How to find (x,y) coordinates of white pixel.

I want to find (x,y) coordinates of the white pixel as marked in the attached Figure. I have tried some things but it is not giving me the exact solution. Can anyone please help me in this. I will be forever grateful for your help.

DDD=imread('binaryimage.png'); % Read an image
[rows, columns] = find(DDD',1,'last');  % Transpose 'DDD'
xTop = rows(1)
yTop = columns(1)
% Plot it
hold on;
plot(xTop, yTop, 'r+', 'MarkerSize', 10, 'LineWidth', 3);
hold off;

Answer 1

[Image Analyst]

You can get all the coordinates of the white pixels using find().

[rows, columns] = find(binaryImage);

That gives yo a list of coordinates for every white pixel ignoring which blob it belongs to.

Or you can do it on a blob-by-blob basis using regionprops() and asking for PixelList

props = regionprops(binaryImage, 'PixelList');

[kanika bhalla]

Thank you Sir @Image Analyst for your help. But I am not looking for all white coordinates. But I just want that four coordinate positions as shown in figures automatically to be used for further analysis.

As we can see from the image. It is the last rightmost coordinate from the top and bottom in the first half of the image. And first left most top and bottom coordinates to the second half of the image.

Any help is much appreciated.

Thank you for your time.

[Image Analyst]

Do you want the coordinates of the bounding box (row1, row2, col1, col2)? If so

props = regionprops(mask, 'BoundingBox');

Or do you want the coordinates of the pixel closest to the nearest corner? If so, something like

[rows, columns, numberOfColorChannels] = size(mask);
[r, c] = find(mask); % Find coordinates of all white pixels in mask.
% Find distance from lower left corner at row=rows, column = 1.
distances = sqrt((r - rows) .^ 2 + (c - 1) .^ 2);
[minDistance, indexOfMin] = min(distances)
cornerRow = r(indexOfMin)
cornerCol = c(indexOfMin)

[kanika bhalla]

Thank you Sir @Image Analyst for your help.

But I am looking for the coorner coordinates position values as shown in attached figure.

I have tried to get the coordinate values by dividing the image into two halves. And then calculated the coordinates. But I don't want to divide the image into two halves.

I want to calculate these 4 cordinates because my ultimate task is to draw lines between them.

Can you please help me in this.

Thank you so much for your time and help.

mask=imread('mask.png');
[height, widthl, ncols] = size(mask); 
n1 =  coloredObjectsMask(:, 1 : end/2);
figure; imshow(n1) % calculate left half
 % Below is to get top and bottom coordinates position values from left
 % half of the image.
[column,row] = find(n1, 1, 'last'); % calculate coordinate from bottom rightmost non zero pixel
hold on;
plot(row,column,'r.', 'MarkerSize',45,'LineWidth',45);

Ir = fliplr(n1); % n1 is flipped to find top coordinate
figure; imshow(Ir);
[rows0 columns0]=size(Ir);
 
topleft=Ir(1:rows0/2,:);
[Ptrxx Ptryy]=find(topleft==1,1,'first')
hold on;
plot(Ptryy, Ptrxx, 'r*', 'MarkerSize', 5, 'LineWidth', 2);
Ptryy1=columns0-Ptryy+1;
% Now calculate the coordinates in the second half of the image.
 
n2 =  coloredObjectsMask(:, end/2+1 : end );
figure; imshow(n2)
% To Extract the left most one.
[rows1 columns1]=size(n2)
topleft=n2(1:rows1/2,:);
[Ptrx Ptry]=find(topleft==1,1,'first')
hold on;
plot(Ptry, Ptrx, 'r*', 'MarkerSize', 5, 'LineWidth', 1);
Ptry=Ptry+columns1; % I got right most top coordinate

bbb=fliplr(n2);
figure; imshow(bbb);
[co,ro] = find(bbb, 1, 'last'); % calculate coordinate from bottom rightmost non zero pixel
hold on;
plot(ro,co,'r.', 'MarkerSize',45,'LineWidth',45); % here ro got chnaged
% Now map back the coodinates positions into original mask image.
ro=widthl-ro+1;
figure; imshow( coloredObjectsMask);
hold on;
line([row ro],[column co],'Color','c','LineWidth',3);
line([Ptryy1 Ptry],[Ptrxx Ptrx],'Color','c','LineWidth',3);

[Image Analyst]

But why those particular pixels? There are dozens of separate, unique blobs there. How did you pick only those 4?

[kanika bhalla]

Thank you for your reply @Image Analyst

I want only those particular coordinates because I am working on some project where I have thousands of images where I am segmenting images in a way where I need to find those coordinates to draw lines over an image.

I have attached one Figure which illustrates what I am trying to achieve.

I am using this methodology for all the images.

Can you please help me in this.

[Image Analyst]

I'd probably do a morphological closing with a 1 pixel high and 7 pixel wide line. Then call bwareafilt(mask, 8) to take just the 8 largest blobs. Then I'd find the blobs with the two lowest centroids. Label the image and call ismember to get blobs 1 and 2 individually. Use find() to find the pixel in the rightmost column for blob #1 on the left, and the leftmost pixel in blob #2 on the right. Try it - I'm sure you can do it.

mask = imclose(mask, true(1, 7));
mask = bwareafilt(mask, 8);
props = regionprops(mask, 'Centroid');
xy = vertcat(props.Centroid)
xCentroids = xy(:, 1);
yCentroids = xy(:, 2);
[sortedY, sortOrder] = sort(yCentroids, 'descend');
blob1 = ismember(mask, sortOrder(1)); % Get just one of the two lowest blobs.
blob2 = ismember(mask, sortOrder(2)); % Get other of the two lowest blobs.
% Find coordinates
[r1, c1] = find(blob1);
[r2, c2] = find(blob2);
% Find distances
xy1 = [c1(:), r1(:)];
xy2 = [c2(:), r2(:)];
distances = pdist2(xy1, xy1);
minDistance = min(distances)
[rowIndexOfMin, colIndexOfMin] = find(distances == minDistance)
% Find the tip of one blob.
xTip1 = c1(rowIndexOfMin)
yTip1 = r1(rowIndexOfMin)
% Find the tip of other blob.
xTip2 = c2(colIndexOfMin)
yTip2 = r2(colIndexOfMin)
% Draw line in the overlay between them
hold on;
plot([xTip1, xTip2], [ytip1, yTip2], 'r.-', 'LineWidth', 4, 'MarkerSize', 25);
% Burn line into image
coefficients = polyfit([xTip1, xTip2], [ytip1, yTip2], 1)
xFit = min([xTip1, xTip2]) : 0.5 : max([xTip1, xTip2]); % Less than a pixel to make sure rounding doesn't skip any pixels.
yFit = polyval(coefficients, xFit);
for k = 1 : length(xFit)
    r = round(yFit(k));
    c = round(xFit(k));
    mask(r, c) = true;
end

This is untested, just off the top of my head, but it's a start. If something doesn't work, you can probably fix it.

[Image Analyst]

You have not attached your binary image, so I can't even try the code I gave you.

[kanika bhalla]

Thank you so much for your help Sir @Image Analyst.

But it is giving error.

Any help is much appreciated.

Thank you for your time and help.

[Image Analyst]

Did you read my last comment? No more help will come unless you attach the binary image.

[kanika bhalla]

I am very sorry Sir @Image Analyst for not attaching image earlier.

I have attached image here for your reference.

Thank you for your time and help!!

Answer 2

[KSSV]

I0 = imread('https://www.mathworks.com/matlabcentral/answers/uploaded_files/670538/image.png') ;

I1 = rgb2gray(I0) ;
I2 = imbinarize(I1) ; 

[y1,x1] = find(I2==0) ;   % get black pixels to reduce white background 

I = I0(min(y1):max(y1),min(x1):max(x1),:) ;  % Get the only black part of the image 
I1 = rgb2gray(I) ; 
I2 = imbinarize(I1) ; 

[y,x] = find(I2) ;   % get white pixels in image I 
x = x+min(x1) ; y = y+min(y1) ;   % white pxiels in original image 

imshow(I0)
hold on
plot(x,y,'.r')

[kanika bhalla]

Thank you so much Sir @KSSVfor your answer. But I had already tried this. This is not exactly what I want. I only want one coordinate as marked in my attached figure. Even I was trying to figure out how I can get single coordinate from these detected coordinates.

Could you help me regarding this.

Thank you for your time and help!!

[kanika bhalla]

Sir @Walter Roberson, @Jan, @Chad Greene, @Stephen Cobeldickand @KSSV can you please help me to find the four coordinates (x,y) automatically as marked in the attached Figure. I do not want to find coordinates (x,y) values of all white pixels.

Thank you for your time and help!!

[Walter Roberson]

Sorry, I do not presently have the resources to work on this topic.

[kanika bhalla]

Thank you Sir @Walter Roberson for your time and reply.

[Andrea]

@KSSV could you please explain me the

I = I0(min(y1):max(y1),min(x1):max(x1),:) ;

and the

x = x+min(x1) ; y = y+min(y1) ;

lines? Sorry but I have just started to use Matlab and I am still learning:)

Thank you very much!