摘要:本文讲解基于傅里叶变换的高通滤波和低通滤波。
一.高通滤波
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过滤的方法一般有三种:低通(Low-pass)、高通(High-pass)、带通(Band-pass)。所谓低通就是保留图像中的低频成分,过滤高频成分,可以把过滤器想象成一张渔网,想要低通过滤器,就是将高频区域的信号全部拉黑,而低频区域全部保留。例如,在一幅大草原的图像中,低频对应着广袤且颜色趋于一致的草原,表示图像变换缓慢的灰度分量;高频对应着草原图像中的老虎等边缘信息,表示图像变换较快的灰度分量,由于灰度尖锐过度造成
高通滤波器是指通过高频的滤波器,衰减低频而通过高频,常用于增强尖锐的细节,但会导致图像的对比度会降低。该滤波器将检测图像的某个区域,根据像素与周围像素的差值来提升像素的亮度。图展示了”Lena”图对应的频谱图像,其中心区域为低频部分。
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输出结果如下图所示,第一幅图为原始”Lena”图,第二幅图为高通滤波器提取的边缘轮廓图像。它通过傅里叶变换转换为频谱图像,再将中心的低频部分设置为0,再通过傅里叶逆变换转换为最终输出图像”Result Image”。
二.低通滤波
低通滤波器是指通过低频的滤波器,衰减高频而通过低频,常用于模糊图像。低通滤波器与高通滤波器相反,当一个像素与周围像素的插值小于一个特定值时,平滑该像素的亮度,常用于去燥和模糊化处理。如PS软件中的高斯模糊,就是常见的模糊滤波器之一,属于削弱高频信号的低通滤波器。
下图展示了”Lena”图对应的频谱图像,其中心区域为低频部分。如果构造低通滤波器,则将频谱图像中心低频部分保留,其他部分替换为黑色0,其处理过程如图所示,最终得到的效果图为模糊图像。
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输出结果如图所示,第一幅图为原始”Lena”图,第二幅图为低通滤波器模糊处理后的图像。
Original: https://www.cnblogs.com/huaweiyun/p/16737458.html
Author: 华为云开发者联盟
Title: 跟我学Python图像处理丨傅里叶变换之高通滤波和低通滤波
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