Color Temperature in the Digital Age


A look at color

temperature concepts and some strategies for capturing the best possible color

in all your videos in the analog world, which we seem to be moving away from at warp speed, serious videographers pay close attention to the color temperature of their light and their camcorder’s white balance settings. This helps them avoid the tints of pallid blue or auburn tan that can ruin their beautiful footage. Digital units, however, have improved color compensation circuitry, and software editing packages now let video artists adjust and paint their footage like virtual Rembrandts. So on this great new digital planet, who needs to worry about color temperature and white balance?

You do. No matter how sophisticated the circuits and software become, two axioms remain:

  •   It is usually better to record the best quality footage possible (including color balance) and then play with it safely in post production.

  •   No digital algorithm can match human judgement when it comes to difficult lighting situations.

    So let’s take a fresh look at color recording, with today’s cameras and today’s editors in mind. We’ll visit the concept of color temperature, review the way camcorders react to it and spend some time looking at strategies for capturing the best possible color in every single shot you make.



    How Hot is White?

    "White" light is really a mixture of light frequencies between infrared and ultraviolet. Depending on the proportions of the frequencies in the mix, "nominal white" can be anywhere from strong orange (firelight) to pale blue, like an overcast winter sky.

    Kelvin scale temperatures express the overall white light colorcast (See Figure 1). Firelight may be described as 1,200K (pronounced "twelve-hundred degrees Kelvin") and high overcast diffused sunlight might be 7,000K. Note that the "hotter" the color temperature, the "cooler" the light. That’s not as nutty as it seems, because red is "warm" and blue is "cool" in a psychological rather than a physical sense.

    We don’t often notice these color-casts because our brains remove them automatically. Since we carry mental reference colors for things like flesh tones, green grass, blue sky, white milk, etc., we unconsciously compensate for shifts in their actual colors.

    Recording systems do not have brains, however, so they stubbornly record what they see: pasty gray foreheads in high overcast light, and rosy red cheeks under lamplight.



    Camcorder White Balance

    To fix the problem, camcorders include "white balance" circuits that evaluate the colorcast of the incoming light and assign a value for neutral white. Then, hues are accordingly assigned for all colors, from red to violet. Since the system converts (almost) every colorcast into the same neutral white, the component colors also record the same, regardless of the light source. In effect, the white balance circuits perform the chore of the human brain.

    Unlike auto exposure and focus systems, white balance circuits have no default setting that is, they automatically set white balance each time you turn on the camcorder. Left on "auto," the white balance system will adjust continuously to record neutral colors in every shot.

    Camcorders also have other ways to control white balance. All but the simplest units include switchable settings, usually "outdoor," "indoor" and "fluorescent." More advanced models also include manual white balance control. To use it, illuminate a white card with the prevailing light source (skylight, incandescent or fluorescent), fill the camcorder frame with the card, and enable the manual setting. (Some camcorders use a milky translucent lens cap aimed directly at the light source instead.) Manual white balance is more precise because the circuits are reading only the local "white" instead of trying to deduce it by averaging a whole spectrum of incoming colors.

    Professional-grade cameras, including high-end Mini DV models, have white balance that is not only manually settable but tweakable as well. You can get a basic balance and then fine-tune the look of your particular color by studying the effect in a reference monitor as you adjust your primary colors.

    More often than not, the auto white balance system works amazingly well, and for quick, documentary-style shooting, this setting is usually the best choice. Then why bother with the switchable and manual settings? Because there are lighting situations that are just too complex for auto circuits to cope with.



    Coping with Unusual Situations

    There are three situations in which you need to go off autopilot:

  •   When color temperatures change within a shot.

  •   When you want to preserve the actual colorcast of the shot.

  •   When you want a custom look.

    The most common problem is shifting color temperatures. Imagine an interior with actor A sitting by a picture window and actor B working under a hanging table lamp. If you start the shot with A and then pan to B, the white balance will adjust to compensate, and the color shift will be clearly visible on screen. If you want A and B balanced alike, replace the pan with two separate shots, setting white balance for each one. But if you want the contrast between the two performers, lock the balance to prevent the shift.

    By selecting "outdoor" balance, you can make the person in the lamp light look exceptionally warm and cozy. If you choose "indoor" instead, the person at the window will appear cold and bleak. If you have full manual adjustment, you can dial in a compromise that will record the window person slightly warmer and record the table person slightly cooler.

    In other situations, you may want to keep the colorcast that the camera is trying so hard to "correct." In Red Rock Canyon, California (which you’ve seen in countless Westerns) the rusty soil and rock walls radiate a distinctive desert orange over everything. If you’ve taken the trouble to shoot there, you want to record that distinctive color. In a situation like that, flipping the white balance switch to "outdoor" will record direct sunlight neutrally, while maintaining the clay-colored tint of your setting.

    Finally, there are situations (such as sodium vapor factory lighting) that can push the auto circuits beyond their competence. Here, you’ll often find that you can dial in a subjectively pleasing color balance by looking at a monitor and experimenting with various camcorder settings.

    For casual snap shooting, the auto white balance works great, but for advanced amateur and professional projects, you’ll want to control white balance as carefully as you regulate focus, exposure and shutter speed. Don’t forget that half of videography is controlling the light, and half of accomplishing that is fine-tuning the white balance.

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