Imagine yourself standing in a magnificent setting, full of rich colors and textures. You want to be able to capture the image as faithfully as possible. When you get your video home you are disappointed to see that some shots look blue and lifeless. The colors are washed-out and the amazing scene is all but a memory. Unfortunately, when you shoot video with your camcorder, what you see is not always what you get. One of the biggest problems with video is that it does not render the colors your eye sees unless you carefully set the camera for the lighting in each specific shot.
In this column, we’ll look at how to control the color of light by using colored gels. We’ll also discuss color temperature and how to control it. Finally, we’ll show you how you can use this knowledge to create beautiful video every time you shoot.
The Colors of Light
As you look out at the sky, you may see brilliant blues. Turning your gaze to the warm glow of a fire, you will see light with a yellow/orange tint. These differences are especially visible to the video camera. Technically, we call this color difference "color temperature" and measure it in degrees Kelvin (see Figure 1). In this case, temperature is not a measurement of heat, but a measurement of color. The temperature scale was devised by noting the color of pure carbon as it burns. At lower temperatures (3,200 degrees Kelvin) it burns with a yellowish/orange flame, as the temperature of the flame rises, it changes color from orange to yellow to green, then to blue and eventually white.
Different light sources have differences in color temperature. The sun is a very bright, hot light source that fills our world with a white/blue light. The color temperature for sunlight can range from 5,400 degrees Kelvin (5,400K) to over 12,000K, depending on the cloud cover and the time of day. The average color temperature for daylight is 5,600K. Incandescent lamps, like the ones in your living room, give off a yellow/orange light and have a color temperature that runs between 2,800K to around 3,400K with the average being 3,200K. Most camcorders have the ability to set their image capturing electronics to 3,200K (for shooting indoors) or 5,600K (for shooting outdoors). However, sometimes this is not enough. Just when you think it is safe to use your camcorder, you step into an office lit by fluorescent lamps and get green video. Why? Fluorescent lamps have a color temperature between 3,800K and 5,000K depending on the type of tube used. Unfortunately this is in the green range of the lighting spectrum and unless you are able to white balance your camera, your video will have a greenish tint.
Color Correction Gels
If you find yourself in a situation where there is both indoor and outdoor light, or indoor and fluorescent light, you will be pleased to know that with a few inexpensive gels, your video can still look great. By carefully placing colored gels over the light sources, you will take care of the differences in color temperature and the video will look spectacular.
Color correction gels are optically clear, pliable material that you place in front of lighting instruments or on windows to change the color temperature of a light source. By using them, you can match the color temperatures of various light sources. Color correction gel comes in standard sheets of 20" x 24" or 48" x 25′ rolls. The gels are heat resistant and you can easily cut them to fit a window or the filter holders or gel frames that come with most professional lighting instruments.
The Most Common Gels
There are three major categories of color correction gels that are handy to a videographer. The color temperature blue (CTB) gel which changes the color temperature of your lights from 3,200K (indoor) to 5,600K (outdoor). The color temperature orange (CTO) gel which changes the color temperature of the light coming through a window from 5,600K (outdoor) to 3,200K (indoor), and the various gels that help you deal with fluorescent light sources.
The fluorescent gels are divided into plus and minus green gels which do what their name implies and take the green out when you are trying to go from 4,000K (Fluorescent) to 5,600K (outdoor). Alternately, you can use them to add green if you are trying to convert 3,200K (indoor) light to fluorescent. Finally, there is the fluorofilter which converts the color temperature of a fluorescent lamp to that of an indoor light source.
The most important thing for you to remember is that you should avoid mixing light of different colors. With bluish daylight hitting one side of your subject’s face and reddish lamp light hitting the other, your camcorder will not record good color quality. When confronted with a mixed light situation the first, and best choice, is to eliminate one type of light. You might close the curtains to block the sunlight and light the scene entirely with lamps, or switch off your lamps and use a reflector to re-direct the daylight streaming through a large window. The goal is to use only one type of light to light each shot.
Another option is to color-correct using gels. In an indoor scenario, with light coming from multiple sources, you might color-correct your lamps to match the color of the outdoor light (see Figure 2). This is done by placing a CTB gel in front of each light.
Instead, you might place a CTO over the window to match the color temperature of the inside lights. To the eye, the light coming through the window might look orange and unnatural, but to the camera, it will look like ordinary indoor light and the scene will look great. If a scene is taking on a greenish tint because of fluorescent lights, again you have some choices. You can gel the fluorescent lights with fluorofilters to convert them to an indoor color temperature or you could put a plusgreen gel in front of your indoor lights to convert them to a fluorescent color temperature. To make life easier, some filter manufacturers have created filter tubes that you can slip over your fluorescent lights for the purpose of color correction. Deciding which lights or windows to gel depends on the source and direction of your primary light. Try to make the least work for yourself by changing the light source that is the least trouble. If you are in an office filled with windows, you will not want to gel every window so that they will match your one incandescent light. Simply place a sheet of CTB in front of your lighting instrument and white balance as if you are outdoors. If you only have a small window to contend with, Tape a CTO over it and white balance using the indoor setting [see The White is in the Balance sidebar].
Colors Right but way too Bright?
You know all of those great shots in movies where two lovers stand talking with a magnificent view of the city filling the screen through the penthouse window? If you were on the set, it might look as if you had landed on Mars. To be able to see the sunlit cityscape, the director of photography has likely covered the window with a charcoal gray filter called a Neutral Density (ND) filter. This optically clear filter reduces the amount of light coming through the window without changing the color temperature.
Although it looks like someone just painted the window a smoky gray color, the camera sees the cityscape in all of its marvelous grandeur. If the director lights the scene with outdoor color temperature lights, they treat the window with just the ND filter. If however, they light the scene with incandescent lights, they add a CTO gel to the ND filter. This not only reduces the amount of light coming in, but also changes its color. If you choose, you can get these two filters combined into one.
Mixing different light sources can be a bit of a challenge. By using color correcting gels and filters, you can mix and match light to your heart’s content. You can find these useful tools at your local video or theatre supply house, or look up lighting gels on the Web.
Remember, never trust your eyes, while they may see one thing, the camera may see something totally different. These techniques can help you overcome that problem and allow you to capture what your eyes see onto video.