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What is the minimum illumination?

2011-10-26

Minimum illumination is a method of measuring the sensitivity of a camera. In other words, the camera can see the available images in how dark it is. But because there is no international standard for management, each large CCD manufacturer has its own method of measuring the CCD sensitivity. However, a camera labeled ( 1Lux , F10 ) can be exactly the same as a camera labeled ( 0.01Lux , F10 )! !! !! Is it strange? why?

Another: The most commonly used method for measuring the lowest illuminance is called the target illuminance method. The target illuminance indicates how strong the light reaches the position where the CCD surface is placed. Although the definitions are clear, there are three main parameters that determine the outcome. Is:

F value of the lens ( used to test the lens F value of the camera )

Color temperature ( the color temperature of the light source, that is, the spectral content )

IRE ( IRE level of video amplitude )

Reflectivity ( reflectivity and background of the target )

Lens F- number

The F value is a method to measure the ability of the lens to collect light. A good lens can collect more light and focus it on the CCD sensor. The F1.4 lens can collect 2 times the light than the F2.0 lens . In other words, the F1.0 lens can capture 100 times more light than the F10 lens , so it is very important to mark the F value in the measurement , otherwise the results are meaningless.

Color temperature

Color temperature is a way to express the wavelength content of light in a light source. A 3200k light source has most of its wavelength between 600 nm and 900 nm, while a 9300k light source has most of its wavelength between 300 and 500 nm. Therefore, different color temperatures will change completely Test Results. On a typical CCD sensor, a light source with a wavelength of 600 nm will generate 10 times more electrons than a light source with a wavelength of 900 nm . That's why the color temperature is specifically annotated for the results.

IRE rating

The maximum amplitude of the video output of a CCD camera is generally set at 100IRE or 700 millivolts. A 100IRE video indicates that it can fully drive a monitor to display a high-quality image with the best brightness and contrast. A video with only 50IRE indicates only half the contrast, 30IRE or 210 Millivolt means that it is only 30% of the original amplitude . Usually 30IRE is the lowest value for the available image. A standard camera should have a noise level of 10IRE when the automatic gain is increased to the maximum gain , so it can provide 3: 1 or 10dB signal noise. Than acceptable image.

A result measured at 10IRE can be 10 times higher than the result measured at 100IRE , so a result without an IRE rating is actually meaningless.

Reflection ratio

The target's reflectance and background can completely change the measurement result. A target plane with 100% reflectivity can produce 100 times more light than a target with only 1% reflectivity .

How to set parameters in general:

Sensitivity is measured by reputable companies in the following standards.

F value F1.2

Color temperature 5600K

Video Rating 30 IRE

80% reflectance

Therefore, a sincere camera manufacturer will mark the minimum illumination as follows

3 lux (F1.4 5600K 30 IRE 80%)

If any parameter is omitted, the result may be 10 to 1000 times different.

For example, the same camera can be marked differently.

1 lux (F1.4 5600K 30 IRE 80%)

0.001 lux (F 0.75 5600K 10 IRE 1%)

Some irresponsible manufacturers will mark the ultra-high-sensitivity cameras measured as follows

1 lux (F1.4 5600K 30 IRE 80%) but marked as 0.0001 lux.

Now you know the reason! !! !! Because they are marked in the following cases

(F 0.75 5600K 10 IRE 0.1%)

Wondering what this (F 0.75 5600K 10 IRE 0.1%) means?

F 0.75 is a lens that will cost you $ 30,000 or more to purchase, and this is generally not used in the CCTV industry.

10 IRE video is below noise level, so nothing can be seen.

0.1% reflectance can only be obtained by placing a thin white line against a completely dark background.