【作者】 李立；

【导师】 田逢春；

【作者基本信息】 重庆大学 ， 信号与信息处理， 2009， 硕士

【摘要】 光学小波变换是光学信息处理与小波理论的结合,具有并行性、超高速、大容量的优点。4f系统是实现光学小波变换的一种重要光路,研究4f系统特点与特性是研究光学小波变换的基础。论文以光学小波变换的4f系统为研究对象,对系统的原理和实现方法、线性和时不变特性、误差特性以及改进方法进行了较深入的分析和研究。首先,论文从傅立叶光学原理出发,分析了4f系统的基本原理和组成,构建了光学小波变换需要的4f系统光路,提出了一种4f系统自动加载和采集图像的实现方法。其次,通过4f系统的叠加性和零输入响应实验以及输出信号的坐标位置稳定性和能量稳定性实验,表明了在目前的器件工艺和光路调节水平下,4f系统的线性与时不变特性均不理想。再次,根据误差理论将4f系统误差分为系统误差和偶然误差两大类,讨论了各种误差的来源以及减小误差的方法和措施,利用PSNR定量地衡量了系统的误差(目前系统PSNR达到24.33dB);计算得到了4f系统仿真时需要的理想低通滤波器的通带大小,并对典型图像进行了4f系统低通滤波仿真;通过分析图像的高频能量百分比与图像通过4f系统后PSNR,得出了高频能量越丰富的图像通过4f系统后PSNR越低的结论。最后,本文还利用光栅衍射理论和傅立叶变换理论,提出一种测量4f系统输入函数载体与滤波函数载体之间角位移的方法,利用该方法的测量结果可以补偿4f系统滤波函数的角位移,并且利用光学实验证明了该方法的有效性和准确性。论文创新之一是提出了一种4f系统自动加载和采集图像的方法,该方法可以提高实验的效率、降低实验的劳动强度以及减少实验的出错概率;创新之二是提出一种测量4f系统输入函数载体与滤波函数载体之间角位移的方法,该测量方法具有无需修改光路、无需购买额外设备、操作简单以及精度高等特点。通过文献参考、理论分析、理论仿真以及光学实验,论文研究得到4f系统部分特点与特性,为4f系统误差进一步减小以及最终实现高精度滤波处理打下了一定的基础。更多还原

【Abstract】 Optical wavelet transform is the combination of optical information processing and wavelet theory. It integrates many advantages of optical science and wavelet transform such as parallelism, high-speed and large capacity. The 4f system is an important optical path for the realization of optical wavelet transform. Study on the characteristics of the 4f system is a basis of studying optical wavelet transform. The author takes the 4f system of optical wavelet transform as the research object, carries out thorough analysis and study on the system’s principle, realization, linear and time-invariant characteristics, error characteristics and improved method.First of all, according to the principle of Fourier optics, the 4f system’s basic principle and the system structure were analyzed. The optical path of the 4f system needed by optical wavelet transform was constructed. The realization method which could automatically load and acquire images in the 4f system was proposed. Secondly, it is proved by experiments of the addition, zero-input response, stability of the output signal coordinate position and the stability of the output signal energy value that the 4f system’s linear and time-invariant characteristics is not ideal under the condition of the present device technology and optical path adjusting level. Thirdly, the errors of the 4f system were divided into two major categories as systematic error and accidental error according to error theory. A variety of error sources were discussed and the methods of reducing errors were elaborated. Peak-to-peak signal to noise ratio (PSNR) were used to measure quantitatively the system’s error, and the system’s PSNR reached 24.33 dB right now. The size of the ideal low-pass filter’s passband in the 4f system needed by the simulation was achieved by computing. Then, the 4f system’s low-pass filtering simulation to the typical image was carried out. The analysis of the percentage of images’high-frequency energy and the PSNR of images passed through the 4f system proved that the images including more high-frequency energy have lower PSNR. Finally, a method which could measure the angular displacement formed by the 4f system’s input function carrier and filter function carrier according to the theory of grating diffraction and Fourier transform theory. The measurement result of the method can compensate the 4f system’s angular displacement of the filter function, while optical experiments have proved the effectiveness and accuracy of the method.One of the paper’s innovative points is that a method of automatically loading and acquiring images in the 4f system has been proposed, which could improve the experimental efficiency, reduce experimental labor intensity and reduce the experimental error probability. Another one is that a method measuring the angular displacement formed by the 4f system’s input function carrier and filter function carrier has also been proposed, it features no need to change light path, no need to purchase additional equipment, simple operation and high precision.Through the literature reference, the theoretical analysis, simulation as well as optics experiments, some characteristics of the 4f system was got. This has lay the foundation for further reducing of the 4f system’s error and high accuracy filtering.更多还原