Polarized neutron radiography allows the direct and real-space visualization of magnetic field distribution by detecting the polarization change in the transmitted beam. Two approaches to magnetic field quantification by means of polarized neutron images are studied. They are energy-selective method and spin-echo method. Both approaches need no corrections of parameters, such as polarization efficiency, and can quantify magnetic field integral without periodic uncertainty. The quantification ability, applicability and feasibility of two approaches at research reactor neutron source are verified by numerical simulation with key parameters such as monochromator resolution and polarization efficiency. The results will be helpful to process image data and designing instruments.