The application of network video monitoring technology, makes the image with a
qualitative leap. First, the network cabling instead of the traditional video
simulation wiring, a video, audio, three nets (data), and network camera plug
and play, project implementation is simple, convenient, expansion system,
Secondly, the trans-regional remote monitoring, especially the use of the
Internet, have no image from limitation, and clear, stable image by,
Furthermore, the image of storage and retrieval is very safe and convenient, but
different storage, storage and fast backup machine nonlinear search.
Principle
Network camera lens, generally by the sound image sensor, sensor, the A/D
converter, images, sounds, controller, external web server alarm, control
interface components.
lens
In front of the camera lens as network components, have fixed aperture,
automatic aperture, automatic zoom, automatic variable times, and such as analog
camera.
Image sensor, sound sensor
Image sensor has CMOS and two patterns of CCD. Both complementary metal
oxide semiconductor CMOS, CMOS mainly using silicon germanium and made the two
elements of semiconductor CMOS, through with negative electricity and positively
charged to realize the basic function of the transistor. These two complementary
effect can be produced by the current record and interpret chip. For most of the
major CMOS CCD advantage is very province electricity. Unlike the CCD composed
by the CPU CMOS circuit with almost no static electricity consumption. This
makes the power only common CMOS 1/3 of CCD, CMOS is rapidly changing in shadow
like, due to current transform too frequent and overheating. Dark current
suppression is good, if the problem is very easy to restrain appear speckles.
CCD image sensor in silicon substrate by a two-dimension photoelectric
diodes and arranged transmission circuit. Photoelectric diode light into the
charge transfer and conversion circuit output.
Usually, excellent image quality of transmitting devices using CCD image
sensor, and pay attention to power and cost of product chooses CMOS image
sensors. But new technologies are overcome each bodies inherent weakness, while
retaining a suitable for specific purposes of certain features. This part of the
same camera with simulation.
Sound is picked up sound editor or sensor, and the traditional called
microphone microphone principle.
A/D converter
A/D converter is the function of graphics and sound, etc will be converted
into analog signals digital signal.
Based on the CMOS image sensors module has the mode of digital signal
output interface directly, without A/D converter, While the image sensor based
on CCD mode as A direct digital output module interface, also need A/D
converter, but because this module mainly for analog camera, only the analog
output interface design, it needs A/D conversion.
Image, sound encoder
After the A/D conversion of images, sounds, digital signals, according to
certain format or coding standard compressed. The compression coding purpose is
to facilitate realize sound/visual signals and digital multimedia signal, To
facilitate the computer system, network, as well as the world wide web and the
signal transmission distortion of no.
At present, image compression encoding technology has two kinds: one kind
is hardware encoding compression coding algorithm, the chip curing, Another is
based on DSP software compression coding, namely software running on DSP on the
image compression coding. Also, the voice of compression coding using hardware
or software compression, the compression and coding standards have MP3 format
etc.
Controller,
The network camera controller is shouldering the heart, and its network
management and control of the camera. If a hardware compression coding,
controller is an independent components, If the software code compression
coding, controller is running the DSP, namely compression software between one.
Network video server
Network video server providing a network of camera, it adopts the function
of network your RTP/RTCP, UDP, HTTP, TCP/IP related network protocol that allows
users to from your PC using standard browser according to the network video
cameras to the IP address network access, watch, and real-time image of camera
lens and yuntai control.
External alarm, control interface
Network camera provides practical engineering application for the external
interface, such as the control of the interface, yuntai rmb465 warning signal
input and output of the I/O port. Such as infrared sensor is found to have
goals, send warning signal to the network video camera, network video camera
automatically adjust the camera and real-time video direction, On the other
hand, when the network video camera to detect moving target, also issued a
warning signal to the outside.
The basic principle of network video camera image signal is input signal
and pass through the microphone, after the input by the image sensor signals
into the voice sensor, A/D converter will be converted to digital signals analog
signals, repass encoder according to certain coding standard coding compression,
under the control of the controller, the web server according to certain network
protocol on LAN or INTERNET, the controller can connect to collect alarming
signals and sent alarming signals, and the control signal is sent by
requirements.
Image coding standards
At present, network video image compression standards are mainly MPEG4, h.
263, h.264, M - JPEG, etc.
MPEG4
So-called MPEG refers to the activities of ISO image of a series of expert
audio signal and multimedia signal compression and compression technology
standards. So far, has completed and the implementation of accurate: 1991
approved MPEG1, MP3, In 1994, approved MPEG2, In 1999, the approval and MP4
MPEG4. Is there MPEG7: the standards formulated and MEPG21.
H. 263
H.263 itu-t is proposed as h. 324 terminal use video decoding Suggestions,
h.263 after continuously improve and upgrade has been gradually maturing, now
most instead of h. 261 and h.263 because of the low bandwidth in the
transmission of high quality video and increasingly popular.
H.263 DPCM is based on the movement of the compensation of hybrid coding,
in motion compensation DPCM hybrid coding, in search is conducted on the basis
of motion compensation, then apply the DCT transformation and "zig-zag Saul to
draw coding, output stream. H. h. 263 on the basis of the tra, motion vector
search for half a pixel search, Increased again at the same time, motion vector
unlimited arithmetic based on grammar Ed, senior prediction technology and PB
frame coding four advanced options, To achieve further reduce code rate and
improve the quality of coding.
H. 264
H.264 itu-t is the VCEG and ISO/IEC MPEG video of the joint development of
a new group of digital video coding standard, it is both itu-t h.264, and ISO/IEC
MPEG4 tenth part.
In the same image quality, h.264 than h.263 saves 50% of the code rate
than the present, according to the realization of video format in MPEG4
properties increased by 33%.
M - JPEG
M - JPEG image compression technique that the movement of technology, it
is a video sequence of still images to deal with continuously, the compression
technology means completely separate compression each frame, in the editorial
process can be random storage each frame, can be precisely to edit frame. But
only to the frame, JPEG compress mainland space redundancy, not the time frame,
redundant compression compression efficiency is not high.
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