Obtaining coordinate values within circular ROI

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Brian
Brian 2016-1-21
评论： Michael Werthmann 2019-2-28
Hello all,
I have a function that receives xlist (vector of row coordinates) and ylist (vector of column coordinates) as inputs. I would like create another function that allows users to just select a starting coordinate (x, y) and it will capture all coordinates within a circular region of radius r (predefined) in the format of xlist and ylist.
My image is always 512*512 (grayscale CT). How do I do this?
Thank you so much!

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回答（1 个）

KSSV
KSSV 2019-2-28
Check this demo example:
I = imread('cameraman.tif') ;
[ny,nx] = size(I) ;
C = input('Enter center of circle C(x,y), should be less then 256:','s') ;
R = input('Enter Radius of circle:','s') ;
%
C = str2num(C) ;
R = str2num(R) ;
%
th = linspace(0,2*pi) ;
xc = C(1)+R*cos(th) ;
yc = C(2)+R*sin(th) ;
[X,Y] = meshgrid(1:nx,1:ny) ;
idx = inpolygon(X(:),Y(:),xc,yc) ;
I(~idx) = 255 ;
imshow(I)

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