Before we can talk about how to control the white balance in your camera we need to know a little bit about color temperature.
Color temperature is measured in 'kelvins' formerly known as 'degrees kelvin'. To get the idea, think of a piece of metal being heated in a fire. First it gives off a reddish glow and, as it gets hotter, the color gets whiter and then, as it really warms up, it starts to give off a bluish glow. In Physics of course, we can't use any old bit of metal for the kelvin scale, we need a 'theoretical black object'. The photographer's color temperature chart is a loose interpretation of the kelvin scale, the numbers are not used in any precise manner.
As photographers all we need to know is that different types of light source emit different colors. 5000 kelvins is what we photographers call white light and is represented by 'average daylight', whatever that is, actually it's fairly obvious if you look at the chart below. We also need to know that household bulbs give off an orange light and a cloudy day will appear blue. Here's a color temperature chart covering typical light sources. In the last column I have put my recommended camera setting for each type of light. As you can see, one setting can cover several steps on the scale.
|Temp||Typical Sources||WB Setting|
|1000K||Candles, oil lamps|
|2000K||Very early sunrise, low effect tungsten lamps|
|2500K||Household light bulbs|
|3000K||Studio lights (continuous), photo floods|
|4000K||Clear flashbulbs (now obsolete)|
|5000K||Typical average daylight, electronic flash|
|5500K||The sun at noon|
|6000K||Bright sunshine with clear sky|
|7000K||Slightly overcast sky|
|9000K||Open shade on clear day|
|10,000K||Heavily overcast sky|
|11,000K||Sunless blue skies|
|20,000+K||Open shade in mountains on a really clear day|
When we look at objects with our eyes, we perceive white objects as white, and gray objects as gray, no matter what sort of light source we are viewing them by. This is because our brain is making the conversion for us. We 'know' that wall is white so we don't notice that it looks yellow at night (with the room lights on). If you really start to look, you can see these color differences to some extent, but they are not as noticeable as they are to the camera.
Can I just use Auto White Balance?
Modern cameras have 'automatic white balance' so why can't we just leave it all to that? The AWB does do quite a good job but it isn't 100% accurate all the time. So sometimes we need to be able to do a few corrections ourselves.
The most common example of incorrect white balance occurs when you are taking pictures indoors at night without using flash. Everything will be distinctly orange. This is perfectly correct, things do look more orange under tungsten lighting but our eyes (and our minds as explained above) make an adjustment for this whereas the camera is not quite so good at making the adjustment.
|Even with AWB (auto white balance) and bounced flash, the picture straight out of the camera looked distinctly orange.||A quick tweak in the computer restored the color balance to a more natural look. I didn't want to lose the warm glow completely so I didn't go too far with the color correction.|
Although, as I have done with the shot above, you can retrieve the color balance afterwards in the computer, you do lose a bit of quality when you do this. It is much better to get it right in the camera if you can, the shot will just have that little extra 'zing' that sorts the good pictures from the mediocre.
Using RAW files
If you shoot your pictures in RAW format (and if you don't then you really ought to try it), you have much more information to play with. You have all the imformation that every pixel recorded at the time of the exposure rather than the cut down 'sub-set' of information that is saved after the camera has compressed your picture into jpeg format, hence the much larger file size. So, when you need to make adjustments like this color correction, the result is much better than if you tried to edit a jpeg. Basically when you view your picture on the screen or as a print, you are only viewing a sub-set of the information from the original exposure anyway but, by using the RAW format, you get to decide which bits of the original information you keep instead of letting the camera choose for you by automatically making a jpeg file. On a 'perfect' day in 'perfect' conditions the camera will choose very well but, when things go slightly wrong and need correcting, it's nice to be able to go back to the source material, ie the RAW file.
Interestingly there is no way in Photoshop to overwrite a RAW file. You can delete it of course and you can make non-destructive edits to it, which are saved in a separate file, but you cannot overwrite the file by pressing 'save', you can only save your changes as another type of file. So that means that you always have the original material to go back to and re-edit it.
Although by no means a 'masterpiece' the picture above is quite interesting as it shows different color temperatures in one shot. I deliberately shot the picture using a slow shutter speed to get some blur into the background. The foreground is being lit by my flashgun which has a color temperature of 5,000 kelvins. The background to the left is being lit by the wall lighting at around 2,500 kelvins and so looks quite orange. The man in the middle is being lit by both sources so there is a sharp image of him lit by the flash and a red smudge which is him lit by the tungsten light. Even though I set the camera to a slow shutter speed (1.6secs), the duration of the flash put out by the flashgun was under 1/1000th of a second so the bits of the photo lit by flash are sharp, the only movement blur is from the continuous light.
This system (setting a slow shutter speed and using flash) can be a fun way to get a bit of atmosphere and movement into your night shots but be prepared for quite a few failures as you cannot really predict exactly how they will turn out.
See also my tutorial about white balance.
An introduction to the color temperature scale.
How to set up your camera's manual white balance.
Using a gray card for color balance and exposure measurement.
Ever had the problem of washed out colors, either on a print or on the screen? The chances are the reason for it is that you're using the wrong color space.
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