∫Found out myself:
A = sgI(:,:,1);
B = scI(:,:,2);
C = scI(:,:,3);
[m,n,l] = size(A);
[m1,n1,l1] = size(B);
[m2,n2,l2] = size(C);
ntscIm(1:m,1:n,1) = A;
ntscIm(1:m1,1:n1,2) = B;
ntscIm(1:m2,1:n2,3) = C;
is the correct solution. and it works!!!! :))))