How to resolve error from bwtraceboundary function

Hello! I tried using bwtraceboundary to trace the edge of object in a specific region.

im = imread('block.jpg');
im = rgb2gray(im);
BW = im2bw(im);
imshow(BW,[]);

r = 200;
c = 66;
contour = bwtraceboundary(BW,[r c],'W',8,Inf,'counterclockwise');

hold on;
plot(contour(:,2),contour(:,1),'g','LineWidth',2);

After I have computed, it return with error:

>> bwtrace
Index exceeds matrix dimensions.

Error in bwtrace (line 11)
plot(contour(:,2),contour(:,1),'g','LineWidth',2);

Please kindly help me on this issue.

Answer 1

[Walter Roberson]

The starting location you provided, [r,c], does not happen to be part of any boundary.

[Issara Laosuwan]

Thank you very much! The code work fine now.