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Tips for a Good Chromakey

Tips for a Good Chromakey

Editing for green screen begins before you sit down at the keyboard. A good key begins with proper lighting and shooting techniques.

Time was that a video producer had to spend a lot of money on equipment then had to paint a lot of stuff a special blue or green to achieve acceptable chromakey effects. The producer also had to find and pay experts at lighting, shooting and editing the segment if she even thought about doing it for a commercial production. This story looks at three essential elements in generating a successful chroma key.

Chroma keying, also referred to as blue or green screen effect, still requires attention to lighting and acquisition. While a myriad of both dedicated chroma key programs and software that includes keying capabilities make the editing job easier, some can be more difficult than others to apply. Good keying can be accomplished with relative ease if close attention is given to lighting, shooting and editing details. Great keying can be had with just a little more effort.

By now you realize there are three essential elements to generating a successful chroma key production: lighting, shooting and editing. The more time you allocate for lighting your screen and subjects, the less time you will spend shooting, re-shooting and editing for the effect. While you certainly can often "fix it in post" close attention to lighting will mitigate you having to do so as often.

1. Lighting:

Light your screen first. Wait until you are satisfied with an even and consistent lighting free of patterns or shadows and wrinkles or creases before you start lighting your subject. Applying a lot of soft light (softboxes, etc.) helps achieve the desired effect when using a flat, non-reflective color. Set up your lights at a slight angle to your screen and work to avoid hotspots caused by overlapping light sources.

Plan your screen lighting so that your subject isn't closer than 7 feet or so in front. Plan your subject lighting so that your key and spots or hair lights do not fall onto the screen, throwing your screen lighting efforts out the window.

Having a decent quality, color-accurate, monitor on hand will help you judge the effects of your screen illumination, spillover problems and your subject lighting - making more obvious unwanted effects, if any, that either might generate. The power and portability of today's laptop computers and NLE programs help tremendously when it is commercially important to get your key right, if not perfect. Not all of us have the luxury of such equipment making it all the more important to pay close attention to getting the lighting right before shooting, than later in post.

Some producers like to use a spot meter to determine a uniform spread of lighting. Such attention to detail isn't critical, however and you will eventually be able to virtually "eyeball" it and get close enough to the desired clean, uniform look you want and need.

Patience is a virtue and giving yourself extra time to get the lighting right will make you downright virtuous. I cannot stress enough the importance of giving yourself the time, especially on your first few attempts, to focus on lighting without feeling rushed or under pressure to start shooting. Lighting is everything when it comes to creating a clean key.

2. Shooting:

Critical to shooting is focus, camera angle, framing, what the talent is wearing and avoiding reflective components that can pick up the screen's coloration. Sunglasses, for example, should they be necessary to the production; even chrome or gold eyeglass frames and shiny pens in pockets can cause headaches.

Again, attention to detail is key (no pun intended) to a successful chroma key experience. Simple elements such as reflectivity and lazy focusing can create serious problems later - time consuming and often commercially expensive to correct later.

Sharp focus on your subject has always been important to successful chroma key work and with the advent of high definition production this is even more critical. Alternately, if your screen is slightly out of focus it often can smooth unnoticed unevenly lit spots, making for an easier key. Keep this in mind when shooting and monitoring your production.

Watch for shadows thrown onto the screen by the subject you're shooting. This is another of those "gotcha" moments that can get past you in the rush of doing a chroma key shoot and not blocking adequate time to check details. It is sometimes surprising to do a chroma key production, thinking you took all the precautions necessary, then discover that the guy's white hair and beard (yeah, me) actually reflected the screen, making editing a bit more of a challenge. Did I also mention that I have one green eye and one blue eye? Work that one out if you can.

It is always a good idea to do a second, even a third take if time permits - that much more to work with, providing more chances to get one take that is significantly better and easier to work with when it comes time to start editing your chroma key effect. Like Billy Idol once said: "Too much is not enough!"

3. Editing:

The vast majority of NLE programs available today make chroma key work a relatively simple, almost ho-hum event. Ho-hum, that is, so long as you planned your production up front and took the time necessary to get your lighting correct the first time. Sorry but that bears repeating. Also sharp focus when shooting and watching for those frustrating little things that can become big things in post.

Even colors beyond the standard chroma key blue and green or variations in shade can be successfully and cleanly keyed out. In the interest of keeping consistent with the art of chroma key let's presume blue and green are the background screen colors.

Assuming you've achieved the clean key effect you wanted and that you have planned the background with which you want to replace it - again with today's NLEs this is virtually a drag-and-drop process. Familiarity with your favorite NLE will help you achieve the quality you are looking for. If your particular flavor isn't as satisfying as you'd hoped, there are many choices and options on the market for third-party filters and special effects to help you achieve a better quality key.

Stand-alone programs like the popular Ultra Key by Serious Magic and a host of others work hand-in-hand with popular programs such as Final Cut Pro Studio, Adobe Premiere Pro, After Effects, even Photoshop to help generate the desired chroma key effect for images and video shot in front of a chroma key screen. A search on the web for "third party video editing software plug-ins" for your particular program will bring up a bunch of possibilities.

But check out your NLEs capabilities first before spending extra money - your program just might offer you all the power you need to achieve the chroma key effect you desire.

Keep in mind too that another option, all but forgotten, is the luma key filter also found in many video editing programs. Luma (or luminance) key filters can often provide a simple alternative to chroma keying by keying out either bright or dark areas of the video. Again, this may be all you need or want for the effect you have in mind.

After a few chroma key adventures you will discover the strengths and limits of your current program and either figure out a workaround or what you have to do to make things better. Just know that whatever the challenge, a solution is out there.

It's a Wrap

Fear and inexperience are the two greatest factors, deterrents if you will, in attempting chroma key production work. Obviously you do not want to promise a paying client you can create a professional result if you've never made the attempt.

The beauty of chroma key work using today's technology is that you can quickly and easily assess your needs by taking a few practice turns - and it likely doesn't have to cost you a dime.

While many chroma key pundits expound on getting just the right color of blue or green, purchasing expensive lighting rigs and even using specific camcorders, this isn't totally necessary. (digital, by the way is a tad more challenging when it comes to extracting the edges of your subject, avoiding reflection, splash or spill - which is why some suggest using other gear over today's huge selection of digital camcorders). I can almost guarantee that you will gain enough confidence after a few rounds of practice at lighting, shooting and editing that you will not hesitate to offer or accept a chroma key production gig.

In fact, while you're checking out the possibilities do some experimenting with various lighting rigs - branded or homemade - and even different cameras if you have that option. See which applications generate what results. Be prepared to pinch hit when you have to and know when to demand the right fee for productions calling for more expensive setups.

Putting the essentials to practice will also go a long way in reducing your frustration factor, making it less likely that you will give up on an effect that can not only be fun to work with, but can generate income to support your hobby or business. Good chroma key work will generate accolades. Great chroma key will generate checks!

Just always keep in mind that there are three essential elements to generating a successful chroma key production: Lighting, shooting and editing. Each in turn is easier if sufficient attention is given the element before it.

Sidebar: HD, Painted Walls and other Tips

There's a lot to know and understand about the art of chroma key but it does not have be nearly as complex or daunting as it might seem. Do I use a blue or green screen? How can I do more than a head-and-shoulders shot with my portable screen? I'm going to paint the walls and ceiling of my spare room with one-half green and one-half blue, what are the color specs I need to know to get my paint mixed right?

  • Blue or green? While chroma (or digital) blue and chroma green are the colors of choice, again pretty much any solid color evenly applied and evenly lit will work, depending on colors appearing (or not) with the subject.
  • A bigger screen? You want to specifically focus on getting clean, sharp edges when you isolate your subject from the background color. This means that pretty much anything at hand that is close to or similar to your immediate background color can be brought into use. Once you get the edges clean the rest of it can often be rotoscoped (using a program to "paint" something out or into the background) or garbage mattes (elements replacing parts of images or video frames to cover up what is behind them) even multiple keys can be used successfully.
  • To paint or not? Unless you absolutely, positively have to have such a room in your home or apartment, don't do it! Just as there's an art to lighting, shooting and editing chromakey, so is there an art to applying chroma key or digital blue or green paints. They can dry unevenly leaving spots that are a consistent challenge to light properly or key out and that's only one concern. Believe me, there are more than enough others to exceed sidebar word count limits.
  • Shoot it clean. What I mean is don't use (until you've experimented and discovered) settings and filters on your camera - such as those image enhancement options some models provide. Shoot it raw and do what you have to do in post to alter anything after you've achieved a successful key.
  • High definition? HD will certainly give you more detail and information in the video and that can result in better key results.
  • Colors to avoid. Well, not everyone has one blue eye and one green eye, but there are a host of complimentary colors that are not complimentary to chroma key screens, regardless of the color. Familiarize yourself with the primary colors and their mixes and make sure your talent or subjects know beforehand to not wear blue jeans or denim shirts to the shoot. Brown will sometimes mess with you when using green chroma key and purples can wreak havoc on a blue screen.

Earl Chessher is a veteran career journalist and professional video producer, working in California and marketing throughout the U.S.A.

Tags:  November 2010
Earl
Chessher
Mon, 11/01/2010 - 12:00am

Comments

Jaimie's picture

Good article on a subject with relatively little practical info. I've never used chromakey, but sooner or later the need will arise and it's good to know what to watch for.