How to I get the coordinates of a given pixel?
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James Richards
le 21 Mar 2016
Commenté : Pablo Velez
le 6 Mai 2021
I was wondering if there was a method to get the X,Y coordinate of a pixel in an image? I have the pixels that I'd like to get the coordinates of, but as they aren't regions, a regionprops centroid doesn't help, and I need it to be done without user input, so I can't click on them with ginput.
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Walter Roberson
le 21 Mar 2016
X coordinate 1003.87333157056 with Y coordinate 989.636902390572 would be found at index (989.636902390572, 1003.87333157056) in the array. Y then X.
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Image Analyst
le 22 Mar 2016
Use bilinear interpolation, like interp2() if you want the exact value of fractional coordinates. However, it may be good enough for you to do a much simpler operation of just rounding the coordinates to the nearest integer and just getting the array element
grayLevel = grayImage(round(y), round(x));
Remember, like Walter said above, it's (y,x) not (x,y) because the first index is rows and y is the row.
You might also like the impixel() function, but I don't find that any more convenient than simple indexing.
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Image Analyst
le 3 Fév 2020
No, it's (x, y) not (row, column), which would be (y, x). That's one thing you always have to keep mindful of and a common cause of beginners' problems. It's described in the help documentation.
props = regionprops(mask, 'Centroid');
xy = vertcat(props.Centroid);
x = xy(:, 1); % Columns
y = xy(:, 2); % Rows
I can't help you with the conversion to geographical coordinates. Look into functions of the Mapping Toolbox.
Pablo Velez
le 6 Mai 2021
"a common cause of beginners' problems" happend to me but I didn't find it in the documentation https://www.mathworks.com/help/matlab/ref/imread.html I could only infer it from the example, is that what you mean with "described in the help documentation" or am I missing something.
Also I don't undertand why they switch x y places, python matplotlib does the same, why?
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