sky matt painting (replace the sky)

[Anonymous]

I got project coming up that would require me to do sky matts.
By “doing” sky I need to live them up a bit and I may need to fill some
holes my self (in the new sky matt painting).
I do sky replacments like living old horizon a bit and then using soft matte to transition from old to new sky. But, Im just not happy with it.
In most cases I am, but if the shot has a slower almost still move and its
longer then 2 sec I find it… not a live enough. If you can understand what
I mean : )
Any tips, info, help would be great.

Thanx for help,
Kiki

[John Montgomery]

A lot of the time, I simply replace the whole sky from high resolution digital stills which I have. I then use shearing in x, with the axis center placed at the horizon to fake a little bit of movement in the sky. You can also use a bilinear to enlarge the clouds near the top of the frame while keeping them smaller towards the horizon. This helps with perspective issues. Play around with the amount of movement to maintain a “realistic” look

Regraining to match the original scene is also critical. As is tracking your clouds to the original scene…that is even if it is a static shot — match the film ride.

Also pay attention to the qualities of the telecine scene — is the sky already blown out? If it is, you should maintain realism by keeping your sky a bit blown out. This is because the edges of your matte won’t look correct if you replace a bright sky with a much darker sky…they’ll be all rounded and blown out (which would not occur if foreground objects were blending to a darker sky). Whenever I know I’m doing sky replacements, I’ll ask for a corrected pass as well as a flat pass where the sky isn’t blown out. This way, I can more accurate blend the fgd with the sky (maybe by using the edges from the darker pass intgrated with the lighter hereo pass). It is certaily a pet peeve of mine, but I hate seeing totally obvious sky replacements (aka rounded edge borders or white rimming around fgd objects).

[Anonymous]

Scew on x and bilinear scaling the top 😉 thats the things I didnt think of. Thanks, Great tips!

I usualy get two color Passes from Telecine. One, Subject CC and then Sky CC. Subject is almost always on burned sky Great for luma key but bad for later sky replacement. I always fight with White halo and trying to minimaze it as much as I can.
Thanx 😛

[John Montgomery]

If you are using flame, a great way to help workaround the halo problem is to use the MK and edge tool….you can isolate the edges using a color blend node and treat them separately. By making the edge blend soft, you can easily blend it to the foreground pass.

so then you have:

1. Your sky
2. Key your foreground back in, foreground made up of:
a. foreground pass
b. edge pass, which is a brightened color corrected dark sky pass
(the foreground matte would be generated from the darker sky pass)
[/list]

[Anonymous]

Im actualy using Smoke but Its just a bit more work, use Edge detect on Alfa (or blurr and then exclude from original) then use that as alfa for CC darker sky 🙂

Thank you very much,
Kiki 😛

[sinancg]

another point that can help at the edges is, changing the blend mode. if the version of smoke you are using supports blending modes try max (or min, sorry I am not at the box now). this helps a lot at the edges.

hope this helps

sinan

[Anonymous]

I will try that in a minute. I worked on one close up shot with woman’s hair flying on wind and its very narrow dof so when hair is in front its sharp and gets defocused while moving in the back and all that on burned sky. Good for keying was my first thought. In the end director simply didn’t like how it turned out even do I think its good. Hair detail is there the only part I think is still a question was the last 3 frames where hair moves far in to defocus.

Ahh…maybe I should export the clip and let you guys here give it a try.

[Author]

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