An Embedded Network Monitor With Capacity Of Optimizing Capture Parameter Automatically

Recently, the video monitoring system has a rapid development because there is a great need in security and alarm for many fields such as banks, powers and traffics.It is a trend that the video monitoring system is implemented based on embedded processor.There are some problems in the actual applications althrough the video monitor technology has been relatively mature. It is a key factor which affects monitoring efficiency that the detail of object is lost due to the incorrect exposure control in the video monitoring system.This becomes an outstanding problem in the monitoring system which is used for boiler instrument in power plant. The traditional exposure control method can not work normally when there is a great brightness contrast between boiler instrment and background so that the instrument value is hard to recognize.We design and implement an embedded network monitor system which is able to adjust its capture parameter automatically to address the issue. The system can locate the object by analyzing digital image and then control exposure based on its visual effect. Then the PC receives the compressed video via Ethernet and displays it in real time. The overrall system design is divided into four parts as follows: The first part is the research about the auto exposure control method.Exposure control is usually implemented by auto iris and electronic shutter in the existing monitoring system. These methods can get a good effect except for a great luminance contrast between object and background. Because the auto iris in most cameras measures the light intensity for central area, it will cause incorrect exposure when the object is not in the central area or the area of object is much smaller than the central area. The basic method to resolve this problem is to measure the light identity of the object's area. In our design, the object is the boiler instrument. We use the sobel operator to make edge detection and recognation because of the neat edge of boiler instrument. And we can measure the light identity of the object's area to implement exposure control after the boiler instrument is located.The second part is about the implementation of the hardware platform.The hardware platform surpports following functions:1. Digital image processing.2. Video caputureing and displaying.3. Data transmission via Ethernet.After analyzing the popular digital media processors in the market, we use the TMS320DM642 as the central processing unit in our design.The TMS320DM642 is based on the c64x dsp core. It has a second generation advanced very long instruction word architecture. The processor could reach 4800MIPS when it works on 600MHz. Besides of the high speed, the DM642 has rich peripherals which could interface with SDRAM, Ehernet PHY, Flash and video CODEC. The system is mainly composed by TVP5150AM1 (PAL decoder), SAA7121H (PAL encoder), BCM5221 (Ehernet PHY), MT48LC4M32B2 (SDRAM) and S29AL032D (FLASH). It has 256Mbit SDRAM space and 32Mbit nonvolatile space. At the same time, it has PAL codec function and 10/100Mbps Ehernet transceivers.The third part is about the design of application which runs on DSP server.The program works on DSP server has the following functions:1. Controling exposure by analyzing the captured image.2. Video caputureing and displaying.3. Compressing the captured image and transfer them to PC client.4. Receiving the command form PC client then make actions.According to the functions of application, we use DSP|BIOS as our real time operating system kernal and Reference framework 5 as our application architecture. In the applications, we use the JPEG lib provided by TI to compress the captured image then transfer them via Ehernet using TCP protocals. Because the JPEG lib needs a video format in YUV420, we implement the format transformation in the video driver layer by using EDMA chaining and linking in order to improve the system performence.The forth part is about the application which runs on the PC client.The application runs on the PC client has the following functions:1. Receiving the compressed video from DSP then decompressing and displaying them in real time.2. Sending command to DSP server in order to control the lens and pan/tilt.According to the functions of application, we use DirectShow technology to develop the program based on the WINDOWS platform. In the application, we design a source filter which use pull mode to transfer data buffer. Becaue the entire application is simple, we implement the functions of transform filter in the source filter so that we do not need to design a new transform filter.The application shows that the system is able to transmit compressed video and get a better quality of image by the exposure control method which is based on the object. And the system has reached the expected design purpose.