The division of focal plane polarimeters is fabricated out of nanowire polarization filters attached to the surface of a focal plane array. Due to limitations in the manufacturing process, the transmissivity of each nanowire polarization filter is different, resulting in a combination of inhomogeneities in transmittance and detector response, and which also yields the problem of polarization imaging uniformity, a more complicated method than traditional intensity imaging. This study presents a brand new nonuniformity correction method for solving the correction inaccuracies in the traditional method. The method corrected the polarization filter transmittance with detector gain based on a new method for calculating the degree of linear polarization (DoLP). This paper includes the theoretical derivation, experimental testing, and numerical simulation. In this simulation environment, the DoLP value was accurately calculated.