Accelarating image processing algorithm on GPU

Hi, I want to accelerate my algorithm because I need to run it on hundreds of images,so I tried to use unvectorized GPU code, running the same code on GPU, I have nvidia Geforce GT 650M with 2 GB on my PC, however it was very slow than the CPU version. After searching I am convinced to pass to vectorized GPU code using batch process (pagefun, bsxfun), I tried so much to solve this problem without a solution. can some one help me about this code:

Q=100;
       for i=3:n-2
        for j=3:m-2 
         A(i,j)=0;
            for c=1:Q
                        if B(i,j,c)~=0
                        A(i,j)=A(i,j)+(-(B(i,j,c)).*log(B(i,j,c)));
                        end
            end
        end
       end

Another question Why Matlab uses just 20% of my CPU? How I can take benefits of my CPU to accelerate my processing

Is Matlab a single threaded app?

Thanks in advance