Results of EGS4 based calculations to study the spatial resolution of gas detectors are described. The calculations include radial distribution of electrons generated by photons of various energies penetrating into variable thickness of Ar and Xe gas layers. Given a desired spatial resolution, the maximum allowed thickness of gas layer for each energy level is determined. In order to obtain 0.1mm spatial resolution, the maximum thickness for the Ar gas is found to be 2mm for photon energies below 14keV while the optimum energy of photons for Xe gas with the same thickness is about 45keV. The results of calculations performed to compare the number of electrons generated by CsI coated micro-channel plate and the number of electrons generated by the Ar and Xe gas layers are described. The results show that the number of electrons generated by the gases is about 10 times higher than the one generated by CsI coated micro-channel plate. A few sample gray scale images generated by these calculations are included.