A method is disclosed for generating an image of earth formations penetrated by a wellbore. The method includes generating an initial model of the earth formations using formation resistivity measured by a direct current signal. A response to the initial model of an instrument used to make the direct current resistivity measurements is calculated. The calculated response is compared to the measurements of resistivity. The model is adjusted, and the calculating and comparing are repeated until a difference between the calculated response and measurements reaches a minimum. The adjusted model is refined based on resistivity measurements made using an electromagnetic measuring instrument, and the refined model is constrained using acoustic velocity measurements.