matlab对一幅图像，采用半径值为20、80、200的截止频率进行理想低通滤波，观察其结果。要求给出原图像及相应的付利叶频谱图和滤波结果-For an image, using the radius value of the cutoff frequency 20,80,200 ideal low-pass filter to observe the results. Required to give the original image and the corresponding Fourier spectrum and filtering results