:: 04. Understanding White Balance

You may not have noticed in your daily surroundings that sunlight and electric light are composite beams of light of various colors with differing wavelengths. This fact can be confirmed by looking at a rainbow, a natural prism that separates and shows individual colors. During the day, sunlight appears white with no color bias. The early evening has a red tint while the shade is blue-tinged. You may wonder what causes this phenomenon.

Light has interesting properties. Sunlight contains light of every wavelength from the long end of the spectrum to short, invisible ultraviolet rays. There is blue, which can be seen with the naked eye, then equally visible green and red as well as invisible infrared. Blue, red and green are called the primary colors of light. Almost all the other visible colors can be expressed as some mixture of these three. For example, yellow is achieved by mixing red and green. The whiteness of the daylight that humans perceive is the result of an equal mix of the three primary colors. The red-tinted light seen in the early evening results from the red light being the strongest of the three, and the blue-toned shade is a state where the blue light is stronger.

Human perceptions of light are also interesting. Under certain circumstances the human brain corrects light that has a color bias, such as light in the early evening or in the shade, to ïwhiteî based on its memory of white. Cameras, on the other hand, record the real state of the light more closely so that red-colored light appears red in a picture. This is why you may find it strange that there are differences between the resulting picture and your recollection of the colors when you shot it.

To deal with this situation, digital cameras are equipped with an auto white balance feature that automatically adjusts images more closely to the human perception of light. For example, if it detects too much red in an image, it finds the balance between the three primary colors so that white objects appear white to us.

You may be wondering why the term white balance is used. A camera lacks artificial intelligence and cannot judge what is scenery, the subject or even the color of the subject in the pictures it shoots. Instead, it takes the data it captures, finds the portion that is closest to white, and assumes that this is white as the basis on which to balance the colors in the remaining part of the image. That is why the term white balance is used.

The Colors and Characteristics of Light Underwater

Underwater light has characteristics that are quite different from the same light on land. On land, for instance, the color tones we perceive are the result of a bias in one or more of the three primary colors. Underwater, however, the deeper you go, the more most light frequencies are diffused so that at close to 40 meters, the deepest depth for recreational dives, almost all the frequencies are diffused into the water, except for blue light. This is the reason why the seas appear blue when you look at the sky from underwater, only the blue light can penetrate that far.

Since the special lighting conditions underwater are naturally not the same as on land, a cameraÍs automatic white balance capabilities may occasionally be overwhelmed or non-white objects may be mistakenly judged white with the result that it corrects colors inappropriately. With some cameras, images may have a bluish tint and extremely thin colors or they may have no blue whatsoever despite being taken underwater. This not really a problem, however, with digital cameras.

When shooting underwater, use the manual white balance settings instead of the auto setting. The setting you select will depend upon the clarity of the water, but the Daylight mode is generally good for shallow water as deep as 5 or 10 meters or for flash-assisted macro shots. For deeper water, or when flash-assisted macro mode produces an overly strong blue tone, use the Cloudy setting to reproduce bright colors without the blue bias.

The Elements of Light

The area of the graph under the horseshoe-shaped curve indicates the visible spectrum, the range of light frequencies that the human eye can sense unaided. The most vivid colors appear on the edges and the three primary colors„red, green and blue„almost form a triangle at the apex. It is the various combinations of these three light frequencies that make us perceive all the other colors.

Specific Light Frequencies Fail to Penetrate Water

The greater the depth of water, the more the light frequencies other than blue diffuse and fail to penetrate to that level. Even if a camera tries to correct the color balance, it lacks the required data, especially in the case of red light, which becomes completely diffused at relatively shallow depths. The cameraÍs auto white balance function will produce errors in that case.

Differences in the Balances of Red, Green and Blue Light on Land and Underwater

On Land

If you look at the three graphs for the primary colors in an image shot on land, you will notice that all three colors are nicely balanced and form similarly shaped curves.

Underwater

In contrast, the graphs for the underwater picture shot at an ideal exposure are less uniform. You can see that only the green graph is balanced: red is almost nonexistent and blue is too bright.

This section has been extracted from Canon Japan on how to prepare your digital investment.

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