With various industries to the requirement of video image is increasing, people's project is no longer the image resolution is not high. However, since last year, a new high-definition cameras on the market for engineering contractor shine at the moment, let them see the hope. In this paper, the key technology of high definition camera and make simple considerations, including share exchange and industry.

The market demand

Video security monitoring technology development so far, with various industries to the requirement of image is increasing, people's project is no longer the image resolution is not high. Around security technology to guard against and departments of the project acceptance, certainly must be able to see the license plates of the video image, color model characteristics, the person's facial features on sensory requirements. The latest since January 1, 2008 the implementation of the national standard of GB20815 video security monitoring of image in the digital video equipment monitoring and playback resolution requirements, including grade A products: all the apparent frequency channel (sound) is in A state of recording single-channel monitoring image resolution should be 400 or more TVL level. Single way playback the level of the image resolution should be 300 TVL or higher. Such standards will be put forward higher request to the system. Currently on the market of new high definition camera makes us shine at the moment, like the rising new moon, lit up the night sky of the industry, we saw new hope engineering contractor.

The key technology and factors

Currently on the market sales of high-definition cameras mainly nominal horizontal resolution 500 lines, 520 lines, 530 lines, 540 lines, 550 lines of several kinds of. There are some 480 TVL and 540 TVL CCD camera is basically the same, mainly is the video digital processing chip (DSP) are different. Some vendors have powerful r&d ability, they developed 15? 16 (bits) video digital processing chip, compared with 480 TVL cameras on the market of SONY 10 (bits) chip has more powerful data processing ability and faster speed of image processing.

Due to the chip using 15? 16-bit data bus, the logic of a built-in precision processing circuit, with a strong ability of rapid accurate image processing, built-in pixels enhance unit, fully compatible with SONY, sharp, panasonic CCD on the market, can make the ordinary high resolution CCD image acquisition of 540 more than the TLV high definition, at the same time also has the ultra high speed data operation ability, can carry out super wide white balance compensation scope and zero run. Due to these cameras can guarantee to pass by 540 TVL above the level of resolution color images, and of course use SONY 10 (bits) than the market more popular chip 480 TVL cameras.

High-definition cameras are mainly embodied in the picture on the definition of to do the sharpness of the picture, is not only a horizontal resolution of 540 TVL, must be in ultra wide dynamic, automatic white balance, image sharpness adjustment, super digital noise (SNR), intelligent digital automatic metering compensation, luminance and chrominance correction, the automatic adjustment and restore damaged pixels, the color adjustment, wide dynamic range and other indicators have concentrated on. Then only is only reached the requirements of the comprehensive high definition video camera.

In terms of resolution, of course, 540 TVL is better than 520 TVL and 480 TVL. Higher-end high-definition cameras must deal with gamma correction problem, according to relevant data display gamma correction is an important technology to produce high quality image, most of the CRT tube only 1/0.45 = 2.22 gamma curve, and the liquid crystal display gamma curve only 1/0.3 = 3.33, thus a high quality video signal is sent to the CRT to display, because only 80% 80% of the lumen is compressed into the grey scale of the remaining poor image. Scenery blurs and darkness, and the human eye to see something completely different. In order to overcome the CRT tube this natural physical features, video must be conducted before sent to the CRT gamma correction, in the dark areas must be amplified gamma curve of the bottom line to 0.45, and 2.22 x0.45 = 1, this can gain a 1:1 image on a CRT screen. Thus, in the process of gamma correction, digital signal processor must provide greater than 2.22 times more information. Better gamma correction method is the use of digital signal processor of 12, 8 bits as digital signal processing (DSP), four used for correction, make its produce a perfect image. Of course 15? 16 chips will be more outstanding, and the conventional camera only 10 digital processing chip, can only provide 12 correction, the dark area of the image transfer loss of part of the gray scale and color information. So the processing capacity of DSP chip and the number of bits is we in the choice and identify one of the important indexes of high definition video camera.

Matters needing attention

Installation and debugging

In daily video security engineering, high-definition cameras and ordinary camera installation and debugging method are basically the same, but must pay attention to the good shot selection, or matching is bad, because of the bad quality of the lens will greatly affect the definition of the images, such as infrared night vision system of cameras had better choose the infrared camera, and a third of an inch general with 1/3 inch lens, CCD 1/2 inch general with 1/2 inch lens, CCD lens focus when installation debugging must adjust good, especially the back focal plane of the camera to alignment, the focus of most of the time the camera will cause image fuzzy, could not reach the requirements of high-definition. Also cannot ignore other camera shield, the front end of the gun type shield glass cannot adopt the general flat glass, and must use good optical glass, ordinary flat glass on the interpretation of the image force has a very much weakened effect, choose spherical cover more should pay attention to, the curvature of the spherical must transition is smooth, it is best not to put on the upper edge of the spherical shell, the force is bigger, the refraction of light even seriously affect the image clarity. It is very important, that is, no matter what kind of cover shell, the lower the cover in the best light, the better, the lens to cover the distance as short as possible, so that can make the camera light pollution reduced to a minimum, to improve image clarity.

The system must be high definition

High definition video camera in addition to the front-end installation and must pay attention to select material, must also have a transmission system, intermediate system and terminal display system used to achieve a high definition of actual effect.

In terms of transmission system, video image transmission would coaxial cable, twisted pair, UTP line (that is, the network transmission), wireless transmission, optical transmission, transmission either way, must make the image transmitted from the front to the back end of the whole system bandwidth > 6 m each ring, so as to ensure to achieve the requirement of the high resolution image, and accord with the requirement of engineering and dimension inspection. Normally when the coaxial cable of more than 150 m or 150 m image quality is significantly lower, this is due to the nature of the coaxial cable, therefore, must take various measures to guarantee its terminal bandwidth is not less than 6 m, when it is necessary to add video compensation amplifier, the general role of video amplifier. Indicators should guarantee the high frequency compensation of the compensation amount, amplitude frequency characteristics, SNR, common mode rejection ratio, delayed differential phase distortion degree, color brightness, chroma width etc to make the cable loss or gain attenuation compensation defects caused by, so as to ensure the high definition of images that enter the system.

At the moment, the copper price is rising, falling cost of video images using the optical cable transmission, in the long distance transmission, of one or more images using the optical cable transmission is fully staffed solutions are widely adopted. Due to the bandwidth of the fiber optic cable, low attenuation, high characteristics of strong anti-interference, small size, confidentiality, can better ensure that the indicators of image transmission. When using other ways to transmit the image, also must ensure that the bandwidth of the channel.

High resolution image must also rely on good terminal display device of performing in front of the person's visual, so the best choice progressive-scan monitor. Because in the actual use of the interlaced scanning monitor image flicker severity, easy to make the person produces visual fatigue. If the monitor the sharpness of the low, also could not reach the requirements of the overall resolution. Because the monitor when the sharpness of the monitor, video channel bandwidth and kinescope of distance and distance. , according to data between the channel bandwidth and resolution conversion theory up to 1 m / 80 or so, if we consider factors, the amplitude of high definition video signal to show 400 lines of video image, the monitor articulation index should be adopted according to the experience of more than 600 line machine.

For use with high definition camera, processing equipment, including matrix, hard disk video recorder, video server, and so on, all kinds of video encoder must meet the requirements of bandwidth and image compression, in order to give full play to the role of the intrinsic high-definition cameras. By using high resolution cameras and ignore other selection of form a complete set of equipment is short of real purpose.

conclusion

Believe that as the user recognition of high-definition cameras, market demand will be further expanded. Security industry should make full use of the high-tech chip brings us an opportunity again, the fruits of this video field application in various fields, make the whole society can share the achievements of this brings us to the Gospel.