Color Keying A Neutral Backdrop

[burroshooter]

I've got an interesting situation I am not sure how to handle. I have a chunk of footages (several chunks in fact) that were shot on a gray screen. I was hooting background for a still calendar shoot where they used a gray screen for a number of shots. I ended up shooting a bunch of the stuff the client wanted against the same screen. Of course, the standard keying software doesn't seem to touch it. I am wondering if anyone knows the trick to keying out a neutral background like gray in either AE or Premirse pro. I am thinking color correcting to make the screen blueish and then keying out the blue, rending it it and then using the render in some sequences they need. ????????

 

[Sol M.]

Having a blue backdrop isn't necessary to pull a key, what's essential is that the color you want to key out is not present in the talent. Blue and green are generally used because they don't occur in skin tone and are easy to work around with wardrobe.

Pretty much all standard keying plugins allow you select a color sample from a frame of video in your composition, so I'm not sure why the keying plugins you're using are having no effect. What plugins have you tried? You should be able to select a color sample from the backdrop, but since it's not a very unique color, you'll likely find that parts of your talent may be keyed out as well.

Shifting the color of your footage so that the background is blue will likely not really make any difference. If you can't key the gray backdrop out without affecting the talent, then shifting the colors of the footage will give you the same results.

One alternative is rotoscoping. It can be time-consuming, but with tools like Mocha Pro, the talent can be extracted in a reasonable amount of time (depending on the complexity of the footage).

 

[james candy]

My first suggestion would be to use a luma key on it. If necessary, you may want to adjust the levels of the image to pull a better key, then apply the matte/mask from this footage, to a copy of the original footage.

If this doesn't work, then I would say either use the autoroto brush, or try the "Selective Color" adjustment layer in Photoshop to shift the neutral tones toward a more distinct color. In either case, some cleanup may be required.

Definitely see what results you can get with the Luma Key, though. This would be the fastest way.

 

[burroshooter]

JIve:

Thanks for the thoughtful epistle.

I've done keys with green, red, blue, even white. Yes, success does depend on what colors the talent or "keep" objects contain (I am not a beginner). In this case the talent has no "gray" and on visual appraisal it really looks keyable. Using, either Keylight in AE or Ultra key in Premiere the pixel selection is virtual useless. Just for grins I took a few seconds of one clip into color correction and changed the hue of the overall scene, giving the background a blueish tint -- that then actually keyed out pretty well. I could render that clip and then recorrect the color...but by then I'm three generations down the road to degradation. I did try the roto brush, not my favorite tool, with some passable results. But you're right it takes time. Interestingly, the still shooter on this project, the one who wanted to use the gray drop, isn't having fun right now either. When you think about it gray is a midtone and while other colors (skins tones?) don't look "gray" they certainly contain much the same values.

 

[burroshooter]

James:

Thanks for the thoughts. Luma Key seemed like the right answer to me as well. I had already tried it, and perhaps didn't succeed because it is not a function I've used before. The selective color thing seems like a good route. I had already taken a few seconds of one clip into Finense and shifted the background to a bluer tint, of course the whole scene shifted a little as well, but once I key it, I can render a good H.264 and color correct that back. This footage is mostly for web presentation do I can allow for the slight degradation.