System Design, Based On Usb2.0 High-resolution Video Collection

The USB Specification was proposed by Intel, Compaq, Microsoft and other companies in1994. This Specification has many advantages such as high transmission speed, facility in connection and supporting of hot insert&plug. After the 2.0 revision of the specification is issued, USB has been widely used in PC peripherals equipments, and it has become one of the most important directions of video acquisition. So it's very important to develop a video acquisition and management system based on USB specification revision 2.0.In this thesis, both hardware and software designs of the video capture system based on USB specification revision 2.0 are presented. The system is connected to the host computer throw the USB interface. And it is capable of processing real-time video signal. Besides, an auto—focus camera lens is used in the system, and the control signals are got by the program to process an auto-focus arithmetic in the software. So the system has the ability of auto-focus control.The whole system is composed of three parts: the image acquiring circuit, the USB interface circuit and the video processing and display port. In the acquiring circuit, the image sensor OV9620 is used to complete the acquisition of digital images. The USB controller EZ-USB FX2 that supports USB 2.0 is used to control the USB interface. VFW (Video For Windows) technology is used in the display port. The control signals got by the auto-focus program is embedded in the display program is sent to the device through USB to control the auto-focus camera lens.A new algorithm of auto— focus(AF) is presented and embedded in this system. The thesis discusses the fluctuation of high frequency energy in the process of auto-focus by using the PSF theory, on which based the new arithmetic is presented by improving existing deviation evaluation function. The algorithm bases on WT(wavelet transform) and adopts MRA(multi-resolution analysis) method to strengthen high frequency energy, and improves focusing precision and robustness. When compared to existing image intensity deviation and gradient evaluation functions, the algorithm proposed has the characteristics of unimodality, sharpness and precision. Besides it is simple and uses less time relatively to complete the algorithm using computer language. So it is more quickly and exactly to auto-focus.The implementation of the USB interface, the firmware programming is discussed in detail in the dissertation. And also the principle and PCB chart, the key codes and the flow diagrams are given.All together, a new video capture and display system based on the USB 2.0 is described in this thesis. In the system a low power CMOS image sensor is used to catch the image. And a new algorithm of auto—focus is presented and embedded in this system to realize the function of auto-focus. The auto-focus algorithm used the fluctuation of high frequency energy can get the precise focus. By simplifying the clarity-evaluation-functions, less processing time is used to complete the algorithm. The system works well in the real time acquiring and display of the 1.3M pixel video signal.