how can I find whether the x and y values are within an image ?

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busra dogru 2019-4-12

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https://ww2.mathworks.cn/matlabcentral/answers/456089-how-can-i-find-whether-the-x-and-y-values-are-within-an-image

评论： Walter Roberson 2019-4-13

Hello to everyone. I have binary pictures and x y coordinate values. I want to check if these points are in the picture. How can I do this using the loop ?

Thanks in advance ...

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Answer 1

Walter Roberson 2019-4-12

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https://ww2.mathworks.cn/matlabcentral/answers/456089-how-can-i-find-whether-the-x-and-y-values-are-within-an-image#answer_370440

在 MATLAB Online 中打开

margin = 0.5;
in_image = x >= margin & x <= size(YourImage,2) + margin & y >= margin & y <= size(YourImage,1) + margin;

The margin is there to account for pixel width. When you position an image at (1,1) on one side and (maxcolumn,maxrow) on the other, then those are the coordinates of pixel centers so down to (0.5,0.5) and up to (maxcolumn+0.5,maxrow+0.5) is still "within" the image.

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busra dogru 2019-4-12

Firstly, thanks for your response. Actually I want to check if x and y values are inside a letter written in white on top of the black background. That is, if the values are in the white part. There are no spaces in my pictures. How do you think I can do that?

Walter Roberson 2019-4-13

在 MATLAB Online 中打开

margin = 0.5;
in_image = x >= margin & x < size(YourImage,2) + margin & y >= margin & y < size(YourImage,1) + margin;
ind = sub2ind(size(YourImage), round(y(in_image)), round(x(in_image)) );
is_white = false(size(in_image));
is_white(ind) = YourImage(ind) == 1;

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