1. An image processing apparatus comprising: one or more processors; and at least one memory storing instructions which, when executed by the one or more processors, cause the image processing apparatus to: specify, based on a first instruction from a user, a subject of interest within a parallax image obtained by performing image capturing from a plurality of different viewpoints; notify a user of a capability to refocus on the specified subject of interest in an image to be generated by performing image combination processing using the parallax image; and if a second subject of interest within a parallax image obtained by performing image capturing from a plurality of different viewpoints is specified based on a second instruction from the user after the subject of interest is specified by the user, simultaneously notify the user of a capability to refocus on the specified subject of interest and a capability to refocus on the second specified subject of interest in the image to be generated by performing image combination processing using the parallax image.