Impulse response of the system image processing
You imagine several representations. A first one is the standard image representation: flat in the $(x_1,x_2)$ and a color scale  of the intensity value (left plot). A second one is a 3D vision as a topographical or elevation map, with homogeneous color (middle plot). The visualization might be a bit more complicated. A third one combine the two preceding aspects (right plot). The latter helps understanding some mathematical morphology operators (like the watershed).

L = membrane(1,100);
f = figure;
ax = axes;
subplot(1,3,1)
imagesc(L);
subplot(1,3,3)
s = surface(L);
s.EdgeColor = 'none';
view(3);axis tight
subplot(1,3,2)
s = surface(L);
s.EdgeColor = 'none';
s.FaceColor = 'b';
view(3);axis tight