Sky Replacement

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OVERVIEW

Sometimes it is useful to know how to replace or augment the sky in our footage. For example, you can change the weather, turn a gray sky to cloudy blue, change the time of day, add sci-fi moons, eclipses, etc.

Very generally, “sky replacement” involves
(a) matching one or more new sky layers to the motion of the original footage,
(b) performing masking so that the new sky doesn’t overlap the ground, and
(c) color correction to match everything up.

“Keying” and “Track Matte”  
If you can easily separate the original sky from the ground with keying tools(e.g., Keylight, Luma Key, Extract, etc) then you can use the silhouette of either the ground or sky for masking other layers. In After Effects this is called using a Track Matte.

In simpler shots you can use simple mask shape animation to separate the sky from the ground. Sometimes basic 2D motion tracking is all that’s needed.

1. Removing The Original Sky

Masking

Keying

Track Matte

2. Tracking The Motion Of The Original Shot

Basic 2D Tracking

3D Camera Tracking

 

3. Color Correction

Levels effect

Curves effect

Hue/Saturation