entropy_and_jointentropy.m

%????????

%??????
A=floor(rand(8,8).*255);

[M,N]=size(A);
temp=zeros(1,256);

%????????[0,255]????
for m=1:M;
    for n=1:N;
        if A(m,n)==0;
           i=1;
        else
           i=A(m,n);
        end
        temp(i)=temp(i)+1;
    end
end
temp=temp./(M*N);

%????????
result=0;
for i=1:length(temp)
    if temp(i)==0;
        result=result;
    else
        result=result-temp(i)*log2(temp(i));
    end
end
result

%?????

%??????
A=floor(rand(18,18).*255);
B=floor(rand(18,18).*255);

[M,N]=size(A);
temp=zeros(256,256);

%?????????????
for m=1:M;
    for n=1:N;
        if A(m,n)==0;
           i=1;
        else
           i=A(m,n);
        end
        if B(m,n)==0;
           j=1;
        else
           j=B(m,n);
        end
        temp(i,j)=temp(i,j)+1;
    end
end
temp=temp./(M*N);

%????????
result=0;
for i=1:size(temp,1)
    for j=1:size(temp,2)
        if temp(i,j)==0;
            result=result;
        else
            result=result-temp(i,j)*log2(temp(i,j));
        end
    end
end

result