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keying problem – pixelated edges
Hi guys, i’ve come across a problem producing a video for DVD.
Normally i work for web resolution and key out greenscreen from a decent 3-chip camera into a 640×480 comp, with the original video shrunk to 70% and with square pixels. I keep the original video on separate fields, i don’t bother frame blending and the comp is set to PAL 25 fps. And i have no problems achieving a decent key using keylight.
However, i’ve been asked to produce a DVD with a similar video on it. So, the comp is PAL DV (1:1.07 pixel ratio), 25fps and the orginal video is 100% and i’m getting a really poor key. The talent’s outline is horribly pixelated and i can’t seem to get rid of it. The subject was lit properly and should key well, but i’m really struggling. Is there something basic i’m missing out?
Please shout out any ideas.
Graham
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6 Replies
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The entire issue of pixellation is caused by the chroma downsampling in 4:2:0 or 4:1:1 video.
You can smooth out the colors a bit by placing your source footage in a comp, placing an adjustment layer on top with a 4 pixel gaussian blur applied and setting blend mode of the adjustment layer to ‘color’.
This essentially smoothes out the colors while leaving luma details intact.
Drag this comp into a new one and apply your keyer there. It’ll look a lot smoother.
Bar3nd
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I have to say that I have a similar problem with keylight and digital betacam footage (captured in SDI in symphony, uncompressed). I have to put heavy chroma blur before it disappear. I’ve not done alot of keying in my life, but this seems odd that about the cleanest footage I can get shows those artifacts.
I’ve searched the forums and on the net, and I find a few ppl having the same problem, but never a real solution. The keylight tutorals aren’t very helpfu since there’s no moving image, just stills, so we don’t even know if they show how to get a proper key.
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Hi guys,
there is a pretty good preset for keylight on http://www.aenhancers.com in the animation presets library that deals with this problem.
Greez Martin
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Thanks guys for all your help.
To answer your questions Dave, the footage is captured in Premiere Pro via firewire, and i must confess i don’t know which codec it is, although it’s the same capture codec i use for the web video stuff.
Thanks Barend and Martin, i’m going to try both techniques side by side to see which one gives me the best results.
Graham
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Wow, thanx. This preset does the thing right… it does a very great chroma blur in yuv mode. Better than doing the trick of the blurred adjustement layer set to color blend mode precomped with source.
The keylight values seem a bit too high for good greenscreen footage, tho. But it’s normal to have different values for different shots…
thanx again
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I’m glad my post helped others too 🙂
I’ve ended up combining Barend’s technique with the preset, but reducing the strength of the key the preset produced. As with all these things, i think tweaking is always essential, i’m just really, really happy a place like the Cow exists.
Thanks for all your help guys.
Graham
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