How do I crop out a certain part within a matrix of numbers?

Question

Steven Gangano 2022-4-18

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1698905-how-do-i-crop-out-a-certain-part-within-a-matrix-of-numbers

评论： Steven Gangano 2022-4-19

采纳的回答： Chunru

This example is a small matrix, but I would like to crop out part of this matrix.

The part I want to crop out is: a(2,3:5) and a(3,3:5) which is part of row 2: 639 and underneath it is row 3: 413.

A = [1 2 3 4 5 ;

4 9 6 3 9;

2 5 4 1 3

];

I want to achieve this using the following function below.

Input parameters:

origImageMatrix = A

rowTopLeft = a(2, 3:5) => 6 3 9

colTopLeft = a(2:3, 3) => 6 4

rowBotRight = a(3,5:-1:3) => 3 1 4

colBotRight = a(3:-1:2,5) => 3 9

function [resultMatrix] = cropImg( origImageMatrix, rowTopLeft, colTopLeft, rowBotRight, colBotRight)

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Matt J 2022-4-18

And what should the result look like?

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Answer 1

Chunru 2022-4-18

1
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1698905-how-do-i-crop-out-a-certain-part-within-a-matrix-of-numbers#answer_944970

编辑：Chunru 2022-4-18

在 MATLAB Online 中打开

Are you looking for this?

A = [1 2 3 4 5 ;
       4 9 6 3 9;
       2 5 4 1 3
]
A = 3×5
     1     2     3     4     5
     4     9     6     3     9
     2     5     4     1     3
B = A(2:3, 3:5)
B = 2×3
     6     3     9
     4     1     3
%% More general
X = [1 2 5 9 2 7
     4 8 4 2 3 0
     2 7 8 2 3 0
     2 4 6 9 1 3
     2 7 9 1 7 2
     4 8 9 2 1 3];
% My input would be the borders: 
% Are you sure you want to have border numbers (which you need to search
% from X) instead of the corner coordinates?
%
% Anyway, here you can search the matrix for border numbers (it may not be
% robust if there are multiple matches)
%
% You just need two borders actually
rowTop = [8 4 2 3];
rowBot = [7 9 1 7];
colLeft = [8 7 4 7];
colRight = [3 3 1 7];
[mx, nx] = size(X)
mx = 6
nx = 6
for i=1:mx
    k = strfind(X(i, :), rowTop);
    if ~isempty(k)
        r1 = i; c1 = k;
        break
    end
end
for i=1:mx
    k = strfind(X(i, :), rowBot);
    if ~isempty(k)
        r2 = i; c1 = k;
        break
    end
end
c2 = c1 + length(rowBot) - 1;
Y = X(r1:r2, c1:c2)
Y = 4×4
     8     4     2     3
     7     8     2     3
     4     6     9     1
     7     9     1     7

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Chunru 2022-4-18

See update above.

Steven Gangano 2022-4-19

Thank you! But I just realized that it just needs to be corner coordinates and it can be one line of code. How do you do that? Top left and bottom right coordinates.

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