Fast Parsing of Line Segments in a BW Mask

Quickly determines the portions of a line/curve that are inside and outside of a binary mask.
Updated 12 Sep 2011

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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

[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.

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');
hold on;
h1 = plot(inX,inY,'r');
h2 = plot(outX,outY,'b');
legend([h1 h2],'Inside Mask','Outside Mask');

By J Sullivan, August 2011

Cite As

Jonathan Sullivan (2024). Fast Parsing of Line Segments in a BW Mask (, MATLAB Central File Exchange. Retrieved .

MATLAB Release Compatibility
Created with R2011a
Compatible with any release
Platform Compatibility
Windows macOS Linux

Inspired by: Curve intersections

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