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Troublesome Sky Replacement

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Chris Wood
Troublesome Sky Replacement
on Apr 28, 2012 at 3:38:25 pm

Man, my posts are racking up! Apologies.. At least it helps other people too if they have the same problem. You'll all get a shout out in my film!



So I have this footage shot on top of the Malverns. Take a look:

http://img193.imageshack.us/img193/6086/mvi221900258.jpg

Trouble is, the side of the actors face on the right (Jon) is blown out a bit. This means that when I try to remove the sky using a Luma key, it removes a big chunk of his head, the other actors hands and parts of the path.

Yes, I realise the tripod is there, it's for tracking ;)


Aaanyway. I've tried a few different approaches to removing the sky with no luck. Now my student deadline is coming up next Thursday and I still have plenty of shots to do, I'm panicking!

Does anybody know of a good technique to seperate the foreground (the actors and the hill they are stood on) from the background and the sky?


Thank you very much.


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Declan Smith
Re: Troublesome Sky Replacement
on Apr 28, 2012 at 4:47:35 pm

Hi Chris,
Without seeing the whole shot in motion it's difficult to say, but I would look to use something like the rotobrush or just a plain animated mask on a copy of the footage to preserve the details that get lost with the Luma keyed footage, then put that layer on top of your keyed footage.

Declan Smith
http://www.madpanic.tv
After Effects CS5.5/ FCS3 / Canon 7D / Canon XL2 / Reason / Cubase

"it's either binary or it's not"


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 28, 2012 at 5:56:10 pm

Here's the whole shot:

http://www.mediafire.com/?72u8v3yyveb44ho


It's 137 frames.


Let me know if you have any suggestions. Thank you.


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Declan Smith
Re: Troublesome Sky Replacement
on Apr 28, 2012 at 8:48:11 pm

Hi,

This is doable.

1. Stabalize the shot then make 3 copies
2. The lower copy, draw a mask around the hill edge that you want to keep (shown in blue below). Note I did a rough mask in the screen grab.
3. On the next layer up, use the rotobrush and roto the left actor
4. On the top layer, use the rotobrush and roto the right actor. On both of these you need only roto the parts of the actors that go above the horizon.



Now drop in the sky / background of choice. You may need to add some choke to the rotobrush layers to fine tune the edges.

Declan Smith
http://www.madpanic.tv
After Effects CS5.5/ FCS3 / Canon 7D / Canon XL2 / Reason / Cubase

"it's either binary or it's not"


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 28, 2012 at 9:04:58 pm

Hi Declan,

Much Appreciated. I just roto'd the footage as is though.


A side effect, my AE now seems to be extremely unresponsive once I have Rotobrush applied. I don't recall it being this sluggish before. It's abnormally sluggish for my i5 Quad core, 8GB RAM machine.

Even with no other comps open and no other layers, just selecting the layer makes it go slow.


Here is my current progress.

I just need to soften the edges of the hills, add a nice shadow for the stone, make the background look more natural, then finally colour correct!


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 28, 2012 at 9:05:19 pm

No way to edit -___-

https://vimeo.com/41211547


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Tudor "Ted" Jelescu
Re: Troublesome Sky Replacement
on Apr 29, 2012 at 7:10:08 pm

I did a little test- about 20 min of work. If you duplicate the layer- precomp and crush blacks to make the image contrasty enough in the precomp- roto brush does a pretty good job of picking up the foreground with the two actors. A bit of tweaking for the matte edge, short track, comping the pillar (or whatever that may be- pardon my lack of knowledge on the subject)with blacks cut to match the plate and whites a bit brighter and you have a decent replacement. The background plate for the new sky/mountains should be adjusted to where the edge on the right of the foreground almost blends in with it.
Of course the tracking should be better and the shadow adjusted + a patch to cover the tripod shadow, but not bad me thinks.
4051_malvernhillfatherhiredtj.mp4.zip

Tudor "Ted" Jelescu
Senior VFX Artist


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 29, 2012 at 7:27:31 pm

Nice one Ted (hope you don't mind the use of the nickname)


I'm going to start again from scratch as I hadn't used Rotobrush before, so I think I can get better results. I'm sure I did something wrong as it really is unnaturally sluggish once Rotobrush is turned on, there's a purple dialogue box that says make sure something is turned off for the best results.. I don't know..


Anyway, this is good for hand in, more or less. I'm just going to concentrate on the other shots.

However, the shadow. I can't get it to look right. I've rendered out a shadow in Cinema 4D but its just making it look good is the problem. I can't seem to mimic nature here. The natural shadow is quite sharp and it seems to mute the colours nicely. Any shadow I make just looks like a black mess on the screen, like a burn mark. I can't make it look real :(

Thanks


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Tudor "Ted" Jelescu
Re: Troublesome Sky Replacement
on Apr 29, 2012 at 8:08:38 pm

Yep- shadows are messy to deal with. My suggestion is to place the stone pillar a bit more in front of the guy in the back, thus making it lower in the frame, blow up the image 10% and position it as low on the y axis as possible- this way you cut the shadow in half. Since you have a simple shape, I suggest using a solid that is the same gray as the darkest gray in the image (excluding the character in front that walks in) with 90% transparency. Mask the shape of the shadow and feather 2-5 pixels. That should do the trick.

Tudor "Ted" Jelescu
Senior VFX Artist


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 29, 2012 at 8:28:47 pm

Due to my film being an adaptation of the source material, I kinda have to have this Standing Stone be about 6-7 feet high. I don't think I'll be able to place it behind the actor on that axis. I'll keep in mind what you said about the shadows though, Danke.


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Tudor "Ted" Jelescu
Re: Troublesome Sky Replacement
on Apr 29, 2012 at 8:56:50 pm

Maybe I was not clear- not behind he actor- just lower it in the frame- giving the impression that is closer to the camera, and enlarge the elements in the comp by 7-10%. This will bring the base of the Standing Stone under the bottom of the frame eliminating the need for a shadow and making (in my opinion a better looking composition.

Tudor "Ted" Jelescu
Senior VFX Artist


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 29, 2012 at 10:04:53 pm

Hi Ted, could I possibly have the settings you used for the Rotobrush? I'm having trouble getting a decent roto unfortunately.

Thanks.


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Chris Wright
Re: Troublesome Sky Replacement
on Apr 30, 2012 at 2:04:04 am

you should definitely read up on the rotobrush. It's not intuitive per se.

http://help.adobe.com/en_US/aftereffects/cs/using/WS3bf812c123007fb8513559d...

-----------

as another random experiment, I layered 3 linear color keys on top of each other.
one RGB
one Hue
one Chroma

they worked together to key out the white without any roto. I also experimented with using timewarp to act like the rotobrush's chatter reduce feature. It seemed to work well. And hey, who can argue with zero roto work right?


AE cs3 aep
http://www.mediafire.com/?6mzb25m2ndxku3i


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 30, 2012 at 8:31:34 am

Yeah I did read that and found it quite helpful.

The trouble is that I'm getting a lot of boiling on the edge of the hills in the centre and on the right. My friend looked at the video and said that it looks like heat waves coming off the ground from a formula one race.


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Tudor "Ted" Jelescu
Re: Troublesome Sky Replacement
on Apr 30, 2012 at 8:30:50 am

I did not see this till now- I'm away from my machine- I can post the project when I get back.

Tudor "Ted" Jelescu
Senior VFX Artist


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 30, 2012 at 7:32:17 pm

Thanks, I look forward to getting this shot done! And then it's the next shot :( Haha.. What have I gotten myself into?


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Tudor "Ted" Jelescu
Re: Troublesome Sky Replacement
on Apr 30, 2012 at 10:07:39 pm

Here's the project file (CS 5.5)- replace with your footage and your sky plate.
4058_skyreplacetest01.aep.zip

Tudor "Ted" Jelescu
Senior VFX Artist


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Chris Wood
Re: Troublesome Sky Replacement
on Apr 30, 2012 at 10:41:28 pm

Primo. Rest assured I will learn from it, and not just use it mindlessly.

Thank you!


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