A new method is developed to calculate the scattering of light at the surface of a photonic crystal. The problem is solved in terms of virtual surface-current distributions and the calculation takes full advantage of the infinite-space plane-wave expansion method for obtaining the photonic band structure. Working with surface currents makes the calculations less time-consuming by means of reduction of the dimensionality in the problem. The method is applied to a semi-infinite dielectric continuum and for semi-infinite two-dimensional photonic crystals of small and large dielectric contrast.