How to get the value from Structure array ?

Dear Matlab experts,

I need some help from someone.

I want to get the location value from the structure array (stat). Then use them to crop image with the size is 64x64.

This is my step:

1. Detect the centroid of image

2. Use the value of centroid location and crop the original to many 64x64 image.( this step i stuck because i don't know how to get the

value of centroid location).

My code:

% Step 1 centroid detection
I=imread("2_mask.png")
Ibw = im2bw(I);
stat = regionprops(Ibw,'centroid');
imshow(I); hold on;
for x = 1: numel(stat)
    plot(stat(x).Centroid(1),stat(x).Centroid(2),'+',LineWidth=2);
end
hold off
%Step 2 crop image 
I2 = imcrop(I,[??-32 ??-32 63 63])

This is the structure array value of centroid location.

This is what i want to do

Thanks

Han

Answer 1

[Matt J]

I=imread("https://www.mathworks.com/matlabcentral/answers/uploaded_files/996660/2_mask.png");
Ibw = im2bw(I);


stat = regionprops(Ibw,'Image');
for i=1:numel(stat)
    
    I=stat(i).Image;
    I(end+1:64,end+1:64)=0;

    s=regionprops(I,'Centroid');
    
    I=imtranslate(I,32-s.Centroid);
    
    if ~isequal(size(I),[64,64])

      win = centerCropWindow2d(size(I),[64,64]);

      I=imcrop(I,win);

    end


    stat(i).Image=I;
end

montage({stat.Image},'Back','w','Bor',5)

[Jenifer NG]

Thanks you so much.

I want to use the centroid location in this image to crop another image then save the cropped area to separate file.

Could you help me to modify this code?

Answer 2

[Matt J]

I want to use the centroid location in this image to crop another image then save the cropped area to separate file.

I=imread("https://www.mathworks.com/matlabcentral/answers/uploaded_files/996660/2_mask.png");
Ibw = im2bw(I);


stat = regionprops(Ibw,'Centroid');
N=numel(stat);
for i=1:N
    stat(i).BoundingBox=[stat(i).Centroid-32.5, 64,64];
end

And now you can extract the cropped subimages from an arbitrary image with the following, although I use the original image Ibw just for illustration.

subimages=arrayfun(@(s)imcrop(Ibw,s.BoundingBox),  stat,'uni',0); %You can use a new image here

montage(subimages,'Back','w','Bor',5)

[Jenifer NG]

Wow it work fine.

Thanks you

how to save 9 cropped areas to 9 image files ?

[Matt J]

Why not save them all to the same file, as follows?

save myFile subimages

[Jenifer NG]

I mean save to 'JPG' file. by using imwrite but i dont know how to use

[Jenifer NG]

Dear Matt J,

I am using the function to convert subimage from array to mat (array2mat) then i can save the cropped image by using imwrite and the code as bellow . Could you advise me to modify the code ?

clear all
I=imread("https://www.mathworks.com/matlabcentral/answers/uploaded_files/996660/2_mask.png");
Ibw = im2bw(I);
stat = regionprops(Ibw,'Centroid');
N=numel(stat);
for i=1:N
    stat(i).BoundingBox=[stat(i).Centroid-32.5, 63,63];
end

I2=imread("2.png")
subimages=arrayfun(@(s)imcrop(I2,s.BoundingBox),  stat,'uni',0); %You can use a new image here
montage(subimages,'Back','w','Bor',5)
for k = 1:N
    b{k}=cell2mat(subimages(k,1))
    filename=sprintf('file%d.jpg',k)
    imwrite(b{k},filename)
end

Thanks

[Matt J]

Why is modification necessary?