Cut around the center of a matrix

Question

I.G 2015-4-29

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评论： Image Analyst 2021-4-1

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Hi everyone,

I have a quick question which may be simple to answer. I have a matrix,

A = [ 5 5 5 5 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 5 5 5 5 ]

'A' is always an odd number of lines and columns, and may be 100s of them. I want to cut at my own convenience a portion around the center, like

B = [ 4 4 4 ; 4 4 4 ; 4 4 4 ]

How can I do it?

Thanks

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Answer 1

Image Analyst 2015-4-29

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Try this:

margin = 1; % Whatever you want.
B = A(margin+1:margin+1, end-margin:end-margin);

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maubars 2021-4-1

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Results

B=4

Image Analyst 2021-4-1

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Thanks. Fix:

A = [ 5 5 5 5 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 4 4 4 5 ; 5 5 5 5 5 ]
margin = 1; % Whatever you want.
B = A(margin + 1 : (end - margin), margin + 1 : (end - margin))

A =

5 5 5 5 5

5 4 4 4 5

5 5 5 5 5

B =

4 4 4

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Answer 2

Thorsten 2015-4-29

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编辑：Thorsten 2015-4-29

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 szcut = 3;
 i1 = (size(A, 1) - szcut)/2;
 ind1 = i1+1:i1+szcut;
 B = A(ind1, ind2);

If A is not square or if you want to cut out non-square parts, define ind2 analogously.

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Answer 3

Michael Haderlein 2015-4-29

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If c indicates the range you want to remove and would be 3 in your example, just use

B=A((end-c)/2+1:(end+c)/2,(end-c)/2+1:(end+c)/2);

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Image Analyst 2015-4-29

In general it's B = A(row1:row2, column1:column2). You can decide on the rows and columns in any way that you want. If you want to get only a particular value (like 4) automatically (even if it's not a rectangle) then let me know. It's possible.

I.G 2015-4-29

I made it like this:

cx=ceil(size(A,1)/2); % cx is the center line cy=ceil(size(A,2)/2); % cy is the center row x= ... % the steps in x axis from center x y= ... % the steps in y axis from center y B=A((cx-y):(cx+y),(cy-x):(cy+x));

Thanks for the help!

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