The composition of the network camera

1, the lens

The lens is a front-end component of a network camera, and has fixed aperture, auto iris, auto zoom, auto zoom, and the like, the same as an analog camera.

2, image sensor, sound sensor

The image sensor has both CMOS and CCD modes. CMOS is a complementary metal oxide semiconductor, and CMOS is mainly a semiconductor made of silicon and germanium. Basic functions are realized by a negatively-charged and positively-charged transistor on the CMOS. The currents generated by these two complementary effects can be recorded and interpreted by the processing chip as images. The main advantage of CMOS for CCD is very low power consumption. Unlike CCD and CMOS circuits composed of diodes, there is almost no static power consumption. This makes the power consumption of the CMOS only about 1/3 of that of an ordinary CCD. An important issue of the CMOS is that when processing a fast-converted image, the current is overheated because the current conversion is too frequent. Dark current suppression is not a problem. If the suppression is not good, noise is very likely to appear.

The CCD image sensor consists of a photodiode arranged two-dimensionally on a monocrystalline silicon substrate and its transmission circuit. Photodiodes convert light into electric charge, which is then transmitted and output via a conversion circuit.

In general, CCD image sensors are used in devices that deliver superior image quality, and CMOS image sensors are used in products that focus on power consumption and cost. But new technologies are overcoming the inherent weaknesses of each device while retaining certain features that are suitable for a particular application. This section is the same as the analog camera. The sound sensor is a pickup or a microphone, which is the same as the traditional microphone principle.

3, A/D converter

The function of the A/D converter is to convert analog signals such as images and sounds into digital signals.

The image sensor module based on the CMOS mode has a direct digital signal output interface and does not require an A/D converter. However, if the image sensor module based on the CCD mode has a direct digital output interface, there is no need for an A/D converter, but due to this module Mainly for analog camera design, only the analog output interface, it requires A/D conversion.

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 coding compression is to facilitate the digitization of audio/visual signals and multimedia signals; to facilitate the transmission of the signals without distortion in computer systems, networks, and the World Wide Web.

There are two kinds of image coding compression techniques: one is hardware coding compression, which means the coding compression algorithm is solidified on the chip; the other is software coding compression based on DSP, that is, the software runs on the DSP to perform image coding and compression. Similarly, voice compression can also use hardware-coded compression and software compression, and its encoding standard is MP3 format.

5, the controller

The controller is the heart of the webcam and it shoulders the management and control of the webcam. If it is hardware compression coding, the controller is an independent component; if it is software coding compression, the controller is a DSP running code compression software, that is, they are combined into one.

6, the network server

The network server provides network functions of the network camera. It uses related network protocols such as RTP/RTCP, UDP, HTTP, and TCP/IP, allowing users to use a standard browser from their own PC according to the IP address of the network camera.

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Network Robot Atlas

Network cameras access, view live images, and control the camera's lens and head.

7, external alarm, control interface

The network camera provides a practical external interface for engineering applications, such as controlling the 485 interface of the PTZ, and I/O ports for alarm input and output. If the infrared sensor finds a target, an alarm signal is sent to the network camera. The network camera automatically adjusts the lens direction and records in real time. On the other hand, when the network camera detects the presence of a moving target, it can also send out an alarm signal.

The basic principle of the network camera is: After the image signal is input through the lens and the sound signal is input through the microphone, the sound sensor of the image sensor is converted into an electric signal, and the A/D converter converts the analog electric signal into a digital electric signal, and then passes through the encoder. According to a certain coding standard for encoding and compression, under the control of the controller, the network server sends a LAN or INTERNET according to a certain network protocol. The controller can also receive alarm signals and send out alarm signals, and send out control signals as required. .

8, the image coding standard

Network camera image compression coding standards mainly include MPEG4, H.263, H.264, M-JPEG and so on.

MPEG4

The so-called MPEG standard refers to a set of standards developed by ISO's Moving Picture Experts Group on compression and decompression technologies for audio and video signals and multimedia signals. So far, MPEG1 and MP3 have been established and approved for implementation in 1991; MPEG2 has been approved in 1994; and MPEG4 and MP4 have been approved in 1999. The standards being worked out are: mpeg7 and MEPG21.

H.263

H.263 is an ITU-T video encoding/decoding proposal used as an H.324 terminal. H.263 has been continuously improved and has undergone many upgrades. Today, H.263 has largely replaced H.261 and H.263. 263 is increasingly popular because it can transmit high-quality video streams over low bandwidth.

H.263 is a hybrid coding of motion compensated DPCM. In motion-compensated DPCM hybrid coding, motion compensation is performed on the basis of motion search, and then DCT transform and zigzag scan coding are used to obtain an output stream. On the basis of the H.261 recommendation, H.263 adds search for motion vectors to half-pixel search; at the same time, it adds four unrestricted motion vectors, syntax-based arithmetic coding, advanced prediction techniques, and PB frame coding. Advanced options; thus achieving the goal of further reducing the code rate and improving the encoding quality.

H.264

H.264 is a new digital video coding standard developed by the Joint Video Group of ITU-T VCEG and ISO/IEC MPEG. It is both the H.264 of ITU-T and the tenth part of MPEG4 of ISO/IEC. .

With the same reconstructed image quality, H.264 can save about 50% of the code rate compared with H.263, which is about 33% more performance than the current video format based on MPEG4.

M-JPEG

M-JPEG technology is motion still image compression technology. It processes moving video sequences as continuous still images. This compression technique compresses each frame individually and completely. Each frame can be stored randomly in the editing process. Make frame-accurate edits. However, M-JPEG only compresses intra-domain spatial redundancy and does not compress the time redundancy between frames. Therefore, the compression efficiency is not high.