1. A scatter component estimating method for estimating scatter components of radiation from data collected in a radiation tomography apparatus, the method comprising: a reconstruction processing step of performing reconstruction processing to event data obtained by detecting the radiation to capture a reconstruction image; a projecting step of projecting the reconstruction image obtained in the reconstruction processing to capture a projection image; and a scatter component extracting step of extracting low-frequency components from the projection image obtained in the projecting step to obtain scatter components.