An image processing apparatus obtains a black image captured in the light-shielded state, and applies a cyclic type filter to each line in a direction parallel to the streak in the black image, reducing random noise in the first direction. The image processing apparatus deletes, from a black image obtained by applying the cyclic type filter, lines in the second direction by the group delay of the cyclic type filter. Further, the image processing apparatus generates an image having a line count corresponding to the group delay by using a final line in the second direction in the image from which lines corresponding to the group delay have been deleted. The image processing apparatus adds the generated image to the image from which lines corresponding to the group delay have been deleted, and outputs the resultant image.