[Aim] To generate a high quality image in which a periodic pattern, such as a folding distortion component, which is caused by a spatial frequency component of a grid image, is suppressed while a subject component is maintained in an image signal generation method and apparatus that generates an image signal by reading a storable phosphor sheet on which a radiographic image including the grid image is recorded.[Solution Means] A first processed signal (Sh) is extracted by extracting an input spatial frequency component corresponding to a periodic pattern by performing filtering processing on an image signal. A subject component (Sc) of an image included in the extracted first processed signal is extracted from the first processed signal. A second processed signal (Sp) is extracted by subtracting the first processed signal (Sh) from the image signal (Sd) and also by adding the extracted subject component (Sc) to the image signal (Sd).
