Part 24a - White Balance

Or... when is white white?

One mysterious control on a DSLR is usually identified by the letters WB or AWB. Its function is so elusive and seemingly complex that most beginning photographers elect to ignore it altogether. "After all", as logic would say, "my pictures look good enough without messing around with this control. Hub's already got me thinking about a dozen other things while I'm shooting. Why bother?"

To help calm those photographic nerves, an incorrect White Balance setting doesn't necessarily spell doom to your picture. But it might keep you from making the best picture possible. So, for DSLR owners, although it's preferable to set the White Balance as accurately as possible "in-camera" to avoid increased time and workflow in post-processing, there is some margin for White Balance error. This is especially true if you are shooting in RAW mode. In this case, you will establish the White Balance when the picture is converted by your image editing software.

Having the flexibility to specify the White Balance of a scene also provides the photographer an additional creative tool.

To begin our understanding, it's important to make a critical distinction: White Balance and Color Temperature refer to the color of the light striking our subject -- NOT the color of the subject itself. When changes are made using the White Balance feature of your camera, you are compensating for the color of the light that is illuminating your subject.


So, when is white white? The answer to the eye/mind combination is, nearly always. The answer to your DSLR camera is, occasionally. The illustration above shows a white card as it appears under three different main lighting conditions. Remember, the differences in colors of white shown above are the result of the color of the light striking and then reflecting from the cards -- not the actual color of the cards.

• Normal sunny daylight between about 10 a.m. and 3 p.m. (left)
• The same card seen under your living room incandescent table lamp (middle)
  
• The same card seen under your kitchen fluorescent lighting (right)
  

The human eye/mind ADAPTS. The white card will be seen as "noon time" daylight white under all three lighting conditions. The camera is a different animal. The sensor in a DSLR "sees" and records these differences and produces the three very different white card renditions shown above.

Occasionally we are able to see these differences in real life when our eye/mind can't adapt to multiple light sources.


Shown above is a black and white print lying on a counter next to a window. The incandescent light on the right of the picture is also lighting the scene. Where the picture is mostly illuminated by the daylight from the window, the picture appears to be a normal black and white image. Where the picture is lit primarily by the lamp on the right, the b&w picture takes on a yellow/red cast. Our eye/mind "shows" us this color difference when the two light sources are part of the same scene. If, however, this print was illuminated only by the incandescent lamp (as in your living room at night) our mind would ADAPT and we would perceive a normal b&w print. The pages of the novel you are reading appear to be white when reading in bed with your table lamp. That's our eye/mind hard at work ADAPTING.

So, the light falling on our photographic subject can be different in color. That difference is expressed in a scale called Kelvin and is measured in degrees Kelvin. Don't panic. This is not difficult, but it is important to understand.

The range of color temperatures that we might typically encounter varies from about 1,700 degrees Kelvin for the light of a candle (pretty reddish in color) to the light of a bright northern sky at 15,000 to 30,000 degrees Kelvin (a brilliant blue white). Yes, believe it or not, reds are the cool colors while blues are the hottest colors -- counter-intuitive, like lots of things in photography. Specifically, the color scale progresses through this order as the light increases in Kelvin degrees: red, orange, yellow, white, blue.

The sun itself, because of the effect of our atmosphere, appears to produce different colors of light as the day progresses. At sunrise and sunset, the sun's light is approximately 2,000 degrees Kelvin (red/orange end of the scale). An hour after sunrise, the light has reached a Kelvin temperature of 3,500 degrees. You may have heard landscape photographers talk about the "golden hours" for taking pictures. They are referring to the time of day when the color temperature is between 2,000 and 3,500 degrees Kelvin -- early morning or late afternoon. This is the time when scenics are bathed in a dramatic red/yellow light. You have to be quick, because the color temperature changes rapidly.

This Grand Teton picture was taken 30 minutes after sunrise to produce a dramatic red/orange landscape.

By noon on a sunny day the light is in the 5,400 to 5,800 Kelvin range. This is the light your camera's automatic color balance system has been looking for.

Although not precise, the chart below illustrates the colors of the predominant light sources we encounter in our everyday life:


The graph hints at the remarkable flexibility of our eye/mind. When the predominant source of light is at any of the above temperatures, our internal system automatically re-calibrates itself to render white as white, and place all other colors in the scene in their proper relationship to white.

I said earlier not to panic. For our purposes, if you can mentally capture the graphic above, you will have no problem understanding White Balance.

Our cameras, however, must be told how to interpret the prevailing light source. That is the function of White Balance. The electronic flexibility afforded the photographer using White Balance control allows the scene to be rendered as the eye perceives it, or in even more creative and imaginative ways.

How we manipulate White Balance on a DSLR for its intended purpose, or expand its use for our own creative vision, is the subject of Part 24b.