How to understand the technical index of the camera (Knowledge)

In the circle of cameras, the technical indicators in a color page actually cover most of the technology. I do n’t believe it. Several people dare to say that he knows everything. Whether it is a salesperson or an engineering company, the first thing I get is A coloring page, and most of that coloring page is bragging. Only the final technical indicators are "slightly" a little learned. Today I will take you to do it:

It is expected to be divided into "knowledge articles" and "actual combat articles". For the knowledge articles, the actual combat articles will be provided by everyone. Everyone will come to the drill together. Manufacturers who are interested in playing the museum may also wish to participate together to add some fun ...

Before clarifying the technical indicators, we must first clarify the following:

1. The imaging element is the CCD! (Of course there is also C-MOS), mainly divided into color, black and white, 1/3 ", 1/4", 1/2 "and brand,

size:
The difference in size is mainly the sensitivity, which is the minimum illuminance, 1/4 illuminance will be worse than 1/3, the principle is very simple: the same number of photosensitive points, each point placed on 1/4 must be relatively small, he The light is less, of course, the illumination is worse, the advantage is that it is cheaper, and the volume is smaller, and the board can be made smaller.

Brand:
In terms of price, from expensive to cheap, they are Sony, Panasonic, Sharp, A1 (L.G),
If you use Sony, the usual logo "Sony Super-HAD CCD" is a registered trademark of Sony, or the low illumination logo "Sony Ex-View CCD". There is a process called "HAD" in the manufacturing process of CCD, so no matter All the CCDs can be called "HAD CCD," but Sony improved the process and thought that the quality of the produced CCD was better, so it was called "Super-HAD" and registered the name, so only Sony has the so-called Super-HAD. CCD, it is common to see "1/3" SONY Super-HAD CCD "in the general catalogues. It is impossible to mark" 1/3 "Sharp Super-HAD CCD". That would be a joke.

Ex-view is a proprietary name registered by Sony CCD. It emphasizes that the illuminance is lower than Super-HAD. Of course, the price is much more expensive. Other features and pins are similar to the original Super-HAD.

Instead of using SONY, just mark "1/3" Color CCD "

2. Pixel:
In the PAL system, there are 752 (H) x 582 (V), which is called 440,000 pixels, and 500 (H) x 582 (V), which is called 250,000 pixels, in the NTSC system, there are 768 (H) x 494 (V), which is the so-called 380,000 pixels, and 510 (H) x 492 (V), which is the so-called 250,000 pixels, 440,000 pixels, is called the high solution, and 250,000 is called the low solution, the general solution or the medium solution. The pixels mentioned above refer to "effective pixels

3. Resolution:
This is more fun. The technical limit of a 250,000-pixel camera is about 320. In more than ten years ago, Taiwan produced a camera, which is probably between 280 and 300, but it is worse than Japanese goods. One piece, what should I do? Then the 350 line will be ok, and then a new company and South Korea will come up with it, probably about 300, then the 380 line will be ok. In recent years, the mainland has also come up with it, how Do? Then mark 420 is good! Now that it ’s all marked with 420, shameless is also marked with 450. What is even more confusing is that no matter whether it is sent in Taiwan or mainland China for testing, it is actually 420. ? It's incredible!

The technical limit of 440,000 is about 480 lines. Generally, Taiwan and South Korea make between 400-450. For the same reason, the standard is 480, 500, 520, 550! Each has its own conscience.

In addition, the so-called 520 line is more popular recently. Why did he say 520 line? It is because the main chip uses Sony HQ1 (CXD3172AR), through the original information, can not find the word 520, only unofficial saying: yes There are 520 lines, but only Y / C output. So as long as it is HQ1 plan, everyone will mark 520, with the addition of irrigation method, 550 and 560 will come out, it is estimated that 580 will soon be available.

4. Minimum illumination:
The simplest definition: In a dark room, the camera is facing the object to be measured, and then slowly dimming the light until the object to be seen is not clear on the display. At this time, the amount of light illuminance is the minimum illuminance. Ambiguous enough! In fact, we still have to consider using a few millimeter lens, how much light is received, the camera AGC must be turned off, how much IRE the video signal is reduced to, and so on. Few manufacturers will do this kind of test,
that…. . The old story has come again. A long time ago, Panasonic and Sony's machine had a low resolution of 1.1 Lux (F1.2). Then Taiwan made it with a label of 0.5. Later, it had to be marked with 0.2. .2, I marked 0. 1, he marked 0. 05 ...... That's all.

In addition, the illuminance of the high-resolution CCD will be worse than that of the low-resolution. As an old saying goes, with the same chip area, one puts 440,000 points and one puts 250,000 points. Which big point?

5. Signal to noise ratio:
Any circuit will generate noise as long as it is powered, including components and lines themselves. Of course, the smaller the noise, the cleaner the picture will look. We use the ratio of video signal to noise to express it. Of course, the larger the better, The mathematical formula is 20log (V2 / V1), V2 refers to the video signal, V1 refers to the size of the noise signal, the unit is "dB"

It's still an old story. A long time ago, the noise ratio of Panasonic and Sony's camera was 50 dB. Then Taiwan made it ... . Hey! It seems to be poor, I am sorry to brag, then mark 48 as good, but it is not good-looking? Modify it: "greater than 48 dB", so "> 48dB" is the way to go, no matter the camera made by a cat and a dog , It ’s all marked like this, is there a test? I ’ll chop it to him!

6. Electronic shutter:
In order to make the image brightness correct, we must correctly control the incident light amount of the camera. To adjust the incident light amount, we must start with the aperture of the lens and the shutter of the camera. Generally, when we use a manual lens, the aperture adjustment is fixed. If this happens, What should I do in strong light? Very simple, before the CCD is overexposed, D. S. P quickly "sweep" down the signal on the CCD, that is, when the light is strong, grab it faster, and when the light is weaker, grab it slower. One grab is equivalent to when I use a SLR camera. Slight? Cavity? Stool Jiao Niu Niu? Yi Qin 預 缱 缱 Post sword ?? The smaller the barium 銱 犱 犀 緀 緀 equipment ??. SP specifications, electronic shutter speed in the PAL system is 1/50 seconds to 100,000 One second, so everyone marks it this way. In practical applications, if the machine is poorly calibrated, it will not reach one in 100,000. If the machine looks like a thin layer of mask in the sun, it is not very clear, then 80% The shutter speed is not enough.

Also, if you use an automatic iris lens, the amount of incident light is controlled by the lens iris. At this time, the shutter speed of the camera itself is set at 1/50 second.

7.Gamma compensation:
What is Gamma? Simply explain, the CRT tube is based on the intensity of the electron beam hitting the screen to determine the brightness. The stronger the hit, the brighter, but not 1: 1, that is, when it is very strong It will not be so bright in proportion, this is the characteristic of the CRT tube, so the video output must be deliberately enhanced at high brightness. This is called Gamma compensation, and the compensation curve is called 0.45. Just give the DSP the next instruction Just fine, there is no technology at all, some machines will add a switch, let you choose 0.45 or 1, the compensation curve of 1 is 1: 1, it is quite easy to use in some strong light environments (it is strong light Under, non-backlit)

8. Backlight compensation:
What is backlight compensation, which is related to the shutter speed again, for example, when a camera is installed on the ATM, facing the street, under the big sun, the environment is very bright, so the camera shutter speed is of course very fast. It will not be overexposed. At this time, if someone comes to withdraw money and the face is facing the lens, because the machine is currently fully metered, it is basically affected by the environment, and the whole is still very bright. Under high-speed shutter, the exposure of the face is insufficient It is black, which is what the photography says "backlight", that is: there is a strong light on the back, which causes the subject to be underexposed and become black.

So the problem lies in full exposure. If we only take a part of the face to measure the light, for example, in the middle, the face is in the middle of the face. At this time, the DSP will detect underexposure and slow the shutter speed. At this time, the face is clear, but because the shutter speed is slow, the background (on the street) is overexposed and white.

Therefore, backlight compensation is to adjust the electronic shutter (or auto iris) according to the specific metering area, so that the exposure value in the metering area is normal, and it does not matter if it is not in the metering area. The metering area is set by the DSP parameters. Generally, take the middle 1/9 place, or add the lower 1/3 place to form a convex shape.

As for what is "broad dynamic", it will write another article to talk about.

9. Synchronization system:

Internal synchronization, external synchronization and power synchronization.

Power supply synchronization: The story is long. To put it simply, the time point when each camera loses the picture field must be the same. For example, when traveling against Wu, although the speed of each person is the same, if no one is whistling or calling If the password is used, the steps will not be consistent. This function is used when the matrix is ​​switched, and the screen will not shake once and then return to normal, otherwise the administrator's eyes will not be spent. A switching power supply, take the synchronization signal from the AC power (the power supply is fixed for 50 weeks) as the basis for synchronization.
In addition, in the NTSC system, due to D. S. The oscillation frequency in P cannot be consistent with the 60-week power supply, and there will be a color roll-up under the light, especially the SONY 2163 program is more serious. At this time, it is necessary to add power synchronization to solve it and force D. S. The frequency of P is consistent with the light.

In addition, the AC power supply we use has three phases, which are 120 degrees different from each other. If the power supply synchronization machine is connected to different phase power supplies, there will be a phase difference that will not synchronize with each other, so there is also a phase adjustment knob that will trigger each other. Tune to the same.

External synchronization:
Is to let the outside step trigger the drop of the screen, this function is now rarely used

Internal synchronization:
Is to output 25 frames per second, regardless of others

10.AGC
It is electronic automatic gain, which is the basic function of the camera. Some people deliberately adjust the height very high to make the picture look brighter, so that it is easy to be white in low light, so some people just put a switch here, to be high Be low, come by yourself

The following are irrelevant:

Connector type:
With C-Mount and C / S Mount:
I have to tell a story again. When I first made the camera, I had to get a lens, so I made an interface standard:
"Pitch diameter is 25.4mm, 2 screws per inch, distance from edge to CCD is 17.526mm"
This is called the C interface, and the camera and the lens can match each other according to this standard.

After that, there were eight lenses in the lens, and Panasonic made a five-glass lens. The cost was saved, but the imaging distance was shorter by about five millimeters, which means that the lens should be closer to the CCD by five millimeters.

What should I do? Then change the standard and change the "edge to CCD distance from the top to 17.526mm" to 12.5mm. No, it's called C / S interface. Now almost all the machines use C / S interface, and then pay an extension ring for C / S to C interface.

Automatic iris:
That is, there are two types of auto-iris lenses that can be connected: video drive (Video) and direct drive (DC). Because the direct drive method needs to add a small circuit, some cheap machines simply remove it. Bet you ca n’t afford to buy a DC auto iris lens.

Video output:
The standard is 1 Vpp, which is 1 volt (peak-to-peak). The standard is the same, but there are often manufacturers who want to look "bright" and intentionally increase the strength of the interrogation signal, which will cause some problems when connected to DVR and wiring. Bothered.

Power consumption:
When the general machine is at 12V, it is generally between 90-130 mA

power supply:
Divided into 12VDC, 24VAC, 220VAC, usually 24VAC is also compatible with 12VDC

The above is some basic knowledge. Knowing these means understanding most of the cameras, which may be difficult, but first treat it as a martial art mentality. Be sure to understand it and recite it in detail. I'm looking for someone to practice boxing. You may wish to post some indicators and everyone will come to fight and fight together as a textbook for the next "actual combat".