1. An imaging system that applies noise reduction processing to image signals captured in time series via an image pickup block, comprising: a first extraction section that extracts a local region that includes a pixel of interest from an image signal to be processed; a second extraction section that extracts, from another image signal captured at a different time from the image signal to be processed, a local region located at almost the same position as the local region extracted by the first extraction section; a first noise reduction section that applies a first noise reduction process to the local region extracted by the first extraction section, by using the local region extracted by the second extraction section; a noise estimation section that estimates an amount of noise included in the pixel of interest based on the local region that has been subjected to the first noise reduction process in the first noise reduction section; a residual image detection section that detects a residual image component included in the local region that has been subjected to the first noise reduction process and that is output from the first noise reduction section, based on the amount of noise estimated by the noise estimation section; and a second noise reduction section that performs a second noise reduction process on the pixel of interest based on the residual image component detected by the residual image detection section.