%% chi square test for image data
function [X_R X_G X_B]=chisquare(C)
B1=uint8(C); % C=cipher image
v=0;
a1=imhist(B1(:,:,1));
a2=imhist(B1(:,:,2));
a3=imhist(B1(:,:,3));
for i=1:256
z1=((a1(i)-256).^2)/256;
v=v+z1;
end
z2=((a2-256).^2)/256;
z3=((a3-256).^2)/256;
X_R=v;
X_G=sum(z2);
X_B=sum(z3);
end