Median Filter• Are nonlinear filters • Smoothens the image by utilizing the median of the

neighborhood • Introduced by Tukey in 1997, which is extension to 2D

images was discussed by Pratt in 1978• Performs the following tasks to find each pixel value in

the processed image– All pixels in the neighborhood of the pixels in the

original image which are identified by the mask are sorted in the ascending or descending order.

– The median of the sorted value is computed and is chosen as the pixel value for the processed image.

Median Filter

Spatial averaging & Spatial low pass filtering

Spatial averaging & Spatial low pass filtering

Spatial averaging & Spatial low pass filtering

Spatial averaging & Spatial low pass filtering

Image sharpening or Edge enhancement or Spatial domain high-pass filtering

• is used to highlight fine details in the image.• Is used to enhance high-frequency components.

Image sharpening or Edge enhancement or Spatial domain high-pass filtering

Image enhancement in frequency domain• If filtering in spatial domain is done by convolving the input

image f(m,n) with the filter kernel h(m,n)

Filtering in spatial domain = f(m,n) * h(m,n)• In the frequency domain, filtering corresponds to the

multiplication of the image spectrum by the fourier transform of the filter kernel, which is referred to as the frequency response of the filter

Filtering in frequency domain = F(k,l) x H(k,l)here F(k,l) is the spectrum of i/p image

H(k,l) is the spectrum of the filter kernel Convolution in spatial domain = Multiplication in the frequency domain