draw line in a picture

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lena kappa
lena kappa on 26 Mar 2021
Edited: Walter Roberson on 4 Apr 2021
Hello guys does anyone know how can i draw a line in a picture.
For example i want to draw a 45 degree red line in the next picture starting from the top left corner of the picture and ending n the other end of the picture.

Accepted Answer

Walter Roberson
Walter Roberson on 26 Mar 2021
Edited: Walter Roberson on 4 Apr 2021
img = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/562881/image.jpeg');
sz = size(img);
endx = min(sz(1), sz(2));
h(1) = image(img);
hold on
h(2) = plot([1 endx], [1 endx], 'r');
hold off
Or if you need the line "burned in" to the image:
img = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/562881/image.jpeg');
sz = size(img);
endx = min(sz(1), sz(2));
nimg = insertShape(img, 'Line', [1 1 endx endx], 'Color', 'r');
h(1) = image(nimg);
The difference between these two is that in the first version, the red line is only visible in what is drawn, with it not being made part of the image array; h will end up as a vector containing the handle to the image display object that only knows about the gray scale image, and a handle to the line display object. In the second version, the red line is part of the array stored in nimg, suitable for further processing (or writing to a file), and h will be the handle of the image display object that only knows about displaying the array that inherently has the red line as part of the data.
  11 Comments
Walter Roberson
Walter Roberson on 4 Apr 2021
I corrected the insertShape call,
nimg = insertShape(nimg, 'Line', [0 0 endx endy], 'Color', line_cols{k});

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More Answers (1)

MG
MG on 26 Mar 2021
Would this work for you:
hold on
ax=axis;
x = ax(1:2);
y = ax([3 4]); %might want to change cordinates (check with 'axis on')
line(x,y,'Color','red','LineStyle','-')
  4 Comments
lena kappa
lena kappa on 26 Mar 2021
thanks for the answer michael

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