# Describe the low pass filter.

Low Pass Filter : Considering the grey-scale values of a part of an image as below,
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.

(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.

Describe the median pass filter. DIP