I am a newbie to Natron and VFX. I am trying to black out the contents of a TV Set in a series of Frames, where there is an Actor who is moving on front of it (but not that much).
My approach was to use the RotoPaint/bezier tool to draw polygons (and not use the Clone Tool as it is just a circle, and need to get close to the perimeter of the actor - or can the Clone Tool work with a Bezier curve?), and have the color of the enclosed region match another pixel on screen (which would be black), so the black used matches the shade of black already on the screen.
Could someone please explain how I can do this? Or if this approach is wrong, the right way to do this?
Basically you’re trying to turn off the TV set in post? Here’s how I’d go about it:
Create a single frame “clean plate” with the TV set off. This can be done in Photoshop or Natron, wherever you like really. You just need one frame with the entire screen visible and not on. This clean plate should also be de-grained so that we can add moving grain overtop later. Once you’re done painting mask out just the screen with a roto and premult node.
Track the four corners of the TV set.
Apply that tracked movement to your single frame plate with the TV off. Now the TV off element moves like the original shot!
Add grain back to your tracked on element and match it to the original footage grain so that it looks like the source footage
Roto your characters out and plonk them back overtop the TV off element, you may have to do some finaggling of the edges if the TV was super bright and caused some light bleed onto their clothing / arms or whatever.
For bonus points add some slight specular reflections if any are present in the scene to make the TV look like a glass surface (if it is one). Be sure to match the black point of the screen that is turned off to the black point of your footage or else it will look too dark.