White Balance

Article and Photography by Ron Bigelow

www.ronbigelow.com

Imagine an artist who wants to create an oil painting. He has the materials, skill, and a beautiful scene before him. There is only one problem. All of his oil paints have a color cast to them. Perhaps he wishes to create a desert sunset painting with beautiful warm colors, but all of his paints contain a cold, blue tint to them. It would be nearly impossible for the artist to render the warmth of the sunset with his blue tinted paint.

Photography is basically painting with light. The film or sensor is the canvas, the camera is the brush, and light is the paint. While the artist scenario described above might seem absurd, the photographer faces this challenge with every photo opportunity. The light that the photographer paints with often has a colorcast to it. Film and sensor capture this color, which then affects the quality and mood of the image.

To create an image that accurately depicts what the photographer intended, the photographer must be aware of the color of light and must make adjustments when necessary. The subject of the color of light, and the techniques of dealing with it, are referred to as white balance -- the subject of this article. The tools and techniques that photographers use to deal with white balance will be covered at the conceptual level. The actual implementation of these tools and techniques vary from camera to camera and are beyond the scope of this article. It is left up to the photographer to look up the instructions in his camera manual.

Color and the Human Brain

Unfortunately, the human eye and brain do not always properly interpret light color correctly. At the risk of repeating myself, the next two paragraphs, from my The Nature of Light article, cover the issue of color and human perception.

When dealing with the color of light, certain matters need to be kept in mind. Probably the first issue is the human brain. It turns out that the human brain does not passively receive or passively process sensory information. Instead, the brain does a significant amount of data altering before it allows the human that owns it to perceive. Quite often, the altering that the brain does changes the reality that the human perceives.

Quite simply, the brain adjusts the color that we see. The vast majority of the time, we are not even aware that this is happening. For instance, when you walk from a parking lot into a building, you are probably not even aware that the color of the light has changed significantly. For photographers, this creates a problem: the brain monkeys with the color we see. Thus, we do not always see color correctly. In particular, when dealing with warm or cool colored light, the brain functions on a principle of constancy. It expects the colors of objects to remain fairly constant throughout the day. If the color of objects changes during the day because the light that is illuminating them changes, the brain tends to filter out at least part of that color change. As a consequence, the color that we see during times of strong warm or cool light tends to be less intense than the color of the actual light and, possibly, less intense than what the camera will see and record. For instance, a casual photographer may not be aware that the light has become warm toned in the afternoon until he gets his film back and discovers that his wife's skin has an odd yellow tone.

Color Temperature

Before getting into the tools, the concept of color temperature needs to be introduced. Color temperature is just a way of quantifying the color of light. It is measured in degrees Kelvin (K). Normal daylight has a color temperature of around 6,500K. Warmer light has a lower color temperature. The warm light that occurs late in the afternoon might have a color temperature of around 4,000K. Cooler light has a higher color temperature. The bluish light that sometimes occurs in twilight periods of the day might have a color temperature of about 7,5000K. So, our concept of warm and cool light is tied directly to the color temperature. The more warm (yellow) the light is the lower the color temperature; the cooler the light (blue) is the higher the color temperature.

The temperature of the light illuminating an object is extremely important. Experienced photographers strive to match the light to the photographic subject and the mood that they are trying to create. However, just having the right light temperature is not enough. The photographer must capture that color temperature in a way that correctly portrays what the photographer intends. This is demonstrated in Figures 1 and 2. The image in Figure 1 was shot on a beach during the last few minutes of a colorful sunset. The sunset was backlighting the birds and illuminating the sand with a golden hue. In this Figure, the temperature of the light was correctly set. Figure 2 is the exact same image except that the temperature was deliberately set to an improper value. As can be seen, the entire mood of the image has been lost due to the incorrect temperature setting.

Figure 1: Correct Color Temperature
Figure 2: Incorrect Color Temperature

Color Temperature and Film

Color temperature is very important when using film. Each film emulsion is formulated to render accurate colors under light of a specific color temperature. For example, some films are designed to give accurate color when used in daylight of around 6,500K. As long as the film is used in the correct light, it will render accurate color. However, if the color of the light does not match the film, the colors rendered by the film will be inaccurate. For example, if a daylight film is used indoors with tungsten lighting (a warm light source), the images will have a yellow cast. If the film is used under florescent lighting (a cool light source), it will have a green cast. Conversely, if film balanced for tungsten lighting is used outdoors, the images will also have an unnatural colorcast.

So, when using film, it is important to match the film to the light in order to get accurate colors. Now, a problem arises. There is not a specific film for each possible light temperature that one might encounter. Furthermore, the light changes color during the day. The film that was loaded in mid morning, might not perfectly match the light source used in the afternoon. Not to worry, the problem is easily solved. Color filters can be used to correct the problem and deliver accurate color. For instance, a photographer with film balanced for daylight conditions that finds herself shooting under heavy clouds (a bluish light) might use a warming filter to correct the color issue and deliver accurate color.

So, how does one know when to use filters and how much filtration to use? In practice, most film photographers base their judgments on experience. Novice photographers can find information from the film manufacturers with recommendations about which filters to use with which films under different light sources.

Color Temperature and Digital Cameras

Color temperature is also important for those that use digital cameras. Some of you may be thinking, "I have used digital cameras for years and have never had to worry about color temperature". You may not have worried about it, but the camera did. The camera manufacturers knew that the color of the light would affect the colors delivered by the camera. Therefore, they decided to deal with the problem by designing the cameras to automatically measure the light temperature and to make adjustments as the light changes color. That is why you can shoot in the relatively neutral light with your digital camera in the afternoon and then shoot the next day in the cool light of early morning and still, probably, get reasonable color in both situations -- even though the color of the light was different. Your digital camera corrected for the change in light temperature.

The function on the camera that does this is called the white balance function. When the camera does this automatically, it is called auto white balancing (not surprisingly). So, if the camera does this automatically, why even bother discussing it? Well, it turns out that many cameras have other white balance options than auto white balance. While the auto white balance on the newer digital cameras is pretty good, it is not perfect. In some cases, you may not get the color you expected or desired when using auto white balance. When that is the case, one of the other white balance options may be more desirable. More advanced cameras generally have three types of white balancing: 1) automatic, 2) preset, and 3) custom. When all else fails, photographers that use the raw format can set the white balance manually. Since each of these white balance options has advantages and disadvantages, and can change the colors in an image, it is important to understand each option.

Auto White Balance

With auto white balance, the camera attempts to determine the color temperature of the light and automatically adjust for that color temperature. Many people just leave the camera set to auto white balance all the time. This is certainly the easiest option. Auto white balance works reasonably well under the following conditions: (1) the application does not require absolute maximum color accuracy, (2) there is not a preponderance of one color in the scene being photographed, and (3) the photographer wants adjustments made for the color temperature of the light. It is also a good option for situations where the light changes over time and speed is an issue (e.g., animal photography). This is usually the case for general family and vacation type photography. It is often true for even serious landscape and animal photography. After all, who would even know if the blue color of the sky was off by 2%? Figure 3 shows an image that works well with auto white balance. This image is a landscape shot where reasonable, but not fanatical, color accuracy is required. Also, the image has a mixture of colors without one color dominating the image.

Figure 3: Good Image for Auto White Balance

As mentioned in the previous paragraph, in auto white balance mode, the camera does its best to determine the color of the light and make adjustments. However, the methodology that is used to do this requires that certain assumptions be made. These assumptions do not always match perfectly with the scene being photographed. As a consequence, the auto white balance option does not always yield perfect results. Accordingly, photographers may experience problems using auto white balance when the conditions listed above are violated. Therefore, auto white balance may not be a good choice if:

  1. Absolute Color Accuracy is Required: If you were to photograph the introduction of a new fall lineup of a major fashion company, you would not want to risk using auto white balance. If the color of the models' outfits in your photographs came out slightly off, you would no longer be employed in that industry.

  2. There is a Lot of One Color in the Scene: The preponderance of one color can fool the auto white balance function into assuming that the light has a lot of that color in it. This can result in an incorrect white balance and a color cast. This is illustrated in Figure 4. There are only two major colors in this image (with green accounting for the majority of the color). This caused the camera to adjust the image due to the predominance of green. As a result, the grass picked up a tint. The color balance of the image had to be manually adjusted to bring back the lush, green, springtime feel that was observed when the image was taken. Figure 5 shows the image after the color balance adjustment.
Figure 4: Problem for Auto White Balance (too much of one color)
Figure 5: After Color Balance Adjustment
  1. The Photographer doesn't Want Adjustments Made for the Temperature of the Light: In certain cases, the color of the light is what makes the photograph. A sunset is an example. Without the rich, warm colors of the light, a sunset just isn't a sunset. Auto white balance may attempt to make adjustments to correct for the warm color of the sunset light. This would produce an image with less saturated colors or colors that were different than what the photographer saw. Figure 6 shows just such an image. In this case, auto white balance is a poor option because the color of the light is an integral part of the image. What the photographer saw was a gorgeous, orange sunset. The camera saw the same thing and immediately adjusted for it. The result is the rather unimpressive sunset shown in this image. Figure 7 shows the exact same image except that auto white balance was not used. Rather, the color temperature was set to a daylight setting (a preset white balance option). This produced an image that much more accurately portrays what the photographer saw.
Figure 6: Problem for Auto White Balance (adjustments should not have been made for the color of the light)
Figure 7: Image with a Daylight Color Temperature Used.
Table 1 sums up the strengths and weaknesses of the auto white balance option.
Table 1: Auto White Balance Strengths and Weaknesses
Strengths
Fast and easy to use. Provides reasonable color accuracy under many conditions.
Weaknesses
Does not provide maximum color accuracy. Can be fooled when a scene has a preponderance of one color. Poor choice when the color of the light is an integral part of the image.
Works Best
Best for scenes that do not require maximum color accuracy, do not have a preponderance of one color, and where the color of the light is not an integral part of the scene. Is a good option for situations where the light changes over time and speed is an issue (e.g., animal photography).

Preset White Balance

With preset white balance, the color temperature is assigned by the photographer, prior to a shot being taken, by selecting one of the preset white balance options. Many cameras have multiple preset white balance options. For instance, a camera may have settings for bright sunny outdoors, cloudy outdoors, shady outdoors, tungsten, fluorescent, and flash. Preset white balance works well when: (1) The application does not require absolute maximum color accuracy, and (2) the light source matches one of the preset white balance options. An indoor company party is a good example of when preset white balance might be used. Reasonable color accuracy, not absolute color perfection, is required, and the indoor lighting will likely be either tungsten or fluorescent, which will match one of the preset options. One advantage of the preset white balance is that it is not fooled if there is a lot of one color in the scene. So, if you photograph Santa and a large group of red clad elves under fluorescent light, the fluorescent white balance preset option will give a fairly good color result while the auto white balance might have problems. Figure 8 is an example of a situation where a preset white balance worked well. The large amount of very lush, green vegetation was pleasant to the eye, but it might have caused problems for auto white balance. Therefore, a daylight preset white balance was used to ensure a more accurate white balance.

Figure 8: A Good Scene for a Daylight Preset White Balance

Preset white balance is a logical choice in one other situation: when the photographer doesn't want automatic adjustments made for the temperature of the light. Looking back at Figures 6 and 7, it can be seen how preset white balance solved a white balance problem with the image in those figures. The auto white balance setting in Figure 6 caused the camera to make automatic adjustments for the warm, saturated light of the sunset. This resulted in a desaturated sunset. Changing the white balance to a daylight preset white balance resolved the problem and produced the saturated sunset that the photographer saw.

Preset white balance is not always the perfect choice. Photographers may experience problems using preset white balance when the conditions listed above are violated. Therefore, preset white balance may not be a good choice if:

  1. Absolute Color Accuracy is Required: Even a small mismatch between the light source and the preset white balance will result in some inaccuracy in color rendition. In those cases where absolute color accuracy is required, preset white balance is not a good option since it is unlikely that there is a perfect match between the light source and the preset white balance options. Back to that fashion show example, if you were to photograph the introduction of a new fall lineup of a major fashion company at a New York fashion show, you would not want to risk using preset white balance.
  1. The Light Source does not Match One of the Preset White Balance Options: There may be occasions when the light source does not match any of the preset white balance options. In these cases, another white balance method must be used.

Table 2 sums up the strengths and weaknesses of the preset white balance option.

Table 2: Preset White Balance Strengths and Weaknesses
Strengths
Fast and easy to use. Provides reasonable color accuracy when the light source matches one of the preset white balance options. Is not fooled if there is a lot of one color in the scene. Can be used when the photographer doesn't want automatic adjustments made for the temperature of the light.
Weaknesses
Does not provide maximum color accuracy. Can not be used when the light source doesn't match one of the preset white balance options.
Works Best
Best for scenes that do not require maximum color accuracy and the light source is a reasonable match for one of the preset white balance options. Is often a good solution when there is a lot of one color in the scene or the photographer does not want the camera to automatically make adjustments for the color of the light.

Custom White Balance  

Rather than make assumptions about the color temperature of light (auto white balance) or fixing the color temperature at a given value (preset white balance), custom white balance actually uses the camera to measure the color of the light hitting the sensor. To make sure that the camera is measuring the color of the light source and not the color of some object from which light has been reflected, the photographer must use a neutral gray or white object to establish the white balance. Typically, the photographer will photograph a gray card, or other similar object, and use that to establish the white balance.

Two options exist for the photographer once the gray object has been photographed. In the first option, the photographer can follow the procedures for her specific camera to direct the camera to use the image of the gray object to establish the white balance for future shots. The camera will analyze the gray image information to determine the color temperature of the light and to set the white balance. As shots are then taken, the camera applies this custom white balance to the images. In this case, the images come out of the camera with the white balance already set. This is often the best option for those shooting JPEG. Since the white balance is set in the camera, no additional post processing will be required for white balance purposes. In the second option, the image of the gray object is simply saved. The gray image is used during post processing to set the white balance. This procedure is particularly popular with photographers that shoot raw as the raw converters have functionality that make it easy to use the gray image to set the white balance during the raw conversion process. With this procedure, the image does not come out of the camera properly white balanced and requires some post processing. The advantage of the second option is that it is quicker for the photographer while in the field. The photographer does not have to take the time to follow the camera's step-by-step procedure, as in the first option, before taking a shot. This is of great value in situations involving rapidly changing light.

The advantage of the custom white balance is that it accurately records the color of objects as they would appear if the objects were photographed in neutral colored light. Furthermore, custom white balance sets the white balance much more accurately than either the auto white balance or the preset white balance. Therefore, custom white balance is the best option when (1) maximum color accuracy is required and (2) the photographer wants the colors in the image to appear as they would under neutral light.

Figures 9 and 10 show a situation where custom white balance was a good choice. The predominant feature of the scene shown in these two figures is the vivid fall color displayed by the trees. Therefore, it was desired to show the true color of the trees. The problem was a combination of a predominance of yellow in the image, a heavily overcast sky, and a very late afternoon shot. The yellow was almost sure to cause the auto white balance to incorrectly read the light. One might consider a cloudy preset white balance. This setting assumes that the light has a blue tint, which is usually correct for cloudy conditions. However, this shot was taken very late in the afternoon. The light, above the cloud cover, would be expected to have become warm. Thus, it was suspected that there was a warm colored light being filtered through a cloud cover that should add a cold, blue tint. In short, there was no way of knowing what color the light would be and no way to be confident that a cloudy preset, white balance option would yield correct color. It was decided to set the camera to auto white balance and then to shoot a gray card to use for setting a custom white balance in the raw converter if the results of the auto white balance were unacceptable. Comparing these two figures shows that the custom white balance captured richer, more saturated colors (which is what I saw when taking the image).

Figure 9: Auto White Balance
Figure 10: Custom White Balance

It was mentioned that one of the advantages of custom white balance is that it accurately records the color of objects as they would appear if the objects were photographed in neutral light. On the other hand, one of the disadvantages of custom white balance is that it accurately records the color of objects as they would appear if the objects were photographed in neutral colored light. In other words, accurate color according to how the colors would appear in neutral light can be either a good or a bad thing. For the fashion show photographer, it is a good thing. The fashion designer probably wants the colors of the clothing to photograph as they would look under neutral lighting. On the other hand, richly colored sunsets are beautiful precisely because of the very warm color of the light that is prevalent at that time. Using a custom white balance would remove much of the color and would result in desaturated sunsets – the exact opposite of what most photographers would want. Therefore, custom white balance may not be a good choice if:

  1. The Photographer doesn't Want Adjustments Made for the Temperature of the Light: The custom white balance will make a very accurate adjustment for the color temperature of the light, which may ruin the feel of images that depend on the color of the light to set the proper mood. Figures 11 and 12 demonstrate this issue. The scene is a meadow flooded from snow pack runoff. The temperature was cold as a storm front passed through the area. The heavy cloud cover cast a cold, blue light on the scene, which set the mood. The same image is shown in both figures. Figure 11 used auto white balance. This left the image with a slight blue tint that is especially noticeable in the distant mountains (I was a bit surprised that the auto white balance did not remove more of the blue from the image). This properly coveys the cold feeling of the scene. Figure 12 had a custom white balance applied in the raw converter. The custom white balance corrected for the blue in the light. The result is an image in which the mood has been destroyed. Clearly, custom white balance is not always the best way to go.
Figure 11: Auto White Balance
Figure 12: Custom White Balance
Table 3 sums up the strengths and weaknesses of the custom white balance option.
Table 3: Custom White Balance Strengths and Weaknesses
Strengths
Very accurately determines the color temperature of the light and very accurately sets the white balance.
Weaknesses
Poor choice when the color of the light is an integral part of the image. Requires more time and effort than auto white balance or preset white balance.
Works Best
Best for scenes that require an accurate rendering of colors as they would appear if the objects were photographed in neutral light.

Manual White Balance

We now have to face an ugly truth. At times, white balance can be a tricky issue. Imagine photographing a forest scene. The green trees fill up much of the image, the sky above has a beautiful warm toned sunset, and the mountains at the side cast a large shadow across part of the forest. This is a major mix of color temperatures and white balance problems. Who knows what auto white balance would do. It could easily be fooled by the large amount of green forest, the large bluish shadow, the warm sunset, or a combination of all of these. Under such condition of mixed light, how would one even know what the proper preset white balance option would be? Most likely, none of the preset white balance options would be a perfect match. The effect a custom white balance would have would depend on whether the photographer was standing in an area illuminated by the warm sunset or in the shadows. If standing in the light of the sunset, a custom white balance would adjust for the warm color of the light and desaturate the sunset colors. If standing in the shadows, a custom white balance might cause the trees that were not in shadow, to have a color cast.

In short, at times, none of the three white balance options just covered will yield the results the photographer desires. For those that shoot raw, an easy solution awaits. For the ultimate in white balance customization, the white balance of raw files can be set manually in the raw converter. Thus, if one of the other white balance options does not render the colors the way the photographer wishes, the white balance can be manually set in the raw converter to a setting that does create the proper rendering.

Figures 13 to 15 illustrate this issue. The image in these figures consists of old mining ruins that were illuminated by the warm rays of the setting sun. Consequently, the ruins were bathed in a warm glow. The sky behind the ruins was blue from the blue rays that had been scattered by the atmosphere (for an explanation of this scattering, see Rayleigh scattering in the article The Magic Hour Times Two). Figure 13 shows the image with auto white balance. The ruins are a bit too yellow and the sky has turned into an unpleasant gray. Obviously, the white balance has not been properly determined. Frankly, this is not what I had expected; I had expected the auto white balance to desaturate the warm tones. It just goes to show that you can not always predict what auto white balance will do when dealing with very saturated colors. Figure 14 shows the image with a daylight preset white balance. The image isn't much different from the auto balanced image and is unacceptable. A custom white balance was not even considered at the time that the image was taken as it would have adjusted for the warm light and desaturated the warm glow on the building. The only option left was to set the white balance manually in the raw converter. Image 15 shows the results. The warm glow on the building now looks more like what was seen at the time the image was taken and a small amount of blue has been added back into the sky. The manual white balance has given the desired setting and look to the image.

Figure 13: Auto White Balance
Figure 14: Daylight Preset White Balance
Figure 15: Manual White Balance

While manual white balance can be used in cases where the other white balance options fail, it has its own set of problems. Perhaps foremost is that the photographer must set the white balance from memory. Unless one has a photographic memory (no pun intended), this will likely lead to inaccuracies, especially when large numbers of images are taken. In addition, setting the white balance manually takes more time than the other techniques.

Table 4 sums up the strengths and weaknesses of the custom white balance option.
Table 4: Manual White Balance Strengths and Weaknesses
Strengths
Can be used when the other white balance options fail.
Weaknesses
Time consuming and can lead to inaccuracies unless the photographer can remember exactly how the scene looked at the time it was taken.
Works Best
Best for scenes with mixed or complicated light sources.

Options, Options – How Does One Decide

For the photographer in the field or studio, the question becomes, "Which white balance option is the best for any given circumstance". Essentially, it is a matter of knowledge of the basic information covered above combined with some experience.

So, how important is white balance? When one understands that great photography is about communicating an emotion, that the emotion communicated by an image is often largely determined by the colors in the image, and that the white balance will determine those colors, the setting of the proper white balance becomes a critical part of the image capture process.

Articles