Provided are an image processing device, an imaging device, an image processing method, and an image processing program which can instantly switch display between a chromatic image indicating an in-focus state and an achromatic image indicating an out-of-focus state. A control unit performs control such that a chromatic split image, which is obtained by giving a chromatic color included in a normal image to an achromatic split image, is displayed in a case in which the result of comparison between an output value of a first image signal and an output value of a second image signal is less than a threshold value. In addition, the control unit performs control such that an achromatic split image, which is obtained based on a left eye image and a right eye image, is displayed in a case in which the comparison result is equal to or greater than the threshold value.