The camera's minimum illumination analysis
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Another: The most commonly used method for measuring the minimum illuminance is called the target illuminance method, and the target illuminance indicates how strong the light reaches the surface of the CCD. Although the definition is clearly different, there are three main parameters that determine the result. Is:
F value (used to test the lens F value for the camera)
Color temperature (color temperature of the light source, that is, spectral content)
IRE (IRE amplitude of video amplitude)
Reflectance (target reflectivity and background)
F value F value is a method of measuring the lens with the ability to collect light, a good lens can collect more light and concentrated emission to the CCD sensor, F1.4 lens can capture 2 times the light than the F2.0 lens, change In other words, the lens of F1.0 can collect 100 times more light than the lens of F10, so it is very important to mark the F stop in the measurement, otherwise the result is meaningless.
Color temperature The color temperature is a method of expressing the wavelength of the light in the light source. A 3200K light source has a wavelength of 600 nm, and a 9300K light source has a wavelength of 300 to 500 nm. Therefore, different color temperatures will completely change the test results. . On a typical CCD sensor, a light source with a wavelength of 600 nanometers will produce 10 times more electrons than a light source with a wavelength of 900 nanometers. This is why color temperature is particularly marked for the result.
The maximum amplitude of the video output of the IRE grade CCD camera is generally set at 100 IRE or 700 mV. A 100 IRE video representation can completely drive a monitor to display the best brightness and contrast. Only 50 IRE video represents only half the contrast, 30 IRE Or 210 mV represents only 30% of the original amplitude, usually 30IRE is the lowest value of the available image. A standard camera should have a noise level of 10 IRE when the auto gain is increased to maximum gain, thus providing 3:1 or 10 dB The signal to noise ratio is acceptable.
A result measured at 10 IRE can be 10 times higher than that measured at 100 IRE, so no results that indicate the IRE level are actually meaningless.
Reflectance The target's reflectance and background can completely alter the measurement result. A target with 100% reflectance can produce 100 times more light than a target with only 1% reflectivity.
How to set parameters generally:
Generally reputable companies will measure sensitivity under the following standards.
F stops F1.2
Color temperature 5600K
Video level 30 IRE
80% reflectance
Therefore, a sincere camera manufacturer will label the minimum illumination 3lux as follows (F1.45600K30IRE80%)
If any of the parameters are omitted, the result may be 10 to 1000 times different.
For example, an identical camera can be marked with a completely different 1lux (F1.45600K30IRE80%)
0.001lux (F0.755600K10IRE1%)
Some irresponsible producers will mark the following high-sensitivity camera 1lux (F1.45600K30IRE80%) but is marked as 0.0001lux.
Now you should know why! ! ! Because they are marked in the following cases (F0.755600K10IRE0.1%)
Do you want to know what this (F0.755600K10IRE0.1%) shows?
F0.75 is a lens that will cost you $30,000 or more to buy, and this is generally not used in the closed-circuit monitoring industry.
10IRE video is below the noise level, so nothing can be seen.
The 0.1% reflectance can only be obtained by placing a thin white line on a completely dark background.