Comments on: General connectivity

By: Steve

Steve — Mon, 16 Jun 2008 13:28:24 +0000

Dave—I think you’re pushing the idea of pixel connectivity way past where it was meant to go. :-) You might try using a Hough circle detection algorithm. Some of these do a good job detecting partial circles. Once you have the center and radius, you can fill in the perimeter pixels.

By: dave

dave — Thu, 12 Jun 2008 22:21:58 +0000

hey Steve,

thanks for your great blog. i had a question extending the general connectivity (perhaps we could call it specific connectivity?:)

can you think of a way to extend bwperim (or any function or set of functions) to connect open objects, such as the incomplete perimeters of circles? for example, let’s say i have the following matrix, and i want to complete the circle… perhaps by recursively checking for 8-pixel connectivity. any ideas?

circperim = bwperim(fspecial(’disk’,8)>0);
circperim(1:5,1:5) = zeros(5);
imshow(circperim);

0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
0 0 1 0 0 0 0 0 0 0 0 0 0 0 1 0 0
0 0 0 1 1 0 0 0 0 0 0 0 1 1 0 0 0
0 0 0 0 0 1 1 1 1 1 1 1 0 0 0 0 0

thanks!

dave

By: Harun

Harun — Mon, 04 Feb 2008 17:55:04 +0000

Tried it and works like a charm. But there’s the additional hassle of removing the pads once bwperim does its work, hope this can be addressed in future versions. Thanks a lot Steve!

By: Steve

Steve — Tue, 15 Jan 2008 12:12:40 +0000

Harun—There is an implicit assumption in bwperim that pixels “outside” the image are background pixels. That’s why A(1,4:6) are identified as perimeter pixels. You could get your desired result by prepadding the boundary with ones using padarray.

By: Harun Koku

Harun Koku — Tue, 15 Jan 2008 01:54:16 +0000

Hi Steve,

Thanks for the great blog, and hope you keep this up. I have a question about the bwperim - connectivity example here. When I try this simple code:

conn1 = 4
A = [0 0 1 1 1 1 1 0 0
0 0 1 1 1 1 1 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0]
B = bwperim(A,conn1)

I get the resulting perim matrix B:
B =

0 0 1 1 1 1 1 0 0
0 0 1 1 1 1 1 0 0
0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0

Ideally A(1,4), A(1,5) and A(1,6) shouldn’t be perimeter pixels. Is there some way to get the right perimeter? Thanks in advance!