Research On Auto-focus And Auto-exposure Technology Of Video Camera Based On Image Processing

As a key technology in digital imaging system, auto-focus and auto-exposure are widely applied in many occasions. In order to meet the demand of "Tundish Molten Steel Level Measuring System" to realize the functions of auto-focus and auto-exposure, thorough research has been done in this thesis on the investigation of auto-focus and auto-exposure technology based on image processing. This design overcomes the shortcoming of manual control such as inefficiency and low accuracy, improving the system’s level of automation and measurement accuracy.At first, the thesis analyses the basic theory and methods of auto-focus and auto-exposure. According to the theory of auto-focus and auto-exposure based on image processing, embedded controlling circuits based on DSP (for image processing) and FPGA (for image acquisition) are designed and implemented to realize auto-focus and auto-exposure function.After that, methods of the auto-focus and auto-exposure based on image processing are also investigated in this thesis. In the evaluation of image sharpness, the thesis presents the single reference focus measure function based on SSIM, overcoming the defects of traditional focus measure methods with a reference and unbounded output. In terms of focus search algorithm, an improved hill-climbing method based on defocus estimation is proposed, which improves the system’s focus speed and anti-interference ability using self-adapted step. To the analytical methods of image exposure, an analytical methods of image exposure based on image brightness is put forward in the thesis, in which weighted average brightness is applied to reduce the performance of background of the subject.Finally, the video camera auto-focus and auto-exposure system is built and tested to study the performance of the system by varying experimental conditions. Results of the tests indicate that the system can accomplish accurate auto-focus and auto-exposure in general environment, fulfilling the anticipated requirements satisfactorily.