Median filter without medfilt2

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Franzi
Franzi el 7 de Jun. de 2020
Comentada: Rena Berman el 12 de Oct. de 2020
Hello everyone,
I have to implement the median filter for a gray-scale picture and a variable window(for example 3x3, 5x5, 9x9, etc) without the built in function medfilt2. It's allowed to use median() and sort() and reshape(). In the edges where you cannot build the median, we should output the original value.
Can someone help me?
  2 comentarios
Rik
Rik el 19 de Jun. de 2020
Question recovered from Google cache:
Hello everyone,
I have to implement the median filter for a gray-scale picture and a variable window(for example 3x3, 5x5, 9x9, etc) without the built in function medfilt2. It's allowed to use median() and sort() and reshape(). In the edges where you cannot build the median, we should output the original value.
Can someone help me?
Rena Berman
Rena Berman el 12 de Oct. de 2020
(Answers Dev) Restored edit

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Respuestas (2)

Matt J
Matt J el 7 de Jun. de 2020
Editada: Matt J el 7 de Jun. de 2020
Since it's a homework assignment, I don't think you need to be computationally eficient. Just loop over all the appropriately sized sub-matrices of the image and apply median() to each... You could alos use blockproc()
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Matt J
Matt J el 7 de Jun. de 2020
Editada: Matt J el 7 de Jun. de 2020
None that minimizes memory consumption, I don't believe. You could unfold all of the window data using a very small loop like so,
Image=rand(300); %fake image
N=3; %window size
C=cell(1,N^2);
for i=1:N
for j=1:N
C{i,j} = reshape( Image(i:end+i-N,j:end+j-N) ,[],1);
end
end
C=cell2mat(C(:).');
Now you have a matrix C whos rows are the different NxN window data. You can now conveniently operate across the rows using sort() or whatever you want.. But note that this consumes N^2 times the amount of memory as a single image:
>> whos C
Name Size Bytes Class Attributes
C 88804x9 6393888 double
Franzi
Franzi el 8 de Jun. de 2020
ok, thank you!

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Image Analyst
Image Analyst el 7 de Jun. de 2020
Franzi: I think I already gave you my nlfilter demo in your other question. All you had to do was change the function to do median() instead of thresholding. Here, I've attached a new m-file where I've done this easy change for you. I just replaced about 5 lines of code with a call to median - pretty easy.

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