Program to find the median of the matrix (need to use for loop)

Question

Manpreet Kapoor 2011-4-17

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Hi,

I need to make a progrqam for the following logic:

1. Consider a matrix of size 120x120. Now consider a section of 3x3 and find the median of the 3x3 section, replacing the values of the matrix to make a new matrix (of a smaller size). The new 3x3 section will be taking the next element as the central element.

2. Please see that there is a command in MATLAB, called medfilt, medfilt2, which does the same, but I need to develop a program which does this manually i.e. it first sorts our the elements in ascending or descending order and then selects the middle value as the median thereby forming a new matrix with the median values.

The program that I am building is more complex than the section which I need help on. Any help in deleveloping this program will be highly appreciated.

 Thanks and Regards
 Manpreet Kaur

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bym 2011-4-17

what have you tried so far?

Paulo Silva 2011-4-17

interesting homework!

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Answer 1

Andrei Bobrov 2011-4-17

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在 MATLAB Online 中打开

variant % size(Min) = [m1 n1], size(Msection) = [m2 n2]

mn1 = size(Min)+2;
Min1 = zeros(mn1);
Min1(2:end-1,2:end-1) = Min;
Mout = zeros(mn1-2);
IJ = arrayfun(@(x)subsref(buffer(1:x,3,2),struct('type','()','subs',{{':',3:x}})),mn1,'UniformOutput', false);
[I,J] = IJ{:};
for ii = 1:length(I)
    for jj = 1:length(J)
        Mout(ii,jj) = median(median(Min1(I(:,ii),J(:,jj))));
    end
end

as in the previous variant without a loop (as in medfilt2)

mn1 = size(Min)+2;
Min1 = zeros(mn1);
Min1(2:end-1,2:end-1) = Min;
IJ = arrayfun(@(x)subsref(buffer(1:x,3,2),struct('type','()','subs',{{':',3:x}})),mn1,'Un', false);
[I,J] = IJ{:};
[j3,i3] = meshgrid((1:mn1(2)-2),(1:mn1(1)-2));
Mout = arrayfun(@(x,y)median( reshape(Min1(I(:,x),J(:,y)),[],1)),i3,j3);

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Manpreet Kapoor 2011-4-18

i dint get wat is m1, n1 and m2,n2?

plz describe all the notations.....

Andrei Bobrov 2011-4-18

analogy to your task: m1 = 120, n1 = 120, m2 = 3, n2 = 3

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Answer 2

Manpreet Kapoor 2011-4-21

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mr. Andrei, I went through ur solution, but it does not sort out the elements in consideration. U have created a matrix of 0s which does not serve the purpose. Please help..... Regards Manpreet Kaur

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Manpreet Kapoor 2011-4-27

Mr. Matt,

I have crossed the age where u get homeworks. I am now a lecturer and give homeworks to budding engineers. I joined this site not to get some homework done, but to learn MATLAB, hence posted the question.

Regards

Manpreet Kaur

Sean de Wolski 2011-4-27

I wouldn't want to take a class taught by someone who: A) doesn't know how to follow instructions (this post, and your identical duplicate post) and B) Can't read documentation. $0.02

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