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Fast Parsing of Line Segments in a BW Mask

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Fast Parsing of Line Segments in a BW Mask

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Quickly determines the portions of a line/curve that are inside and outside of a binary mask.

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Description

LINEINMASK determines portions of the line in and out of a mask

  [inX inY] = LINEINMASK(XS,YS,BW,XV,YV) computes a the segments of the
      line specified by verticies XV and YV that are inside the mask BW.
      Points XS and YS specify the limits (or pixel values) of the
      coordinates of the matrix BW.

  [inX inY] = LINEINMASK(BW,XV,YV) assumes XS=1:N and YS=1:M where
      [M,N]=SIZE(BW).

  [inX inY] = LINEINMASK(...,METHOD) Uses the given method to create the
      polygon from the mask.
          Inner | Outer | {Exact}

  [inX inY outX outY] = LINEINMASK(...) outputs the segments of the line
      both in and out of the mask.

  Example:
      I = imread('rice.png');
      level = graythresh(I);
      bw = im2bw(I,level);
      bw = bwareaopen(bw, 50);
      [a b] = size(bw);
      xv = b*rand(10,1);
      yv = a*rand(10,1);
      [inX inY outX outY] = lineinmask(bw,xv,yv,'exact');
      figure
      imagesc(bw)
      colormap(bone)
      hold on;
      h1 = plot(inX,inY,'r');
      h2 = plot(outX,outY,'b');
      legend([h1 h2],'Inside Mask','Outside Mask');

By J Sullivan, August 2011

Acknowledgements

Curve Intersections inspired this file.

MATLAB release MATLAB 7.12 (R2011a)
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