Filters in image processing are used to smooth or sharpen the images, there are mainly two classes of filters Low Pass Filters and High Pass Filters. In Low pass filters process blocks the high-frequency pixel and allows low-intensity values or frequency to pass through it. In High pass filter process blocks the low-frequency pixels and pass the high-frequency pixels. The main use of LPF and HPF is to remove the following noise from the images.
1)-Gaussian Noise
2)-salt and Pepper Noise
3)-Gamma Noise
In LPF we have two types of filters:
1)-Low pass Averaging filter: If the image is having gaussian noise, In this method we place the mask on the image and then find the average.
the standard format of the mask is numpy.ones(3,3)/9.
2)-Low pass Median filter: If the image size is large or consist of salt and pepper noise.
Refrerences:
https://docs.opencv.org/3.0-beta/modules/imgproc/doc/filtering.html