# How to convert a closed curve into a binary mask

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Maura E. Monville on 9 Jul 2019
Answered: Rob Campbell on 30 May 2021
I have a set of 2D closed curves represented by their X and Y ordered coordinates in a text file.
I have attached one of the curves as an example.
My goal is to convert the enclosed area into a binary image.
Builtin dunction "poly2mask" generates a completely black square whereas I would like the region inside the closed curve to be black
and the region outside the curve to be white.
Thank you in advance for any suggestion and help.
Regards,
Maura

KSSV on 9 Jul 2019
Edited: KSSV on 9 Jul 2019
data = importdata('data.txt') ;
x = data(:,1) ;
y = data(:,2) ;
N = 500 ;
xi = linspace(min(x),max(x),N) ;
yi = linspace(min(y),max(y),N) ;
[X,Y] = meshgrid(xi,yi) ;
idx = inpolygon(X,Y,x,y) ;
Z = ones(size(X)) ;
Z(idx) = 0 ;
imshow(Z)

Rob Campbell on 30 May 2021
I think you want the built-in function poly2mask

R2019a

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