March 29, 2011
Like many things in this world, light is not quite what it seems. What passes for white light is often far from white when photographed by a camera. Light has a temperature, which gives it a colour cast. Shadows and cloudy light have fewer red wavelengths and render with a blue tinge, whereas light from candles or incandescent light has more red wavelengths and has a warm tinge.
The reason we see light as white is that our brain automatically compensates for any cast, based upon our knowledge of the world around us. We know that a white wall is white, so our brains ignore any more obvious casts.
The main colour range that you will find on your images is from deep red through to a cool blue, measured in degrees Kelvin. The reddest light is from fires or candles (1600°K). This moves to a deep orange at sunset, then a distinctly yellow cast from incandescent light (2800°K). White daylight is defined as that which occurs around midday (5500°K). Light from overcast days has a blue tinge, moving to a deeper cast in the shadows (7000°K), or when reflected from snow.
Off this scale, most fluorescent light renders with a nasty green cast. This is somewhat sickly, and most of the time you’ll want to filter this out, though it can be left in as a special effect.
Luckily, your camera has the same functionality as your brain when it comes to correcting unwanted colour casts. If you switch on the Auto White Balance, your camera will do its best to neutralise any casts in your image. But this is only half the story – to really get the best pictures you won’t always want to remove the colour casts. Sometimes you’ll want to preserve them, and at other times even enhance them.
If, like most people, you’re shooting in the JPEG format, the best bet is to get everything right ‘in camera’. You can correct things on a computer, but this will result in a loss of quality. If you simply switch on the Auto White Balance function, your camera will seek to remove every colour cast, where you might want to preserve some. My advice is to switch the white balance to daylight. This means that the camera will emulate an old film camera. Sunsets won’t be neutralised, and if you’re shooting in the morning the warm tones will be preserved.
If you shoot in any artificial light, select the incandescent or fluorescent settings. To warm up the picture, use the cloudy or the more pronounced shade setting. This would be a good setting for shooting in snow or at the top of a mountain. The problem with all of this of course is that you have to remember to change your settings once you move into a different type of light or everything will go horribly wrong. These presets also don’t allow you any easy way to fine-tune without delving into the confusing depths of the advanced settings. If you want fine-tuning, the best way is to shoot using the RAW format.
If you’re shooting with RAW format, you can adjust the white balance later on a computer, without any loss of quality. This has a lot of advantages. You can make slight corrections in controlled conditions, and not by squinting at the screen on the back of the camera in direct sunshine. You can also make sure that the colours are precisely how you want them: subtly warming up a snow shot, enhancing the colours of a sunset, and removing most of the colour cast from candlelight, but leaving enough for it to still have warmth.
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