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Understanding WHITE BALANCE by Mark Jamieson

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Understanding WHITE BALANCE by Mark Jamieson

Post Number:#1  Postby Snafu » Thu Dec 06, 2007 5:47 pm

Understanding White Balance

By Mark Jamieson

    When shooting underwater video, it’s natural to expect that your camcorder will accurately capture the beautiful colors of the underwater realm. However, when your underwater video sequences have an overall color shift with images that appear reddish-yellow or blue, it likely indicates that the white balance setting on your camcorder was incorrectly set when you shot the video.

    White balance is a term that refers to how a digital camera (video or still) electronically calibrates the color spectrum that is reflected back through the lens to the CCD sensor, using the color white as a reference point. The theory behind this is if the color white is calibrated correctly, the other colors will be calibrated as well.

    While many non-linear editing applications allow you to color balance a video sequence in order to correct video footage that was shot with an incorrect white balance, it is good practice (and less time consuming) to ensure the white balance preset on your camcorder is correctly set or that you manually perform a white balance calibration for the current lighting conditions before you record your video footage. Your video sequences will match better from shot to shot as a result.

    Whether you shoot your video primarily using natural light (sunlight), video lights, or a combination of both types of light sources, you’ll need to know how to set your camera’s white balance so that your underwater video images appear correct.

    You might recall from your high school physics class that light is composed of various colors of light that make up the color spectrum. When the composition of these various colors of light is equal, the light appears white. However, white light is often filtered when it passes through another medium such as air or water, which alters the resulting color spectrum so that the light no longer appears white. When objects in the scene reflect this non-white light back to the lens of the video camera, their color won’t appear correct.

    One method for understanding how the color of light affects the appearance of objects is by observing the changes in the color of sunlight throughout the day. In the morning and evening hours, when the sun is low on the horizon, the color of sunlight appears shifted towards the warmer range of the color spectrum, causing objects to appear lit by a warm toned yellow-reddish light. At midday, the color of sunlight is usually balanced towards white light so objects appear without color casts of any type. On an overcast day, when sunlight is filtered through the clouds and haze, the color of light is shifted towards the bluish end of the color spectrum.

    In technical terms, the amount of red or blue in light sources is described using a term called color temperature.  The color of light is measured as a theoretical temperature of a black body object radiating the same color as if it were heated to that particular temperature. The units of measurement are in degrees Kelvin (°K). Many light sources are rated using this standard of measurement. The color temperature of a light source can be accurately measured using a color meter, a handheld device that works in a similar fashion to a photographer’s light meter. The color meter measures the color temperature and indicates the Kelvin temperature as a digital value.


The lower end of the Kelvin color temperature scale indicates the warmer colors of the light spectrum, while the higher end of the scale indicates the cooler colors. In the middle of the scale, light appears white - all colors of the light spectrum are in balance.

Light Source             Color Temperature
Daylight (Sunrise/Sunset)       3200 °K
Tungsten/Halogen Lights       2800-3400 °K
Sunlight (Midday)                     5500 °K
HID Lights                     5500-7500 °K
Sunlight (Overcast sky)       6500-7500 °K

Example light sources and their approximate color temperatures

Your eyes compensate for varying light levels by automatically enlarging or constricting the pupils. Likewise, your brain automatically compensates for the range of color temperatures possible with light throughout the day so that a white object appears white regardless of the lighting conditions. A digital camcorder will record the light exactly as it senses it unless you recalibrate it using its white balance settings.

PART 1
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Re: Understanding WHITE BALANCE by Mark Jamieson

Post Number:#2  Postby Snafu » Thu Dec 06, 2007 5:50 pm

Using white balance camera settings
    In order to obtain an accurate white balance setting with your underwater video camera system, you’ll need to understand the various white balance presets that exist for camcorders, how they work, and the limitations for each type. The following white balance presets are standard with most camcorders, although there may be less or more presets depending on your camcorder model. If in doubt, check your camcorder’s user guide to be sure.

Automatic white balance
      Automatic white balance is the default white balance setting on most camcorders. All camcorders have an automatic white balance setting and some camcorders have only an automatic white balance and nothing else. In Automatic white balance mode, the camcorder is continuously evaluating the light that is reflected back through the lens onto the CCD and compensating the color palette for the image. This continuous evaluation and calibration of the white balance occurs in a gradual manner, so you won’t notice any sudden color shifts when looking through the viewfinder and recording your footage, unlike what occurs with other automatic functions like focus and exposure.

    If you shoot at relatively shallow depths (20-60 feet), use available light with a color correction filter (except when shooting at depths of less than 20 feet), and are the type of underwater videographer who doesn’t want to concern yourself with too many camera settings, then the Automatic white balance setting will be an overall good choice.

    If you power off your camcorder at various times throughout the dive to save on battery power, and are shooting using the Automatic white balance setting, then you must remember to allow a few minutes for your camcorder to calibrate the white balance for your current lighting conditions, depending on your depth, when you power on the camcorder before you begin shooting.

    In addition, since there may not be anything white in the scene for the camcorder to calibrate against - especially when you descend deeper and more of the available light’s color spectrum is absorbed - the Automatic white balance may not produce an accurate result.

Hold/Auto Lock
    Some camcorders are equipped with a Hold/Auto Lock feature that lets you lock the current exposure, shutter speed, and recording level, as well as the white balance settings as determined by the automatic features of the camera. This setting is useful above water when the lighting conditions are relatively consistent and you don’t want the above listed automatic functions to be continuously changing when you are shooting. That is, it’s a useful option provided you can turn it on or off at will.

    However, locking the exposure and white balance settings is of limited use underwater in situations where the intensity of light and its color temperature changes with depth.

    Most housing’s require that you turn off the camcorder’s Hold/Auto Lock setting prior to placing it into the housing. Check the manual that came with your video housing for the preferred camera presets before placing your camcorder in the housing.

Daylight/Outdoor white balance
    The Outdoor white balance setting calibrates the camcorder’s white balance for a 5500 °K light source. This white balance preset setting is indicated in the viewfinder by a small sun icon. The Outdoor white balance setting is also useful when you’re shooting in shallow water (less than 20 ft) without a color correction filter. Beyond a depth of 20 ft the light source will begin to lose other colors of the spectrum due to absorption etc. and you’ll need to either rely on the Automatic white balance setting or manually white balance your camcorder (see below).

    You can also use the Outdoor white balance preset when you are shooting with HID video lights as these light sources have a color temperature very close to that of sunlight at midday. The advantage of using the Outdoor white balance setting in the above scenario is that the camcorder will be properly white balanced for the primary light source (HID lights), as well as the secondary background light source (sunlight) to some extent.

Tungsten/Indoor white balance
    The Indoor white balance setting calibrates the camcorder’s white balance for an incandescent/tungsten light source in the 3400 °K color temperature range. This white balance preset setting is indicated in the viewfinder by a small light bulb icon. Use this setting when you are shooting with quartz halogen video lights, as their light source exists in the warmer range of the color temperature spectrum.

    The Indoor white balance setting will compensate by removing the excessive warm color provided by this light source. However, shooting with halogen video lights as your primary light source with sunlight as your secondary light source using the Indoor white balance setting will cause the background areas not lit by the halogen lights to appear bluer in color. You can color correct the lights by mounting blue color correction filters on the lights and using the Outdoor white balance setting, but the light filtration will reduce the intensity of the halogen lights.

Part 2
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Re: Understanding WHITE BALANCE by Mark Jamieson

Post Number:#3  Postby Snafu » Thu Dec 06, 2007 5:53 pm

Manual white balance
    The Manual white balance setting calibrates the camcorder’s white balance by sampling the actual light that is reflected from the scene through the lens of the camcorder. This white balance setting is indicated in the viewfinder by an icon that looks like a square with two triangles on either side. Not all camcorders and video housing combinations provide the manual white balance capability, but it is by far the best method for obtaining an accurate white balance. It does require some extra work on your part, but calibrates the camera’s white balance much more quickly and accurately than the Automatic white balance setting.

To perform a manual white balance calibration with your underwater camera system you must do the following:
-        Point the camera lens at a white reference object such as a white plastic card or dive slate.
-        Ensure that the white card fills the entire frame.
-        Ensure that the white card is illuminated in a similar fashion as your scene. That is, the white card is not within your shadow or your camera’s, and that your video lights (if used) illuminate the card.
-        Press the white balance button on your housing to sample the light source as it gets reflected off the white card. This causes the white balance icon to flash for a few seconds as the camera performs the calibration. Do not move your camera away from the white card while this is occurring. When the icon stops flashing it indicates that the white balance calibration is complete and locked. You’ll also likely notice an immediate color shift through the viewfinder.

    Once you’ve completed a manual white balance calibration, you can go ahead and compose your shot and record your video sequence. The camera’s white balance will be locked at that setting until you perform another white balance calibration. If your lighting conditions do not change (shooting at the same depth, shooting with video lights, etc.) you can repeatedly capture video with the same white balance setting. However, you’ll likely want to perform frequent manual white balance calibrations just to be sure the colors being recorded in your sequences are accurate.

    You can also trick the camera’s manual white balance calibration by using a reference object that is not white. For example, if you use a reference card that is light blue in color, the camcorder will attempt to calibrate the white balance as if it were actually seeing a white card. The resulting white balance will be slightly warmer than normal as a result of the compensation that occurs. Professionals often use this technique to obtain better skin tones when compared to the “technically accurate” results produced by the standard white balance. These specialized white balance cards are commercially available for purchase on the Internet.

    Light plays an important role in the outcome of your video footage. Whether you shoot with available light, artificial light, or both, by paying attention to the color of the light, and calibrating your camera’s white balance settings accordingly, you’ll produce underwater video that rivals the footage shot by professionals.

That is all folks & hope it would help you to have better understanding about White Balance
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Re: Understanding WHITE BALANCE by Mark Jamieson

Post Number:#4  Postby Scorpenesub » Fri Dec 07, 2007 7:32 pm

Thanks for the article, snafu.

Will be testing it out. Next thing i need is an UW casing for my JVC... :)
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Re: Understanding WHITE BALANCE by Mark Jamieson

Post Number:#5  Postby Snafu » Sun Dec 09, 2007 12:21 am

scorpenesub wrote:Thanks for the article, snafu.

Will be testing it out. Next thing i need is an UW casing for my JVC... :)




What type of JVC video cam you have?

Any preference with the housing?

:D
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Re: Understanding WHITE BALANCE by Mark Jamieson

Post Number:#6  Postby Adzri » Tue Dec 11, 2007 1:03 pm

Thanks snafu for the infos !!!

Very well written facts from a pro on the importance of WB.
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