Wednesday, December 29, 2010

It's winter. It's snowing . . . blue?

At the South Rim of the Grand CanyonIf you live in the northeastern US, the weather this past weekend ensured you knew it was winter. The snow came down, and some areas got as much as a couple of feet.

Many went out in the last few days to make photographs of snow scenes, only to review the photos and see blue or gray snow.

Unfortunately, digital cameras aren't as good as the combination of our eyes and brains, which are fantastic at color and contrast correction and have a large dynamic range. Whether we see snow in the sun, or shade, or even at night, unless the light illuminating the snow is colored, we see the snow as white.

Cameras don't see the same way we do. They can be fooled by blue skies or shady conditions for snow scenes. The problem is, in snow conditions, the camera often can't set the image's white balance correctly. This is even true with expensive DSLR cameras.

Each light source, even though it might look white to the “naked eye” has a color or hue, called “color temperature” measured in degrees Kelvin. The color or hue of the light illuminating the scene you're photographing affects the color of each object in the scene as captured by your camera. Even if the sun is your light source, according to the time of day, if it's sunny or cloudy, or if your subject is in the shade, your scene will be lighted by a different sunlight hue.

Think about how skin looks when illuminated by the light from incandescent bulbs versus fluorescent tubes. While both light sources appear to be “white,” they aren't. Under incandescent light, skin will look somewhat warm, or with a reddish hue, while the same skin will look somewhat harsh or ghostly, or with a bluish hue under fluorescent light.

Here's a brief list of light conditions' color temperature:
  • 1000-2000 K   Candlelight
  • 2500-3500 K   Tungsten Bulb (incandescent light)
  • 3000-4000 K   Sunrise/Sunset (clear sky)
  • 4000-5000 K   Fluorescent Lamps
  • 5000-5500 K   Electronic Flash
  • 5000-6500 K   Daylight with Clear Sky
  • 6500-8000 K   Moderately Overcast Sky
  • 9000-10000 K   Shade or Heavily Overcast Sky
Grand Canyon - South RimIt's important to understand that a digital camera has the ability to determine the actual color temperature of the scene under auto white balance, generally only between 4,200K and 7,000K, though some digital cameras have a wider range. If your subject is lighted by incandescent bulbs, for example, it's unlikely your camera will be able to automatically set its white balance properly. The same is true if your subject is in dark shade or under a heavily overcast sky.

Because snow is white, and often predominant in photographs containing it, and because it reflects considerable ultraviolet light, it's difficult for digital cameras to automatically set white balance correctly. Snow picks up the color cast of the scene's light source and predominant colors of the scene. On a bright sunny day, for example, the snow picks up the blue of the sky. As ultraviolet light is at the blue end of light spectrum, that adds to the snow's bluish tone.

If you take a snow filled photo in the shade, the snow will often appear gray, as once again, the camera can't get the white balance set correctly, and in this case it often misreads the exposure too.

How do you get the white balance of a snow scene right?

I have three suggestion to use to get an image's white balance right, so the snow is white, and the other colors also correct.

You can utilize the white balance option settings, such as “cloudy,” or “shade” to adjust white balance manually toward higher color temperatures. This will adjust the white balance higher to account for the blue cast of snow scenes. While this can help quite a bit, it will often produce inconsistent results.

El Tovar Hotel at the South Rim of the Grand CanyonA better solution would be to use a “preset” or “custom” white balance setting. This is when you use the camera's ability to manually measure the scene's actual color temperature and set the white balance accordingly. For cameras which can create a custom white balance, in the measurement mode, a photo is taken of a neutral gray or white object (usually a gray or white card, such as the WhiBal card) directly in the scene's light. The camera analyzes the incoming light's color temperature and sets the white balance properly. Rather than a gray or white card, I use an ExpoDisc to make my presets.

Finally, if your digital camera has the capability of storing its photos in the RAW format, instead of JPG, I strongly suggest you take advantage of RAW for your snow scene photographs. In post-processing, computer software, such as Photoshop, you can directly correct the image's white balance. This isn't possible if your camera stores your photos in other formats.

Have fun with your digital camera in the snow this winter.

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