An image that is not color balanced is said to have a “color cast” as everything in the image appears to have been shifted towards one color or another. Color balancing is the removing this color cast.
Digital cameras have a built in automatic white balance feature: the camera judges the overall color of the image and calculates the white balance for you to achieve an accurate color representation for the photo. However, the camera’s auto white-balance system is often fooled, especially if there are NO white or neutral colors in the image or if a single color is dominating the scene.
Most digital cameras will allow you to choose a white balance manually: sunlight, cloudy, incandescent, fluorescent etc. Better digital cameras allow you to define your own white balance reference.
Before making the actual shot, you focus at an area in the scene which should be white or neutral grey (or, better, at a white balance reference card). The camera will then use this reference when taking the actual shot. You can continue taking additional photos with accurate white balance, assuming you remain in the same lighting.
Pre-made portable white balance reference cards are the most accurate, since what appears to be a neutral object in an image may not be as neutral as you think.
A color cast is caused by the fact that different light sources emit light at different color temperatures, which are measured in degrees Kelvin. A low color temperature shifts light toward the red; a high color temperature shifts light toward the blue. Photos can have a yellow or orange cast in incandescent (tungsten) lighting and bluish tint in fluorescent lighting.
5000° Kelvin produces roughly neutral light. Light spectrums below 3000° K shift to contain more yellow-orange, and above 6000° K shift towards blue wavelengths. As the color temperature rises, the color distribution becomes cooler because shorter wavelengths contain light of higher energy.
|1700 K||Match flame, low pressure sodium lamps (LPS/SOX)|
|1850 K||Candle flame, sunset/sunrise|
|2400 K||Standard incandescent lamps|
|2550 K||Soft white incandescent lamps|
|2700 K||"Soft white" compact fluorescent and LED lamps|
|3000 K||Warm white compact fluorescent and LED lamps|
|3200 K||Studio lamps, photofloods, etc.|
|3350 K||Studio "CP" light|
|5000 K||Horizon daylight|
|5000 K||Tubular fluorescent lamps or cool white/daylight compact fluorescent lamps (CFL)|
|5500–6000 K||Vertical daylight, electronic flash|
|6200 K||Xenon short-arc lamp|
|6500 K||Daylight, overcast|
|6500–9500 K||LCD or CRT screen|
|15000–27000 K||Clear blue poleward sky|
|These temperatures are merely characteristic;
considerable variation may be present.
Color balance in photography and Photoshop is the global adjustment of color intensities typically the primary colors: red, green, and blue). The starting point of this adjustment is to render neutral colors accurately; hence, the terms white balance, gray balance, or neutral balance.
Color balancing an image affects not only the neutrals, but all of the other colors as well. By correcting the white balance, colors other than neutrals to also appear correct too.
If you must do your color balancing later, the best solution is to photograph using the RAW file format (if your camera supports them), and setting the white balance to the correct light source or Kelvin temperature after the photo has been taken.
There is also an "eye dropper" white balance tool in the RAW format dialogue box. Select the white balance tool, and then click an area in the preview image that should be a neutral gray or white. The temperature and tint sliders automatically adjust to make the selected color exactly neutral (if possible).
If you’re clicking whites, choose a highlight area that contains significant white detail rather than a specular highlight. Even if only ONE of your photos contains an accurate reference point, you can use the settings from that image for the remainder of your photos (in the same lighting).
Although white balance is best corrected before taking a photo, or manipulated afterwards on an image take in the RAW format, we often don't have that luxury. A color cast can be removed in Photoshop by adjusting the color balance or by using the "levels" tool.
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