Sky Replacement

[Dynamite23]

Hi guys!

My name is Stephan and i`m from Austria. I`m very new to AE and try a few things and tutorials with my own footage.

And there i got one problem.

I have an short clip and wanted to try the newest tutorial to add dark clouds an rain into an almost blue sky.

My problem now is, the sky is greyish blue and not that white like in the tutorial. I`m not able to make a clean matte because the color of the sky is also in other parts of the shot.

I tried to key the color but there are a view palms and flags in the foreground an keying doesn`t work clean enough.

Could someone help me?

[gregalan]

Hi Stephan, welcome. Getting a clean matt is one of the most difficult things to do, especially if you are trying to key out something like a sky, and every shot is different so there is no magic answer. This is one of many ways (none of them perfect, but this one is fairly simple to explain) and see if it works with your shot.
Duplicate the footage and make a mask on the top layer so that you cut out all the sky part (you'll probably have your flag and bits of palm tree, horizon etc. cut out as well - you can turn off the eye icon on the lower layer so that you can't see it while your drawing the mask if that helps, but turn it back on when you've finished).
On the lower layer (the sky one) add Effects/Keying/Color Key. Use its eydropper to select the darkest bit of sky and increase the color tolerence to no more than 50% . Then repeat that another 2or 3 times selecting the darkest color that is still left until the sky has disappeared - you will end up with 3 or 4 or more Color Key plugins in a row. Then add Effects/Keying/Spill Suppressor at the bottom of the Color Keys and use its eyedropper to select the color that is in the box of the first Color Key.
You might find it useful to make a black solid as the lowest layer so that you can see what bits of sky are disappearing - as well as if anything else is disappearing like bits of your flag (in which case make the color tolerance lower).
You can play with the settings to get it as clean as possible - but it's unlikely it will ever be perfect.
Let us know how you get on, or post an image of the actual footage if you're still having trouble.

EDIT: You can then just add your cloud layer as the lowest layer - I think the tutorial does it a different way? How stupid am I

[Dynamite23]

Thank you very much for this detailed answer!
I try this and will post an answer when i gut my result (or not).

Here is an image from the movie so you can see that the color of the sky is very near the color of the street in the background.

[gregalan]

Hi Dynamite23, thanks for the shot. Mmmmmmm. I've had a play with it and come up with not good results as there are so many greys in the pipes, etc. You might want to forget the Spill Suppressor and add a Simple Choker. The other thought, if it's a fixed shot from a tripod, would be to mask out the sky areas individually, but it's certainly not an easy one.