graythresh

>> D=cat(3, M, T, S);
>> size(D)

ans =

        1080        1920           9

>> [m,n,q]=size(M)

m =

        1080


n =

        1920


q =

     3

>> E = reshape(D,[],size(D,3));
>> size(E)

ans =

     2073600           9

>> [~,~,F] = unique(E,'rows');
>> result=reshape(F, [m,n]);
>> image(result)

>> size(result)

ans =

        1080        1920

>> level=graythresh(result)

level =

     0