H.P. - Inserting Extras VFX

We had enough extras in our performance section, in fact at one point we thought we may have too many to manage, but it worked out fine in the end. So there was no necessity to add in extras with VFX, this post is about something we did purely because we felt like testing a new skill and letting a friend who was unable to make it to filming get into the footage.

I'm going to break down this one second of footage to show all of the processes required to complete this seemingly simple task. All processes took place in Adobe After Effects CS6.

The Process

Starting with the original footage, I identified a spot between two extras which would accommodate another person. I then found some footage of my friend from a previous social event and stabilized the camera with Warp Stabilizer, completely removing handheld camera movement. 

I then began to Rotoscope the person. This is a process by which you essentially cut out an object in your footage, removing it from its background. I used After Effects' Roto Brush Tool, a powerful part of the program which allows you to make brush strokes over the area you want to keep and the area you wish to remove. The program does a pretty good job of tracking this object, but due to the motion blur in the footage I found that I had to manually adjust most frames in order to get a clean cut.

After I had completed this I scaled the image down to a size more in line with the other extras in the scene. After this I began to adjust the look of the footage to match the look of the rest of the film. I started by changing the colour of his jacket to black using the Change to Color effect. Then with curves I made the whole image much darker as I was placing him into a shaded area behind the other extras. Minor adjustments to the look were made with a warm Photo Filter, Hue/Saturation adjustment and an Optical Flare placed to his left to create a brighter highlight on that side, as the other extras in the scene are all lit from their right.

I made more visual adjustments with Brightness/Contrast and a Camera Lens Blur to match the focus of the rest of the image, which was not entirely clear. The next step was very important. Using the Match Grain effect, I applied visible camera grain to the image to match that caused by the high ISO of the rest of the footage. I had to make a few manual adjustments to the grain here as the automatic process struggled to get it right. I finished the visual adjustments with another instance of Curves and another Hue/Saturation Adjustment. 

Next I had to place my friend behind the other extras. I duplicated the base footage of the other extras and placed this footage over the footage of my friend. Then using the Masking Tool I cut a hole between two of the extras and adjusted this shape frame by frame to match their movement and the movement of the camera. My friend is now behind the other extras, however he did not move with the movement of the camera, breaking any realism in the effect.

To fix this I used After Effects' inbuilt 3D Camera Tracker to generate a number of tracking points in the footage. I chose a point on one of the extras and created a Null Object and Camera attached to this point. Using the Whip tool I told the footage of my friend to follow the movement defined by the Null Object and I converted the layer into a 3D Object.

The finished effect is brief, intentionally unnoticeable and serves no further purpose than to advance a skill and get my friend into the finished film, but I see that as fair enough reason to test the effect.