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stubborn black outline artifact on chromakey

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Lisa Inserra
stubborn black outline artifact on chromakey
on Feb 21, 2010 at 3:05:03 pm

I'm always getting a doggone black outline around my subject when keying out a background using a green screen and using a magenta hairlight. I'm using an ancient DSR250 with 4:1:1 compression (not great). Anyway, messing around with all the controls in keylight I can't get any satisfaction in getting rid of the black outline. Shrinking the matte makes the talent look really unnatural. I tried using Adobe Ultra, which does a great job of keying. The lighting is even, the whole thing keys out fine except for that crummy black outline. Any suggestions?
Thanks,
Lisa


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Kevin Camp
Re: stubborn black outline artifact on chromakey
on Feb 21, 2010 at 11:53:16 pm

try unchecking the 'unpremultiply' option.


Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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Daniel Christie
Re: stubborn black outline artifact on chromakey
on Feb 22, 2010 at 4:08:20 am

Any suggestions for Primatte?

I have the same issue. When I apply Colour Finesse to a keyed layer, the translucent parts of the matte turn dark, producing a dark halo around hair etc. On an adjustment layer above? No problem, but then it affects the background of course.

Cheers,

Daniel



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Lisa Inserra
Re: stubborn black outline artifact on chromakey
on Feb 22, 2010 at 6:58:06 pm

I don't think it has anything to do with what we're doing in AE or Primatte - the software seems to be just a way to make the best of a bad situation. I think it has more to do with the in camera compression and how it interprets the chroma (or perhaps luma) difference. I'm just wondering if there's a plug-in out there that deals with just that issue....or maybe a lighting technique, or a setting in the camera I can change (besides sharpening - which doesn't exist on the 250 anyway).
Like, is there an F-stop difference between the foreground and background that would add up to the compression NOT making this black outline? Jeez, this is really bugging me.
L


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Dave LaRonde
Re: stubborn black outline artifact on chromakey
on Feb 22, 2010 at 9:50:17 pm

[Lisa Inserra] "...I'm just wondering if there's a plug-in out there that deals with just that issue....or maybe a lighting technique, or a setting in the camera I can change (besides sharp"

Lighting is the #1 thing you can do to get a good key. Are you following established techniques for lighting for chroma key, or making it up as you go along?

But even then, it's still DV, and outside of HDV, it's the worst codec to which you can record for effects work. Take 15 minutes to watch this video podcast, which explains about color resolution.... and keep in mind that it's done by a guy who SELLS chroma keying plugins for DV:

http://macbreak.libsyn.com/index.php?post_id=70596



Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Daniel Christie
Re: stubborn black outline artifact on chromakey
on Feb 22, 2010 at 11:05:00 pm

Sorry, I misread the original post. My problem is slightly different. Having shot on DVCPRO HD and supervised the shoot, under the circumstances the footage couldn't be much better. The key is fine, that is until I apply Colour Finesse at which point the grey parts of the matte turn dark in the key. This is before I have even tweaked any of the settings in CF. Other colour correction filters cause no problems and CF doesn't either if it is on an adjustment layer, but using an adjustment layer means that all the layers are affected.

Regards,

Daniel


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Dave LaRonde
Re: stubborn black outline artifact on chromakey
on Feb 22, 2010 at 11:25:46 pm

[Daniel Christie] "The key is fine, that is until I apply Colour Finesse at which point the grey parts of the matte turn dark in the key. "

So try precomping the chroma key layer(s), and THEN applying Color Finesse. Sometimes effects simply don't play nice together. I was reminded of this just today when I tried to use the Levels and Auto Color effects in the wrong sequence.




Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Daniel Christie
Re: stubborn black outline artifact on chromakey
on Feb 23, 2010 at 12:04:26 am

Thanks Dave, I was trying to avoid pre comping as I would end up with quite a few of them but you got my brain ticking and the way I have things set up already I'm pretty sure I will be able to get away with putting most of them in the one pre comp.

Cheers,

Daniel


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Lisa Inserra
Re: stubborn black outline artifact on chromakey
on Feb 23, 2010 at 3:36:25 pm

Hi Dave,
don't have an iPod and when I click on the link you provided, I get a blank screen. But to answer your question, yes, I believe I'm following the established protocol for shooting chromakey. I'm lighting subject and background separately, evenly lit background (even tested it with a light meter), no spill from foreground lights (key and fill on the subject with magenta hair light). So, the only thing I feel like I'm missing in the equation is that perhaps the ratio of light from foreground to background might be too much, or too little?
Lisa


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Dave LaRonde
Re: stubborn black outline artifact on chromakey
on Feb 23, 2010 at 4:21:10 pm

Okay, if your lighting is good, which it sounds like it is, there may something else going on in that comp, or else it's a basic AE goof. Lets eliminate the common stuff first.

If you're running AE9, and you haven't done the free apgrade to 9.02, you should do so.

If you have Open GL enabled, disable it for both rendering and previewing.

Besides the chroma key footage, what OTHER kinds of footage are in that comp? Here's why I ask:

Dave's Stock Answer #1:

If the footage you imported into AE is any kind of the following -- footage in an HDV acquisition codec, MPEG1, MPEG2, AVCHD, 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


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Lisa Inserra
Re: stubborn black outline artifact on chromakey
on Feb 23, 2010 at 5:37:37 pm

Dave,
This is very thorough, and I'm very glad to know this information.
The situation here is that I have a background that is a .mov file behind an After Effects animation of Illustrator, Photoshop and .jpg graphics with my subject chromakeyed in front of all that. But I've gotten this black outline in front of just still .jpg images before as well.

Doggonit.

This is why I have to suspect that it's something to do with the lighting or maybe just the 4:1:1 compression of the SD footage taken on a DSR-250. When I look at just the footage of the subject on the green background, there IS a black outline around her but it's only visible on her red sweater against the green, not her flesh tones or her blonde hair against the green. So I think it must have something to do with the way either A) the camera is interpreting the chrominance or B) the saturation of color or C) the luminance difference (or lack of it). That's why I keep figuring that maybe a change in lighting or F-stop or something might help. Or maybe changing the knee or something.

Lisa


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Dave LaRonde
Re: stubborn black outline artifact on chromakey
on Feb 23, 2010 at 5:58:33 pm

[Lisa Inserra] "...I have to suspect that it's something to do with the lighting or maybe just the 4:1:1 compression of the SD footage taken on a DSR-250. When I look at just the footage of the subject on the green background, there IS a black outline around her but it's only visible on her red sweater against the green..."

Stinky color resolution strikes again!

The thing that puzzles me is why it's BLACK.

I had a similar problem a few years back shooting a lady in a red jacket against a green screen: there was a yellow fringe on the chroma key from Beta SP footage. It was shot on a studio camera which was set up using a waveform monitor & vectorscope, the lighting was checked on the same scopes, then we recorded from camera's Digital Out to the deck's Digital In. What could be better than that?

Then I remembered that Beta SP is ROUGHLY 4-2-2, and probably less. On those edge pixels, I was getting a combination of red & green -- yellow. The lesson I learned was that the purer the color on the subject, the tougher they key becomes.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Lisa Inserra
Re: stubborn black outline artifact on chromakey
on Feb 24, 2010 at 10:57:26 pm

OK I surrender. I hate it, but I surrender. You know, come to think of it, the last time I had a black outline my talent was also wearing red. Hm. So maybe if my talent this time doesn't have the black outline on her flesh tones and her blonde hair, I'll tell my talent to wear peach or yellow on green screen. Well, I guess I'm just dealing with a compression issue. Ugh.
Thanks for your help.
Lisa


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Dave LaRonde
Re: stubborn black outline artifact on chromakey
on Feb 24, 2010 at 11:32:18 pm

[Lisa Inserra] "I guess I'm just dealing with a compression issue. Ugh. "

Sorry to say it, but yup. When it comes to chroma keying, DV really stinks on ice.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Lisa Inserra
Re: stubborn black outline artifact on chromakey
on Feb 23, 2010 at 3:39:07 pm

Hi Kevin,
thanks for the suggestion. I checked (and unchecked) premultiply in Keylight, but all it does is add a sort of grimy-looking black blur around everything. I see that it HAS some effect, just not the one I need.
L


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Danny Hays
Re: stubborn black outline artifact on chromakey
on Jun 16, 2010 at 1:17:31 am

I have been able to ket a good key with both Ultra and Keylight. If you post a link to download a small sample clip, I'll see what I can do and give you the preset for it.



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Dale Paquette
Re: stubborn black outline artifact on chromakey
on Jan 3, 2011 at 6:40:46 pm

I may be a day late and a dollar short on this one - but - I have also experienced this problem and have made the observation that the brightness of the BG seems to affect the situation. Namely, a darkish BG clearly shows the black outline whereas a bright one doesn't. Just to check this, I moved the FG around to examine it over different parts of the BG and sure enough, the outline disappears whenever the BG is bright enough. BTW, I'm keying HDV (m2t) rendered as an uncompressed AVI, 16 bit project, and Keylight. Also, before keying, I have added a channel blur and blurred the R and B channels 1 pixel while retaining edges. Maybe this will help someone. Dale


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Lisa Inserra
Re: stubborn black outline artifact on chromakey
on Jan 7, 2011 at 4:02:46 am

No, you're not too late...I regularly check this post to see what people are trying. However, for the most part I've moved on to HD so I rarely have this problem anymore. My keys are flawless. Your info will be helpful, though, if I need to shoot with the older cameras for some reason.
thanks!


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