I wonder, what is the color temperature control in photography?

color temperature

The most common index of spectral quality of light source. 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 proportion of blue radiation in the energy distribution 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.

When discussing the light used in color photography, photographers often mention the concept of "color temperature". What exactly does color temperature mean? As we know, the light usually seen by human eyes is composed of the spectra of seven colors of light. But some are blue and some are red. Color temperature is a method specially used to measure and calculate the color composition of light. It was founded by the British physicist Lord Kelvin at the end of 19. He developed a set of color temperature calculation method, the specific standard is based on the wavelength emitted by a blackbody radiator.

Kelvin believes that if a pure black object 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", then the wavelength of its maximum radiation intensity will change with the change of temperature. For example, when the thermal stress on the blackbody is equivalent to 500-550 degrees Celsius, it will turn dark red (the radiation intensity of a certain red wavelength is the highest), and it will turn yellow when it reaches1050-150 degrees Celsius ... Therefore, the color composition of the light source corresponds to the temperature on the blackbody. Color temperature is usually expressed in kelvin temperature (k), not in degrees-days. In the process of striking iron, black iron gradually turns red in the furnace temperature, which is the best example of blackbody theory. Usually, the tungsten wire in the bulb we use is equivalent to this black body. The calculation method of color temperature is based on the above principle, and K is used to correspond to the color representing the maximum wavelength of an object when it radiates at a specific temperature.

According to this principle, the color temperature of any light is equivalent to the "temperature" when the black body emits the same color. Color is actually a psychological and physiological function. All color impressions are caused by intermittent spectral reactions on the eyes, so color temperature is only used to express the visual impression of color.

Application of color temperature in photography;

The design of color film is generally based on the illumination of a light source that can truly record a certain color temperature, and it is divided into 5500K daylight type, 3400K intense light type and 3200K tungsten lamp type. Therefore, the photographer must know how to use the color film with the same color temperature as the light source in order to get accurate color reproduction. If the color temperature of the light source and the color temperature of the film are not balanced with each other, it is necessary to raise or lower the color temperature of the light source through a filter to match the color temperature of the film, so that accurate color reproduction can be realized.

Generally speaking, there are two types of filters used to balance the color temperature. One is the red 8 1 series filter, and the other is the blue 82 series filter. The former is used when the light is too blue (that is, when the color temperature is too high); The latter is used to treat red light and improve color temperature. Series 82 filters are not used as often as series 8 1 filters. In fact, the experience of many photographers is to increase the color temperature as much as possible, not to decrease it. Shooting the most common sunset phenomenon with a light yellow filter will produce an extremely spectacular effect.

The experience of an American photographer is that the red filter can reduce the color temperature when the color temperature is as high as 8000K, while the blue filter for solar film can be applied to the color temperature as low as 4400K K. Usually, by using these filters, you can shoot at almost any time of the day and get natural colors. However, under special circumstances, when the color temperature exceeds this range, it is necessary to use a color conversion filter, such as amber 85B filter, which can make the color temperature as high as 19000K suitable for solar films. On the contrary, the color temperature of the optical film with 82 series filters can be reduced to 2800K K.

If it is necessary to shoot with sunlight film under the condition of tungsten lamp lighting, you can also use 80 filter. If you didn't use TTL exposure meter to measure light at that time, you should add 2-level aperture to make up for the loss of light. However, when shooting with a light film in the sun, you need to use an 85B filter and increase the aperture by 2/3.

However, the codes of filters commonly used in the market are very confusing and difficult to identify, and not all manufacturers adopt standard codes and designs. Therefore, it is not easy to choose a suitable filter among many filters. In order to systematize the confusion of filter classification and simplify the work of selecting filters, Canadian photographer Schwartz introduced a new internationally popular color temperature calibration method for light sources.

The ratio of long and short wavelength light in the spectrum is the color temperature.

How to choose the appropriate color temperature;

Color temperature is the feeling of human eyes to luminous body or white reflector, and it is a feeling of physical, physiological, psychological and other complex factors, which also varies from person to person. The color temperature can be artificially changed on TV (luminous body) or photography (reflector). For example, in photography, we use a 3200K incandescent lamp (3200K), but we add a red filter on the lens to filter out a little red light to make the photo look a little higher in color temperature. Similarly, we can also reduce a little red on TV (but too much reduction will also affect the performance of normal red) to make the picture look a little higher in color temperature.

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.

How to define the color temperature of TV or display screen? Because the average color temperature of scenery in China is around 8000 K ~ 9500 K all year round, TV stations take pictures with the color temperature of 9300K when making programs. However, because of the differences in the usual color temperature between Europe and America, the average color temperature of the four seasons is about 6000K as a reference, so we will find that 5600 K ~ 6500 K is the most suitable for watching when we look at those foreign films. Of course, this difference makes us feel that when we see the screens of computers or televisions in Europe and America, we feel that the color temperature is red and warm, and some of them are inappropriate.

That is, people with black eyes see that 9300K is white, and people with blue eyes look blue. People with blue eyes look white, and we in China look yellow.