Chroma Key, What is it?
In plain English, chroma key photography allows you to film in front of a solid color background and then replace the solid color background with another image or movie. This is what is happening when the weather forecaster stands in front of a weather map. They are actually standing in front of a green or blue screen and the map is inserted digitally.
Wikipedia has a detailed explanation.
This used to be a complicated and time consuming process involving masking and compositing. Now it is fairly simple with either the software or the camera doing the work automatically.
Using green screen in education
2nd Grade example
At the end of a fairy tale unit, students wrote fractured fairy tales. Background scenery was drawn in KidPix and exported as a .jpg. Filming was done in front of a green bed sheet.
3rd Grade example
One option to demonstrate learning at the end of a solar system unit was to create a commercial for your planet. Students were filmed in front of a green bed sheet.
4th Grade example
Students studying the regions of the United States created top ten lists of places to visit.
5th grade examples
Students chose to create a movie on bystander behavior in front of a green screen.
Students wrote this play and filmed it outside the school day. After the filming was done and the background inserted, the students added a black and white effect to the film.
Jason Ohler provides an overview of an elementary green screen storytelling project. This is from 2006 before iMovie included green scrren functionality within the software and a plug in was required.
A quickie guide to lighting your movie for better results from Howcast.
Silvia Rosenthal Tolisano blogged about green screen digital storytelling on her Langwitches blog.
A teacher in Sheffield, England blogs about projects in their school and ho-tos for PC users, How to: Green Screen for Schools.
There is a TV show that uses student submitted writing and turns it into a Green Screen Adventure. Students can submit stories in the hopes of having them chosen to be made into a TV show.
Topics include matting and keying basics; setups using fabric, portable background panels, or paint; lighting and digital camera essentials; broadcast TV hardware switchers; professional HD and major motion picture compositing; multiple-colored screen composites (background, foregrounds, and objects); directing storyboards and talent; working with virtual sets; motion tracking; and much more.
- See how to plan, set up, and execute your shots to reduce fixes in post
- Choose the right keying process for your project
- Master basic shooting setups and live broadcast keying
- Understand proper lighting and how to match subjects to the background
- Create a working storyboard and learn how to select and direct talent
- Composite your footage and fix problem shots
- Work creatively with virtual sets, motion tracking, and match moving
- Master techniques that apply to all compositing software and plug-ins
The DVD includes sample footage and all project files to accompany the chapters in the book.
Note: CD-ROM/DVD and other supplementary materials are not included as part of eBook file.
If you are using a Mac, your software will be iMovie. In iMovie general preferences, make sure you have show advanced tools checked or you will not be able to do green screen.
Film your movie in front of a green screen.
- subject as far in front of screen as possible
- attempt to eliminate shadows or uneven lighting
- no green clothing or props
Import the movie into iMovie
Import your selected background, either an image or a movie
Make sure the background clip lasts as long, or longer than the movie
Drop the movie onto the beginning of the background clip
Select green screen from the pop up window list (if no pop up list, see first direction)
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Any camera will do, if you have the funds to go high end, many professional cameras have the green screen capability built in. Flip type cameras will be fine, if sound quality is an issue, move up to a standard video camera.
The "screen" for the green screen can be accomplished in many ways. If you can find a wall to paint, it is always ready for you, no set up. Actual green screen paint costs at least $75 a gallon, however a quick online search will give you several hardware store options that will work fine. You can buy a green bed sheet or yardage of fabric and hang it, try not to get a color that anyone is likely to be wearing. Varying sizes of green screens are available for purchase from large fabric pieces that hang from frames to small pop up frames similar to windshield shades. If you purchase a fabric screen, look for one that won't wrinkle. What will work best for you depends on the available space and budget.
Lighting choices also vary by space and budget. We are doing student projects in an elementary school, we usually don't worry about lighting. If you want better results, you need to do a better job of lighting. If you buy dedicated lighting for filming, you will need to store it. Inexpensive clamp lights from the hardware store can be used if you take a bit of time to set them up and use reflection to reduce glare. As with the screen, you can purchase lighting in multiple types and price ranges.