Welcome to...

Light Colour Temperature

The reason that pictures turn out with a yellow/orange cast in incandescent (tungsten) lighting and bluish in fluorescent lighting is because light has a colour temperature. A low colour temperature shifts light toward the red; a high colour temperature shifts light toward the blue. Different light sources emit light at different colour temperatures, and thus the colour cast.

By using an orange or blue filter, we absorb the orange and blue light to correct for the "imbalance" -- the net effect is a shift in the colour temperature.

Auto White Balance

Since the days of the Kodak Brownie cameras, manufacturers have tried to automate everything for us. Hence, today's digital cameras also all sport an Auto White Balance (AWB) function. Depending on the camera brand, some AWB works better than others. On the whole, though, AWB works very well in sunny and cloudy outdoors, and fine for most indoors situations (a little orange or bluish cast does sometimes contribute to the mood of the picture anyway, e.g. the warm orangle glow of a candle).

Set your digital camera to AWB and take pictures under tungsten, fluorescent, and mixed lighting (i.e. tungsten or fluorescent, plus natural light coming through the window), and see if the results are OK. If they are, you can just use AWB.

Snow

Pictures of snow scenes typically reproduce the snow not as white but with a bluish tinge. Sometimes, the blue adds to the mood of the picture, but at other times you may want to remove the blue.

If your digital camera allows custom WB, then set the White to the snow and the blue should disappear.

Special Effects

Once you've selected a WB setting, just remember to reset this white balance setting when you head back outdoors into natural light, or you may end up with some strange, out of this world, colours.

In fact, by dialing in a WB setting inappropriate for the lighting situation allows us to create some special effects.

Let's say you are taking a picture outdoors and you want to make the light warmer, perhaps creating a late evening, sunset effect. To do that, we dial in a Fluorescent WB, in effect telling the camera that the light is too cool. The camera responds by shifting every colour toward the warm, red values. Dial in a Tungsten WB, and the camera shifts all colours toward the cool, blue values. Lots of trial and error recommended here.

RAW File Format

A discussion in WB would not be complete without a mention of the RAW file format available in many advanced digital cameras. When you save an image in RAW file format, you are saving it the way the image sensor sees it -- without applying any adjustments (including white balance) to it. In fact, the camera ignores any WB setting you dial in.

Later, in an image editing software with the appropriate RAW plug-in, you can convert the RAW image to JPEG, and apply any colour temperature shift. Undo your change and try again, ad infinitum, in as fine an increment as you wish, until you obtain perfect colour balance.

Some professional photographers always use RAW file format. Saving in RAW file format comes at a price because it takes so much longer to save a RAW image that it might not be practical in many picture taking situations. Professional dSLRs (and some prosumer models) have internal buffers that allow RAW images to be taken one after the other in quite rapid succession without having to wait for the saving of one image to be completed before you can take the next picture.

If you are taking landscapes, and it's early in the morning or late in the evening, or you are not too sure of which WB setting to use, try it in RAW.

A few digital cameras even allow you to save an image in both RAW and JPEG simultaneously, though time to write to memory card is proportionally increased.

Summary

For most of us, Auto WB is fine and does a pretty good job in diverse situations, outdoors and indoors.

For those occasions when you are not happy with the colour cast of your picture, choose one of the preset WB settings.

If this still does not give you what you want, consider manually setting the white balance by using a white card or sheet of paper (or white T-Shirt, etc.).

And, for ultimate control over white balance, consider shooting in RAW file format, and adjust in post-processing.

Posted in: photography basics, white balance on Thursday, May 8, 2008 at at 6:21 PM