A method of selectively exposing a liquid photopolymer printing blank to actinic radiation to create a relief image printing plate and a liquid platemaking exposure system. The method includes: (1) positioning a programmable screen programmed with an image file of a desired image between the top glass and an upper source of actinic radiation; (2) exposing the layer of liquid photopolymer to actinic radiation from the upper source of actinic radiation through the programmable screen to crosslink and cure at least a portion of the liquid photopolymer adjacent to the backing sheet and create a floor layer therein; and (3) imagewise exposing the layer of liquid photopolymer to actinic radiation from a lower source of actinic radiation through a negative of the relief image to crosslink and cure selective portions of the liquid photopolymer on the floor layer and create the relief image therein.