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Keylight (1.2)- Noise in my blacks on subject
I have used keylight (1.2) for my blue screen working for a while now. I shoot on digital IMX with a full television studio lighting grid. So I know it is being lit properly. I normally do a rough key, so I can run an auto trace to create a tight junk matte, and then re-key my subject. I normally look at the screen matte mode to determine my transparency. Even though it was showing a solid transparency, when I looked at the Final output, I was getting a lot of noise in my blacks on my subject. I started looking around and noticed another option called status. When I looked at my subject with that mode on, I saw my whites, or transparency wasn’t a true solid in the areas that had the noise. When I clipped my white levels, it seemed to clean up a lot of the noise. (But didn’t clean up all of it completely). Does anyone know what the difference is between the two options on Keylight, and any further advice for better keying techniques? Thanks!
John Jackowiak
Brand New Motion***Recent Work***
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2 Replies
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Status is definitely the mode you should use for dialing in your matte. In this mode, black is transparent, white is opaque, and gray is partially transparent just like you would expect. However, what’s great about status is that ANY partially transparent pixel shows up as fully gray, and they’re much more easily spotted as you make your refinements regardless.
The fastest way to clean up a noisy matte is to play with the clip white and clip black values in the screen matte portion of the plugin. Depending on how much you want to finesse it, you could add a simple choker with a value of a pixel or two to kill any stray pixels too.
Truly professional mattes are often done in multiple keys with several passes: one for the innner portion of the subject, another for the outer portion, and a third (or several) for refining the edge – all of which are combined into a final matte for the alpha channel.
If the noise you are referring to is showing up in the darkly colored areas of the image that you want to keep, try changing your replace method to hard color instead of soft color.
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My first fix for my first professional problem! I key out a lot of subjects with blacks and they always seem to turn out noisy. This fix also works with blues which often don’t turn out well over green (yellows over blue screens), and even weird instances when the green just won’t go away around the edges without making the inside look like mud.
A personal note: I HATE white and black clipping. It always turns my blacks to pitch black and never ends up looking good. I prefer the following method much more.
The key is to make an outside AND and inside matte. The outside is pretty easy. Simply key until green around the edges go away. Don’t worry about the inside for now.
Duplicate and precomp that layer. Go into the comp and set your keylight to “Screen Matte”. You will get the white on black matte along with the gray areas where parts of your subject are translucent. Of course, you will notice there are translucent parts to your black areas. Yuk. Dial your blance to make the matte as white as solid as possible.
Set “Screen Shrink/Grow” for the layer in your precomp to between -2 and -4. If not, you may end up with dark borders that don’t always look too neat in the end.
Go back to the main comp.
Jack up the highlights and jack down the shadows on your precomp layer so the gray areas disappear and you are left with a solid white shape.
Duplicate the original layer and delete its Keylight plugin. Set the new layer TrkMat to Luma for the pre-comp above it.
You now have an outer and inner matte for your subject! There are no longer any noisy blacks, blues are radiant and perhaps even some highlights came back too.
Set the blend mode for the middle layer to Luminosity to use the chroma values from the original layer. This will remove any green spill that may have snuck back onto your subject.
Good luck!
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