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From: Kenneth Galea on 31 Dec 2009 12:38
Hi everyone.

I have a problem. I'm currently doing some image processing of different objects. I have already thresholded, made edge detection and labelled the different objects using bwlabel. Now since my final aim is to grasp different objects by a robotic arm, my task is to search around the borders/contours of different objects in order to find regions of minimum curvature in the image in order to be able to have a stable grasp/contact.

My problem is that to achieve this, I need to go pixel by pixel around the object border/contour in order to be able to evaluate it. Pls check this image link which explains what I need:
http://drop.io/curvature_computation

As can be seen from this link, P(x[i] , y[i]) is the current pixel on the border to be evaluated while P(x[i+k], y[i+k]) is another pixel on the border (5 pixels after the current pixel where k=5).
When using regionprops 'PixelList' I noticed that the pixels (x,y) coordinates are not listed according to the next pixel on the contour but are listed column by column which is not what I need since I cannot evaluate them in the manner explained above.

Please any suggestions would be appreciated?

Thanks
Kenneth
From: ImageAnalyst on 31 Dec 2009 12:43
Kenneth
You need to check out bwboundaries(), which WILL give you the chain
code for your border/perimeter.
Regards,
ImageAnalyst

From: Kenneth Galea on 31 Dec 2009 13:00
ImageAnalyst <imageanalyst(a)mailinator.com> wrote in message <a4066a04-75cf-4685-a957-2b759ab91d8e(a)m16g2000yqc.googlegroups.com>...
> Kenneth
> You need to check out bwboundaries(), which WILL give you the chain
> code for your border/perimeter.
> Regards,
> ImageAnalyst
Hi. Thanks for your reply.
Ok so if I have two objects labelled objects (1) and (2) and use bwboundaries in this manner: B = bwboundaries(BW,conn) ...... where conn must be taken as 8 ....... how can I put these 2 objects in two different arrays with theri x,y coordinates??

Thanks
Kenneth
From: ImageAnalyst on 31 Dec 2009 13:57
Kenneth:
You should be able to figure it out from this snippet of code pulled
from my demo at
http://www.mathworks.com/matlabcentral/fileexchange/25157

% bwboundaries returns a cell array, where each cell
% contains the row/column coordinates for an object in the image.
% Plot the borders of all the coins on the original
% grayscale image using the coordinates returned by bwboundaries.
subplot(3, 3, 6); imagesc(originalImage); title('Outlines, from
bwboundaries()'); axis square;
hold on;
boundaries = bwboundaries(binaryImage);
for k = 1 : numberOfBlobs
thisBoundary = boundaries{k}; % Stuff into a double array.
plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth', 2);
end
hold off;

From: Kenneth Galea on 2 Jan 2010 04:57
ImageAnalyst <imageanalyst(a)mailinator.com> wrote in message <61ea651b-6322-46a6-9889-cc22e81be27a(a)u41g2000yqe.googlegroups.com>...
> Kenneth:
> You should be able to figure it out from this snippet of code pulled
> from my demo at
> http://www.mathworks.com/matlabcentral/fileexchange/25157
>
> % bwboundaries returns a cell array, where each cell
> % contains the row/column coordinates for an object in the image.
> % Plot the borders of all the coins on the original
> % grayscale image using the coordinates returned by bwboundaries.
> subplot(3, 3, 6); imagesc(originalImage); title('Outlines, from
> bwboundaries()'); axis square;
> hold on;
> boundaries = bwboundaries(binaryImage);
> for k = 1 : numberOfBlobs
> thisBoundary = boundaries{k}; % Stuff into a double array.
> plot(thisBoundary(:,2), thisBoundary(:,1), 'g', 'LineWidth', 2);
> end
> hold off;

Hi, thanks for your reply
I think I didn't explain myself clearly. I'm not using a binary image in bwboundaries but a matrix L where 0 = background, 1 = 1st object, 2 = 2nd object.....this still worked well with the following code:
B = bwboundaries(L,8, 'noholes')
for counter = 1:num
tB = B{counter}
end

Now what I'll need is that tB (i.e. the array name) changes with every object i.e. tB1 represents object 1 and tB2 represents object 2. When trying this:
tB{counter}= B{counter}
matlab gives me an error. Sorry for such a basic question but I cannot implement it...what I'll need is just a change in string name.
Thnaks Kenneth
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