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

Question

kanika bhalla 2021-7-1

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/869338-how-to-find-x-y-coordinates-of-white-pixel

评论： Andrea 2023-3-22

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;

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Answer 1

Image Analyst 2021-7-11

1
链接

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https://ww2.mathworks.cn/matlabcentral/answers/869338-how-to-find-x-y-coordinates-of-white-pixel#answer_744203

在 MATLAB Online 中打开

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');

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kanika bhalla 2021-7-13

在 MATLAB Online 中打开

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 2021-7-13

在 MATLAB Online 中打开

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