Signal-to-noise ratio, the English name is called SNR or S/N (SIGNAL-NOISE RATIO) , also known as signal-to-noise ratio. Refers to the ratio of signal to noise in an electronic device or electronic system. The signal here refers to the electronic signal from the outside of the device that needs to be processed by this device, and the noise refers to the irregular extra signal (or information) that does not exist in the original signal generated after passing through the device, and this kind The signal does not change with the original signal.
Image SNR
The signal-to-noise ratio of an image should be equal to the ratio of the power spectrum of the signal to the noise , but usually the power spectrum is difficult to calculate. There is a method to approximate the signal-to-noise ratio of the image, that is, the ratio of the variance of the signal to the noise . First calculate the local variance of all pixels in the image , consider the maximum value of the local variance as the signal variance, and the minimum value as the noise variance, calculate their ratio, convert it into dB , and finally use the empirical formula to correct it. For specific parameters, please refer to " Deconvolution and Signal Restoration (Zou Mouyan)". s/n is called the signal-to-noise ratio. Since the ratio of S to N is too large in actual use, the decibel number (db) is often taken. The relationship between decibel and signal-to-noise ratio is: db=10lg (s/n)
example
The image signal-to-noise ratio of a general surveillance camera is 50dB, like the American Electric Bell series BL-CB800ATM-N.
The signal-to-noise ratio is the ratio of the signal voltage to the noise voltage , usually expressed by the symbol s/n . Because in general, the signal voltage is much higher than the noise voltage, the ratio is very large, and the unit of the signal-to-noise ratio is expressed in db. Generally, the signal-to-noise ratio value given by the camera is the value when the AGC (automatic gain control) is turned off, because when the AGC is turned on, the small signal will be boosted, so that the noise level will also increase accordingly . The typical value of the signal-to-noise ratio is 45~55db. If it is 50db, the image has a small amount of noise, but the image quality is good; if it is 60db, the image quality is excellent without noise.