  We present a robust method for measuring the diffusion coefficients of warm
atoms in buffer gases. Using optical pumping, we manipulate the atomic spin in
a thin cylinder inside the cell. Then we observe the spatial spread of
optically pumped atoms in time using a camera, which allows us to determine the
diffusion coefficient. As an example, we demonstrate measurements of diffusion
coefficients of rubidium in neon, krypton and xenon acting as buffer gases. We
have determined the normalized (273 K, 760 Torr) diffusion coefficients to be
0.18$\pm$0.03 cm$^2$/s for neon, 0.07$\pm$0.01 cm$^2$/s for krypton, and
0.052$\pm$0.006 cm$^2$/s for xenon.
