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keying, masking, replacing with flames

Posted: Mon, 18th Jan 2010, 7:58pm

Post 1 of 9

khobar95

Force: 1000 | Joined: 30th Dec 2009 | Posts: 16

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Earlier today I shot video of my son doing karate moves against a blue screen. I captured the footage in Edius Neo and then exported it as lossless AVI. I was very pleased to see that FxHome opened the file.

I applied an auto color difference key and it knocked out the blue very nicely. But I actually wanted the inverse of this, so I selected "invert selection: on". This put the blue back and removed my son. I then put "inferno" behind the clip and see flames where my son was. Okay, that's progress.

Now I want to replace the remaining blue with a different background. However, when I do, the "inferno" layer shows through the whole thing.

One thought that comes to mind - render the clip with the inferno and blue in place, then bring that in as a clip and then key on the blue. Any other way to do it in one pass?
Posted: Mon, 18th Jan 2010, 10:37pm

Post 2 of 9

Axeman

Force: 17995 | Joined: 20th Jan 2002 | Posts: 6124

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SuperUser

Use an Object mask to apply the alpha info from the bluescreen clip to the inferno layer. Apply the Object mask to the Inferno layer, then select the bluescreen clip as the alpha source.
Posted: Mon, 18th Jan 2010, 11:45pm

Post 3 of 9

khobar95

Force: 1000 | Joined: 30th Dec 2009 | Posts: 16

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Hi Axeman and thanks.

I'm messing it up somewhere.

I have my bluescreen clip, karate_blue. I applied the color diff key and invert the result. This leaves the blue and removes my son.

On the "Flaming Death v2.0" (not inferno as I had said, sorry), I change the object mask to use "karate_blue" as the source, but nothing seems to happen. However, if I turn "Invert shape" to on, then I see flames in the black area where my son was removed from. This is the same result as when I don't use the object mask (which would seem to indicate I'm already missing something?).

If I add another color diff key to karate_blue, then the blue gets replaced with "Flaming Death" and the original mask doesn't seem to do anything.

What am I doing wrong?
Posted: Tue, 19th Jan 2010, 12:47am

Post 4 of 9

khobar95

Force: 1000 | Joined: 30th Dec 2009 | Posts: 16

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Uh, hmm...for grins I swapped the order of the tracks - the "flaming death" track is now above the karate_blue track and the results are, well, different (much closer to what I'm wanting). Seems to now be a combination of my son and flames.

Placing another plate underneath/below everything reveals the mask has transparency.

I think I'm making progress though.
Posted: Tue, 19th Jan 2010, 3:31am

Post 5 of 9

khobar95

Force: 1000 | Joined: 30th Dec 2009 | Posts: 16

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Okay, I've discovered something is screwy. In FxHome the results look absolutely perfect, but when I open the resulting render in Quicktime it looks awful - wrong aspect ratio and lots of artifacts.

Compare: http://i120.photobucket.com/albums/o183/khobar/matthew_flames1.jpg
and: http://i120.photobucket.com/albums/o183/khobar/matthew_flames2.jpg

Saved using Quicktime "Animation", millions of colors+, 100% quality.

Arg - I rendered to .png and it also looks perfect.

Okay, don't preserve alpha channel.

But what about the aspect ratio?
Posted: Tue, 19th Jan 2010, 9:48am

Post 6 of 9

Simon K Jones

Force: 27955 | Joined: 1st Jan 2002 | Posts: 11683

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FXhome Team Member

The artefacts might be highlighted due to the alpha channel, which won't be displayed correctly inside Quicktime Player. However, it does look like the key need a bit of tweaking.

In your editing program, you should be able to manually set the aspect ratio of the clip to 16:9, which will make it display correctly.
Posted: Wed, 20th Jan 2010, 12:31am

Post 7 of 9

khobar95

Force: 1000 | Joined: 30th Dec 2009 | Posts: 16

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Thanks Tarn,

The alpha channel does look a little noisy. I changed from "auto color difference" to "color difference" and tweaked the black and white settings and that seems to have helped a lot.

As for the aspect ratio, I'm sure I can fix that.

Can I use the "object mask" from the source clip *on itself*? Once I remove the blue and isolate my son, can I not use that to produce an "exact fit" garbage matte that would cut out every undesirable artifact? What I'm having to do at the moment is use a square garbage matte and move it around to avoid a couple of spots where artifacts still exist. While this seems to work okay, it's not perfect.
Posted: Wed, 20th Jan 2010, 9:30am

Post 8 of 9

Axeman

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SuperUser

Any artifacts left by the key will be in the alpha channel. An Object Mask using the same alpha channel won't help remove them. that is the purpose of having garbage mattes.
Posted: Wed, 20th Jan 2010, 4:59pm

Post 9 of 9

khobar95

Force: 1000 | Joined: 30th Dec 2009 | Posts: 16

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Gold Member

Thanks.

I came to that same conclusion late last night. I'll do better next time on the setup.

On the plus side, I was able to improve the overall matte. Learning something new each day.