how can i get each coordinates of binary image

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 1

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.

its really helpful

thanks Image Analyst

I did already. Hence, my edited answer - it's not the same as before (I guess you didn't notice).

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')

i dont know how to move my post to comments, so i deleted and moved my last post to this comments section. but i can't move yours.

and your answers works perfectly, thanks.

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.