At present, the demand for digital consumer electronics is amazing. In these products, imaging and video products are large. And the technological accumulation is increasingly mature, the JPEG standard of still images, MPEG1, MPEG2, MPEG3, and H.263, H.264, and trends with H.264. Applying relevant image technology to production will be an important direction we consider. In banks, substations, stations and other places, you need to focus on the extraction analysis requirements for single-picture images, and control application costs, so it is appropriate to use the M-JPEG algorithm.
This monitoring system is based on TMS320DSC21 embedded processor platform and embedded Linux system, divided into remote field acquisition terminals and local monitoring terminals, transmitted via CDMA wireless network, as shown in Figure 1. The field acquisition end acquisitions the monitoring on-site single frame image and video continuous frames and encodes compressed into M-JPEG and saves the file, and then passes through the CDMA network to the local monitoring end. After the monitoring terminal receives image data, enter M-JPEG decoding and displayed on the analog LCD screen. M-JPEG adopts an intra compression algorithm that can reach a higher compression ratio for long-term, low cost, thereby achieving remote observations in the case of limited bandwidth. This article mainly introduces the design of the monitoring terminal.
Figure 1 Wireless image monitoring system structure
System hardware structure
The system monitoring terminal hardware composition structure is shown in Figure 2.
Figure 2 System hardware structure
The CPU uses TI company chip TMS320DSC21. This chip is a DSP digital image processor based on multiprocessor architecture launched by TI. It uses an ARM7 32-bit RISC microcontroller to handle non-imaging functions and serve as the main controller of the entire system, while using programmable C5409 DSP core processing image decoding. In addition, the DSC 21 also integrates a programmable coprocessor specifically used to handle most of the complex calculation image tasks. One of the coprocessor-image processing engine IMX executes DCT, reverse DCT, and other coprocessors perform variable length encoding / decoding, quantization and inverse quantization.
The power module is responsible for the smooth output and monitoring of the power supply.
The CDMA wireless receiving module receives the JPEG data stream and stored in the SDRAM. The image display module displays the unzipped original image on a television or analog LCD screen.
The memory module consists of Flash and SDRAM. Flash memory is used to store programs, which is an indispensable component of system independent operation (offline operation). SDRAM memory is used for the operation of the system software and storage of image data. This can call the previous image data for research.
The debug simulation module is used to debug the simulation, and it can also be imported into the computer from the SDRAM by it.
System software structure
The system is designed based on an open source LINUX operating system. This system is transplanted 2.4 version. The hierarchy of the entire Linux system is shown in Figure 3.
The entire Linux system is based on the TMS320DSC21 hardware platform described earlier, and the main drivers for this system hardware requires CDMA module drivers and OSD image display drivers. The driver is abstracted on the underlying hardware and provides a consistent underlayer interface for the top application. JPEG image data reception, the management program is always monitored as a resident CDMA module, and provides a related interface function to the upper application layer program.
The top-layer application layer program receives the JPEG image data, the management service program acquires image data from the CDMA driver, and then invokes the HUFFMAN decoder to decompress the image, then store the decompressed YUV data into the SDRAM, then map to the OSD area, Displayed by the LCD screen.
Image of JPEG decoding implementation
The μClinux system controls the DSP side for JPEG decoding, pre-processing, Huffman decoding, inverse quantization, IDCT transform, recovering JPEG image data into image data before compression encoding, and then the OSD is finally displayed on the LCD screen Image is coming. The detailed process is shown in Figure 4.
Figure 4 JPEG decoding flow chart
Wireless transmission image data with CDMA modules
CDMA is a Code Division Multiple Access, which is a mobile communication technology developed in digital technology branch-spreading communication technology. Different mobile stations share a frequency application spread spectrum communication technology allocate a unique, random code sequence, each of which is different from each other, and each other is not related to each other. Its capacity is close to twice the previous CDMA 1 × system capacity, thereby adapting to the growing voice services and wireless Internet new services. Second, its highest download speed can reach 153kbps (307kbps in the future), upload speed of 64K. Such speeds are sufficient for transmission of M-JPEG compressed image data for 352x288 per second of 4 frames.
In order to transfer data accurately, the underlying system of the system refers to the XMODEM protocol with accurate transmission of data in the case of less data redundancy.
The XMODEM protocol is an asynchronous file transport protocol widely used in personal computer communication using dial-up modems. This protocol transmits data in the form of 128-by-block, and each block uses a checksum process for error detection. If the recipient's checksum is the same as the sender's checksum, if the package is successfully received, the recipient returns a positive response signal (ACK), if an error is found, returns a negative response signal ( NAK) and resend the packet. However, this policy for each block will result in low performance, especially when there is a case where a very long propagation delay is, the problem is more serious.
The main data of this system is JPEG compressed packets, combined with this feature, we have set a set of corresponding transfer protocols based on XMODEM. The retransmission request is only transmitted when the data packet is lost and the subsequent decoding is indeed, and only the corresponding package is retransmitted. If it does not affect, it will be discarded. This can maximize the normal transmission of data using CDMA limited bandwidth.
Conclusion
This paper mainly completed the monitoring terminal design and tested. When the monitoring object did not move vigorously, the transmission speed of 4 frames per second was reached, and the expected target is achieved. Figure 5 is an original image, and FIG. 6 is an image obtained by decoding using the above-described processing flow. Application This article is used to complete image acquisition and remote transmission, which can be widely used in banks, substations, stations, office buildings and other places. More convenient than traditional monitoring, and low cost, with broad market and application prospects.
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