%%  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

