How to get X and Y coordinates from a Sparse Matrix?

Hey all,

I want to get X and Y coordinates of an image, so that I can generate the graph in an Excel File with those coordinates. I used below code to process an binary image:

    img = imread(app.SelectImageEditField.Value);
    Icomplement = imcomplement(img);
    Icomplement = rgb2gray(Icomplement);
    BW = imbinarize(Icomplement, 'adaptive');
    out2 = bwskel(BW,'MinBranchLength',15);
    BW2 = bwperim(out2,8);

Then I used the following code lines to get a digital graph:

    M = sparse(BW2);
    spy(M);

Now I want to grab the equivalent X and Y coordinates of this sparse matrix so that I can generate the same graph in Excel. Please suggest a solution. Thank you.

Answer 1

[KSSV]

If A is your sparse matrices. You can get positions using:

[y,x] = find(A) ;    % x, y are the positons/indices of non-zeros 

plot(x,y'.r')

[MAKESH VINEETH]

The below command is giving me an error:

    plot(x,y'.r')

However I tried this:

    [y,x] = find(A); 
    plot(app.UIAxes, x,y);

But it was not able to plot the same graph. Figure 1 is done using spy function and the right side image is plot.

[KSSV]

You should be able to find the indices from the matrix.....What is your matrix? If A is an matrix, you have to find the indices from it.

[i,j] = find(A) ; 
spy(A)
hold on
plot(i,j,'.r')

[MAKESH VINEETH]

This has worked, Thanks a lot! I used below to get a vertical graph:

plot(j,i,'.r')

However, the axis is now in a reverse order as compared to spy function, May I know how to reverse the axis (or to the data itself) to make it look exactly like in spy function?

[KSSV]

Use plot(i,j,'.r')

[Bruno Luong]

To reverse y-axis

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

Full script

A=rand(1000,100)>0.98;

[i,j] = find(A) ;

subplot(1,2,1);
plot(j,i,'.r');
set(gca,'YDir','reverse')
axis equal
axis tight

subplot(1,2,2)
spy(A)

[KSSV]

:)

[MAKESH VINEETH]

Thanks, it worked!