White Balance Principle（1）
First of all, we must understand what white balance is. It refers to the color reproduction of the image of the original white object in the process of image processing. By removing the influence of the color temperature of the external light source, the image on the final photo is also presented. The original white is consistent. How does the color temperature understand? This concept is actually not easy to understand. It is defined by Kelvin through the ideal source of blackbody, different colors of light at different temperatures. (Black body is an idealized concept. It refers to such an object that emits light, but absorbs any light from the outside, and at the same time releases all the absorbed energy in the form of light, so it is called black body.)
The temperature unit of the black body is called Kelvin (K). From 3300K to 9300K, the color of the light is red, white, and blue. Easy to understand, everyone can imagine that, like a flame, the inner flame temperature is lower, the outer flame temperature is higher (blue), and the inner flame temperature is lower (yellow), so the flame has the highest outermost temperature. The place will be blue (cold), a little bit of common sense. The color temperature is based on the temperature variation characteristics of the black body to quantify the color tendency. The color temperature is low, yellowish, and the color temperature is high and blue. The so-called warm and cold color is a more emotional name.
To understand the concept of color temperature, we can expand it to discuss. Simply put, the purpose of white balance correction is to make the color look exactly the same as the human eye under the color temperature adjustment. The current algorithmic basis in white balance correction is about two very important theories which are Gray world theory and Total reflection theory.
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