Nuke Comp: Day to Night
In Nuke, I have made some Day to Night Comp using the Keyer(Luminance Key) node to help create an alpha so I can easily mask out the sky without having to Roto and animate it to save time.
Since the Keyer does not perfectly create a clean alpha, I have create a garbage mask to clean up the alpha mask. After that, I can easily change the original sky it to a night sky with star with the help of the Copy node to copy the alpha and use it as a mask. Some color correct and grading are also made to adjusted the colors to match the night scene.
Before trying it on a video, I have first tested the method on still images. The images below are done with the same method I mention previously. But in addition, I also used Roto to mask out the windows on the building, then color correct and blur to create a glow effect.
