An image processing apparatus that inputs an image, detects a pixel value of each pixel of an input image and obtain at least one of a maximum value, a minimum value, and an average value of pixel values for each of predetermined sections of the input image, generates a first image indicating a frequency of pixel values of the input image, where a position of a pixel and a pixel value are associated, generates a second image in which additional information including at least one of the maximum value, the minimum value, and the average value is superimposed on the first image, and superimposes the second image on the input image and display the result.