Photography Stack Exchange is a question and answer site for professional, enthusiast and amateur photographers. It only takes a minute to sign up.
Sign up to join this community
I would like to understand the term white balance. My camera has settings for white balance with the following options:
Can anyone throw some, well, light on this? Also, is there any relation of white balance with the exposure while taking snaps? This is, if the exposure is high, then do we need to set white balance to low, or something like that?
Different light sources have different color temperature and when you want natural colors, you need to correct them for that particular light source. Basically white balance says what is rendered as neutral gray. You can find a more thorough explanation here: http://www.cambridgeincolour.com/tutorials/white-balance.htm. Wikipedia lists different light sources with their approximate color temperatures in Kelvins.
Try setting your camera to different white balances and take some shots - when you use Cloudy under incandescent light, you'll get yellow results and when you use Incandescent under daylight, you'll get very blue results.
Whenever you need correct white balance, you should use gray card as a reference when shooting and apply WB corrections based on that. Usually just believable white balance will do and might be even useful for artistic purposes (when you want to make your sunset just a bit warmer).
When shooting with digital camera, the easiest approach is to shoot RAW and use AWB (automatic white balance). This gives pretty usable results in most of the cameras and you can always fine tune your WB during RAW conversion. When shooting RAW, this correction is lossless. Most of the RAW converters have a tool called WB picker, which you can use to set neutral gray, meaning correction curves will be applied to the whole picture so that whatever you pick will appear as gray. This tool is very useful in mixed lightning situations or whenever the light source has strong tint either towards green or purple.
When you shoot and correct large batches of pictures, you want consistent WB and it's best to use the same non-auto white balance setting for all of them (even if it's slightly off), so you can apply the same correction to whole set. (Thanks, Matt)
When shooting film, you have to mess with color correction filters.
White balance affects exposure, but the effects are quite small to care in most common situations. There is a technique called UniWB, whci is used to minimize white balance effects on exposure, but this is already an advanced topic.
Don't underestimate the effect of correct white balance to the photo. Here is an example:
In-camera auto white balance:
Software auto white balance:
Hand-picked white balance (final image with some other adjustments):
There are some good answers so far, so I'll take a slightly different tack. Here is a more scientific description of white balance. White balance is a combination of two factors: Color Temperature and Tint, aimed at eliminating unnatural color casts and making white look "white" in a photograph.
Color Temperature refers to the "warmth" or "coolness" of the light that illuminates a scene, and therefor the primary color cast a scene has. The term "color temperature" is used, as it refers to the actual temperature, rated in Kelvins, that an ideal black body must be heated to in order to give off light of that color. At lower temperatures, a black body will emit redder, light, and as temperature is increased, it will progress through orange, white, and eventually blue. This is why the Color Temperature part of the white balance plot is a progression from reds and oranges to whites and blues. Sunlight is generally considered to be about 5500K-6000K, which is about as middle-ground as you get. Not 100% pure white, but very nearly so. Your average light bulbs are around 2500K - 3300K, more on the warm side (orange cast).
Tint is similar to Color Temperature, however it covers ground for illuminating objects that do not behave like a black body. This tends to involve gas plasma emissions, such as the light emitted from a fluorescent tube. Fluorescent lighting is not a solid object heated to the point where it emits light, it is a phosphorescent tube filled with a noble gas, through which electricity is passed. The color casts produced by such lighting often fall along the green/magenta plane, rather than the orange/blue plane. As such, tint allows adjustments to eliminate a green or magenta color cast in a picture.
Full white balance is the adjustments along both planes, color temperature and tint, required to make a white object appear white to the human eye. Generally speaking, when fine tuning the white balance of an image, you'll likely make much larger adjustments to color temperature than to tint, as most light sources emit more light along the temperature plane than the tint plane.
Diffent kinds of light have different color temperature. Light in the shade for example consists of reflected light, and as light in the blue end of the spectrum has more energy it bounces better, so shade light is bluer than direct sunlight.
Photographic film is usually made for daylight/flash, but there are films specially made for other light conditions, like lightbulb (incandescent) light. If you use a daylight film in lightbulb light, the images end up yellow, and if you use lightbulb film in daylight, the images end up blue.
The settings on the digital camera corresponds to using different kinds of film.
When shooting film, the photo lab compensates for differences in lighting when copying the images, so even if you use daylight (regular) film in lightbulb light, your prints end up looking reasonably correct anyway.
When shooting digital, you could do the same as the photo labs in the post processing. If you shoot RAW/DNG, the image data is stored before applying color temperature correction, so you can change the color temperature setting afterwards. If you shoot JPEG, you should try to use the correct color temperature setting, as the image data is stored after applying color temperature correction. You can still adjust the temperature somewhat afterwards, but you should be as close as possible so that you don't lose too much information in the process.
