The focal length of a surveillance camera refers to the distance between the lens and the photosensitive element. The magnification of the lens is approximately equal to the ratio of focal length to object distance. That is to say, with the increase of the focal length of the surveillance camera, the magnification increases, and the close-up can be zoomed out, and the details of the distant view are clearer, on the contrary, it is established, so what are the types of surveillance cameras? According to different installation areas, it can be divided into indoor and outdoor; According to the different transmitted signals, it can be divided into analog and digital; According to different illuminance, it can be divided into pure color, low illumination, ultra-low illumination, starlight level; According to the different types of fill light, it can be divided into white light, infrared and laser; According to the different image quality, it can be divided into standard definition and high definition; According to different imaging principles, it can be divided into active imaging and thermal imaging; According to the different appearance, it can be divided into pinholes, domes, bolts, ball machines, integrated gimbals, let’s take a look at what is the principle of network surveillance cameras?

1. Lens
As the front-end component of a network camera, the lens has fixed aperture, auto aperture, auto zoom, auto zoom, etc., which are the same as analog cameras.

2. Image and sound sensor
Image sensors are available in CMOS and CCD modes. CMOS is complementary to metal-oxide semiconductors, and CMOS is mainly a semiconductor made of silicon and germanium, which achieves basic functions through negatively charged and positively charged transistors on CMOS. The current generated by these two complementary effects can then be recorded and interpreted into an image by the processing chip. The main advantage of CMOS for CCDs is that it is very power-efficient. Unlike CCDs, which consist of diodes, CMOS circuits consume almost no quiescent power. This makes the power consumption of CMOS only about 1/3 of that of ordinary CCDs, and the important problem of CMOS is that when processing fast-changing images, it overheats due to excessive current conversion. The good suppression of dark current is not a big problem, and if the suppression is not good, it is very easy to have dead pixels.

CCD image sensors consist of photodiodes arranged in two dimensions on a single crystal silicon substrate and their transmission circuits. Photodiodes convert light into an electric charge, which is then transmitted and output by a conversion circuit. Typically, CCD image sensors are used for devices that deliver excellent image quality, while CMOS image sensors are chosen for products that are concerned about power consumption and cost. But new technologies are overcoming the inherent weaknesses of each body, while retaining certain characteristics that are suitable for specific uses. This section is the same as for analog cameras. A sound sensor is a pickup, or microphone, and works on the same principle as a traditional microphone.

3. A/D converter
The function of A/D converters is to convert analog signals such as images and sound into digital signals.

The image sensor module based on CMOS mode has an interface for direct digital signal output, without the need for an A/D converter; The image sensor module based on CCD mode does not need an A/D converter if it has a direct digital output interface, but because this module is mainly designed for analog cameras and only has an analog output interface, A/D conversion is required.

4. Image and sound encoder
The A/D converted image and sound digital signals are encoded and compressed according to a certain format or standard. The purpose of encoding and compression is to facilitate the digitization of audio/visual signals and multimedia signals; It is convenient to transmit the above signals without distortion in computer systems, networks and the World Wide Web.