Chroma keying is a technique used for combining two frames or images by replacing a color or a color range in one frame with that from the another frame.
It is often used in film industry to replace a scene's background by using a blue or green screen as the initial background and placing the actor in the foreground. The principle behind chroma keying is that the color blue is the opposite color of skin tone, so a distinction between the two is very clear, making it easier to select the color without worrying about any part of the actor being included in the selection. The whole blue selection is then replaced with another frame as the background.
Chroma key is also known as color keying and color separation overlay; it is also commonly called blue screen or green screen.
The chroma key process is widely used because it is cheaper to do this than to shoot in expensive or inaccessible locations. It can also be done in real time, making it ideal for weather report or entertainment shows.
Lighting The single most important aspect to successful green screen photography is lighting. You need uniform lighting across the entire background to quickly remove the green color from your photographs during post production. To create the optimal lighting conditions, you practically need to have professional quality studio lighting available. Many photographers have successfully performed green screen techniques without high-end lighting systems, but processing these images with Photoshop or another chroma key program takes much longer.
Evenly lighting the background requires at least two lights. These lights should be set up as sidelights pointing toward the green screen from approximately a 45° angle. Typically, these lights should be about 6 feet away from the green screen although the material your green screen background is made of will determine the exact distance your light should be.
Remember that the goal is even lighting so move the lights around until you find a good, balanced light value across the entire green background. Avoid hot spots whenever possible. If these two sidelights are not enough, you can also add a third light above or below. Some photographers actually put a small light behind the subject. This helps to remove any shadows cast by your subject and is typically not visible in the photograph.
Learning to light your green screen properly is probably the most difficult task; however, the other consideration is lighting your subject. This follows all normal photography lighting principles; however, you have to keep in mind the final background you plan on adding whenever possible.
For instance, if you light your subject very well and plan on placing this person in a nighttime city skyline background, it won’t look natural because the subject will be lit much more than the rest of the picture. Minor differences in lighting can be overcome using Photoshop lighting effects, but more obvious differences may be difficult to cover up using software.
Subject/Background Separation As a final note, you should always try to keep you are subject at least 5 feet from the background. In large group shots, this may not always be possible, but the closer your subject is to the background, the more likely you are to have “green spill” on your subject’s face and other body parts. This can be extremely difficult (if not impossible) to remove during post production.
Hopefully you’re not put off by the lighting requirements of green screen photography. Please keep in mind that the “requirements” above are illustrated for optimal conditions. Many photographers successfully use green screens without special lighting equipment. It may take longer to remove the green screen during post production, but it is certainly less expensive than purchasing studio lights if you do not already own them.
The best way to learn green screen photography is to start practicing. You don’t have to run out and purchase a professional green screen background right away – start with something basic like a wall painted green or even green construction paper taped to a wall. Once you understand the basics, you may decide to invest in professional grade green screen equipment. Either way, mastering green screen photography adds an entirely new facet to your photography skills that can quickly place you into a new category of professionalism and potential income opportunities in the future.
The Possiblities with Chroma Key:
EDITING:
For Premiere users:
For Final Cut Pro Users:
Your Assignment: (No violence of ANY kind - not even jokingly - No drug references - No foul language - Nothing that will go against school policies - Don't push the limit) Put yourself in your favorite scene, i.e. on the beach of Hawaii, at brunch with friends, in Mountains, etc. -Film yourself in front of the green screen for 20 seconds (YOU WILL NEED TWO different VIDEOS of YOURSELF) one in front of a picture and one in front of a video -Put yourself in your favorite spot -Your actions, speech/audio, etc. should make sense with your location -Lighting on you should match your lighting in your scene -Each person will need to turn in their own video of themselves. You may choose a partner to shoot with as the cameras/green screens are limited. Due Date: MONDAY, 2/24 at the end of the block
To submit: Please rename your video to lastname_still.mov or lastname_moving.mov
*If you finish early, please come see Ms. Dogoli about what's next! :)