Here, we have taken 9 grey scale values. It is seen that the 5th value is very different than the other 8 values, that is a big change is occurring at that point due to the big change of the grey-scale value at that point than the other points.
So to change the center value to a closer value to the neighboring values, low pass filter can be applied. This filter is also called averaging filter. Implementation of this filter is as follows,(i) First a mask of odd number such as 3×3, 5×5 etc has to be taken. Here 3×3 mask has been taken.
(ii) Now, all the values will be added. Here all the 9 values will be added.
(iii) In this case, the summation will be divided by 9 to get the average. In a 5×5 mask the summation will be divided by 25 etc.
(iv) Finally the center value of the mask will be replaced by the obtained average value.
Places to Imply This Filter :
(i) To reduce noise.
(ii) To eradicate unwanted spots on images.
Disadvantages :
(i) It causes “Blur” effect for which the sharpness of the image will be reduced.
As for averaging it tends to turn an image to an image consisting almost similar grey-scale levels everywhere.