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keying problem with bright sky

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Andi Wand
keying problem with bright sky
on Jan 12, 2010 at 12:09:15 pm

Hi,

I have some footage where the sky must be keyed, but I don't get any good results at all. A sample is attached, unfortunately it was sized down, but if anybody wants to try his/her hands on it I could send it in full resolution via Email.
keyingsample
I tried all the keys there is in AFX, so far I got the best results with stacking several Color-Keys on another and set the tolerance to a low value. BUT even with low tolerance values some parts of the arm and the bracelets get effected by the keys as well so that I get 'holes' where I don't want them.

How would you approach that?, any idea is highly appreciated!

Thanks, Andi


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adam taylor
Re: keying problem with bright sky
on Jan 12, 2010 at 2:06:49 pm

your problem is the shiny bangles are actually reflecting the sky, and so your keys are actually doing their job correctly...they are removing all your sky!

What you will need to do is mask the areas where the sky needs to remain (Rotoscoping). As the girl looks to be dancing, then i'm sorry to say you will have to do a lot of rotoscoping. Its a good skill to learn, so don't be too disheartened.

Adam Taylor
Video Editor/Audio Mixer/ Compositor/Motion GFX/Barista
Character Options Ltd
Oldham, UK

http://www.sculptedbliss.co.uk


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Andi Wand
Re: keying problem with bright sky
on Jan 12, 2010 at 3:36:28 pm

Thanks for the reply, that's exactly what I'm doing but I'm only half way through and it's takes ages. I thought there might be a trick I couldn't think of (I'm still relatively new to AFX). But I had an idea, which makes things a little easier (unfortunately I just got it when I was already halfway through). The major problem is where the sky is nearly white or completly white, so I came up with the idea, to put a white layer with a rough mask underneath, so that I don't have to care about anything on the green ('lawn'). As the camera moves it has to be attached to the tracked layer above (which I have to do anyway, as the sky replacement has to follow the camera movements). Now, the only parts which I have to take care of are the parts close to the horizon and in the sky (when she raises her arms for example). Still a lot of work, but better than before.

Thanks so far,
Andi


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Andi Wand
next keying problem - the treeline
on Jan 13, 2010 at 1:20:39 pm

Hi,

after I made my way through all that masking yesterday, I'm facing the next keying problem - the treeline.
keyingproblem2treeline
I tried several ways with different keys, including changing colors drastically and use that drastically changed picture (sky more or less completely yellow-greenish, rest nearly completely black) to key with keylight and use that as alphamask for the original footage. the screen matte looks actually fine to me, but the final result isn't as good as I hoped. I still get that white-bluish spill around the treetops.

Any advice what I could try?

Thanks again, Andi


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adam taylor
Re: next keying problem - the treeline
on Jan 13, 2010 at 2:19:14 pm

i think whatever method you use will be a compromise. I am guessing the material was shot dv or hdv? Its hard to tell from the very small sample image, but it looks like you are getting the blockiness in the tree that is indicative of low bit rate color sampling. Its very difficult to get a good key using that video format.

You should find some good tutorials for dealing with dv keys in the tutorial section (Aharon Rabinowitz's stuff is certainly worth watching.

What are you replacing the sky with?
You would be better to put the replacement in place to see how they play together, and then decide how to cure the problem. It will always look bad on black, but the replacement might not be as noticeable, especially with some blending.

The other option is to crop out the treetops all together. I was going to suggest replacing them with graphic trees that have been alpha channelled, but as your source footage was shot with that fisheye lens, then you would have a nightmare trying to replicate the lens distortion...but then again, you will probably have to do that anyway on the sky replacement, otherwise your sky will not look right.

thats quite some task you have ... good luck
adam


Adam Taylor
Video Editor/Audio Mixer/ Compositor/Motion GFX/Barista
Character Options Ltd
Oldham, UK

http://www.sculptedbliss.co.uk


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Andi Wand
Re: next keying problem - the treeline
on Jan 13, 2010 at 6:40:35 pm

Hi Adam,

the footage is red 32bit (or whatever it's capable of)material, so it's actually not bad. But that reminds me of changing the color-bit-setting, that might give a slightly better result.
the sky is supposed to be replaced with a night sky with stars. So the background will be black, which is actually the problem. If it only would be some fluffy clouds or something of that kind it wouldn't be that bad. Well, probably I have to put something bright behind it, like the milky way :D. It's supposed to have kind of an arty/ surreal air about it, so I could do that.
Cropping out treetops isn't a bad idea, actually. I will think about it. The perspective won't be that difficult, as the they are in the far back. It's rather the girl, which is dancing all the time.. On the other hand I have to key her quite carefully anyway.. If the milky way looks crappy, i will give it a try.

Thanks for the good ideas,
Andi


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adam taylor
Re: next keying problem - the treeline
on Jan 14, 2010 at 9:30:28 am

okay - must have been the compression on the little image you posted. Red stuff should look good if sll the hype is to be believed (not worked with any myself).

Another possible you might want to try is to add some small coloured light effects - as if lanterns were hanging in the trees. Use something like Trapcode Lux to add a small amount of volumetric lighting and perhaps experiment with blending modes to bounce the light of nearby objects (such as the trees).

adam

Adam Taylor
Video Editor/Audio Mixer/ Compositor/Motion GFX/Barista
Character Options Ltd
Oldham, UK

http://www.sculptedbliss.co.uk


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Dave LaRonde
Re: keying problem with bright sky
on Jan 13, 2010 at 3:45:18 pm

It appears you're going to learn a hard lesson with this shot. It happens to a lot of people. And the lesson is this:

Dave's Stock Answer #2:

When you're out on a shoot, and you say, "we'll fix this in post" without knowing PRECISELY HOW you're going to fix it in post, don't shoot it! You'll only end up shooting it over again.

Since post typically costs three times the cost of production, fixing something in post is not a way to save money, but rather a way to spend more of it.

And, before you say "well fix it in post," always consider who's doing the work, especially if you're the one doing the work.


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


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Andi Wand
Re: keying problem with bright sky
on Jan 13, 2010 at 7:02:59 pm

Thanks for the support, Dave :). But I didn't shoot that, I'm the guy who is supposed to fix it. But well, fix it, doesn't fit actually; what could they possibly have done? It had to be at that particular spot and it had to be at daytime. cutting down the trees would have been the only option, which really isn't any. I guess the guys had already enough trouble getting onlookers out of the picture (this was shot in Delhi, where nearly every square inch is inhabited).

Well, I think I have to find a way to handle it, that's the only option.

Andi


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