Managing Noise: SNR and DNR
Noisy recorded scenes not only affect visual recognition but also the amount of disk space used up. It is therefore important that images be as noise-free as possible regardless of the number of TV lines of the camera. There are two important attributes to consider: signal to noise ratio and dynamic noise reduction.
Signal to Noise Ratio (SNR)
Signal-to-noise ratio is the ratio of the video signal level to the amount of noise. The higher the signal-to-noise ratio, the higher the camera's image quality. This ratio is usually expressed in decibels but it can also be represented as a normal ratio. A signal-to-noise ratio of 40dB is equivalent to a ratio of 100:1 which means that the video signal is 100 times the noise level. In other words, the noise is 1% of the video signal. The following table provides ratios for different signal-to-noise ratio values
| S/N Ratio (dB) | Ratio | Picture quality |
|---|---|---|
| 60 | 1000:1 | Excellent, no noise apparent |
| 50 | 316:1 | Good, small amount of noise |
| 40 | 100:1 | Reasonable, loss of fine detail |
| 30 | 32:1 | Poor |
| 20 | 10:1 | Unstable |
Dynamic Noise reduction (DNR)
Noise is unavoidable in some situations. To counteract this, some cameras have a dynamic noise reduction function to reduce the amount of noise in their images.
References
- Selecting the Right CCTV Camera. Bosch, Print.
- "3D-DNR." HCBJ5FD SYSCOM 650TVL WDR HBLC Video Analytics Professional Camera. Web. 3 Feb 2011.
