How can specific positions in the below image?

Hello Friends.

I am looking for to find the positions(i,j) of light green boundaries in the below images.

A needed m.file for loading the required data is attached. In the below code, etas and eta are matrix with predefined size.

%code
load Etas
Nx=128;
eta2=zeros(Nx,Nx);
ncount=0;
%original code
for igrain=1:25
    
    ncount=0;
    for i=1:Nx
        for j=1:Nx
            ii =(i-1)*Nx+j;
            
            eta2(i,j) =eta2(i,j)+etas(ii,igrain)^2;
            if(etas(ii,igrain) >= 0.5)
                ncount=ncount+1;
            end
%             
            ncount=ncount/(Nx*Nx);
        end
        
    end
end
%Display
figure
imagesc(eta2)

Answer 1

[Image Analyst]

Threshold eta2 then skeletonize to get single pixel wide lines. Then call find to get the rows and columns of every white pixel.

binaryImage = bwmorph(eta2 < 0.6, 'skel', inf);
[rows, columns] = find(binaryImage);

[Amir Torabi]

Thanks for your assist. It works great. I have another question. How can i only show the above points that greater a specific value on the image?

[Image Analyst]

I don't know what that means. What do you mean by the "above points"? Do you mean the points (row, column pairs) that I used find() to get in my above Answer? They are binary so they don't have values other than 1. Do you mean the gray scale values from the original image that lie in the same location as the skeleton? If so, you can just multiply the gray scale image by the skeleton image, like

graySkel = grayImage .* uint8(binaryImage);

or use indexing like

graySkel = grayImage; % Initialize
graySkel(~binaryImage) = 0; % Set non-skeleton points to black (0).