getring.m

%Function to cut the iris ring from the localised eye image. Ci and Cp are
% 2 element vectors denoting the centres of the iris and the pupil respectively
% rl is the radius of the pupil (lower radius) rh is the iris radius (higher radius).
%INPUT:
%I:Image to be processed
%Ci(x,y) and Cp(x,y) :Centre coordinates of the iris and the pupil
%Coordinate system :
%origin of coordinates is at the top left corner
%positive x axis points vertically down
%and positive y axis horizontally and to the right
%n:number of sides
%r:radius of circumcircle
%
%OUTPUT:
%O:Image with circle
function [O]=getring(I,Cp,Ci,rl,rh,n)
if nargin==5
    n=600;
end
theta=(pi/2)/n;
% angle subtended at the centre by the sides

rows=size(I,1);
cols=size(I,2);

%Get the left 'wing'

angle=7*pi/4:theta:9*pi/4;      %3*pi/4:theta:5*pi/4 for right 'wing' Measured in A.C. Direction


%extract iris ring.
for r=0:rh
    x=Ci(2)-r*sin(angle);%the negative sign occurs because of the particular choice of coordinate system
    y=Ci(1)+r*cos(angle);
    if any(x>=rows)|any(y>=cols)|any(x<=1)|any(y<=1)%if circle is out of bounds return image
        ringi=I;
        return
    end
    for i=1:n
        ringi(round(x(i)),round(y(i)))=I(round(x(i)),round(y(i)));
    end
end

ringp=ringi;

%make the pupil ring black
for r=0:rl
    x=Cp(2)-r*sin(angle);%the negative sign occurs because of the particular choice of coordinate system
    y=Cp(1)+r*cos(angle);
    if any(x>=rows)|any(y>=cols)|any(x<=1)|any(y<=1)%if circle is out of bounds return image itself
        ringp=ringi;
        return
    end
    for i=1:n
        ringp(round(x(i)),round(y(i)))=0;
    end
end

%AND both the rings and put it into O
for i=1:size(ringi,1)
    for j=1:size(ringi,2)
        if ringp(i,j) ==0
            if ringi(i,j) ~=0
                O(i,j)=0;
            else
            end
        else
            O(i,j)=ringp(i,j);
        end
    end
end


%Repeat the above for getting the left 'wing'
angle=3*pi/4:theta:5*pi/4;
%extract iris ring.
for r=0:rh
    x=Ci(2)-r*sin(angle);%the negative sign occurs because of the particular choice of coordinate system
    y=Ci(1)+r*cos(angle);
    if any(x>=rows)|any(y>=cols)|any(x<=1)|any(y<=1)%if circle is out of bounds return image
        ringi1=I;
        return
    end
    for i=1:n
        ringi1(round(x(i)),round(y(i)))=I(round(x(i)),round(y(i)));
    end
end

ringp1=ringi1;

%make the pupil ring black
for r=0:rl
    x=Cp(2)-r*sin(angle);%the negative sign occurs because of the particular choice of coordinate system
    y=Cp(1)+r*cos(angle);
    if any(x>=rows)|any(y>=cols)|any(x<=1)|any(y<=1)%if circle is out of bounds return image itself
        ringp1=ringi1;
        return
    end
    for i=1:n
        ringp1(round(x(i)),round(y(i)))=0;
    end
end

%AND both the rings and put it into O
for i=1:size(ringi1,1)
    for j=1:size(ringi1,2)
        if ringp1(i,j) ==0
            if ringi1(i,j) ~=0
                O(i,j)=0;
            else
            end
        else
            O(i,j)=ringp1(i,j);
        end
    end
end

end