Image processing device, imaging device, image processing method, and image processing program

An image processing device comprising:

• a generation unit that generates a first achromatic image based on a first image signal which is output from an imaging element including first and second pixel groups on which an object image that passes through first and second regions of an imaging lens and is pupil-divided is formed and which output the first image signal and a second image signal, respectively, and a third pixel group on which the object image that passes through the imaging lens and is formed, without being pupil-divided, and which outputs a third image signal, a second achromatic image based on the second image signal that is output from the imaging element, and a third chromatic image based on the third image signal that is output from the imaging element;
• a display unit that displays an image;
• and
• a control unit that performs control such that the display unit displays a chromatic image, which is obtained by giving a chromatic color included in the third image at a position corresponding to the first pixel to a position of the first pixel in the first image and giving a chromatic color included in the third image at a position corresponding to the second pixel to a position of the second pixel in the second image and is used to check a focus, in a case in which a result of comparison between an output value of the first image signal output from a first pixel included in the first pixel group and an output value of the second image signal output from a second pixel corresponding to the first pixel and included in the second pixel group is less than a threshold value and performs control such that the display unit displays an achromatic image, which is obtained on the basis of the first image at a position corresponding to the first pixel and the second image at a position corresponding to the second pixel and is used to check a focus, in a case in which the comparison result is equal to or greater than the threshold value.