How to Use Chroma Key Paint
Chroma key paint is a great way to quickly create a green screen in a studio or location. It can also be used for painting objects needed in the shot that will be removed later. It's one of the most important tools that you can have in your special effects bag of tricks. But chroma key paint is only useful when it's being used properly.
Getting the Right Paint
Chroma key paint is a special paint made for the purposes of aiding in chroma key shots. These paints are available in one gallon cans. You can also get them in spray paint form as well for detailing. Most chroma key paint is green but you can also find it in blue. It is very important that you only use chroma key paint for chroma key effects.
Chroma keying works by isolating a specific color which is then turned transparent. Chroma key paint is matte which means that it is flat and does not reflect light. That spare can of paint in your garage most likely has some shine in it which will cause that paint to have twenty different shades of color when lit. That can be very difficult to key out. A simple search online of "chroma key paint" will direct you to where it can be purchased. It is more expensive than regular green paint but if you're going to do the job right then you need the right materials.
Go with Two Coats
Once you have the right paint it's time to start using it. You paint a green screen just like you would with anything else. Apply an even coat to the surface and allow it to dry. Once drying is complete you will add a second coat. If you painted it properly then it should appear even in color as the second coat dries.
You might have to include objects in your shot that you want to key out later. For example, let's say that a character is walking towards the camera in front of the green screen. To make the walking look real you would place the actor on a treadmill instead of having him/her walk in place. To make the treadmill invisible in the finished shot you would have to paint it green so that it can be keyed out. Obviously you want to keep the number of green objects in the shot to a minimum because each one adds new complications to the keying process because the lighting will be slightly off for each one creating a new shade of green to worry about.