The Advanced Art of Stop-Motion Animation: Visual Effects - Part 2
One of the challenges of shooting with a blue or green screen is the complete removal of the screen’s color from around the animated subject. Often, there may be issues with the green reflecting onto the puppet or remaining as a thin layer around the edges. With today’s digital tools, though, there are ways to deal with this. Removing the color from most of the frame around the subject is the easiest part. Depending on the software, this is usually done by selecting the color (typically with an eye-dropper tool) and hitting a button or adjusting a tolerance slider to wipe it out of the frame. In After Effects, a plug-in called Keylight is commonly used, and Combustion uses a function called the Diamond Keyer for the general removal of the green (Figures 9.28 and 9.29). Once most of the green is keyed out, there will often still be a thin rim of green around the edges of the subject (Figure 9.30). Some additional keying tools can be used for fine tuning the keying out of this remaining color. In Combustion, for example, these tools include the Discreet Keyer and suppressing the green color on the color map (Figure 9.31). To create further atmosphere once the background is comped in behind the puppet, a blur can be added to help create the illusion of a shallow depth of field (Figures 9.32 and 9.33). (Compositing and screen captures for Figures 9.28 to 9.33 courtesy of Shawn Tilling.)
Shooting any object or stop-motion puppet with a color behind it for keying also allows for simple re-sizing and moving of that object into any part of the screen for compositing with other elements. The background that is composited behind the keyed-out animation frames can be a still photograph, a painting, or any type of imagery. A particularly unique use of green-screen compositing was used on a short student film called For Sock’s Sake, made by animator Carlo Vogele at CalArts. The film uses real clothing, like pants, socks, and shirts, as a cast of characters who go on a journey to save a runaway sock. Carlo shot real clothes on a flat green screen with a digital still camera pointing down from above (Figure 9.34). To move the clothes, he placed magnets inside them and moved matching magnets underneath the green panel, which allowed them to be moved without breaking the continuity of the fabric’s folds and wrinkles. The backgrounds were drawn in Photoshop with photo collage and digital drawing, and the animated clothes were composited into them with After Effects (Figure 9.35). The film can be seen on Carlo’s blog (http://carlovogele.blogspot.com).