Five-point reference teaches you to distinguish the merits of surveillance camera specifications

This week to talk about some simple and basic problems, some entered the security that want to know some of the basic camera specifications with the selection relationship, today we started from the network monitoring IT problems to more simple monitoring product problems to talk about .

How to distinguish the merits of the camera specifications to do selection reference?

This can be discussed from the five major parts:

1. What is the S/N ratio? How to calculate?

2. What is the basic statement of resolution?

3. How is the minimum illumination determined?

4. What is the dynamic range enclosure?

5. What is the degree of color reproduction?

S/N (Signal Noise Ratio) As long as the signal-to-noise ratio is an electronic component, resistance, capacitance, CCD, CDS, and DSP generate heat, and heat affects the image signal, causing noise in the image, and the ratio of image to noise. Is the S/N ratio.

The image is as large as the noise, the image occupies 1 and the noise accounts for 1 (1/1=1): 0 dB;

Image accounted for 10, noise accounted for 1 (10/1) = 20dB;

Image accounted for 100, noise accounted for 1 (100/1) = 40dB;

Image accounted for 1000, noise accounted for 1 (1000/1) = 60dB;

The image occupies 10000 and the noise accounts for 1 (10000/1) = 80 dB.

The general specification mentions 48dB, that is, the ratio of image to noise is 300/1 to 250/1.

Reduce the S/N method:

Passive components such as resistors and capacitors, use low S/N, especially CCD, CDS, DSP select low S/N product grade. (taking into account the cost and product level to make a distinction)

Resolution The number of lines that a TV picture can render. The key is from CCD/CMOS sensor (80%), ISP and DSP 15-18%, and filter 2-5%. The recognition rate is usually identified by the number of lines TVL in the analog system, and the IP network camera uses the pixels Pixel as the recognition rate. High-definition 720P and full-HD 1080i/P are methods for recognizing the rate from HDTV's HDTV. The products associated with the recognition rate include lens and monitor. The recognition rate must be increased from the front-end to the back-end. If the camera has 1.3 million pixels, the lens/monitor should have a recognition rate of more than 2 million. This will not affect the screen. Display quality.

Minimum illumination lux

When the external light falls to a low level, the incoming photon produces a lower voltage than the noise, and the signal is covered by the noise. The smallest light the Sensor can sense is called the minimum illumination.

IRE is the measure of illuminance, 30 IRE 0.5 lux, 20 IRE 0.2 lux,...

Ideal lens, F = 1.0, in fact F = 1.2 to 1.4 or more, so the lens will eat some light.

Wide Dynamic Dynamic Range: The image range that is seen from the brightest to the darkest at the same time is called the dynamic range. The dynamic range is 200 (1 lux to 200 lux) = 46 dB.

Dynamic range 400 (1 lux to 400 lux) = 52 dB

Taking 52 dB as an example, the external 2,000 lux can reduce the aperture to make the internal sensation or 400, but only 0.2 lux is left in the area where the outside is less than 1 lux, and the sensor cannot catch it.

At this time, two shots are taken with two exposure times. Then we take a proper part and synthesize it into a picture we want.

The degree of color reproduction close to the human eye. Generally, Panasonic products can be seen as reddish and SONY as blue, but their respective DSPs will make compensation corrections. This of course also has a great relationship with white balance. We can talk about it again next time.

When selecting any kind of professional video camera, you can first look at these five parts to make a basic selection reference. It is only necessary to pay attention to the professional part to take special consideration. For example, if you want to have a wide dynamic WDR Camera, then focus on WDR in the evaluation. Do not compare other cameras without WDR, and that imbalance will lose more significance.

Low lux, Day and Night, IR low light, day and night and infrared are separate things. IR Cutter is called True day and night. During the day, the ray of light filters out infrared rays with a blue filter, so that the picture will not be reddish and clear. Remove the filter at night, the infrared light is colorless, so it turns black and white, so that you can see clearly.

In general day and night, a layer of coating is applied to the lens, visible light comes in, and the infrared part (850 to 940 wavelength) comes in. The disadvantages are that the color saturation is not enough and the infrared light comes in at night is not enough. However, the price is low, and there is no problem that the organic parts are easily damaged (the mechanical action of the IR cutter movement control).

Low lux: In some places, it is not possible to actively project infrared light. For example, coastal observations and earth observations must rely on natural light sources. In this case, low illumination is required.

On the other hand, IR cams can be used to actively project IR light.