[en] The hybrid unsteady-flow simulation, which has been developed to assimilate the Navier–Stokes simulation into a time-resolved particle image velocimetry (PIV) field by synchronizing the frame rate with the direct-numerical-simulation time step, can simultaneously produce an unsteady pressure field. The hybrid process typically introduces a ‘patch function’, which transplants the PIV fields inside the camera window into a larger computational domain. This study evaluates the pressure fields produced by the hybrid simulation inside the patch function (i.e. estimation) and outside of it (i.e. compensation). We take time-resolved planar PIV data of a separated flow past the NACA 0012 airfoil at an angle of attack of 30° in a water tunnel as an example. First, an unsteady pressure field produced from the hybrid simulation is compared with other existing pressure-estimation methods in two dimensions over the entire domain of the camera window. The results of the two-dimensional (2D) hybrid simulation are found to agree best with those of the sequential-integration method with much lower noise levels in time and space. Next, the domain of the forcing is reduced by truncating the patch function in the hybrid simulation, and the pressure fields in the missing parts of the patch function are compared with those solved using the full patch function. When at least the regions in which 2D vortical structures collapse are included in the patch function downstream, the rest of the pressure fields can be compensated for relatively well. In contrast, the forces acting on the airfoil can be estimated accurately only if it is enclosed by the camera window. (paper)