Asked by Adhi
on 23 Nov 2012

i have this image http://www.freeimagehosting.net/n59z8

how can i get the each coordinates that shown in this image http://www.freeimagehosting.net/pd85c (up, down, right, left and center)

Answer by Image Analyst
on 23 Nov 2012

Edited by Image Analyst
on 25 Nov 2012

Accepted answer

Find the centroid with regionprops(). See my Image Segmentation Tutorial if you don't know how. Then convert the centroid to integer to get the row and column.

centroidColumn = int32(centroid(1)); % "X" value centroidRow = int32(centroid(2)); "Y" value.

Then extract a row or column and use find to find the first and last element that's set:

middleColumn = binaryImage(:, centroidColumn); topRowY = find(middleColumn, 1, 'first'); % Find top. bottomRowY = find(middleColumn, 1, 'last'); % Find bottom.

middleRow = binaryImage(centroidRow, :); leftColumnX = find(middleRow, 1, 'first'); % Find left. rightColumnX= find(middleRow, 1, 'last'); % Find right.

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Adhi
on 25 Nov 2012

this is the result: http://www.freeimagehosting.net/twva2

its working for top and bottom, but why its not working for right and left.? always get the wrong result. i got the centroid from your image segmentation tutorial as well.

centroidColumn = int32(blobCentroid(1)); % "X" value centroidRow = int32(blobCentroid(2)); %"Y" value.

Then extract a row or column and use find to find the first and last element that's set:

middleColumn = J(:, centroidColumn); topRowY = find(middleColumn, 1, 'first') % Find top. bottomRowY = find(middleColumn, 1, 'last') % Find bottom. middleRow = J(:, centroidRow); leftColumnX = find(middleRow, 1, 'first') % Find left. rightColumnX= find(middleRow, 1, 'last') % Find right.

and i added this code for mark the coordinate:

line(centroidColumn, centroidRow, 'Marker', '*', 'MarkerEdgeColor', 'r') line(centroidColumn, topRowY, 'Marker', '*', 'MarkerEdgeColor', 'r') line(centroidColumn, bottomRowY, 'Marker', '*', 'MarkerEdgeColor', 'r') line(leftColumnX, centroidRow, 'Marker', '*', 'MarkerEdgeColor', 'r') line(rightColumnX, centroidRow, 'Marker', '*', 'MarkerEdgeColor', 'r')

Image Analyst
on 25 Nov 2012

middleRow should be defined like this:

middleRow = binaryImage(centroidRow, :);

and line() takes 2 x and 2 y coords:

line([x1, x2], [y1 y2]........ Or line([col1, col2], [row1, row2], ......

and I'd recommend using more descriptive names than single letters, for maintainability of the code.

Glad it's finally working for you.

Opportunities for recent engineering grads.

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