How to extract values from a matrix along a certain line (not vertical or horizontal).
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Assume I have the following matrix:
A=[11 13 43 53 66 45 44 83 91;
23 43 54 65 76 78 76 98 33;
23 54 65 76 43 16 38 27 65]
I want to extract values from this matrix, along 45 degrees, to form a new matrix
B=[11 13 43 53 66 45 44;
43 54 55 76 78 76 98;
65 76 43 16 38 27 65]
How I can do it in MATLAB? Thanks.
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Answers (2)
Image Analyst
on 25 Oct 2015
If you have the Image Processing Toolbox, simply use improfile().
2 Comments
Image Analyst
on 25 Oct 2015
Or, call imrotate() to align the image with rows or columns, and extract a row or column. Should be pretty close to the same thing.
Image Analyst
on 25 Oct 2015
improfile() will extract along a line at an arbitrary angle - it doesn't have to be exactly 45 degrees. You just specify the two endpoints of the line and how many points along that line you want to interpolate.
Jan
on 25 Oct 2015
A = [11 13 43 53 66 45 44 83 91; ...
23 43 54 65 76 78 76 98 33; ...
23 54 65 76 43 16 38 27 65];
[m, n] = size(A);
index = true(m, n);
index = tril(triu(index), n - m);
B = reshape(A(index), m, [])
2 Comments
Image Analyst
on 25 Oct 2015
Doesn't give what he wanted, but I'm not sure how he got that anyway. For example it sort of appears that it's a rotation about the middle element, but not quite. Because using
B=imrotate(A, -45, 'crop')
will give
B =
0 54 65 65 53 66 0 0 0
0 0 76 76 76 45 45 0 0
0 0 0 43 16 78 44 83 0
while Jan's code gives:
B =
11 43 53 66 45 44 98
13 54 65 76 78 76 27
43 65 76 43 16 38 65
Neither of which is
B=[11 13 43 53 66 45 44;
43 54 55 76 78 76 98;
65 76 43 16 38 27 65]
which the user asked for. So I need Peng to explain how B was arrived at. Also, Jan's code is for 45 degrees, which is the example angle Peng wanted, but in the subject line Peng asked for an "Arbitrary angle:. So which is it?? 45 or arbitrary? And if it's just a rotation, then why is B two columns (but no rows) shorter? If anything a rotated matrix would be larger, and you can get that with the 'loose' option to imrotate() where it will expand the canvass to hold the entire rotated matrix.
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