Spatially-modulated snapshot imaging polarimeter can encode four Stokes parameters (S0, S1, S2 and S3) into a single interferogram and allow the instantaneous measurement of polarization from a single snapshot.However, the reconstructed polarization information contains aliasing signal, and the reconstructed intensity images suffer low spatial resolution because of the crosstalk between high frequency components of the image and frequency domain filtering for the polarization channels.In this paper, we propose an image superposition and subtraction method to mitigate the aliasing problem and to recover the image resolution.The two interferograms acquired from two snapshot measurements are superposed to obtain the intensity image (S0 component) of an object without the polarization components because the phases of the polarization components in the two interferograms are opposite.In comparison with the intensity of each of the original interferograms, the intensity of S0 component increases twice and its spatial resolution improves up to a maximum value offered by the instrument.Then a subtraction between the two interferograms is performed to derive the pure interference fringes while the intensity image vanishes.The intensity of the pure interference fringes also increases twice compared with that of each original interferogram because phases of the interference terms in original interferograms are opposite.The polarization images (S1, S2 and S3 components) can be reconstructed from the pure interference fringes, and do not include crosstalk signals between the high frequency components of the intensity image. The theoretical basis of the method is presented through a detailed analysis.Its feasibility is verified by both computer simulation and experiment.The simulation results show that the otherness and the structural similarity index between the input and reconstructed intensity images is zero and 1, respectively, indicating a perfect reconstruction of S0.The results also make it clear that the pure interference fringes do not include any component of intensity image, and thus the reconstructed polarization information does not contain any crosstalk signals.Moreover, the experimental results are in accordance with the theoretical expectation and the computer simulations.This research provides a novel means for spatially-modulated snapshot imaging polarization technology to obtain full-resolution object images and high-quality reconstructed polarization information.