Several monitoring product term explanations

1. Pixels:

In the PAL system, there are 752 (H) x 582 (V), which is called 440,000 pixels, and 500 (H) x 582 (V) is also called 250,000 pixels. In NTSC system, there are 768 (H) x 494 (V) , that is, the so-called 380,000 pixels, and 510(H)x492(V) is the so-called 250,000 pixels, 440,000 pixels, it is called high resolution, 250,000 is called low resolution, general solution or middle solution. Means "effective pixel 2. minimum illumination:

The simplest definition: In the darkroom, the camera is facing the object to be measured, and then the light is slowly dimmed until the measured object is not clearly visible on the display. At this time, the illuminance of the amount of light is the minimum illumination.

5. Signal to noise ratio:

Any circuit will generate noise as long as it is powered on, including the components and the line itself. Of course, the smaller the noise, the cleaner the picture will appear. We use the ratio of video signal to noise to indicate that, of course, the bigger the better. Mathematical formula is 20log (V2/V1), V2 refers to the video signal, V1 refers to the noise size, the unit is "dB"

3. Electronic shutter:

In order to make the image brightness correct, we must correctly control the amount of light into the camera, to adjust the amount of light to go from the lens aperture and the camera shutter, generally we use a manual lens, the aperture adjustment will not move fixed, if this time What to do with the glare? Very simple, before the CCD has not been exposed, DSP quickly rushed the signal on the CCD down, that is, catch light faster when the light is strong, when the light is weak, catch slower, catch a When I used the SLR camera to "click", SLR camera is a mechanical shutter, we are electronic, so called "electronic shutter"

According to DSP specifications, the electronic shutter speed is 1/50 second to one hundred thousandth of a second when PAL system is used, so everyone has marked this. If the camera is poorly tuned for practical application, it is less than 100,000. One, if the machine looks like a thin layer of white in the sun, it is not very clear, that is, the shutter speed is not enough.

In addition, if an auto iris lens is used, the amount of light entering is controlled by the lens aperture. At this time, the shutter speed of the rear camera itself is set at 1/50 second. 4. Gamma compensation:

What is Gamma? Simple explanation, CRT tube is based on the intensity of the electron beam hit on the screen to determine the brightness generated, the stronger the stronger the light, but not 1:1, that is to say, in a very strong The latter will not be proportionally bright. This is a characteristic of the CRT tube. Therefore, the video output must be enhanced deliberately at high brightness. This is called Gamma compensation. The compensation curve is called 0.45, as long as the next instruction is given to the DSP. Just fine, no technology at all, and some cameras will add a switch, let you choose 0.45 or 1, 1 of the compensation curve is 1:1, in some bright light environment is also very easy to use (is a strong light Under non-backlight)

5. Backlight compensation:

What is the backlight compensation, which is related to the shutter speed, for example, when a camera is mounted on the ATM, facing the street, in the big sun, the environment is very bright, so the camera shutter speed is of course very fast. Will not be overexposed. At this time, if someone withdraws funds, the face is facing the camera. Because the camera is currently fully metered, it is basically affected by the environment, and the whole is still very bright. Under the high-speed shutter, the exposure of the face is insufficient. Obviously dark, this is the “backlight” mentioned above in photography, that is: the back of the light, causing the subject to underexposure and become dark.

Therefore, the problem lies in the overall exposure. If we only take a part of the surface to measure light, for example, in the middle, the face is in the middle of the stroke. When the DSP detects underexposure, it will slow down the shutter speed. At this time the face is clear, but because the shutter speed is slow, the background (street) is overexposed and white.

Therefore, backlight compensation is based on a specific metering area, adjust the electronic shutter (or auto iris), so that the exposure value in the metering area is normal, not in the metering area, regardless of the metering area set by the DSP parameters, Usually take the middle 1/9, or add the bottom 1/3 into a convex font.

6. Synchronization system:

Internal synchronization, external synchronization and power synchronization.

Power synchronization,

To put it in a long story, to put it simply, it is to make the time at which each camera loses its picture field to be the same, such as when the enemy is marching. Although everyone has the same speed, if no one is whistling or shouting at the side, The pace is not consistent, this function is used in the matrix switch, the screen will not shake and then return to normal, otherwise the administrator eyes do not spend, to achieve power synchronization must be added to the power synchronization circuit, plus a switching power supply , Take the synchronous signal from the alternating current (power is fixed for 50 weeks) as the basis of synchronization.

In addition, in the NTSC system, because the oscillation frequency in the DSP can not be consistent with 60 weeks of commercial power, there will be color rolling in the light, especially the SONY2163 program is more serious, then we must increase the power synchronization to solve, forcing the DSP The frequency is consistent with the light.

In addition, the AC power supply used by us has three phases, which are 120 degrees different from each other. If the power supply synchronization machines are connected to different phase power supplies, there will be a phase difference that cannot be synchronized with each other. Therefore, a phase adjustment knob is needed to trigger the phases to each other. Adjust to match.

External synchronization is triggered by the external step to throw out the screen, this feature is now rarely used internal synchronization is its own output 25 frames per second, regardless of others 7.AGC

It is the electronic automatic gain, it is the basic function of the camera, some people make the screen look bright, deliberately adjusted very high, so that when the low illumination is very easy to white, so some people simply put a switch here, to be high To be low, come by yourself 8. Auto iris:

That is, the type of auto iris lens that can be connected, there are currently two: video and direct drive (DC), because the direct drive method has to add a small circuit, some cheap machine simply removed, Bet you can't afford to buy a DC auto iris lens.

Video output:

The standard is 1Vpp, which is 1 volt (peak-to-peak), the standard is such a mark, but often for some manufacturers to look "bright", intentionally increase the strength of the question mark, in the DVR and wiring will cause some trouble .

Power consumption:

When the general camera is at 12V, it is generally between 90-130mA.

Divided into 12VDC, 24VAC, 220VAC three, usually 24VAC is also compatible with 12VDC