ADOBE AFTER EFFECTS: Forum Expressions Tutorials Creative Cloud

Keylight on green causes white artifacts

COW Forums : Adobe After Effects

<< PREVIOUS   •   FAQ   •   VIEW ALL   •   PRINT   •   NEXT >>
Travis DaoKeylight on green causes white artifacts
by on Nov 13, 2012 at 1:15:09 am

Hi all,

I'm keying DVCPro HD footage shot in a green studio with Keylight. The key creates some white artifacts around parts of the talent. It's most noticeable around the groin area (unfortunately) and where the arms meet the torso.

Does anyone know what is causing this and what I can do to eliminate the white artifacts?

Thanks!

TD


Return to posts index

Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 4:11:08 am

Hard to say exactly but usually when Keylight goes wrong it has something to do with the despill color correction. You can disable this part of the pipeline by using the 'Intermediate Result' instead of the 'Final Result.' Try that and see if the problem goes away.

If it does you'll need to despill your footage by another method. I like to duplicate the footage, use the Channel Mixer effect to clamp the Green values at a combination of the Red & Blue values (start at 50% Red and 50% Blue) and set this to the 'Darken' blend mode above the keyed footage. That's always given me a great result.

You may also try toggling the 'Unpremultiply Result' checkbox to see what you get.

Darby Edelen


Return to posts index

Travis DaoRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 6:17:48 am

Thanks for the response.

I tried untoggling the "Unpremultiply Result" checkbox but nothing changed.

Do you mean to adjust my Keylight values to the "Intermediate Result" and use that as the key?

I wonder if there is an issue using DVCPro HD keying with my computer. It's strange that the key would cause white artifacts just around the legs and arms. I did a search on the internet and couldn't find anyone else posting the same problem.

Thanks,
TD


Return to posts index


Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 7:04:13 am

There is a drop down that usually defaults to something like Final Result (my wording may be off there), try changing that to Intermediate Result (again, might be off there). This is the same key as the Final Result with no color correction/despill applied.

An image might help diagnose this, a project file with a still problematic frame might help even more :)

Also if you're viewing at anything but Full resolution in the Comp Viewer you should see if this also appears at Full resolution.

Darby Edelen


Return to posts index

Travis DaoRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 7:35:52 pm

I tried using Intermediate Result but it just changes the white artifact a little green. I've attached a screen shot of what I'm seeing.

4959_whiteartifacts.png.zip

I put the person on a red background so you can see the white artifacts near his groin and where his arms meet his body.

Thanks,
TD


Return to posts index

Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 7:48:26 pm

Lower your Screen Despot Black value. This runs a Median (smoothing) operation on parts of the matte. What you're seeing is the smoothing of the sharp angles in the man's pits/groin.

Darby Edelen


Return to posts index


Travis DaoRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 8:05:29 pm

Funny you say that I was playing with that setting when you responded. It's already set to 0.0 unfortunately I can't set negative values. If I increase it a gray band extends from his groin. Do you know of any other way I can remove it?

Thanks,
TD


Return to posts index

Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 9:13:49 pm

Reset your values to default, except the screen color, and let us know if you still see it. If not then it's one of the screen settings, screen pre-blur maybe, otherwise it looks more like a footage problem.

Darby Edelen


Return to posts index

Travis DaoRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 11:34:05 pm

You're right it is one of the screen settings. I reset the other values and it came down to screen pre-blur and the clip black settings as the culprits. I can lose the white artifacts but then I lose some of the person. He's standing in front of a grid with two shades of green (unfortunately there was nothing I could have done about it). That's probably what's causing me these issues with the key. How would you go about keying someone in front of two shades of green?

Thanks for your help you've really helped me along.

TD


Return to posts index


Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 13, 2012 at 11:53:12 pm

[Travis Dao] "How would you go about keying someone in front of two shades of green?"

Well, that definitely complicates things :) I'd start by trying to treat them separately. Duplicate the footage, create a mask for each shade of the screen with some overlap in the center then key each instance separately. The overlapping area will be the hardest to manage. To get a clean edge it might require some fairly gnarly roto work.

Darby Edelen


Return to posts index

Travis DaoRe: Keylight on green causes white artifacts
by on Nov 14, 2012 at 7:13:23 pm

There's a grid behind him with two shades of green and then his lower half is in front a third shade of green. I tried keying out each shade of green separately, pre-comping those layers, then luma matting it with the original footage but he looked greenish. My current work-around is to adjust the key so there are no white artifacts (but i lose some of his face) then do a separate key on his head and mask that over. Probably not the most elegant solution but the video is an hour long and I really don't want to rotoscope it!

This is probably a no brainer but I guess I should lose the grid next time we tape.

Thanks for your help.
TD


Return to posts index

Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 14, 2012 at 7:27:59 pm

[Travis Dao] " My current work-around is to adjust the key so there are no white artifacts (but i lose some of his face) then do a separate key on his head and mask that over."

Sounds workable.

Another suggestion is to consider the keying process as it's own discrete process the only purpose of which is to get a good alpha. It doesn't matter if the guy looks purple, orange or yellow at the end of that process. You can always go back to the original RGB, clean up the spill and matte it with the keyed alpha.

Darby Edelen


Return to posts index


Travis DaoRe: Keylight on green causes white artifacts
by on Nov 15, 2012 at 1:22:35 am

This sounds like a good suggestion. To clean up the spill do you mean to use spill suppressor? I played around with screen gain/balance in Keylight and got some decent results.

Thanks,
TD


Return to posts index

Darby EdelenRe: Keylight on green causes white artifacts
by on Nov 15, 2012 at 2:32:40 am

[Travis Dao] "To clean up the spill do you mean to use spill suppressor?"

I find AE's spill suppressor very limiting.

Here's a sure fire way to get rid of spill. Duplicate the keyed footage, remove any other effects so you have the source, add Channel Mixer and set the Green channel to a 50/50 split of Red and Blue. Now put this layer above the keyed footage and set it to the Darken blend mode. You'll also need to clip the layer to the keyed footage either by using a track matte, set matte or preserve transparency.

Here's an image that shows a simple set up.



Darby Edelen


Return to posts index

Dave LaRondeRe: Keylight on green causes white artifacts
by on Nov 15, 2012 at 7:08:28 pm

Hey, that's a neat trick. It's going into my cache of other neat tricks.

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


Return to posts index


Travis DaoRe: Keylight on green causes white artifacts
by on Nov 15, 2012 at 7:29:33 pm

That is a very cool trick. Thanks!

TD


Return to posts index

Dave LaRondeRe: Keylight on green causes white artifacts
by on Nov 14, 2012 at 5:38:43 pm

Jeez, the guy looks like Jim Boeheim.

If Keylight won't work properly -- and it's tough to know if it will because there's no "before" frame to see the non-keyed shot -- you could use Rotobrush to eliminate the tiny-little white areas.

You could also animate some garbage masks on multiple instances of the shot and make the key a little tighter in the problem areas.

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


Return to posts index

Travis DaoRe: Keylight on green causes white artifacts
by on Nov 14, 2012 at 7:20:52 pm

There are three shades of green behind him and the video is about an hour long. I don't really want to animate masks or rotoscope for the full hour. I thought I could key out each shade of green and use that as luma matte but he ends up greenish.

Thanks for the advice,
TD


Return to posts index

Dave LaRondeRe: Keylight on green causes white artifacts
by on Nov 14, 2012 at 7:29:31 pm

After Effects has a Spill Suppressor effect, you know.....

I'd agree you shot against a bad background for keying.

And without knowing basic things like how the shot was lit, the distance between subject and background and the codec in which the shot was recorded, no one can truly say if it was the fault of the background or the fault of the shot planning.

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


Return to posts index

Travis DaoRe: Keylight on green causes white artifacts
by on Nov 15, 2012 at 1:24:48 am

I think the shot was well lit and the distance between subject and background was adequate. The three shades of green is the main problem. It was recorded in DVCPro HD is that a good codec for keying?

Thanks,
TD


Return to posts index

Dave LaRondeRe: Keylight on green causes white artifacts
by on Nov 15, 2012 at 7:03:36 pm

Yup, DVCPro HD is good; it has 4:2:2 color resolution, and you can pull a good key. So I'd agree that the background is the culprit.

If you think of a TV picture as having a B&W layer with a color layer over it, 4:4:4 is the best; there there's a color pixel for every B&W pixel.

H.24 -- used by many DSLR's -- is 4:2:0. Half the color resolution of 4:2:2, and a quarter of the resolution of 4:4:4. Ugh.

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


Return to posts index

<< PREVIOUS   •   VIEW ALL   •   PRINT   •   NEXT >>
© 2017 CreativeCOW.net All Rights Reserved
[TOP]