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Based on STv0676 the network camera solution

    

Network cameras compared to a PC camera in the monitoring and security applications in the field, and many other irreplaceable advantages in the future will have even broader prospects for development. In this paper, based on STMicroelectronics STV0676 the network camera system, working patterns and trends.

Video streaming solutions for applications is rapidly increasing, which include some of the reasons for diseases such as SARS impact on the community, do not need the visualization of the mission, and security / monitoring applications. Video cameras in the programme is the key equipment, in the past we have heard PC cameras and network cameras, but its working principles are quite different. In fact these two concepts has been associated with PC camera, but the network cameras, will be linked with the PC is not correct. PC camera is a video camera with USB interface, the vast majority provided by the operating system using the standard software, used to hold video conferencing or video chat.


The monitoring technology, there are two types of systems available, is based on a CCD technology and the use of analog transmission (PAL / NTSC) of the CCTV cameras, while others are using a CCD or CMOS digital transmission of the new system. Careful look at these two systems used by the technology can be found CMOS technology for the market with greater advantages: First of all, CMOS camera does not require a different voltage, which means that power supply design simple to many Secondly, CMOS camera biggest advantage Integration is the timing and ADC, which means that output is already digital, image, which will help reduce the overall system cost. In low-light brightness of the performance, by STMicroelectronics companies to provide the CMOS technology is gradually close we are to use the low pixel brightness optimization technology level. In addition, sensors have been able to perform some processing algorithms to help improve the video processor performance.

Network Camera

Now let us look at the real network camera, or the so-called IP cameras. Apart from suitable for family security and family outside monitoring, IP cameras will not replace the PC camera. This is because if we want the network to transmit video or audio and video, at least some such as streaming media server equipment. If the PC-based systems that require PC 24-hours boot, which means great waste of electricity and generate a lot of noise. In addition, if we want the system for home use, this application will reduce PC performance. On the contrary, the real IP camera is embedded in the building on the basis of streaming media server, which means that the camera has its own streaming media server, and no longer need to use your PC, and simply insert Ethernet (hub), or use Wireless Ethernet to work.

In Figure 1 can be found in a client using only a PC, the system has the advantage of customers in any part of the world, as long as the Internet connection on the camera can observe and control. The solution will have more applications. As mobile phones have more and more data communications optional, but very fast increase in the future may be passed by motion detection camera noise detection or warning issued, by sending SMS or direct dial phone video streaming will be transferred to Phone. This concept also applies to the office of the situation unattended. Other uses include cameras will be installed in the door, where the doorbell, the camera will make video calls, you can open the door via video phone. Figure 1

System solutions

From technical considerations, STMicroelectronics and Taiwan Taifatech (of the Taiwan IT) companies to work together to provide genuine one-stop solution (see Figure 2). Just change its customers in the hope that the client browser to display the user interface can be, if not revised, then they can use the default interface and direct application. We provide the solution is based on STV0676 co-processor and our VGA sensor VV6501. The package allows USB and the so-called "Digiport (digital port)" to transmit video. We in the solution used in Digiport is a parallel data can be transferred to any embedded system bus (eight data and two control). Maximum clock speed of 1.5 MHz, that is, per second up to 1.5 M-byte data transmission, which is very easy to transfer 30 fps video. Figure 2


Figure 3 diagram of the solution. In the left, video processors and sensors directly linked to, and used to control all the necessary image processing functions, such as automatic white balance (AWB), auto exposure (AE), color transform array (colour shifting matrix), the District increase the exposure , To correct defects and pixel color model, and so on. STV0676 can work in different models to below the image data output system. Figure 3 Model A STV0676 a USB model, through the FIFO (first FIFO) directly to the image data sent to the USB port. Mode B STV0676 use the main mode and can be CCIR-656, YcrCb and RGB 7-bit color data stream sent to the Digiport. STV0676 can mean that the main mode in accordance with the selected frame rate to provide data for the clock. In this mode, it can connect an external TV *** and send signals directly to the TV.

Pattern C STV0676 through FIFO will RGB24, YUV and MJPEG data stream sent to the Digiport. This model restrictions

1.5MHz clock on the data, but from the system will be in a mode, the external controller to control all data transmission. Dynamic Data compression

Embedded in the use of the environment STV0676, C means that the model used in our system could be in asynchronous mode from the STV0676 on Duchushuoju so that the main MC U enough performance to handle other tasks. The solution is a core 4 KB of the FIFO. We are talking about large amounts of data, this capacity is not enough, but for video compression (VC) will help solve this problem. VC have established dynamic compression ratio selection function, which means that space-based FIFO of the VC could decide compression ratio. For example, when the MCU readings fast and FIFO gradually vacated when, VC compression reduced, and when the MCU reading slow, FIFO gradually over time, VC will be compressed as much as possible. However, all of which can not be avoided or FIFO overflow space. FIFO space-time will have a free alarm, and when the MCU is too slow even when not reading, FIFO overflow will occur, and will be issued warning, but did not stop video streaming. In rare cases, in fact, because the system can calculate the data rate. Now let us look at the data, according to the VGA resolution may have the following terms:

Each frame of the Bayer pattern: 640 〜 480 = 307200 (pixels)

YUV every frame: 307200 〜 2B = 614400B / 1024 (KB) = 600KB.

For example, non-compression mode of transmission to 30 fps, up 17.58 MBps means that the amount of data. Thus, the only way is to use data compression. Since JPEG compression is a dynamic compression, it can not predict the size of 100 percent. For example, you want to use the 10:1 compression ratio to one, which means that VC trying to achieve this rate, but in fact sometimes very easy to achieve and sometimes can not be achieved. It is worth mentioning that the calculation of the amount of data not only on the calculator divided by 10 so simple. In view of this, VC adopt a dynamic, and we can have a stable 4 KB FIFO. Therefore, we VC the maximum compression ratio of about 80:1, but the reality is that the compression ratio to 30:1 results can be accepted, and the higher the compression will cause too much noise, is unacceptable. Therefore, in accordance with the 30 fps @ VGA to transmit the necessary data for 600 KBps.


　

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