How to store the perimeter pixels of a semi circle in an array that is drawn over an binary image?

I have a binary image and I want to draw a circle over this image so that it crosses all the active fingers. After that I only want to consider half of the circle(only going over the upper part of the image this will remove lower circle part i.e.the wrist part). Next want to store all the perimeter pixels to an array. How to do that ?

Answer 1

[KSSV]

I = imread('P1_G5_4.png') ;
imshow(I)
hold on

[y,x] = find(I==0) ;
% Centre of circle 
C = [mean(x) mean(y)] ;
% GEt radius of circle 
R = max(sqrt((C(1)-x).^2+(C(2)-y).^2)) ;
th = linspace(0,2*pi) ;

xc = C(1)+R*cos(th) ;
yc = C(2)+R*sin(th) ;

plot(xc,yc,'r') ;

[Zara Khan]

This is not applicable when complementing the image. Moreover I asked about the semi circle which will cross all the fingers. And want to store those semi circle perimeter pixels values to an array .