a1 Photo Tips

A picture taken in red light will look red - won’t it? And the same goes for pictures taken in other types of colored light. What you may not notice is that ordinary daylight can have very different qualities, and give very different results, depending on the time of day and other factors.

When the sun is close to the horizon, most of the blue rays are filtered out in the atmosphere and the light becomes reddish. And conversely, at noontime when the sun is as high up in the sky as it gets, the light is rather more blueish. This is especially true in the tropics - as in the image here above. At high altitudes, the light also has a very blue character since it has a shorter passage thru the atmosphere.

On an overcast day the cloud cover blocks much of the red wavelengths and for this reason the light that reaches the earth is rather cool.

Our human eyes adjust to these varying qualities of light, and unless they are quite extreme we don’t notice them much. The camera, however, faithfully records them as they are. Therefore we may be disappointed when we see how our pictures come out, with color casts we don’t like - unless we learn to understand how to deal with these effects.

You may be familiar with the term “color temperature”. Very cool blueish light is referred to as having a high color temperature, while reddish light as in the sunset picture here has - you guessed it - a low color temperature.

There is an international scale for measuring this, called the Kelvin scale. Unless you are seriously into Physics, you don’t need to know much about it, just take a look at the illustration here below to get a general idea.

A digital camera will be equipped with controls intended to compensate for those differences in color temperature of the light in different situations. For instance, my old Canon digicam has such settings as “Sunny” and “Cloudy”, plus a few more including - of course - “Auto”.

It is tempting to just set the camera on “Auto” and then forget about the whole issue. The problem is, as usual, that when you let the camera “think” for you, you also give up creative control over your pictures.

Naturally, how much creative leeway you have depends on what kind of camera you own. Like with my old Canon, I get to choose between a few standard types of lightning - or else set my own white balance. The latter means you point the digicam on a piece of white, or neutral grey, material; and set the camera to use that surface as a starting point for correct color balance in that particular situation.

With more advanced digicams, you could also have the option to set a number on the Kelvin scale directly. This opens the way for very precise and convenient control over the color rendering of every picture you take - provided you have the basic understanding shown in the illustration here.

Suppose for instance you take a picture on a cloudy day, when the colors are a bit on the cool side. You prefer to add just a bit of a warm “sunny” feeling to that picture. What to do? You set the Kelvin scale to a somewhat high number. By doing so, you tell the camera that the light is VERY blueish, and that this needs to be compensated for - by adding more red.

Or you are snapping a picture indoors in available light from incandescent light bulbs. You can then decide just how much of that “feeling” you want to have in the picture. Do you want to compensate fully for the reddish character of the incandescent light - or do you prefer to immerse the scene in a cozy reddish glow? In the latter case, you set the Kelvin scale to a higher number than the actual color temperature of the tungsten light sources, to get more red.

The Kelvin scale generally sees a color temperature of about 5500 K as “neutral white”, as shown above. Lower numbers mean an excess of red wavelenghts, and higher numbers mean an excess on the blue side.

Another situation where you may want to use a manual setting of the white balance is for very monochrome scenes. For instance, a picture of a person dressed in white and standing in front of a white wall. In this case the camera may have a hard time deciding what color balance setting to use, and needs your help.

Photo credits: bungalows by muha…; sunset by jurvetson.