System integration integrators often face a variety of choices when choosing cameras. Different manufacturers' different expressions of the camera's index parameters are often confusing. However, limited to the actual situation, it is often impossible to test the camera's low illumination effects one by one.
The camera's low illuminance indicator should not be just a simple XX Lux value. On any accurate and professional camera parameter data, the camera low illuminance indicator should at least be expressed as the following format: Color Mode: XX Lux @FX(X IRE ,AGC XX) Black and White Mode: XX Lux @FX (X IRE, AGC XX)
That is, the camera's low illuminance performance is related to at least three parameters, namely, the lens' F value, IRE value, and camera's AGC parameter. With these parameters intact, the previous illuminance values ​​are meaningful and comparable. At the same time, it must be pointed out that if the camera is turned black, it must be listed in the color and black and white state of the respective low-light index.
So what is the significance of the individual quantities in the low-illumination standard expression and what is the relationship between them?
F value F is the aperture coefficient of the lens, which is inversely proportional to the amount of light entering. Because the camera must rely on the aperture of the lens to determine the amount of light, thus determining the shooting effect. Therefore, when expressing the camera's low-lightness indicator, there must be an F-condition. For an automatic aperture zoom lens, the lens will generally indicate the F value. Note that this value only represents the aperture value when the focal length is minimum, that is, in the wide-angle state. It is generally believed that the lens advances with the increase in focal length. The amount of light is gradually reduced, so when the lens is in a wide-angle state, the picture is bright, and when it is in a telephoto state, the picture is darkened. This phenomenon is particularly evident at night. Changes in the focal length of the lens drive the change in the amount of light entering the lens and reflect the change in the corresponding F value. However, the F value on the lens only indicates the maximum amount of light entering the lens. Therefore, only the F value marked on the lens is observed. Can judge the lens into the wide-angle lens into the light efficiency, and can not fully reflect the true performance of the lens, the lens focal length extreme corresponding to the F value is usually very different, so some cameras at night when the wide-angle, the picture is not bad, But once in a telescopic state, the picture is very dark. In a really good shot, when the focal length is maximum and minimum, the F value is not much different, for example, from 1.8 to 1.6, the nighttime effect of this lens is relatively better. The F value usually marked in the low illumination index indicates the F value of the lens used during the test in the wide-angle state, that is, when the amount of light entering is the maximum.
The IRE value is well known. The analog video is an irregular waveform with a peak-to-peak voltage of 1 volt. Below the X-axis is the sync level. The amplitude is 0.3 volts, which is 300 millivolts. Above the X-axis is the actual video waveform. This part of the waveform will follow the video. The brightness and the video content change, and its amplitude is 0.7 volts or 700 millivolts. 700 millivolts is the limit amplitude of the video signal. As the lighting conditions decrease, this value will decrease. If you cover the lens completely, you can see that the amplitude of the video waveform is close to 0 through the oscilloscope. So what is IRE? The IRE is a unit in video measurement. It is specified in the broadcast video level that the luminance level of any video signal during playback cannot exceed 100 IRE, ie, 700 millivolts is equivalent to 100 IRE. That is, the IRE value will indicate The amplitude of the video signal. In general, when the video signal is lower than 250 IRE (a quarter of 700 mV), that is 175 mV, the video signal at this time is considered to be insignificant because it reflects the effect on the monitor at this time. The screen is basically dark and cannot be effectively monitored. In view of this, in the low-illuminance indicator of the camera, the IRE item is generally not less than 25, and is often tagged with 30 majority, and a few products are tagged with 50. Obviously, both the video amplitude and the IRE value decrease as the ambient illumination decreases. When examining the camera's low-light performance, the IRE value may be low, but it must be ensured that the displayed video is still meaningful.
The AGC parameter has an amplifying circuit inside the camera for amplifying the original video signal. The DSP chip in the camera will detect the original video signal sent by the CCD. If the original video signal is too small, the DSP will drive this amplifier circuit to amplify the original signal and then output the amplified video signal. The DSP will detect the amplitude of the original video signal in real time, so as to dynamically control the gain value of the amplifier circuit. This is the so-called 'Auto Gain' function, and the mechanism for determining whether to enable this function is automatic gain control (AGC). When the AGC function is turned on (AGC ON), the automatic gain circuit automatically amplifies the video amplitude in the case of poor illumination, making the screen brighter. (It is worth noting that even when the AGC is ON, under good lighting conditions, The automatic gain circuit will not work, and the picture will not become brighter. On the contrary, if the AGC function is not enabled (AGC OFF), the automatic gain circuit will not work. Obviously, if the AGC is turned on, the amplifier circuit is in working condition when testing the low illumination performance of the camera. It should be noted that the amplifier circuit will amplify the noise in the video signal together, so noise will appear on the screen.
Aluminum Foil Waterproof Pipe Tape
Characteristics of aluminum foil butyl tape:
1) Can maintain elasticity, adhesion, can withstand a certain degree of displacement, deformation has a good following effect;
2) Waterproof seal and chemical corrosion resistance, UV (sunlight) resistance, long service life;
3) The utility model has the advantages of convenient use, accurate consumption, waste reduction and high cost performance.
4) In addition, since butyl tape does not contain solvents, it is a safe and environmentally friendly waterproof material.
Waterproof Aluminum Foil Tape,Aluminum Membrane Duct Tape,Against Moisture Aluminum Adhesive Tape
JINING XUNDA PIPE COATING MATERIALS CO.,LTD , https://www.xundapipelinetape.com