graham

http://www.YouTube.com/ShiveringCactus – Free FX for amateur films

[Blahtor Magnus]

I am not an expert and i don’t know anything about camera sensors, scaling, ratios and the such but my triel and error experience shows that what is said by Brendan Coots is true.
I am having big problems wth the compression artifacts of this camera.
If you shoot against a perfectly lit green screen, you still get problems that are caused by the crappyness of the camera.
Motion blurred areas key out as shapeless spots, the keyers can not get the green out of them and so on.
Still, I will keep trying and hopefully, will end up with a acceptable result.
It’s easy with a good camera and a good green screen setup but it is so much more fun with a bad one (OK, I lied – it’s not fun at all)

Graham, I will try to copy your setup. You’re right – my camera is the weakest link in the chain.

By the way, I just bought a new 500W light. Will see how it goes with this one added to the whole setup.
This time I will not be using direct light with a diffuser.
Will try the trick with the ceiling as the reflector for the two 500W lihts.

_