Abstract: An is an image processing apparatus including: an image memory section to store an image data obtained by reading an image of an original manuscript; an external light memory section to store a data of external light entering to a stage for the original manuscript and to form histograms of each color based on the data of external light; a judging section to calculate an external light level from a higher luminance by each color out of luminance values of a foot of a peak including a maximum frequency value measured on the histograms; and an area detecting section to determine a non-image area erase threshold based on the external light level, so as to detect an image area and to erase a non-image area.