Difference between a Linear and nonlinear Filter in Image processing?

What is the main difference between the linear an nonlinear filters that is being used in Image processing for the reduction of noise.How can i realize a filter is linear or not?

Answer 1

[Image Analyst]

A linear filter is one that can be done with a convolution, which is just the linear sum of values in a sliding window. It can be done equivalently in the Fourier domain by multiplying the spectrum by an image. A blurring filter where you move over the image with a box filter (all the same values in the window) is an example of a linear filter.

A non-linear filter is one that cannot be done with convolution or Fourier multiplication. A sliding median filter is a simple example of a non-linear filter.

Answer 2

[Ramzan Shahid khan]

Linear filtering is the filtering method in which the value of output pixel is linear combinations of the neighbouring input pixels. it can be done with convolution.For examples, mean/average filters or Gaussian filtering.

A non-linear filtering is one that cannot be done with convolution or Fourier multiplication. A sliding median filter is a simple example of a non-linear filter.

Answer 3

[Soe Lei Hnin]

Let me ask a question.I'm a little bit confusing about gaussian kernel.I found a size of [1×11] gaussian kernel.I have no idea how it got.

[Image Analyst]

We don't know either. Maybe it was hard coded in. Maybe is was generated by the fspecial() function. Who knows? Certainly not us. Did you just get this array from an anonymous email, or copy it from a web page, or from your own code? I have no idea, but you must.

[Soe Lei Hnin]

From Barcode recognition code from matlab example.Here it is.

h=single([0.022191,0.045589,0.079811,0.119065,0.151361,0.163967,0.151361,0.119065,0.079811,0.045589,0.022191]) 

That's used as gaussian filter in that algorithm. Is there any equation to generate those values? I tried with fspecial. I failed.Thanks for your answer.

[Image Analyst]

If fspecial doesn't make it, then you can try to fit a Gaussian with fitnlm. See attached example.

Answer 4

[Sudaroli Sandana]

In Linear Spatial filtering the spatial mask in convoltion process is used.In Non Linear , the ordering mechanism is used to produce output pixel ie to replace the centre pixel