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Finding row and column number of values in an image matrix

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Chutiphon Moranon
评论： Voss 2022-2-3
Hi all,
As the picture attached, on line 39, I am trying to use Find to return row and column numbers of a selected area in the image matrix.
However, it returns Col_r and Row_r with unexpected numbers of values (more than 500k values).
I am not sure whether I use the appropriate function to obtain the row and column numbers of values in the image matrix.
Could you please help provide some suggestion for me. Thank you so much.
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Chutiphon Moranon
Chutiphon Moranon 2022-2-3
Thanks for your reply. I think it is because of the threshold (0.415). When I see the histogram, I find that there is a number of the values after the threshold. I have got another question.
How can I obtain a value (in histogram) of a specific location in my image? Thank you.
Voss
Voss 2022-2-3
To create a histogram of the region of 2D matrix Img12 containing rows start_row to end_row and columns start_column to end_column, you can say:
histogram(Img12(start_row:end_row,start_column:end_column))
i.e., just take the relevant part of Img12 using indexing when calling histogram().

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回答（1 个）

KSSV
KSSV 2022-2-3
Ran in:
If your image is a RGB image, the number of column will be product of second and third dimension if you just use size function.
DEmo
I = rand(10,10,3) ;
[m,n] = size(I)
m = 10
n = 30
% You have to use
[m,n,p] = size(I)
m = 10
n = 10
p = 3
Change your line number 28, so that you get Img12L value right.

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