Comments on: POLY2MASK and ROIPOLY – Part 1 http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/ Steve Eddins manages the Image & Geospatial development team at The MathWorks and coauthored Digital Image Processing Using MATLAB. He writes here about image processing concepts, algorithm implementations, and MATLAB. Sat, 11 Feb 2012 18:27:50 +0000 hourly 1 http://wordpress.org/?v=3.2.1 By: Steve Eddins http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-24733 Steve Eddins Fri, 09 Dec 2011 18:18:10 +0000 http://blogs.mathworks.com/steve/?p=99#comment-24733 Leo—Call roipoly twice. Leo—Call roipoly twice.

]]> By: Leo http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-24732 Leo Fri, 09 Dec 2011 16:21:53 +0000 http://blogs.mathworks.com/steve/?p=99#comment-24732 Hi Steve, How can I specify more than one polygon (not connected) on the same image using roipoly? For example, I want to create a mask for two distant apples on a tree. Any suggestions? Hi Steve,
How can I specify more than one polygon (not connected) on the same image using roipoly? For example, I want to create a mask for two distant apples on a tree.
Any suggestions?

]]> By: Steve http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-24461 Steve Tue, 06 Sep 2011 21:12:43 +0000 http://blogs.mathworks.com/steve/?p=99#comment-24461 Jeremy—The answer is in the doc, which gives the following as the syntax for poly2mask: <pre class="code"> bw = poly2mask(x, y, m, n) </pre> and says that m is the number of rows and n is the number of columns. So your first call to poly2mask is incorrect. Perhaps I shouldn't have designed it that way. But I did. Jeremy—The answer is in the doc, which gives the following as the syntax for poly2mask:

bw = poly2mask(x, y, m, n)

and says that m is the number of rows and n is the number of columns. So your first call to poly2mask is incorrect.

Perhaps I shouldn’t have designed it that way. But I did.

]]> By: Jeremy Heil http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-24460 Jeremy Heil Tue, 06 Sep 2011 19:43:46 +0000 http://blogs.mathworks.com/steve/?p=99#comment-24460 Why does this code (which I think is syntactically intuitive) seems to swap the xdim and ydim when it generates the output. <pre> xpts=[ 1 3 3 1]; ypts=[4 4 8 8]; xdim=6; ydim=10; poly2mask( xpts, ypts, xdim, ydim ) </pre> while <pre> poly2mask( xpts, ypts, ydim, xdim ) </pre> gets the output you expect? Why does this code (which I think is syntactically intuitive) seems to swap the xdim and ydim when it generates the output.

xpts=[ 1 3 3 1];
ypts=[4 4 8 8];
xdim=6;
ydim=10;

poly2mask( xpts, ypts, xdim, ydim )

while 

poly2mask( xpts, ypts, ydim, xdim )

gets the output you expect?

]]> By: eric http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-23151 eric Wed, 26 May 2010 10:23:26 +0000 http://blogs.mathworks.com/steve/?p=99#comment-23151 Dear Steve, Any progress on the "mask2poly" function? I tried reading the bwboundary and bwperim and bwtraceboundary, but left with confusion. My goal is to offer an alternative to the use of impoly, by using a simple graythresh command to create a mask. However, where I am having trouble, is that I would like to save the graythresh information in an roi structure (where I store certain aspects of imroi output, such as the accepted position vector, createmask, color,...). Because imroi has a createmask subfunction, it's easy to go from roi vertices to mask. However, I can't seem to go from mask to position vertices in an easy manner. mask2poly seemed like the closest thing I can find (since google returns nothing except answers to the opposite, i.e. "roi to mask", when searching for "convert mask to roi" not in quotations) Lemme know, Eric Dear Steve,

Any progress on the “mask2poly” function? I tried reading the bwboundary and bwperim and bwtraceboundary, but left with confusion.

My goal is to offer an alternative to the use of impoly, by using a simple graythresh command to create a mask. However, where I am having trouble, is that I would like to save the graythresh information in an roi structure (where I store certain aspects of imroi output, such as the accepted position vector, createmask, color,…). Because imroi has a createmask subfunction, it’s easy to go from roi vertices to mask. However, I can’t seem to go from mask to position vertices in an easy manner. mask2poly seemed like the closest thing I can find (since google returns nothing except answers to the opposite, i.e. “roi to mask”, when searching for “convert mask to roi” not in quotations)

Lemme know,

Eric

]]> By: Steve http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-22908 Steve Wed, 24 Mar 2010 22:26:08 +0000 http://blogs.mathworks.com/steve/?p=99#comment-22908 Paul—I'm not really sure what you mean by nonscalar m and n, but it sounds to me like the MATLAB function inpolygon might be useful to you. Just be aware that inpolygon (and poly2mask as well) are plane geometry and not spherical geometry functions. If your boundary polygon wraps a pole, they probably won't work for you. Paul—I’m not really sure what you mean by nonscalar m and n, but it sounds to me like the MATLAB function inpolygon might be useful to you. Just be aware that inpolygon (and poly2mask as well) are plane geometry and not spherical geometry functions. If your boundary polygon wraps a pole, they probably won’t work for you.

]]> By: Paul Alexander http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-22907 Paul Alexander Wed, 24 Mar 2010 22:11:16 +0000 http://blogs.mathworks.com/steve/?p=99#comment-22907 Here is a crazy question for you Steve. I have some gridded files of latitude and longitude. I have vectors of some regions in lat and long too. I need to create a mask that represents where when my gridded lat and long fall within the polygon defined by my boundary vectors. Mask2poly comes close; but I really need to use predefined non-scalars for 'm' and 'n'. Appreciate any help you may be able to offer. Here is a crazy question for you Steve. I have some gridded files of latitude and longitude. I have vectors of some regions in lat and long too. I need to create a mask that represents where when my gridded lat and long fall within the polygon defined by my boundary vectors. Mask2poly comes close; but I really need to use predefined non-scalars for ‘m’ and ‘n’. Appreciate any help you may be able to offer.

]]> By: Steve http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-21928 Steve Wed, 01 Jul 2009 13:12:02 +0000 http://blogs.mathworks.com/steve/?p=99#comment-21928 MoHDa—It might be possible. You'll need to use one of the options that produces closed edge contours, or work out some way of closing them yourself. MoHDa—It might be possible. You’ll need to use one of the options that produces closed edge contours, or work out some way of closing them yourself.

]]> By: MoHDa http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-21927 MoHDa Tue, 30 Jun 2009 20:09:41 +0000 http://blogs.mathworks.com/steve/?p=99#comment-21927 I have one question about the ROIPOLY: I have an image with stripes, I use the "edge" command for finding the edges, is it possible to use the output of edge as input to ROIPOLY and just extract the information that is included in the edges lines? I have one question about the ROIPOLY:

I have an image with stripes, I use the “edge” command for finding the edges, is it possible to use the output of edge as input to ROIPOLY and just extract the information that is included in the edges lines?

]]> By: Steve http://blogs.mathworks.com/steve/2006/12/05/poly2mask-and-roipoly-part-1/#comment-10588 Steve Tue, 25 Sep 2007 13:18:23 +0000 http://blogs.mathworks.com/steve/?p=99#comment-10588 Sridharan—Use your polygon vertices to create a patch object that is superimposed over the image. Then you can adjust the transparency of the patch. Sridharan—Use your polygon vertices to create a patch object that is superimposed over the image. Then you can adjust the transparency of the patch.

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