Photography - Understanding White Balance
If you read digital camera reviews you will come across the term "white balancing" again and again.
Although the term sounds esoteric, it simply refers to the way you can correct for color casts in your final images.
For example, if under a given set of lighting conditions your shots of a perfectly white polystyrene foam surface produce images with a slightly blue color cast, then you will need to know how to white balance your images for that particular lighting situation.
Once you have made the appropriate camera settings, the information will be recorded along with your image in RAW format so that the white balancing information can be applied to the final printable image.
This is typically a JPEG file.
So what is the cause of these color shifts? Photographers who still use film stock may be able to attribute some portion of a color shift to the characteristics of the film itself.
This, of course, is not the case for digital photography, where the chemical nuances of film emulsion have been removed from the digital imaging process.
Most color casting, then, comes from the lighting source used to illuminate the scene before the camera.
Fluorescent lighting, for example, can add a slightly green color shift to images, while a blue cast may result from the diffuse sunlight of an overcast day.
This color bias is sometimes described in terms of an equivalent color temperature.
Bodies which radiate the same neutral color spectrum as the sun are said to have a color temperature of around 5000 degrees Kelvin, whereas cooler bodies radiate more in the red portion of the spectrum, and hotter bodies are shifted to the blue.
As an example, the deep red hue of candlelight is typical of a body radiating at around 1000 degrees Kelvin, while the diffuse light of a heavily overcast day is closer to 9000 degrees Kelvin.
On the one hand, talking about color shifts in terms of the equivalent temperature of the light source may be technically useful, but for the average photographer it will likely only lead to confusion.
For this reason, you will usually find on the back side of your digital camera, a chart that shows the equivalent white balancing modes to offset the effects of different lighting conditions, and no mention of color temperatures is made.
In addition to an auto white balancing mode (AWB) in which the camera itself tries to figure out the best white balancing setting to use, there are several other manual modes that can be selected.
A cloud icon, for example, indicates the white balancing offset that ought to be selected if the scene is being bathed by the light of a fully overcast sky.
This setting will compensate for the bluish cast that would be seen in the absence of a color correction.
The correction for the generally neutral effect of direct sunlight is typically represented with an icon that depicts the sun.
One way to correct for white balancing, at least on a point-and-shoot digital camera, is to monitor the scene before your camera using your LCD screen.
If the image appears too bluish (high temperature light source) you can adjust the white balancing to shift the image slightly to the red.
Most digital SLRs use the LCD screen for image playback only, so you may have to take a test shot and view the result first, or if your camera supports it, you can bracket your white balancing (record a triple of each photograph with varying amounts of white balancing added to each), and then select the best result.
The trouble with this approach, however, is that it is somewhat subjective.
A more accurate means to correct white balancing is to look for an element in the scene which is white and adjust your white balancing setting to ensure that the white object renders as true white.
Carrying a white object with you, such as a white handkerchief, or white card, that can be inserted into the scene, can be very useful.
This is especially the case where the scene itself may predominately contain objects that are either blue or red, since this may cause the camera to select the wrong white balancing if left to itself to decide (in auto white balancing mode).
As an example, if you were photographing blue icebergs in bright sunlight your camera might assume the blue coloration was due to a blue color shift caused by clouds and then try to reduce the amount of true blue in the final image.
By being aware of the causes of color shifts, and analyzing your images, you will find that over time you get better at making the needed white balancing correction before taking your photographs.
But even if you have yet to get the hang of this while shooting, don't forget that you can often correct your mistakes simply by working directly with the RAW format image after the event.
This is one of the real advantages of working with digital images.
Although the term sounds esoteric, it simply refers to the way you can correct for color casts in your final images.
For example, if under a given set of lighting conditions your shots of a perfectly white polystyrene foam surface produce images with a slightly blue color cast, then you will need to know how to white balance your images for that particular lighting situation.
Once you have made the appropriate camera settings, the information will be recorded along with your image in RAW format so that the white balancing information can be applied to the final printable image.
This is typically a JPEG file.
So what is the cause of these color shifts? Photographers who still use film stock may be able to attribute some portion of a color shift to the characteristics of the film itself.
This, of course, is not the case for digital photography, where the chemical nuances of film emulsion have been removed from the digital imaging process.
Most color casting, then, comes from the lighting source used to illuminate the scene before the camera.
Fluorescent lighting, for example, can add a slightly green color shift to images, while a blue cast may result from the diffuse sunlight of an overcast day.
This color bias is sometimes described in terms of an equivalent color temperature.
Bodies which radiate the same neutral color spectrum as the sun are said to have a color temperature of around 5000 degrees Kelvin, whereas cooler bodies radiate more in the red portion of the spectrum, and hotter bodies are shifted to the blue.
As an example, the deep red hue of candlelight is typical of a body radiating at around 1000 degrees Kelvin, while the diffuse light of a heavily overcast day is closer to 9000 degrees Kelvin.
On the one hand, talking about color shifts in terms of the equivalent temperature of the light source may be technically useful, but for the average photographer it will likely only lead to confusion.
For this reason, you will usually find on the back side of your digital camera, a chart that shows the equivalent white balancing modes to offset the effects of different lighting conditions, and no mention of color temperatures is made.
In addition to an auto white balancing mode (AWB) in which the camera itself tries to figure out the best white balancing setting to use, there are several other manual modes that can be selected.
A cloud icon, for example, indicates the white balancing offset that ought to be selected if the scene is being bathed by the light of a fully overcast sky.
This setting will compensate for the bluish cast that would be seen in the absence of a color correction.
The correction for the generally neutral effect of direct sunlight is typically represented with an icon that depicts the sun.
One way to correct for white balancing, at least on a point-and-shoot digital camera, is to monitor the scene before your camera using your LCD screen.
If the image appears too bluish (high temperature light source) you can adjust the white balancing to shift the image slightly to the red.
Most digital SLRs use the LCD screen for image playback only, so you may have to take a test shot and view the result first, or if your camera supports it, you can bracket your white balancing (record a triple of each photograph with varying amounts of white balancing added to each), and then select the best result.
The trouble with this approach, however, is that it is somewhat subjective.
A more accurate means to correct white balancing is to look for an element in the scene which is white and adjust your white balancing setting to ensure that the white object renders as true white.
Carrying a white object with you, such as a white handkerchief, or white card, that can be inserted into the scene, can be very useful.
This is especially the case where the scene itself may predominately contain objects that are either blue or red, since this may cause the camera to select the wrong white balancing if left to itself to decide (in auto white balancing mode).
As an example, if you were photographing blue icebergs in bright sunlight your camera might assume the blue coloration was due to a blue color shift caused by clouds and then try to reduce the amount of true blue in the final image.
By being aware of the causes of color shifts, and analyzing your images, you will find that over time you get better at making the needed white balancing correction before taking your photographs.
But even if you have yet to get the hang of this while shooting, don't forget that you can often correct your mistakes simply by working directly with the RAW format image after the event.
This is one of the real advantages of working with digital images.
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