What does gamma correction in CCD cameras mean?

Gamma

Correction is a method of editing the gamma curve of an image to perform non-linear tone editing on the image.

(Gamma

Correction): The so-called gamma correction is to edit the gamma curve of the image to detect non-linear tone editing of the image. The dark part and the light part in the image signal are increased in proportion, thereby improving the image contrast effect. In the field of computer graphics, the conversion relationship curve between the screen output voltage and the corresponding brightness is called the Gamma Curve. Based on the characteristics of the traditional CRT (Cathode

Ray

Tube) screen, the curve is usually a power function, Y=(X+e)γ, where Y is Brightness, X is the output voltage, e is the compensation coefficient, and the power value (γ) is the gamma value. Changing the power value (γ) can change the gamma curve of the CRT. A typical Gamma value is 0.45, which makes the CRT's image brightness appear linear. Monitor screens such as TV sets using CRT require correction because the luminous grayscale of the input signal is not a linear function but an exponential function.

In TVs and graphics monitors, the electron beam generated by the picture tube and the brightness of the image it generates do not change linearly with the input voltage of the picture tube. The electron flow changes according to an exponential curve compared with the input voltage. The exponent of the input voltage is greater than the exponent of the electron beam. This means that the signal in dark areas is darker than it actually is, and in light areas it's higher than it actually is. So, to reproduce what the camera captured, TVs and monitors must be gamma compensated. This gamma correction can also be done by the camera. Our purpose of gamma compensation for the entire TV system is to make the output signal generated by the camera symmetrical according to the brightness of the incident light and the brightness of the picture tube. Therefore, an opposite non-linear distortion should be introduced into the image signal, which is the same as the gamma curve of the TV system. The corresponding camera gamma curve, its value should be 1/γ, which we call the camera's gamma value. The gamma value of a TV system is about 2.2, so the camera nonlinearity compensation gamma of a TV system is 0.45. The gamma value of the color picture tube is 2.8, and its image signal correction index should be 1/2.8 = 0.35. However, due to the influence of stray light inside and outside the picture tube, the contrast and saturation of the reproduced image are reduced, so today's color cameras The gamma value is still mostly 0.45. In practical applications, we can adjust the gamma value within a certain range according to the actual situation to obtain the best effect.