normal distribution in image data(matrix)

i want to plot the distribution curve for an image data. suppose im(r,c)=[1 2 3 4 ; 2 3 4 5 ; 3 4 5 6; 4 5 6 7]

is a matrix containing the values given above along the axis r,c. I can calculate the mean vector,u=[ur;uc] and variance matrix; now i have problems in plotting the pdf using the calculated mean and variance,var. pdf is given by f(x) f(x)=1/sqrt(((2*pi)^k)*det(var)) exp(-0.5(x-u)*inv(var)*(x-u)');

the above is a general pdf equation for x. in my case x is the matrix im(r,c). i can calculate the mean and variance matrix. but i am stuck for about 15 days with the coding for pdf how do i incorporate the 2D matrix

any comments or suggestions will be helpful