Why white balance is imp in digital photography...?????

                                      white balance in D-SLR

Definition: Determination of the exact color adjustment necessary for a digital camera to render a pure white object so that it appears pure white in the captured image.

The assumption is that if white is rendered correctly, all of the other colors will be also. Conversely, if white has a color cast, it doesn’t matter if the other colors are right—the picture will look wrong.

Lo, the human brain! Among its many wonderful talents, your brain has the ability to restore proper coloration to most of the physical objects your eyes see. If you’ve ever shot daylight-balanced 35mm film under normal tungsten incandescent light you doubtlessly produced images that were brownish-reddish—even though the scene looked normal when you viewed it firsthand. Psychologists have told me the brain makes “corrections” to the signals it receives from the eyes because that’s way the brain copes with altered reality. Your brain replaced the blue coloration that was missing from the scene because it needed to keep things normal-looking.

This ability may be rooted in our evolution from animals that needed to be able to detect subtle color differences in plants so that they could determine which were edible, ripe or spoiled regardless of the time of day or lighting conditions. That’s just my guess, but I’m sticking with it since most human characteristics are one way or another related to survival.

Cameras need help to make these adjustments. Yes, many have Auto White Balance settings. But like many of the other Auto settings, the results are usually pretty close but rarely dead-on accurate. Cameras also offer Preset and Custom settings. More on those later.

First, let’s dispel the misconception that you can easily correct for White Balance miscalculations by using Photoshop. Experts can salvage some poorly balanced images and many people can make the images look better, but there’s no substitute for getting the white balance set correctly in the first place.

White Balance is not difficult to do or hard to understand. In fact, at the most basic level, all you really need to consider are three colors: our old friends R, G and B.

The spectrum of visible light ranges from R (red) to B (blue), or more correctly, from near-infrared to near-ultraviolet. Light color is determined by its wavelength, so it can be objectively measured, filtered and altered. White is a mixture of all colors (even though that may sound counterintuitive). Pure white objects reflect all incident light in the 400-700nm (nanometer) range.

Color is objectively identified by its temperature, which is expressed in degrees Kelvin. A color temperature meter will tell you that noon daylight is around 5,500 degrees and that normal room light generate by a GESoftwhite tungsten light bulb is closer to 2,900 degrees. On a cloudy day, the color temp might be in the 6,600 to 8,800 range. We call reddish light in the 3,000 degree range “warm” and bluish light in the higher 7,000 degree area “cool” even though the numerical value of the cooler temperature is higher. Remember it this way: fire is red and warm; ice is blue and cool. Despite the fact the labels are opposite of what the Kelvin thermometer suggests.

We forgot green, and sadly, many color temperature measuring devices do likewise. In reality it’s as important to achieve the correct balance between Green and Magenta as it is between Red and Blue. In the old says, color temperature meters—with the notable exception of the tri-color Minolta Color Meter III—could read only Red and Blue. Which was largely okay because fluorescent lights were rarely used in the home (except in the garage).

These days the color-impaired CFL—aside from creating an environmental disaster when eventually broken—wreaks havoc on rational attempts to achieve white balance. CFL, at least some of them, burn with a ghostly greenish glow. Others are bluish-green. Some are alleged to be daylight balanced but lose traction with photographers because a) it can take 15 minutes for them to warm up and reach their operating temperature and b) their color can shift as they age. Use at your own risk.

Digital cameras allow the user to choose from Preset settings that match the average conditions found in common situations. You usually find Daylight, Cloudy, Shade, Tungsten (Incandescent) and a Fluorescent option or two. Sometimes there will be a setting for Flash and always one marked Auto. Better cameras (including virtually all digital SLRs) provide Custom White Balance which is sometimes called “Present Manual.” And some cameras allow you to select from a range of color temperatures by choosing the degrees Kelvin from a scale that starts around 2,000 degrees and tops out at about 10,000.

The Custom (or Present Manual) gets its white point value through a procedure whereby you point the camera at a solid pure white object—often a sheet of paper. The exact process differs from camera to camera, so refer to your owner’s manual. This is almost always the single most accurate way to set White Balance. Auto is the worst. The other presets, if correctly set to match conditions, range from fair to okay.

The image that shows six panels of fruit (image left) was shot in shaded daylight with a Nikon D70s at the following settings (starting upper left): Preset Manual (Custom), Incandescent, Fluorescent. Second row: Direct Sunlight, Cloudy, Shade. The Shade preset is amazingly close (in fact, some may prefer it). The point is this: until you experiment and shoot the same scene with every different setting you have only a vague idea how they differ.

If your camera lets you pick the color temperature in Kelvin degrees, or has another mechanism that enables fine-tuning, you can have a lot of fun and enjoy substantial creative expression.

Avoid mixed light sources if at all possible. It’s extraordinarily difficult to achieve white balance in a scene illuminated by a blend of daylight, tungsten and fluorescent. The shot of the Colony Hotel, South Beach (image right) is a good example where the Auto setting produced good results. It was shot with a Panasonic TZ-7 (US name is Lumix DMC-ZS3).

Add caption

Sunsets and sunrises are dramatically influenced by shifts in white balance. Remember that when the sun sets, we still see its red, glowing orb even after it has physically slipped below the horizon. That’s because the long red wavelengths are diffracting—essentially “bending” over the horizon line—long after the star itself has disappeared. All of that light is red. A dissimilar thing happens at sunrise. For creative exercise, set your camera on a tripod, face the sunrise, and make exposures using every available White Balance option. Work quickly, because the color temperature of the light will change as you watch. If your camera allows Custom (Manual Preset) use that setting first to establish a baseline. Wait until sunset and repeat. This will usually require turning to face the opposite direction.Creative Project

Try to use the settings in the order that they appear on the menu or dial, or write down the order that you use them. Lacking that, use the browser software that came with your camera to review the images. It will allow you to read the Metadata where you’ll find a record of the White Balance setting associated with each image.