What's the difference between color temperature and white balance?

Color temperature is the white balance expressed by a specific value.

White balance simply means telling the camera what is white. When the camera knows white, it can calculate other colors. White things will have some differences in color under various light sources.

If your camera can customize the white balance, just check it against white paper or shirt. It is equal to telling the camera: this is white. Generally, cameras have several preset white balances, which can be set to auto.

White balance literally means white balance. Then what is white? This involves some knowledge of chromatics. White refers to the visual response of light reflected to people's eyes because of the same proportion of blue, green and red light and a certain brightness. We all know that white light is made up of seven colors: red, orange, yellow, green, cyan, blue and purple, and these seven colors are made up of red, green and blue in different proportions. When the proportion of the three primary colors of a beam of light is the same, it is customarily called achromatic, and the light reflected by black, white, gray, gold and silver is achromatic. The public's understanding of white is brightness without color components. The white or other colors seen by human eyes are related to the inherent color of the object, the color temperature of the light source, the reflection or transmission characteristics of the object, the visual perception of human eyes and many other factors (please refer to the principles of chromatics). For a simple example, when colored light illuminates an achromatic object, the color of the reflected light of the object is the same as the color of the incident light, that is, the white object is red when illuminated by red light. When two or more colored lights illuminate the achromatic object at the same time, the colors of the object show additive effect. When colored light shines on a colored object, the color of the object decreases. For example, yellow objects appear red under magenta light, green under cyan light, and gray or black under blue light.

Before we understand white balance, we need to understand another very important concept-color temperature. The so-called color temperature, in short, is expressed quantitatively by Kelvin temperature (K). Kelvin, a famous British physicist, believes that if a blackbody substance can absorb all the heat falling on it without loss, and at the same time release all the energy generated by heat in the form of "light", it will become different colors due to the level of heat. For example, the thermal stress on the black body will turn dark red when it is equivalent to 500-550 degrees Celsius, yellow when it reaches 1050- 1 150 degrees Celsius, and blue will appear when the temperature continues to rise. The color composition of the light source corresponds to the thermal temperature of the blackbody, and the color temperature of any light is equivalent to the "temperature" when the blackbody emits the same color. This temperature is used to indicate that a certain color light is different from other characteristics, that is, the color temperature. In the process of striking iron, black iron gradually turns red in the furnace temperature, which is the best example of blackbody theory. Color temperature phenomenon is very common in daily life, and I believe people are no strangers to it. Tungsten lamp is yellow because of its low color temperature, and different street lamps also emit different colors. The flame of natural gas is blue because of its high color temperature. The color temperature of cloudless blue sky in Wan Li is about 10000 K, that of cloudy days is about 7000~9000 K, that of sunny days is about 6000 K, that of sunrise or sunset is about 2000 K, and that of candlelight is about 1000 K. At this time, we can easily find a rule: the higher the color temperature, the bluer the light; The lower the color temperature, the redder it is. When the color temperature of a certain color light is higher than other colors, it means that the color light is bluer than other colors, and vice versa; Similarly, when the light of one color is bluer than the light of other colors, it means that the color temperature of this color light is higher, and vice versa.

Because of the unique adaptability of human eyes, we sometimes can't find the change of color temperature. For example, if you stay in a tungsten lamp for a long time, you won't feel that the white paper under the tungsten lamp is red. If you suddenly change the fluorescent lamp to tungsten lamp, you will feel that the color of white paper is red, but this feeling can only last for a while. The CCD adaptability of the camera is not as good as that of the human eye, so if the color adjustment of the camera is inconsistent with the color temperature of the scene lighting, color cast will occur. So what is white balance? White balance is to adjust the color circuit inside the camera to offset the color cast at different color temperatures, which is closer to the visual habits of human eyes. White balance can be simply understood as that the standard white shot by the camera lens is still white after circuit adjustment under any color temperature condition. This is a common situation, but not all. In fact, white balance is to make the light reflected to the lens achromatic by adjusting the internal circuit of the camera (changing the balance relationship of the three CCD levels of blue, green and red). If the white balance is adjusted with reddish light, then the image of this color light is achromatic color's, and the scenery of other colors is blue (complementary color relationship).

Color temperature is the most commonly used index to indicate the spectral quality of light source. Generally expressed as Pa. Color temperature is defined as absolute black body. When the radiation of the light source is exactly the same as that of the absolute blackbody in the visible region, the temperature of the blackbody is called the color temperature of the light source. Low color temperature light source is characterized by relatively more red radiation in energy distribution, which is usually called "warm light"; After the color temperature rises, the energy distribution is concentrated and the proportion of blue radiation increases, which is usually called "cold light". The color temperature of some common light sources is: standard candle light is 1930K (Kelvin-day); Tungsten lamp 2760-2900K；; The fluorescent lamp is 3000 k; Flash 3800 k; The sunshine at noon is 5400 k; Electronic flash 6000 k; The blue sky is 12000- 18000K.

The preference of color temperature varies from person to person, which is related to the scenery we see every day. For example, people near the equator see an average color temperature of 1 1000K(8000K (dusk) ~ 17000 K (noon)), so they prefer a high color temperature (it looks more realistic), and vice versa. On the contrary, if you watch subtropical customs on TV with low color temperature, you will feel a little red.

Color temperature is an important part of photography, but many photographers simply don't know its true meaning. In the eyes of ordinary readers, color and temperature are two different things, but in the field of photography, the light source is always defined according to its color temperature. The unit of color temperature is Kelvin. Like Fahrenheit and Celsius, Kelvin is a unit of temperature measurement. The relationship between color and Kelvin temperature originates from a blackbody radiator (heating it until it emits light), and the color presented at different temperatures is the color temperature. When this black object is heated and starts to glow, it will turn dark red. If heating is continued, it will turn yellow, then white and finally blue. This color temperature phenomenon is very common in daily life, and I believe everyone is familiar with it. The color temperature of cloudless blue sky in Wan Li is about 10000 K, that of cloudy days is about 7000 ~ 9000k, that of sunny days is about 6000 K, that of fluorescent lamps is about 4500 K, that of tungsten lamps is about 2600 K, that of sunrise or sunset is about 2000 K and that of candlelight is about 1000 K.

Color temperature is a white balance problem of digital cameras, and it is also a headache for many photographers. Under different lighting conditions, the color of the target will change. In this respect, the change of white objects is the most obvious: under indoor tungsten lamp, white objects will look orange, and the scenery photographed under such lighting conditions will look pale yellow; But if it is under the blue sky, there will be blue tones. The scenery taken under such lighting conditions will be blue. In order to minimize the influence of external light on the target color and restore the original color of the target under different color temperature conditions, digital cameras are needed to correct the color to achieve the correct color balance, which is called white balance adjustment.

Nowadays, digital cameras have white balance sensors, which are usually located under the lens. The white balance mechanism will try to turn white into pure white. If the brightest part is yellow, it will strengthen the blue to reduce the yellow in the picture, so as to obtain a more natural color. Digital cameras can correctly restore other colors of white objects under the same lighting conditions as long as they correctly restore the white objects when shooting them.

At present, there are generally 4 ~ 5 modes for white balance adjustment of digital cameras, which are slightly different due to different manufacturers, but there is little difference. Canon's digital cameras are generally divided into automatic, daytime, cloudy, incandescent, fluorescent and other modes. In daytime mode, the white balance function of the digital camera will enhance the yellow color of the image. When shooting outdoors on sunny days, you can set the white balance function in daytime mode. If shooting indoors, it should be set according to the indoor light source. Generally, there are tungsten lamp and fluorescent lamps. In fluorescent light mode, white objects will appear blue. In tungsten lamp mode, the white balance function of the digital camera will enhance the blue color of the image. If the white balance is set to daytime mode by mistake, the picture color will become too yellow.

The photo is greatly influenced by the light of the shooting place. White balance is the function of adjusting this point. When the color is unnatural in automatic mode, you can get better results by choosing "daytime", "tungsten lamp" and "fluorescent lamp" according to the light of the shooting place. If you need more realistic colors, you can set them manually.

In addition to automatic and manual white balance, some advanced digital cameras also provide "white balance surround" function. Generally speaking, this function is to use different white balance modes to take three photos at a time, one is normal, one is blue, and the other is red, which is convenient for users to compare and choose, making shooting more flexible.

Indoor and outdoor mode is only for sunny days, outdoor and indoor lighting with about 60W tungsten filament bulbs. These two typical white balance adjustments under light tone conditions can not represent all white balance adjustments in indoor and outdoor environments, and have no universal significance. Therefore, in some special color temperature environments, the white balance is still adjusted manually.

For example, when shooting a red sunset, you can shoot a picture full of warm atmosphere by manually adjusting the white balance with blue as the reference. If the white balance of the digital camera is set to the automatic position, the digital camera will misjudge the warm color temperature of the sunset as indoor, thus compensating the blue color of the picture and reducing the red color, completely destroying the original warm atmosphere of the sunset. On the contrary, by manually adjusting the white balance with the red reference, you can take a picture with a cool blue tone.

Manual white balance adjustment mode is required under light conditions beyond the automatic white balance adjustment range. Before manual adjustment, you need to find a white reference object, such as pure white paper-something like that. Some digital cameras are equipped with a custom white balance function, so you can adjust the white balance as long as you face a blank sheet of paper. The operation process is roughly as follows: 1. Adjust the zoom lens of the digital camera to the widest angle (short focal length position); 2. Place the white paper; 3. Adjust the white balance to the manual position; 4. Aim the camera at the clear sky, be careful not to face the sun directly, and zoom in until the whole screen turns white; 5. Press the white balance adjustment button until the manual white balance sign in the viewfinder stops flashing, and then the manual white balance adjustment is completed.

Some special effects can be obtained by adjusting the white balance manually, and some color cast effects can be obtained by adjusting the color temperature.

Generally speaking, the white balance function of digital cameras can meet the needs of most situations. Readers should keep practicing in the process of shooting creation, deepen their understanding of white balance adjustment according to their camera characteristics and shooting environment, and make full use of the advantages of digital cameras to take satisfactory photos. Even if the white balance effect is not satisfactory, don't worry, computer post-processing can also relieve these worries for you.