Chroma Key Properly
By Bill Schnarr
How to Light a Chroma Key Shot
So you just got home from the movies, and all the fantastic blue screen action scenes have gotten you all fired up and rariní to go. You can hardly wait to grab your digital video camera and start filming your friends and family doing crazy things.
But where do you begin? If you havenít done much Chroma Keying in the past, all the adjusting and compositing can seem like a daunting task.
While itís true that Chroma Keying requires a lot of work and practice to achieve believable results, itís well worth it. And if you start with a fundamental Chroma Key techniqueóproper lightingóyouíll stand a much better chance of getting that shot you want rather than simply going crazy and tearing out all of your hair.
In this article, will give youíre a few basic tips and pointers on how to properly light your Chroma Key shot.
Step One: Lighting the Background
By far, the first step in successfully lighting a Chroma Key project is the most important one. Lighting the background properly can save you hours of needless frustration and problems.
But how do you properly illuminate your blue screen? That answer is simple. Dump as much light on it as you can. Within reason, that is.
Successful Chroma Keying requires a lot of light to be successful. You need a nice, even glow on the blue screen with absolutely no shadows. In this case, the more even you can get your blue, the better off youíll be.
Start with two large lights, such as 250 watt halogen lights. You can set them up on either side of your screen, high enough so that they wonít interfere too much with your subject. Remember, the only reason these lights are being used is to illuminate the back screen.
In order to achieve a nice, even light over the whole screen, use some bounce cards. Bounce cards should eliminate any hot spots (glare) that would normally occur from direct exposure.
This part of your setup is something that can remain fairly constant from shoot to shoot. Since this process is for Chroma Keying only, you can find a set up you like and use it every single time you take Chroma Key shots. Of course, other things, such as interference from your foreground lights, can cause problems with this lighting, but these are minor adjustments that can be easily fixed.
In some cases, you may end up with too much light. Youíll know that this has occurred because your camera may begin to register your blue screen as white. Obviously, five thousand watts worth of lights is too much.
Another thing to think about when you are setting up your lights is the reflective nature of your blue screen. A lot of light can cause colour bleeding, which is when the blue off of your background is reflected onto your subject.
This bleeding can manifest itself in your shot as a jagged outline around your subject or as a healthy blue backlight. Both of these are undesirable traits in a Chroma Key shot.
If you experience colour bleeding from your background lighting, you can either leave it and fix it later on your digital mixer (a time consuming experience), or you can fix (or at least lessen) the problem by adjusting your lighting.
The easiest way to fix this problem is to get some diffusing amber gels for your lights. Amber gel wonít seriously damage the colour of your light, and at the same time it can greatly reduce the reflective properties of the blue screen. However, amber gels can be expensive, and if you are on a tight budget you may want to try something else.
You can try reducing the amount of light you are using, but this can lead to other problems. Another thing you may want to try is using a bounce card that is a bit darker. Going from a brilliant snow white to a more muted vanilla white may be just the thing you need to fix your bleeding problem.
Step Two: Lighting the Foreground
The second part of lighting your Chroma Key shot is the foreground lighting. Lighting your subject properly can mean the difference between a natural looking shot and a completely fake-looking shot.
The first thing to look at when your setting up your shot is how you can keep your subject lighting different from your background lighting. You donít want your front lights to interfere with your carefully prepared blue screen lighting any more than you want your ambient backdrop lighting from interfering in your foreground shot.
To this, first try moving the subject away from the background. Most experts say to start at least three feet away, but ideally, the farther you can get away from that blue screen the better off youíll be as far as lighting goes.
Another important thing to look at is shadows caused by your front lighting. Since you can easily light your subject any way you want, itís important to keep in mind that the suspension of disbelief will be completely destroyed by errant shadows. If your subjectís shadows donít match up with the shadows in your background, itís something that will be obvious immediately.
If you are running stock footage for your Chroma Key, this problem can be easily fixed by making a note of the time when you shoot, as well as the conditions, and then repeating then matching the lighting effect for your subject.
Of course, itís even easier to simply ignore the shadows or get rid of all of them by washing your subject in light and eliminating the problem altogether.
To do this, youíll want at least a single halogen front and center, and depending on your shooting situation you may want angled lights to eliminate any shadows that occur.
Lighting Tips and Tricks
A good tip for someone just entering the world of Chroma Key shooting is this: Experiment!
Find something that works for you, and then mess it up and start adjusting things. Try different lights, angles on your bounce cards, and gels. Play with your front and background lighting and try to come up with new or interesting combinations.
In an excellent article on Chroma Keying by Charles Roberts (originally posted on www.kenstone.net), he mentions several ways in which Chroma Keying can be done with affordable lighting and cheap equipment. This is for anyone who would like to save money (donít we all?) but still demands high-quality in his or her shooting.
One of the things Roberts mentioned has to do with diffusers. He said that you can get excellent ambient lighting by setting your lights up behind bubble wrap. It would appear that aside from being an excellent way to ship your breakables, the angles made by the plastic bubbles break up the light enough to create a nice warm glow.
Chroma Keying can be a great way to liven up your professional shots or it can be something you do as a hobby with your old home movies. The main thing involved in Chroma Keying is to be patient, and continue to pay particular attention to your lighting.
It can be the source ofóand answer to most of your problems.
About The Author
Bill Schnarr is a successful website copywriter providing tips and advice about video chroma keying, digital cameras and photography. His numerous articles offer moneysaving tips and valuable insight on typically confusing topics.
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