A probability-based model of halftone imaging, which was developed in previous work to describe the Yule–Nielsen effect, is shown in the current work to be easily modified to account for additional physical and optical effects in halftone imaging. In particular, the effects of ink spread and ink penetration on the optics of halftone imaging with an ink-jet printer is modeled. The modified probability model was found to fit the experimental data quite well. However, the model appears to overcompensate for the scattering associated with ink penetration into paper.