In a nutshell, white balance sets a reference the camera uses when rendering the hue of the scene in a photo. Of course, as with any communication medium, there's a two-way street. The image made by the camera is the output. The viewers response to that image is, in a sense, the input. As the photographer, you're first in line to see the image and decide of you like or dislike how colors in the scene are rendered.
Let's take a closer look at the question of how to set white balance so the photo renders hues to one's liking. We'll start by asking a basic question: what's your goal? How do you want the colors to look?
Broadly speaking, there are three possible responses to that question. One, is that you want the colors to appear as they do to your eye at the moment the photo is being made. A second, is that you want colors to appear as they would under a specific kind of lighting; lighting that may or may not match the light illuminating the scene at the time of the photo. A third, is that you want to manipulate the appearance of color in the frame to suit your artistic goals for the image.
Suppose your goal is to render hues as they appear to the eye at the time of the photo. How do we achieve that? We could set the camera to auto white balance (AWB) and trust it to choose a setting that will deliver the goods. Often, it will. But almost certainly, there will come a time when the camera chooses a white balance that results in hues you don't like. How do we intervene and choose a setting that will deliver the goods.
I'd recommend changing from AWB to one of the scene settings - daylight, cloudy, open shade, etc - making a test photo and using the setting that comes closest to what you want. This approach can be effective in that it results in a photo you like. However, it doesn't do much to help the photographer understand why a certain white balance setting produces a specific outcome.
Before reading further, be aware that we're heading down the white balance rabbit hole. Enter at your own risk.
Human vision has evolved so that we're most sensitive to light of a certain wavelength. That wavelength is 555 nanometers, which corresponds to what a person having normal vision would describe as being slightly yellow-green. While light has a wavelength that can be measured, color is about perception. In that context, there is always a subjective element to color identification. Ten people can use a device to measure the wavelength of light and all can get the same result. At the same time, all ten can perceive and describe the color of that light differently.
Science has developed a color temperature system which describes both the color (as perceived by a person having normal vision) and temperature of the light. The color temperature of sunlight is around 5800K or 5,800 kelvins. That color temperature corresponds to - you guessed it - yellow-green.
Cameras are designed so that when you're out in midday light, the AWB or daylight scene white balance setting will result in a color temperature of 5200-5600 as a reference. The result will be a photo that renders hues as they appear to your eye. Reds will look red, greens green, and blues will look blue.
We describe this as looking realistic because the colors look similar to how we see them. We're the reference. As conditions change and the color temperature of the light illuminating a scene changes, we see the scene as having different hues.
For example, the same grassy field that looked green at Noon on a sunny day may have a decidedly warm or reddish hue at 20-30 minutes before sunset. Late in the day, the sun is much lower in the sky. Sunlight travels through more air before reaching the ground. The atmosphere scatters shorter wavelengths more effectively so that longer wavelengths of light are now illuminating the landscape. Longer wavelengths are typically seen as warmer or redder in hue.
On the Kelvin scale temperatures lower than 5000 appear more red as the color temperature drops. Sunset light typically has a color temperature of about 4000K. Our eyes, which are tuned to be most sensitive to a cooler temperature in the 5600-5800K range, see lower color temperature light as warmer. This is why we see so much red in a landscape scene at sunset or sunrise.
By contrast, clouds are more effective at scattering longer wavelengths of light. Shorter wavelengths can make it through thick clouds. The shorter the wavelength of light, the cooler or bluer it looks to us. Blue light also has a higher color temperature. So, under heavy overcast, the color temperature of light illuminating a scene may be 7000K. The scene will look cooler or bluer to our eyes.
The camera works the same way. If we set white balance to sunlight or to a specific color temperature of 5600K, a landscape in midday light will have colors similar to what we see. At sunrise or sunset when the same landscape is illuminated with 4000K light, a camera with a sunlight or 5600K white balance setting will render the scene with warmer, redder hues. On a day with heavy clouds when the scene is illuminated by 7000K light, the camera will render it cooler or more blue if white balance is set to daylight or 5600K.
Keeping the camera's white balance at a daylight setting will simulate how our eyes see a scene. The accuracy of that rendering will be influenced by the custom settings a photographer chooses. If a person shoots JPEG and increases color saturation to the maximum in-camera setting, hues will look unnaturally rich. That's not to say it's wrong to use those settings. If you like horsey color hues, set the camera to render the scene to your liking. However, don't blame the camera for making photos that aren't realistic in their presentation of hues in a scene. Those colors are the result of choices made by the photographer.
Suppose your goal is to render a scene as it would appear under a certain kind of lighting; as if we were seeing everything under midday light. Why, you might ask? Well, if you enjoy nature photography, you may like to render flowers, bird plumage, or animal fur as it appears under "normal" (midday) light. You want the whites to look white, blacks to look black, and so on.
If that's your goal, you can achieve this by matching the camera's white balance setting to the color temperature of the light illuminating the scene. For example, selecting a cloudy scene white balance on a cloudy day will result on the camera choosing a higher color temperature (i.e. 7000K) that more closely matches the color temperature of the light illuminating the scene. The closer the two match, the more the scene will look as it does in midday light.
At sunrise or sunset, a white balance setting in the range of 4000-4500K will produce images looking as if the scene were lit by a midday Sun. After sunset the cooler temperature of the light may be much higher (8000-9000K). Setting the camera's white balance to match will render the scene so that colors look as they would at midday.
Finally, you may want to render color - not as it looks to you at that moment or as it would look at midday - as it pleases your aesthetic sensibility. You may like the warmth of sunset light but have a preference for taming it a bit. Similarly, you may like the cool of a scene's appearance during a storm but you don't want an intense blue in your photos.
Here's the general rule: if you set a white balance color temperature that's lower than the actual color temperature of the light illuminating the scene, you'll make photos having a cooler or bluish hue. If you set a white balance that's higher than the cooler temperature of the light in the scene, you'll make photos having a warm or reddish hue.
For example, if you want to calm the deep reds of a sunset scene, lower the white balance from daylight (5600K) to about 5000K. The scene, which is lit by 4000-4500K light will still look warm in hue but the reds won't be as horsey. They'll be calmed a bit. If you like the cool hue of twilight light but don't want the scene looking deep blue, set white balance in the 6500-7000K range. It'll still be below the 8000K temperature of the light in the scene but the difference - and blue tinge - will be more subtle.
I hope this helps or, at the very least, gives folks a better understanding of how white balance can be used in an intentional manner to render color in a scene to your liking.
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Bill Ferris Photography
Flagstaff, AZ
http://www.billferris.photoshelter.com
