In this article we discuss the line edge roughness of positive chemically amplified resists exposed on the SCALPEL exposure system in terms of the image formation process. The image formation process for a SCALPEL exposure on a positive chemically amplified resist has been simulated using discrete models from exposure through development. Key parameters have been identified that enable image formation simulations without the need of detailed molecular models. Molecular models are needed though to obtain several of these parameters. Surface and line edge roughness, as measured by scanning electron microscopy and atomic force microscopy, have been simulated and compared to experimental results. Results are consistent with a "percolation network formation for diffusion-reaction development" model for chemically amplified resists.