Comments on: Tracing George

By: Steve

Steve — Thu, 21 Jul 2011 14:24:37 +0000

Dustin—bwboundaries and bwtraceboundary do trace pixels in connected order, rather than by order of row or column coordinates. And with both functions you can specify the desired pixel connectivity.

By: Dustin

Dustin — Thu, 21 Jul 2011 02:55:51 +0000

Hi Steve,

Thanks for this post. I am looking for a slightly different function. I have extracted the edge of an object, and I need a list of contiguous edge pixels.

bwboundaries and bwtraceboundary order the pixels according to their row, column coordinates. What I am looking for is something that gives me the pixels in a connected order.

With bwtraceboundary, I have managed to find the end pixels of the boundaries, and find the edge contour from there. However, the way the connectivity works, certain pixels are skipped due to another connecting pixel (e.g. ‘SE’ pixel is taken as adjacent instead of ‘S’). While this has minimal effect on the appearance of the edge, it wreaks havoc on other parts of my code due to dimension mismatch. Is there any way to force the 4-connectivity to be checked before the 8-connectivity i.e. [N,E,S,W,NE,SE,SW,NW] instead of [N,NE,E,SE,S,SW,W,NW]?

Thanks a lot.

By: HANY ELSALAMONY

HANY ELSALAMONY — Tue, 19 Apr 2011 18:12:51 +0000

where is the answer

By: HANY ELSALAMONY

HANY ELSALAMONY — Mon, 18 Apr 2011 22:21:19 +0000

hi Steve

first, my problem that i want to plot a line between every two points in the boundary of the object’s contour by using (bwboundaries), then i want the coordinates of contour that made by this (bwboundaries)

second, i want to plot a perpendicular lines on that lines to get the intersection points with the same contour from inside it

Thank you for your efforts

By: Ahmad

Ahmad — Tue, 25 May 2010 10:15:18 +0000

Thanks a lot for your help

By: Steve

Steve — Tue, 18 May 2010 17:38:49 +0000

Ahmad—Try the Image Processing Toolbox function imfreehand.

By: Ahmad

Ahmad — Tue, 18 May 2010 08:49:30 +0000

hi sir,
Would you please tell me how can I trace mannually an image has been opened in MATLAB software to access (extract) coordinates of the pixels (x and y) in the output (in command window? does any command exist in matlab that i can use? I used getpts command but unfortunately it need to click for each point
thank you too much

By: Matteo

Matteo — Mon, 10 May 2010 15:49:11 +0000

Steve,

as I commented in another of your posts, I was trying to use bwboundaries to digitize some polygons from a scanned geological map. This worked quite well and I was going to use the resulting x and y as a mask to parse coordinates from the matrices with X and Y coordinates associated with the geological map. My problem was I was not sure if points in “boundaries” were stored as consecutive pixels in a loop or by row,column from top left corner to bottom right. I use data cursor to confirm points are stored as consecutive pixels. I thought it’d be of interest to add my comment in here as well. Thank you,
Matteo

By: Steve

Steve — Wed, 17 Feb 2010 16:47:56 +0000

Changan—I don't generally have time to consult on individual image analysis or algorithm development questions. You might consider posting your question to the MATLAB newsgroup.

By: changan

changan — Wed, 17 Feb 2010 16:26:27 +0000

Hi Steve

Thank you very much for posting this series of lectures on image processing. It is very helpful. I have learned a lot. I have a jpeg picture. I am trying to get a good contour with thin option, but I can not keep a continuous line. Basically, I got a broken line. Your advice is highly appreciated.

By the way, how can I send you the jpeg file ?

Thanks

Changan