System Designing For Auto-Focus Based On FPGA

Autofocus is widely used in the optical image system. With the development of electronic technology and digital signal processing, autofocus based on image signal processing is used in the camera system. The method of autofocus is divided into analogy autofocus and digital autofocus. Analogy autofocus is analyzing the high frequency component reflecting the definition of the image extracting from the analogy video signal and controlling the moving of the focusing motor. So the autofocus of the image can be realized. Digital autofocus is analyzing the high frequency component extracting from the digital image signal and realizing the autofocus of the image. Compared with analogy autofocus, digital autofocus has the advantage of accurate focus, simple hardware circuit, etc.This paper researches carefully and design a Auto-Focus and Electric-Zoom system of digital video devices which is based on the CCD image sensor and the FPGA. The main works of the paper can be summarized as follows:(1)Analyzed the gray scale differential algorithm and made some improvement. verified in the reality.The design utilizes an improved gray scale differential algorithm as focus value. The sum of the gray scale differential absolute value of an image is used as the focus value. According to the comparing result of two adjacent fields and utilizing some search strategy to control the remove of step-motor, so the image can be auto-focused. (2)Analyzed the zoom track algorithm and verified.Changing the position of Zoom lens through the keypad and zoom table for the system. Finally, making the motor to wheelling the stepping motor, in order to change the position of lens to make the AF in focus,the multiple of Zoom properly.(3)Design of system hardware structureIn the aspect of hardware mainly includes the image sensor,FPGA, zoom lens and the driveling system of stepping motor. Realizes the hardware circuit design of image signal capturing, image signal processing, signal output and control module.(4)Design of system software describeIn the aspect of software mainly includes the processing for image data, an improved gray scale differential algorithm, search strategy algorithm, controlling the keypads program and the drivering program of stepping motor.This method avoids the complex calculation in math and the system has the characteristics for realizing simply, power lowly, speed of AF quickly and so on, be the same with the all the kinds of AF devices, such as the video presenter, video camera.