This study is concerned with the design of a Mueller imaging polarimeter for the visualization of spatially varying Mueller matrix fields. A simplified calibration procedure is advocated, where all the optical elements are calibrated simultaneously rather than independently as in the state of the art. This is shown to significantly reduce the bias inherent to sequential calibration methods. In addition, this procedure requires no reference sample, it allows calibration both in transmission or in reflection modes, and it relies on ready-to-use cameras. Put together, these novelties should help nonspecialists in optics in designing and calibrating a Mueller imaging polarimeter for applications such as material classification.