I have a well lit studio setup with a Rosco chromakey green background. The background is completely even and smooth. But I can't pull a decent key to save my life. I get insane amounts of noise and a huge color shift toward magenta. I've tried both Keylight and Primatte 4, and I'm just not happy how they look.
Obviously, I'm not doing something right. I'd appreciate some pointers.
Re: HD Chromakey help by Kevin Camp on May 14, 2008 at 3:40:48 pm
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.
Re: HD Chromakey help by Dave LaRonde on May 14, 2008 at 3:48:47 pm
Do you really mean "HD", or is this footage actually HDV? If so......
Dave's Stock Answer #1:
If the footage you imported into AE is any kind of the following -- Native HDV, MPEG1, MPEG2, mp4, m2t, H.261 or H.264 -- you need to convert it to a different codec.
These kinds of footage use temporal, or interframe compression. They have keyframes at regular intervals, containing complete frame information. However, the frames in between do NOT have complete information. Interframe codecs toss out duplicated information.
In order to maintain peak rendering efficiency, AE needs complete information for each and every frame. But because these kinds of footage contain only partial information, AE freaks out, resulting in a wide variety of problems.
Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
Re: HD Chromakey help (1MB image embedded) by Navarro Parker on May 14, 2008 at 9:36:13 pm
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)
Re: HD Chromakey help (1MB image embedded) by Dave LaRonde on May 14, 2008 at 10:32:05 pm
"[Navarro Parker]"This was shot with XDCAM EX 1080p HQ. "
I wasn't sure what kind of camera that was, so I looked up the first blurb I found on Google, and what do you think I found?
"NAB brings the prosumer a new choice in camcorders this morning with this, Sony's XDCAM EX. This tapeless MPEG-2 recorder will snag images captured by a trio of half-inch imagers to a pair of Sony's (and Sandisk's) new SxS 16GB ExpressCard flash modules for up to 120 minutes of high-definition video."
You're using MPEG 2 video, for cryin' out loud! AE HATES MPEG2, for reasons I enumerated earlier!
Go change your footage to a different codec.
Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA
Re: HD Chromakey help (1MB image embedded) by Aharon Rabinowitz on May 14, 2008 at 10:38:28 pm
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).
