Color temperature and White Balance

The color temperature is when a black body absorbs heat and converts all the heat into light. If there is a light source, its color is the same as the color of the light emitted by the black body, then we define that the color temperature of the light source is the heat absorbed by the black body, measured in K. For the definition of the color temperature, refer to [1]. White white balance is achieved by adjusting the RGB channel of the image to restore the color, because the camera may not be able to correctly restore the color during the shooting process, resulting in partial color, such as under the fluorescent lamp, blue may occur, and yellow may occur under incandescent. For details, refer to [2] to get a more detailed definition of white balance. For the reason of color skewness, let's first take a look at the colors of common color temperatures in our lives, which are taken from [3] and copyrighted by the author.

For midday daylight, the color temperature is about KB. Of course, the color temperature of daylight varies at different times. Next, let's analyze the reason for the skewness.

Define the color temperature Space C, which contains the color temperature of all light sources. Define the origin of the color temperature coordinate system as white color temperature, and coordinate System D with the camera color temperature. Assume that the origin of the coordinate system in the color temperature coordinate system is. Define the current environment color temperature coordinate system (that is, the environment we are shooting), the origin is B, at this time, the color temperature space has a color temperature T, then, we need to calculate the coordinates of the color temperature of an object in the camera space.

Where Y is the color temperature coordinate in the environment coordinate system, then the color temperature coordinate in the coordinate system is

Apparently, when the B-A> 0, that is, when the color temperature of the camera we set is lower than the ambient color temperature, x> y, in this case, the deviation from white in the camera color temperature coordinate system is farther (+ direction) than that in the Environmental coordinate system, and the image is blue.

Similarly, when the B-A <0, that is, when the color temperature of the camera we set is higher than the ambient color temperature, x <y, in this case, the deviation from white in the camera color temperature coordinate system is farther (-direction) than that in the Environmental coordinate system, and the image is reddish.

When B = A, the camera will be able to restore the color correctly without any skewness. Reference[1]
Color temperature Wikipedia [2] White Balance Wikipedia [3] color-temporature