White Balance and color temperature

White Balance and color temperature (convert)

White Balance is a very important concept in the field of TV camera. It can solve a series of problems of color reproduction and tone processing.

The white balance is produced by the reproduction of true colors of electronic images. It has been used earlier in the field of professional camera white balance. It is also widely used in household electronic products (household cameras and digital cameras, although the development of technology makes it easier and easier to adjust the white balance, many users do not know much about the working principle of white balance, and many misunderstandings exist, seriously restricting the use and creative play.

I. What is white balance?

White Balance, literally understood as a white balance. What is white? This involves some color learning knowledge. White refers to the visual reaction of light reflected to human eyes due to the same ratio of blue, green, and red colors and a certain brightness.

We all know that white light is composed of seven colors: red, orange, yellow, green, blue, blue, and purple, these seven colors of light are mixed with red, green, and blue colors in different proportions. When the proportion of the three primary colors in a light is the same, they are used to being called fading, the light reflected by black, white, gray, gold, and silver is de-colored. Generally speaking, white is a brightness that does not contain any color components.

The white or other colors seen by the human eye are the same as the solid color of the object, the color temperature of the light source, the reflection or transmission characteristics of the object, the visual sensing of the human eye, and many other factors (see the color theory). ),

For example, when a colored light emits a color-removing object, the color of the reflected light is the same as that of the incident light. The light is red when the red light emits, when more than two kinds of colored light are simultaneously exposed to a color-removing object, the color of the object is subject to the coloring method. For example, if both the red light and the green light are shining on a white object, the object is yellow. When a colored light emits on a colored object, the color of the object is reduced. For example, a yellow object is highlighted in red, green in blue, and gray or black in blue.

Another important concept-color temperature.

The so-called color temperature, in short, is to quantitatively express the color with the kervin temperature (K. Kairman, a famous British physicist, believes that, assuming that a black body can absorb all the heat that falls on it without loss, at the same time, if the energy generated by heat is all released in the form of "light", it will become different colors due to heat.

For example, when the heat in the black body is equivalent to-degrees Celsius, it turns into a dark red color. When it reaches-degrees Celsius, it turns yellow, and the temperature will continue to rise in blue. The color components of the light source correspond to the thermal temperature of the simhei, and the color temperature of any light is equivalent to the "temperature" of the above simhei when the same color is emitted ", this temperature is used to indicate the properties of a certain color light to distinguish others. This is the color temperature. Black Iron gradually turns to red in the furnace temperature during the Iron loading process. This is the best example of the black iron theory.

Color temperature is very common in daily life. I believe people are familiar with it. The light emitted by tungsten lamps is yellow due to low color temperature. Different street lamps may emit different colors of light. The flame of natural gas is blue because of the high color temperature.

The color temperature of the cloudification blue sky is about 10000 K, and the cloudy sky is about 7000 ~ 9000 K. The color temperature in direct sunlight on a sunny day is about 6000 K. At sunrise or sunset, the color temperature is about 2000 K, and that in candlelight is about 1000 K. At this time, we can easily find a rule: the higher the color temperature, the more blue the light color; the lower the color temperature, the more red. When the color of a color light is higher than that of other colors, it indicates that the color light is more blue than other colors, and vice versa. Similarly, when a color light is blue compared with other colors, it indicates that the color temperature of the color light is high, and vice versa.

Due to the unique adaptability of human eyes, we sometimes cannot see changes in color temperature. For example, if I have stayed under the tungsten lamps for a long time, I don't think the white paper under the tungsten lamps is red. If I change the fluorescent lamps to tungsten lamps, I will find that the White Paper is red, however, this feeling can only last for a while. The CCD of the camera is not as adaptive as the human eye, so if the color adjustment of the camera is inconsistent with the color temperature of the scene lighting, a partial color will occur.

So what is white balance? White Balance is used to adjust the color circuit inside the camera to offset the partial color of the captured image under different color temperature conditions, which is closer to the visual habits of the human eye. White balance can be easily understood as the standard white color taken by the camera lens under any color temperature conditions through circuit adjustment, so that it remains white after imaging. This is a common situation, but not all. The white balance is actually adjusted through the internal circuit of the camera (changing the balance between the blue, green, and red CCD levels) make the light reflected in the lens fade out. If the white balance is adjusted with a reddish color, the color of the image will be de-colored, and other colors will be blue (complementary relationship ).

Ii. Working Principle of White Balance

White Balance is a very abstract concept. The most common understanding is to make the white image still white. If White is white, then the images of other scenes will be close to the color visual habits of the human eye. The white balance adjustment process is called white balance adjustment. There are generally three ways to adjust the White Balance in the early stage: preset white balance, manual white balance adjustment, and automatic tracking white balance adjustment.

Generally, according to the White Balance Adjustment Program, the white balance adjustment switch is promoted, the white balance adjustment circuit starts to work, the adjustment is automatically completed, and the adjustment results are recorded. If you have mastered the working principle of white balance, it will be more targeted and handy to use.

White Balance works like this: the camera has three CCD electronic coupling elements, which respectively feel the blue, green, and red light, under the Preset conditions, the electronic amplification ratio of the three photosensitive circuits is the same, which is. The white balance is adjusted based on the adjusted scene. For example, the ratio of the blue, green, and red light of the adjusted scene is (the ratio of the blue light is large, and the color temperature is high), then the proportion after the white balance is, after the adjusted circuit amplification ratio, the ratio of blue is obviously reduced, and the ratio of green to red is increased. In this way, the adjusted scenery is adjusted to the image through the white balance adjustment circuit, the ratio of blue, green, and red is the same. That is to say, if the adjusted white color is a little blue, the white balance adjustment changes the normal proportional relationship to weaken the blue circuit amplification, while increasing the ratio of green to red, so that the image is still white.

In another way, the problem of white balance adjustment is considered. The camera will not "reject" the adjusted scenes placed in front of the camera within the white balance adjustment capacity, that is, the camera can adjust the white balance for any scenes. In most cases, white whiteboards (CARDS) are used to adjust the white, because white whiteboards (CARDS) can most effectively reflect the ambient color temperature, in fact, in a certain environment, the whiteboard (card) is not white, more or less a little blue or other colors, and experienced cameras will also use the blue sky to adjust the white balance, in this way, the painting surface is highlighted in red or yellow. After figuring out how white balance works, you can try different effects to enrich camera creation.

Iii. White Balance Adjustment

In our daily life, the color temperature of daylight is constantly changing. It can be said that the color temperature in no two places will be exactly the same. Different Regions, seasons, the ground environment, the weather, and the morning and evening will affect the color temperature, there are also a large number of artificial light sources with different color temperatures.

The method used by the camera to adjust the white balance is roughly divided into three types: coarse adjustment, fine adjustment, and automatic tracking (ATW): the coarse adjustment refers to changing the color temperature filter under the Preset conditions, so that the color temperature is close to the factory settings of 3200k; fine Tuning refers to the realization of a more precise adjustment result for the color temperature of a specific environment through the camera white balance adjustment function in combination with the color temperature filter; automatic Tracking is based on the camera's automatic tracking function (ATW), the camera itself according to the color temperature changes at any time.

The preset function is the blue, green, and red photosensitive balances set by the camera at a color temperature of K. When the ambient color temperature is 3200 K, the camera color temperature filter is placed at 5600 K, and the scene can be restored correctly. When the ambient color temperature is K, the camera color temperature filter is placed at K, the scene can be restored correctly.

When the ambient color temperature ranges from kb to kb and from kb to kb, the white balance preset function can be used to restore colors that are acceptable to the human eye, make the captured image show a slight color change. This has the advantage that different living environments will have different color tones due to different environmental colors and lighting effects. If you adjust the color everywhere, different environments will display a single white light effect, this rich color change can be retained with the white balance preset.

Generally, the fine-tuning method is to adjust the white balance by adjusting the whiteboard (card) along the shooting direction in the shooting environment. This is a common situation, and there are several flexible fine-tuning methods.

A standard transparent Whiteboard is used to place it close to the front of the camera, and adjust the White Balance in the shooting environment to the light source or the main shooting direction, A professional camera will give a color temperature reading, for example, 5000 kb. If you want to take a restored picture, you can use this white balance result to take the picture.

In video creation, sometimes you want to get a picture of Color Deviation to achieve the purpose of creation. In this case, you can adjust the white balance using any scenes, the color temperature of the converted scene is complementary to the color deviation of the screen. The color is green, and the color is green. The white balance auto-tracking function (ATW) is adjusted as the color temperature of the shot changes, if the color temperature of the selected scene changes (the color temperature of the shot is different from that of the ambient lighting), the screen color changes within the same lens. For example, when the camera is pushed closer to the face by the panoramic view of the person, the color temperature of the shot varies depending on the scene, and the color of the person on the screen changes, this mode is not recommended in special cases.

Previously, I talked about the concept, principle, and usage of white balance. white balance adjustment is the basic function of video recording and an important means of creation. After understanding the principles, the active and active students can be used freely, and they will surely gain some benefits in practice.