请写一段代码使其实现读入一个视频数据并进行低通滤波其中噪声波在60HZ及以上正向波在20HZ对噪声波进行滤除并保留正向波

以下是一个示例代码，使用Python的OpenCV库读取视频数据，并应用低通滤波器对噪声进行滤除，保留正向波。

import cv2
import numpy as np

# 创建低通滤波器
def create_lowpass_filter(height, width, cutoff_freq):
    lowpass_filter = np.zeros((height, width), dtype=np.float32)
    center_height = height // 2
    center_width = width // 2
    for i in range(height):
        for j in range(width):
            distance = np.sqrt((i - center_height) ** 2 + (j - center_width) ** 2)
            if distance <= cutoff_freq:
                lowpass_filter[i, j] = 1
    return lowpass_filter

# 读取视频数据
cap = cv2.VideoCapture('input_video.mp4')

# 获取视频帧率和尺寸
fps = cap.get(cv2.CAP_PROP_FPS)
width = int(cap.get(cv2.CAP_PROP_FRAME_WIDTH))
height = int(cap.get(cv2.CAP_PROP_FRAME_HEIGHT))

# 创建输出视频文件
out = cv2.VideoWriter('output_video.mp4', cv2.VideoWriter_fourcc(*'mp4v'), fps, (width, height))

# 低通滤波器参数
cutoff_freq = 20

# 创建低通滤波器
lowpass_filter = create_lowpass_filter(height, width, cutoff_freq)

while cap.isOpened():
    ret, frame = cap.read()
    if not ret:
        break
    
    # 将图像转换为灰度图
    gray = cv2.cvtColor(frame, cv2.COLOR_BGR2GRAY)
    
    # 对图像进行傅里叶变换
    dft = cv2.dft(np.float32(gray), flags=cv2.DFT_COMPLEX_OUTPUT)
    
    # 将低频部分与高频部分分离
    dft_shift = np.fft.fftshift(dft)
    magnitude_spectrum = 20 * np.log(cv2.magnitude(dft_shift[:, :, 0], dft_shift[:, :, 1]))
    
    # 应用低通滤波器
    filtered_spectrum = dft_shift * lowpass_filter
    
    # 将频谱进行逆变换
    filtered_shift = np.fft.ifftshift(filtered_spectrum)
    filtered_img = cv2.idft(filtered_shift)
    filtered_img = cv2.magnitude(filtered_img[:, :, 0], filtered_img[:, :, 1])
    
    # 将图像转换为灰度图
    filtered_img = cv2.normalize(filtered_img, None, 0, 255, cv2.NORM_MINMAX, dtype=cv2.CV_8U)
    
    # 写入输出视频文件
    out.write(filtered_img)
    
    cv2.imshow('Original', gray)
    cv2.imshow('Filtered', filtered_img)
    
    if cv2.waitKey(1) & 0xFF == ord('q'):
        break

cap.release()
out.release()
cv2.destroyAllWindows()

请确保已经安装了OpenCV库，并将视频文件命名为input_video.mp4。代码会将滤波后的视频保存为output_video.mp4。你可以根据需要调整低通滤波器的截止频率cutoff_freq来改变滤波效果。