What is white balance? How to use white balance? I don't understand a series of questions about white balance ~ ~ Be anxious ~ ~ Who can tell me ~'

White Balance Directory [Hidden] Definition of White Balance LED and Analysis of White Balance Application of White Balance Adjustment of Digital Camera Comparison of Manual White Balance Effects of Different Reference Objects

English name: White Balance[ edit this paragraph] The definition of white balance is a very important concept in the field of TV camera shooting, through which a series of problems such as color reproduction and tone processing can be solved. White balance is produced by the true color reproduction of electronic images. It was used in the field of professional photography earlier, and now it is also widely used in household electronic products (household cameras, digital cameras). However, the development of technology makes white balance adjustment easier and easier, but many users still don't understand the working principle of white balance, and there are many misunderstandings in understanding. It is to realize that the camera image can accurately reflect the color condition of the subject, with manual white balance and automatic white balance.

Many people will encounter such problems when shooting with digital video cameras: the images taken in fluorescent lamp rooms will be green, the scenery taken in indoor tungsten lamp will be yellow, and the photos taken in sunlight shadow will be blue inexplicably. The reason lies in the setting of "white balance". [Edit this paragraph] The white balance between LED and white is a very important concept in the field of TV camera shooting, which can solve a series of problems such as color restoration and tone processing. White balance is produced by the true color reproduction of electronic images. It was used in the field of professional photography earlier, and now it is widely used in household electronic products (household cameras and digital cameras). Although the development of technology makes white balance adjustment easier and easier, many users still don't know the working principle of white balance, and there are many misunderstandings in their understanding.

1. What is white balance?

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.

Another very important concept, color temperature, should be clarified before understanding white balance. 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 release all the energy generated by heat in the form of "light", then 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℃, yellow when it reaches1050-1150℃, and blue 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).

Second, the working principle of white balance

White balance is a very abstract concept. The most popular understanding is to make the image of white still white. If white is white, then the images of other scenes will be close to the color visual habits of human eyes. The process of adjusting white balance is called white balance adjustment. There are generally three ways to adjust the white balance of equipment in the early stage: preset white balance, manual white balance adjustment and automatic tracking white balance adjustment. Usually, according to the procedure of white balance adjustment, press the white balance adjustment switch, the white balance adjustment circuit starts to work, automatically completes the adjustment work, and records the adjustment results. If you master the working principle of white balance, it will be more targeted and handy to use.

White balance works like this: there are three CCD electronic coupling elements in the camera, which feel blue, green and red light respectively. By default, the electronic magnifications of these three photosensitive circuits are the same, which are all 1: 1: 1. The adjustment of white balance changes this proportional relationship according to the adjusted scenery. For example, in the adjusted scene, the ratio of blue, green and red light is 2: 1: 1 (the blue light ratio is high and the color temperature is high), then the white balance adjustment ratio is 1: 2: 2. In the adjusted circuit amplification ratio, the blue ratio is obviously reduced, and the ratio of green and red light is increased, so that the adjusted scene passes through the white balance adjustment circuit to obtain the photographed image. That is to say, if the adjusted white is a little blue, then the white balance adjustment will change the normal proportional relationship, weaken the amplification effect of the blue circuit, increase the ratio of green to red, and make the image still white.

Another way of thinking is to consider the problem of white balance adjustment. The camera will not "reject" the adjusted scene placed in front of the lens within the tolerance range of white balance adjustment, that is, the lens can adjust the white balance of any scene. In most cases, the white palette (card) is used to adjust the white balance, because the white palette (card) can most effectively reflect the color temperature of the environment. In fact, in some cases, the whiteboard (card) is not white, but more or less blue or other colors. Experienced photographers will also use the blue sky to adjust the white balance, so as to get a picture with red and yellow tones. After understanding the working principle of white balance, we will boldly try different effects when using it again, which enriches the camera creation.

Third, white balance adjustment

In life, the color temperature of sunlight is constantly changing. It can be said that no two places are exactly the same. Different regions, seasons, ground environment, weather, morning and evening will affect the color temperature, and there are a large number of artificial light sources, and the color temperature is not the same. There are three methods for photographers to adjust the white balance: coarse adjustment, fine adjustment and automatic tracking (ATW). Coarse adjustment refers to changing the color temperature filter under preset conditions to make the color temperature close to the factory setting. Fine adjustment of 3200-3200 K refers to obtaining more accurate adjustment results for the color temperature in a specific environment with the cooperation of the color temperature filter. Automatic tracking refers to the automatic tracking function (ATW) of the camera, and the camera itself can be adjusted at any time according to the color temperature change of the picture.

The preset function is the blue-green-red photosensitive balance set by the camera at the color temperature of 3200 3200K K. When the ambient color temperature is 3200 K, the camera color temperature filter is set at 3200 K, which can restore the scene correctly. When the ambient color temperature is 5600 K, the camera color temperature filter is set at 5600 K, which can restore the scene correctly. When the ambient color temperature is within the range of 1000 K, 3200 K, and 1000 K, 5600 K, the color reproduction acceptable to human eyes can be obtained by using the white balance preset function. Because the color temperature deviation is not big, the picture taken shows subtle color changes. This has advantages. Different living environments will have different colors due to the influence of environmental colors and light differences. If white light is adjusted everywhere, different environments will show the effect of single white light illumination, and this rich color change can be preserved by using white balance preset.

The general method of white fine-tuning is to adjust the white balance along the shooting direction with a whiteboard (card) in the shooting environment. This is a common situation, and there are several very flexible adjustment methods for fine white. Use a standard whiteboard with good permeability, put it in front of the camera, and adjust the white balance in the shooting environment against the illumination direction of the light source or the main shooting direction. Professional cameras will give a color temperature reading, such as 5000 K. If you want to shoot a normal picture, use this white balance result to shoot. In camera creation, sometimes we want to get a picture with chromatic aberration to achieve the purpose of creation. At this time, we can adjust the white balance with any scene. The color temperature of the white scene is complementary to the color deviation of the picture, that is, the red and white picture is biased towards cyan, the green and white picture is biased towards magenta, and the blue and white picture is biased towards yellow. The automatic white balance tracking function (ATW) is adjusted in real time with the change of the color temperature of the scene shot by the lens. If the color temperature of the scene shot by the push lens or pan lens changes (the color temperature of the scene shot by the lens is different from the color temperature of the ambient lighting), the color of the picture will change within a lens. If you push the lens from the panoramic view to the close-up of the face, it is not recommended to use this mode unless there are special circumstances, because the color temperature of the lens will vary with the change of the scene and the skin color of the person in the picture will also change. [Edit this paragraph] White balance analysis So what is "white balance"? This must first explain what is white. The bright color reflected by an object depends on the color of the light source. The reason why people's eyes see some objects as white is because people's brains can detect and look more like this color change. Therefore, no matter in the sun, cloudy days, indoors or under fluorescence, the color of white objects people see remains unchanged. The human eye can adapt itself, but digital cameras don't have such intelligent functions. This is because the CCD photosensitive element itself does not have this adaptive function. In order to approach the human visual standard, digital cameras must imitate the human brain and adjust the color according to the light, that is, the white balance needs to be adjusted automatically or manually to achieve satisfactory color. The white balance sensor of digital camera is generally located under the lens, which can automatically sense the surrounding environment and adjust the color balance. This is the process of correcting the signal output by the digital camera. By mastering the adjustment of white balance, you can shoot a real color picture. At present, all digital cameras on the market have the function of automatically adjusting the white balance, which is more convenient to use. Some models of digital cameras also have manual white balance adjustment, which is more accurate than automatic adjustment, and are generally equipped with some preset modes, such as cloudy days, sunny days, fluorescent lights and so on. , can be adjusted according to the use environment, which is more convenient. Because of the different spectral characteristics under different lighting conditions, the photos taken are often biased, such as blue under fluorescent light and yellow under incandescent light. In order to eliminate or reduce this color shift, digital cameras and video cameras can adjust the color settings according to different lighting conditions, so that the color of photos is as undistorted as possible and the color can be restored to normal. Because this adjustment is often based on white, it is called white balance.

White balance adjustment is not only the basic skill of camera shooting, but also an important creative means. After the principle is clear, you can use it freely, and you will gain something by groping in practice. [Edit this paragraph] The application of white balance has almost no such concept in traditional photography. The so-called white balance is to adjust the proportion of the three primary colors of red, green and blue under different lighting conditions, so that they become white after mixing. So that the photographic system can obtain accurate color reproduction under different lighting conditions. It should be said that this is like our human eyes, which can distinguish the inherent colors under different colors. It's like correcting colors with a color filter. It's just that digital cameras don't adjust the color temperature by changing color filters, but use circuits to change the gain of electrical signals generated by different colors of light.

There are usually three modes to adjust the white balance of digital cameras; Automatic white balance, step-by-step white balance setting and precise white balance setting (manual setting mode). Different cameras have different ways to adjust the white balance. Most popular digital cameras use automatic white balance. Most quasi-professional digital cameras are equipped with grading to set the white balance. Professional digital cameras are equipped with accurate white balance (manual setting mode). Professional digital cameras have three modes of white balance, and quasi-professional digital cameras have automatic and step-by-step setting of white balance. Can be selected according to different use requirements.

Automatic white balance relies on the color temperature measurement system in digital camera to measure the relative proportion of red light and blue light. Then adjust the exposure according to the secondary data to generate the gains of red, green and blue electrical signals. The biggest advantage of automatic white balance is that it is simple and fast. But sometimes shooting according to its adjustment is far from accurate color reproduction. Sometimes it helps.

Setting white balance by grade is divided into two categories according to light source type and color temperature value. At present, most digital cameras are classified according to the types of light sources. There are icon stalls for sunshine, cloudy day, fluorescent lamp, incandescent lamp and flash lamp on the camera respectively. When shooting, just match the type of light source with the white balance gear on the camera, and you can shoot more accurate colors. However, due to the lack of grading, the grading accuracy is not high, and it is impossible to accurately record colors when shooting under some special lighting conditions. Theoretically, the white balance accuracy classified by color temperature is higher than that classified by light source type. However, it requires users to remember the color temperature values of various light sources, which brings great trouble to users. So there are fewer cameras using this hierarchical white balance.

Accurate white balance (manual setting mode) is to adjust the white balance by filling the lens field of view with white paper or white objects when shooting the scene light. After such debugging and re-shooting, the recorded color will be very accurate, which is the most accurate white balance adjustment method at present.

The function of white balance has brought us a lot of convenience and unexpected effects in photography. For example, studio photography, there is no need to have such high requirements for the color temperature of lights. You can still shoot accurate colors under incandescent lamps. We don't have to worry about the blue color brought by fluorescent lamps. We can set the white balance at a higher color temperature and shoot at a lower color temperature to make the picture warm. On the contrary, it can also be set under the condition of low color temperature, and high color temperature shooting can also produce special effects. When setting different levels of white balance, the light source file can also be deliberately set to be different from the scene lighting settings, and it can also produce different artistic effects. [Edit this paragraph] The English name of White Balance adjustment of digital camera is white balance. The color of the object will change due to the color of the projected light, and the photos taken under different light conditions will have different color temperatures. For example, a photo taken under the illumination of tungsten lamp (light bulb) may be yellow. Generally speaking, CCD can't automatically correct the change of light like human eyes. The following pictures show different images under different colors of light.

The picture uses natural light. After white balance, the image is blue. If white balance is used in light, the color of the picture will return to the primary color state. White balance will immediately adjust the intensity of the red, green and blue colors of the whole image according to the characteristics of the image in the current portrait, and correct the errors caused by external light. Some cameras provide manual white balance adjustment in addition to automatic white balance or specific color temperature white balance function.

Balance means that the digital camera defaults to "white" regardless of the ambient light, that is to say, it can recognize white under colored light and balance the tones of other colors. Color is essentially an explanation of light. What looks white in normal light may not look white in dark light, and "white" under fluorescent light is also "non-white". If the white balance can be adjusted for all this, other colors based on "white" can be correctly restored in the obtained photos. At present, most commercial digital cameras provide white balance adjustment function. As mentioned above, the white balance is closely related to the surrounding light, so the use of the flash will be restricted when the white balance function is started, otherwise the change of ambient light will invalidate the white balance or interfere with the normal white balance. Generally, there are many modes of white balance, which are suitable for different scenes, such as automatic white balance, tungsten wire white balance, fluorescent white balance, indoor white balance and manual adjustment.

Automatic white balance

Automatic white balance is usually the default setting for digital cameras. There is a complex rectangular picture in the camera, and the white balance reference point in the picture can be determined, thus realizing the white balance adjustment. This kind of automatic white balance has high accuracy, but when shooting in light, the effect is poor, and on cloudy days, many automatic white balance systems have poor effects, which may lead to blue.

Tungsten light-white balance

White balance in tungsten lamp is also called "incandescent lamp" or "indoor lamp". This setting is usually used in an environment illuminated by a light bulb (such as home). When the white balance system of the camera knows that it will shoot in this environment without flash, it will start to determine the position of the white balance. When taking photos indoors without a flash, you must use it.

Fluorescent white balance

It is suitable for white balance adjustment under fluorescent lamp, because there are many kinds of fluorescence, such as cold white and warm white, so some cameras have more than one kind of white balance adjustment. The fluorescent lamps used in different places are different, so the "fluorescent" settings are different. The photographer must determine what kind of "fluorescence" the light is so that the camera can set the best white balance. Of all the settings, the "Fluorescent" setting is the most difficult to decide. For example, some offices and schools use various combinations of fluorescent types, and the "fluorescent" setting here is very difficult to handle. The best way is to "shoot".

Indoor white balance

Indoor white balance, or cloudy or cloudy white balance, is suitable for adjusting the light in the dark to the primary color state. Not all digital cameras have this white balance setting. Generally speaking, the outdoor time-white balance system is in the best state, and these settings are not needed. However, some manufacturers add these special white balance settings to cameras, and the use of these white balances varies from camera to camera.

control manually

This white balance has different names in different places, and they describe some white balance settings under ordinary lighting conditions. Generally speaking, users need to point out the reference point of white balance to the camera, that is, which "white" object is used as the white point in the picture. But the question is what is "white". For example, different white paper will have different white colors, some may be slightly yellow, and some may be slightly white, and the light will affect our "white" feeling. So how to determine "true white"? One way to solve this problem is to carry a standard piece of white paper with you and compare the subjects when shooting. This method works very well, so when it is difficult to decide this setting when shooting indoors, you may wish to set the white balance according to the "reference" white paper. When there is no white paper, let the camera aim at the object that the eyeball thinks is white to adjust. [Edit this paragraph] Comparison of manual white balance effects of different reference objects As we all know, in order to obtain the most accurate white balance, the manual white balance mode can be selected on the digital camera, so that the camera can decide how to accurately restore according to the color temperature of the reference object under the light source. The manual white balance function is basically based on a color neutral object, such as standard gray and standard white reference. In principle, as long as the reference object has no color shift, the camera can obtain the best reference data and the best white balance.

Based on this principle, when using manual white balance (or custom white balance), many users will choose something that is easy to see, such as a piece of white paper, and get a certain white balance correction effect. Generally, users who are not strict will use it this way. And some demanding users will choose the standard gray board as the benchmark reference. For example, Kodak professional gray card, its gray side is used for standard metering, and the other side is standard white, which is used for white balance correction. Many professional users of photo studios use grey cards, and so do users in the camera industry.

In principle, the gray face of the gray card can also be used for white balance correction, because it has no other colors, and even quite a few people think that the gray face is the best effect. In order to verify what is used as a benchmark, the corrected white balance will have the best performance, so the following simple tests are planned. Choose a Kodak standard gray card, a Qvanxian Zhang white copy paper and a long-stored white copy paper. As a contrast, look at the difference between professional gray cards (white and gray) and white paper used by ordinary users, and take the automatic white balance and fixed mode white balance of the camera as a reference.

The process is as follows: use common non-professional standard light sources. This time, the warm color fluorescent lamp used indoors is quite different from the standard light source, and obvious contrast effect can be obtained. Canon G3 DC is chosen as the device because it has two sets of functions to define white balance, which can store two sets of data respectively and is convenient to use. Shoot with grey card, white card (back of grey card), new white paper, old white paper, automatic white balance and fluorescent light mode white balance respectively. When shooting, use the gray card to measure light first, and use the M file to fix the exposure. Every photo was taken with this value. The white side of Kodak gray card is placed on the background side of the main body to judge the accuracy of color. Using standard gray card to measure light, the white card as the background is within the linear exposure range, that is, there is no color scale overflow, which will not affect the accuracy of judgment. Each photo uses a color scale function to judge the color value in PS.

Compared with the real shot, it can be seen that the color of the photo based on the white edge of the gray card is the most accurate, and the white card shows the same color value of the three colors everywhere. On the contrary, the performance of the gray card is not good, the color is blue, showing a cooler tone. White paper used by many people (most people like to use copy paper because it looks white) is often cool. In fact, this kind of paper contains a lot of bleaching ingredients, which is obviously blue compared with white cards. Interestingly, another kind of white copy paper, which has been placed for a long time, has achieved the same effect as the gray card standard white, and its white balance is extremely accurate. The reason is that the paper will turn yellow if it is left for a long time, and it just corrects its own blue color. Not to mention the white balance in the other two machines, it is impossible to do it well under such a special light source.

By simple comparison, we can know that a good white balance is finished, which is very important as a benchmark reference. As a standard grey card, it didn't get the best effect. It seems that the gray card is still good as its own metering function. Just balance the white card on the back with white, which will bring you the best effect. Common white papers are unreliable, and those that are not strict can also be used. Of course, you can get a blank sheet of paper like a white card, or you can save dozens of dollars, depending on your luck!