VisualModality
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Joined: 7/30/2005
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Chincillabutt  brought this question to my attention for her digital camera and I will try to explain as best in a lahmen term as I can being this can get a little technical.
What is White Balance?
It all boils down to the concept of color temperature. Color temperature is a way of measuring the quality of a light source. It is based on the ratio of the amount of blue light to the amount of red light. The unit for measuring this ratio is in degree Kelvin (K).
A light with higher color temperature (i.e., larger Kelvin value) has "more" blue lights than a light with lower color temperature (i.e., smaller Kelvin value).
A cooler light has a higher color temperature.
A warmer light has a lower color temperature
The following list shows the color temperature of some light sources.
( this is approx values)
Light Sources Color Temperature in K
Clear Blue Sky 10,000 to 15,000 ß (higher more blue light and is a cooler)
Overcast Sky 6,000 to 8,000
Noon Sun and Clear Sky 6,500
Sunlight Average 5,400 to 6,000 ß (less blue light, getting warmer)
Electronic Flash 5,400 to 6,000
Household Lighting 2,500 to 3,000
200-watt Bulb 2,980 ß (Much less blue light, warmer)
100-watt Bulb 2,900
75-watt Bulb 2,820
60-watt Bulb 2,800
40-watt Bulb 2,650
Candle Flame 1,200 to 1,500 ß (hardly any blue light, warmest)
The human brain can quickly adjust to different color temperatures. More precisely, our eyes. We see a white paper as a white paper no matter if it is viewed under strong sunlight or in a room illuminated with incandescent lights (household bulbs).
Unfortunately, color films can only correctly record the colors in a certain range of color temperatures. Therefore, we have daylight films(for natural light) and tungsten films (for artificial light).
Now, digital cameras are very different! Digital cameras usually have built-in sensors to measure the current color temperature and use an algorithm to process the image so that the final result may be close to what we see (with our eyes).
But, the algorithm(s) being used may not be accurate enough to make every situation correct. Under some difficult situations when the in-camera algorithm is not able to set the color temperature correctly or when some creative and special effects are needed, we can instruct the camera to use a particular color temperature to fulfill our need. This adjustment makes sure the white color we view directly will also appear white in the image. This is referred to as white balance.
In most digital cameras, there is manual settings for this adjustment. You will see Flourescent Light, Incandescent Light (average bulbs, household light), Direct Sunlight, Cloudy, Shade, and sometimes Flash. Which will compensate for the color accuracy.
Setting white balance incorrectly may cause a color shift in the image. For example, suppose the camera is manually set to use a color temperature of sunlight to take an image of an indoor environment lit mainly by incandescent lights. The camera will expect excessive blue light and less red light, and set its algorithm to be more sensitive to the blue light. As a result, we shall see a reddish or yellowish image.
Now, suppose we set the camera to a low color temperature (ex.incandescent light) and take a photo under sunlight. Because the white balance is set to incandescent light, the processing algorithm is more sensitive to the red light rather than the blue one. So, the resulting image will be bluish.
This is just a basic overview of White Balance without getting very very technical.
If you have any questions about this thread..let’s talk about it!
Regards,
Tina
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Regards,
Tina M Maravelis
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