Understanding White Balance and Color Temperature in Photography
If you are shooting your images in any mode other than RAW, the camera will post-process the image to make the colours in the scene as accurate as possible. However, this is not always as easy as it seems − the colour temperature of the light falling onto the scene affects the way the camera sees the colours and, unlike our brains, it does not automatically correct it. For example, with no correction, a white wall photographed under tungsten lighting will appear very yellow, and under a fluorescent light will look very green. In photos, generally, we want white things to look white. This is to do with the white balance which enable all digital EOS cameras have the ability to "compensate" for the color of the light source to produce correct color, no matter how complex the lighting conditions are.
The white balance can significantly impact colour tone of your photographs. Before you can set correct white balance to suit the ambient light, you have to understand what colour temperature means.
What does “temperature” have to do with “color?” Well, color temperature is a measurement of the hue of a particular light source. It is measured in degrees Kelvin. The Scottish mathematician and physicist William Kelvin noticed that, when he heated carbon, an “incandescent radiator,”, as it got hotter, the color of the carbon changed as it heated, we have a color-temperature scale. The hot-or-cold Kelvin temperature scale starts at absolute freezing 0K (-273.15ºC) while the hue-based Kelvin scale relating to color temperature starts with black as the zero point. The visible spectrum of the Kelvin scale ranges from about 1700K to 12000K or more. To the left of the visible portion of the scale is infrared. To the right is ultraviolet.
Surprisingly, the cool colours are red and orange, around 2,000-3,000K, while the warm colours are the blues at the 20,000K end of the spectrum. Neutral white light is 6,504K. Household light bulbs are rated at 3200 degrees Kelvin, sunrise and sunset lighting is virtually the same color as well—3200K.
When you are taking photos outside under the sun and clouds or inside using lamps or strobes, the light emitted from every light source casts its own hue on the scene. Light from a candle or from the sun during sunrise/sunset will cast a lot of red/orange color on the scene; whereas light from a fluorescent strip will cast a lot of blue colour on the scene. This coloured light is reflected off of surfaces, but our brain in clever enough to recognise this and automatically counter the effect, meaning that we still see a white surface as a white surface. However, your camera is not that intelligent, and unless told otherwise, will record the orange or blue tones giving the colour cast to your images.
In the days of film, or if you shoot film today, you can get indoor- or outdoor-balanced film, or add filters to your lens to cancel out the color cast. With digital cameras, you can select a white balance setting for your camera to remove the color cast digitally. White balance (WB) is the process of removing unrealistic color casts, so that objects which appear white in person are rendered white in your photo.
The illustration above gives an idea of the relative "colors" of various light sources, from tungsten lighting (more red) at low temperatures to the blue sky which has a high color temperature (more blue). Also shown is the color required to "compensate" for the color of the light source to produce correct color.
There are seven standard white balance settings, your choice of which will depend on the type of light you are shooting in.
You can use this setting as a default in most straightforward lighting conditions. Auto White Balance works by evaluating the scene and deciding the most appropriate white point in it. The setting works reasonably well if the colour temperature of the ambient light is between 3,000-7,000K. However, if there is an abundance of one colour in the image, or if there is no actual white for the meter to use as a reference, the system can be fooled, resulting in an image with a colour cast.
Use this setting if you are shooting in bright sunshine. It will balance for a colour temperature of around 5,200K, which is actually very slightly cooler than noon sunlight. However, it is very rare that you will actually be shooting at noon and so this setting will work best for the greatest part of the day.
Although we perceive shaded areas to be colder, the colour temperature is actually higher (bluer), usually around 7,000K. This setting is most suited to areas of light shade rather than very heavy shadow.
This sets a colour temperature of around 6,000K. It is best used on days when the sun is behind the clouds, creating a very even and diffuse light.
The first of the artificial lighting settings, this assumes a colour temperature of around 3,200K and is suitable for most tungsten lamps such as incandescent light bulbs or street lights that normally emit a yellow light. It is the equivalent of an 82-series blue filter used with a film camera to correct for the same colour cast.
The second artificial light setting is set for around 4000K, the approximate colour temperature of fluorescent lights. The problem with fluorescent lights is that there are six types, each with a different colour temperature. They also emit an interrupted spectrum with peaks over quite a wide range. To complicate things further, they also change over time, gradually altering the colour temperature of light they emit. This setting has the same effect as fitting an FL-D filter to a film camera.
For use with either a built-in flash or an external Speedlite. Flash is a very white light with a colour temperature around 6,000K which will add a blue cast to the image, so used to add some warmth.
For cloudy and shady environments, use the CLOUDY setting (to add a little yellow) or the SHADE setting (to add a little orange), respectively, to get a near perfect white balance.
Using the incandscent setting (usually a light bulb symbol) on your camera's white balance settigns for an image where there is tungsten lighting present will add blue to the image to color correct the orangish-yellow to a near correct white balance.
Using the fluorescent settting adds a magenta hue to the green environment when in the presenece of fluorescent lighting.
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