HD Chromakey help

[Kevin Camp]

there are two things i would recommend you look at for keying with keylight. the first is aharon rabinowitz’s super tight junk mattes tutorial. the second is page 42 of the keylight maunual (download here if needed).

aharon’s tutorial shows you how to create a very accurate ‘junk matte’ which will be used to ‘crop out’ much of the empty space you are keying out, allowing you to focus on keying the green just around the edges of the subject.

page 42 of the manual, discusses how to use use 2 instances of keylight to create an ‘inside mask’ that will be used to tell keylight not to change the pixels inside that area, allowing you to focus on maintaining just the edges of the subject. this will usually reduce much of the noise that keylight can produce.

together they are very useful.

if you feel comfortable with aharon’s method and under stand the p 42 method, you can actually use those ‘super tight junk’ masks to create the inside mask as described in the keylight docs, without needing the additional keylight effect. just copy and paste the masks from the matte layer onto your footage layer, then shrink the masks (expand in reverse) in the mask properties, then set the keylight inside mask to use the ‘source alpha’ as ‘normal’ (as per the method describe on p 42). the advantage of this is that it will process faster than 2 instances of keylight and produce very similar results, it’s also very easy to feather the edges of the masks a bit to smooth the transition from inside mask to keyed edges.

another tip for using keylight, try setting the replace color method to hard light and don’t be afraid to select a different replacement color to better match your subject. also, selecting the despill bias color from a skin tone of the subject if often useful.

as far as the magenta shift, i haven’t seen that, but there was a post from the other day that mentioned issues with color shift/saturation with keylight on an older powermac g5 (ppc cores), but did not see the same problems on a newer macpro (intel cores). i’m not sure if your issue may be related.

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[Navarro Parker]

Here’s the kind of noise I’m talking about. This was shot with XDCAM EX 1080p HQ. After applying either Keylight or Primatte, I get this lumpy granular noise. (Even though this is an animated GIF, the noise is pretty close to what I’m seeing on my display)

Any idea what’s causing this?

[Aharon Rabinowitz]

Some of that noise may be due to too much keying power. I’d raise the Screen Matt’s Clip Black value to 10, and lower the Clip White to 90. That will tighten up the areas being keyed vs. not keyed, and may get rid of the noise.

On the other hand, if your video has come in with a lot of noise in it – it’s usually due to poor lighting. Short of re-shooting with better lights, You might want to try using AE’s noise reduction tools, or maybe the 3rd party plug-in called Neat Video which does excellent Noise reduction (I’ve used the Vegas version, not the AE one, but they use the same algorithms).

Aharon Rabinowitz
Email: arabinowitz (AT) yahoo (DOT) com
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