Digital Photography - White Balance

Visible light is composed of variations of light waves, from 400 - 790 Tz (Terahertz). Blue for instance has a frequency of 631 - 688 Tz, Green 526 - 606 Tz, and Red 400 - 484 Tz. White light is composed of equal amounts of red, blue, and green. Color shifts occur from daylight sky moisture, reflections from bodies of water, and many other reflective and absorbing materials.

Camera photosensitive devices are manufactured to meet the 6200º K (Kelvin) white light from our sun as measured on an 18% neutral gray card. When photographed the gray card will have no color tint or shading.

White Balance becomes an interesting problem to solve under varying lighting conditions. Normal sunlight will produce a normal white balance to these photographs. An overcast, or cloudy day will produce a color shift toward the blue (some light waves are absorbed by the clouds and their moisture content). An incandescent light will have a light source shifted toward the red (Tungsten filaments burn red). A fluorescent tube may emit a green, red, blue light depending on the internal coating and gas used to fluoresce light.

Film cameras used to require special glass filters threaded onto the objective lens to correct for abnormal light sources.

A slight reddish filter to block some blue and green light gave a warming effect on cloudy days.

A green or blue filter to block the green or blue cast from indoor fluorescent lamps, and a UV filter to absorb the Ultra-Violet cast on a hazy day.

Modern Digital Camera come with a UV coating on the photosensitive device so the only real purpose of the glass filter is to serve as a lens protector against bumps and dropping the expensive lens and causing it to become inoperative.

The modern digital camera comes with user accessible controls to set the color balance in the camera. Most cameras are delivered to you with AWB (Auto White Balance) preset at the factory. For 98% of your photos AWB will be very successful. For the other 2% of your photos you can manually reset the color balance to sunlight, cloudy, fluorescent, tungsten, or a custom light balance. (LED lights (Light Emitting Diodes) may have an entirely different light spectrum to the photosensitive device than the Human Eye.)

The advantage to digital cameras and white balance is the ability to preview the scene using the LCD viewer on the back of the camera body. Depressing the shutter button half way down forces the camera to make a temporary reading of the exposure and display the image on the LCD display. If the camera also has a viewfinder the preview will not be available as the reflex mirror inside the camera body flips up and blocks the optical viewfinder. This is also known as "Live View".

If you find you have not adjusted the color balance correctly to your taste you can always apply additional color balancing in post processing and image editing software.