Conversion of latent electrostatic images on a liquid surface into visible images is analyzed theoretically. The instability growth rate is studied as a function of the spatial frequency and the conversion parameters by treating the diffusion and ohmic surface currents. The growth rate reaches a maximum at a certain spatial frequency. The relative importance of the diffusion and ohmic currents in forming the latent electrostatic image is elucidated, and it is shown that the liquid surfaces used to record optical data may be assumed to be at a constant potential during latent image formation.