CATV image quality subjective evaluation table The subjective evaluation of the user-side image quality is based on the five-level damage standard. It should be implemented in accordance with the international standard GB7401, Article 4.2, five-level damage system. The fourth-level image is the design standard of the CATV system.
Level Subjective evaluation of image quality impairment (S / N) 5MHz (dB) CCIR (S / N)
5 points (Excellent) No damage or interference is noticed on the image 45.5 44.7
4 points (good) There are slightly perceptible damage or interference on the image, but it is not annoying 36.6 34.7
3 points (medium) Obviously perceived damage or interference on the image, which is annoying 29.9 30
2 points (poor) The image is damaged or disturbed seriously, which is quite annoying 25.4 27
1 point (inferior) The image is seriously damaged and cannot be viewed 23.1 21
For Chinese TV system C / N = N + 6.4dB, the image level 4 (S / N = 36.6dB) corresponds to C / N = 43dB.
Meter-weighted signal-to-noise ratio and image level relationship formula (S / N) 5MHz = 23-Q + 1.1Q2 (dB) (European Union experimental formula), (S / N) 5MHz refers to the meter-weighted signal-to-noise measured within the 5MHz bandwidth Ratio (S / N) 6MHz = 21-Q + 1.1Q2 (dB) (Supplementary Formula of the Ministry of Radio and Film)
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