Extracting cartesian coordinates from a binarized image of a curved line

Question

Michiel Firlefyn 2018-4-23

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https://ww2.mathworks.cn/matlabcentral/answers/396858-extracting-cartesian-coordinates-from-a-binarized-image-of-a-curved-line

评论： Michiel Firlefyn 2018-5-1

Hi everyone

After image pre-processing, I obtained the following binarized image:

This is in a 2848x4272 array form and I would like to convert the line to a 2 column matrix with x and y coordinates. Does anyone have any idea how to achieve this?

The code I used to achieve the line is:

img = imread('G1.JPG');

background = imopen(img,strel('disk',60));

surf(double(background(1:8:end,1:8:end))),zlim([0 255]);

set(gca,'ydir','reverse');

I2 = img - background;

grayImage = I2(:, :, 1);

I3 = imadjust(grayImage);

bw = imbinarize(I3);

bw = bwareaopen(bw, 5000);

cc = bwconncomp(bw, 8);

line = false(size(bw));

line(cc.PixelIdxList{1}) = true;

imshow(line);

Thanks!

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Answer 1

Sigurd Askeland 2018-4-27

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在 MATLAB Online 中打开

I don't have the Image Processing Toolbox, so I can't recreate your scenario exactly. However, if you have a 2D array of booleans ( true / false, or 1 / 0), this can be translated to an (Nx2) array of the x and y indices of the true pixels.

    [m,n] = size(my_image); %my_image to be replaced by your image...
    x = ones(m*n,1) * [1:m*n];
    y = [1:m*n]' * ones(1,m*n);
    coordinates = [x,y]; %All coordinates.
    coordinates = coordinates(my_image(:),:); %'true' coordinates.

Note that the x and y values are the number of pixels from the top left corner. A simple transformation can make them into more traditional x- and y-coordinates.