A binary ink developer (BID) assembly for a liquid electrophotography (LEP) printing device can include a developer roller having an electrically insulating exterior coating that receives ink from an ink supply and transfers the received ink to a photoconductive imaging cylinder in accordance with an electrostatic image on the imaging cylinder. A charge-specified boundary condition can exist at the boundary between the exterior coating and the ink. Electrically conductive ink may not be transferred to the imaging cylinder at background portions of the electrostatic image.