Color correction for underwater photography

As an underwater photographer you most likely have encountered it: you experience wonderful colors under water but upon checking your shots at home you discover a blue haze and nothing is left of the beauty.

This article explains the theory of colors in under water and provides some solutions to get the best colors in your underwater pictures.

Colors under water

The color of a subject is both determined by the reflective and absorbing properties of the subject and the colors in the light source. This so called color temperature is measured in Kelvin (K), and ranges from red (warm) to blue (cool) light. Standard daylight is around 5600K, a halogen light at 3200K and candle light at 1200K.

The human brain is familiar with the colors of many subjects and is thus capable of compensating large differences in color temperature and gives us a consistent experience of colors. Cameras do not have such an excellent feature: by default they try to apply the appropriate 'chromatic adaptation' based on the received light and the general conditions in daylight.

This lack of understanding is clearly noticeable under water where the camera is unable to produce natural colored photos. Reason for this is the filtering property of water: colors will disappear as light travels farther through water. This results in loss of red light at 5 meter depth, and at 10 meters only green and blue is left. But there are a number of solutions discussed below that will compensate for this effect.

White balance on the camera

The automatic balancing of colors can be overridden by the White Balance (WB) function that is present on most digital cameras. This option allows you to set the camera at a predefined setting for various light sources/conditions, such as Daylight, Fluorescent lights, Clouds etc.

For good results it is usually sufficient if you select the Daylight WB setting just under the surface, and switch to Clouded at greater depths. Some cameras even provide one or more settings for underwater white balance that enable you to further tune the camera to the conditions during your dive.

The best results are obtained by manually measuring the correct white balance. This involves taking a photo of a white or gray object at the appropriate depth so the camera can determine the correct balance. Not all cameras feature such an option however.

Color correction filters

Photographers use many kinds of special filters to alter the colors in their photos. These change the color balance by selectively letting some colors through.

For good results, special underwater color correction filters are required, like those supplied by UR/Pro and Magic or underwater housing manufacturers.

They offer various types of filters, for use in blue tropical waters, green temperate waters etc. as well as for different depths. These filters can be mounted on the housing's port, or attached to the lens of the camera itself.

A drawback of using filters is that they reduce the total amount of light that reaches the camera, and may therefore induce darker or motion blurred results at greater depths. Additionally, when an external light source with different color temperature than the filter corrects is used, an unwanted color cast may be the result.

It is important to know that color correction by means of the white balance option or a filter still depends on the presence of colors: at depths below 10 meters the effect of these measures will decrease, and a strobe or dive light is then required.

Artificial light sources

The use of additional light sources, such as internal/external strobes and video light will bring back colors at greater depths.

Strobes typically have a temperature of around 5000K-5500K, so their color output can be compared to daylight. Video light usually have a much lower temperature, ranging from 3000K to 3500K, and produce light that is much warmer. For optimal results you must set your camera's white balance to the matching value.

Also, the underwater range of a strobe or light is limited to a few meters, and just as with the sunlight the water will filter the colors of these artificial light sources. Getting close to the subject is thus required to make sure enough light and color will reach it.

Check the tips for using external strobes for more details.

Verification using the RGB histogram

The different light conditions, the housing, and your brain's correction make that the colors of your shot will be difficult to interpret correctly on your camera's LCD display.

Luckily, an increasing number of cameras these days are equipped with an RGB histogram function. This shows graphs based on the presence of red, green and blue pixels in the image, and distributes these according to brigthness, from dark on the left to light to the right.

You can therefore use the RGB histogram under water to determine whether sufficient colors are present in your shot. Also, if the graphs and peaks of each color look fairly similar, a good white balance has been obtained. Obviously shots with a lot of blue water in it will always show up with the blue graph further to the right than the others.

Image processing on the PC

Photo processing software on your computer provides a number of functions to correct colors. Whether these will get you good results depends on the color information that has been stored in the image files. It is therefore still required to get the most light and color in the photo when taking it.

Read the articles on image processing for digital underwater photos and shooting RAW versus JPG for more information on getting the most out of your image files.

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