'An American Girl: McKenna Shoots for the Stars' VFX - Wire Removal

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Some of the most difficult effects are what appear to be simple. This is the case of wire removal shots. The idea is that in production something needs to move on screen by an unseen hand. That is when 'wire' is used to essentially puppet a normally inanimate object from off screen.


There are certain techniques which are used when shooting to make the wire as invisible as possible as it's being filmed, so that extra work won't have to be done in post production to 'remove' it from the shots. This is in deciding to use monofilament, black thread or white thread in relation to the lighting and the background. Or using as little wire as possible, or dressing the wire behind set objects to hide the length and origin. All of these are basic techniques to make life more simple and none of these techniques were used when filming this movie.


Now, to understand the complexity of problems that occur with wires in the shot, it is important to note that in all shots, the camera and/or the wire is moving. This means that you cannot just paint out a simple straight line because it has to match from frame to frame, 24 frames per second, and any little hiccup in the grain pattern or background texture in even one single frame is going to draw your attention. This means that very large sections of background have to be fabricated, motion tracked, and matted for the entire length of the shot, even if the wire is only visible for a few frames. Then there is how the wires effect light and even cast shadows. All of that needs to be corrected as well.


The best example of complexity was the original wide shot that included 4 different wires (why the hell were there 4 different instances of wires? I AM SERIOUSLY ASKING THIS!), moving horses in front of, and behind the wires. Moving tracking shot with out of focus foreground matting, and varying instances of background depth that eliminated the possibility of consistent tracking in different parts of the frame. This took my entire bag of tricks even down to hand rotoscoping the distant horse's hooves to remove the wire in front of them, frame by frame.


Cry me a river.