An image processing apparatus comprising: a degree-of-degradation detector configured to detect, for each area including a pixel of interest of image data formed of pixel data including a plurality of color channels, a degree of degradation of an image indicating visibility of the area from a strength of the plurality of color channels; a degree-of-degradation estimation unit configured to estimate a distribution of the degree of degradation in the image; a correction system selector configured to select either a first gradation correction system or a second gradation correction system in accordance with the distribution of the degree of degradation; and a gradation correction unit configured to perform gradation correction of the image data based on either the selected first or second gradation correction system (110, 111), characterized in that the first gradation correction system is configured to perform adaptive gradation correction based on the degree of degradation of each area of the image data, and the second gradation correction system is configured to perform uniform gradation correction for entirety of the image, the correction system selector is configured to select the first gradation correction system if a range of a distribution of the degree of degradation is equal to or greater than a predetermined value, and select the second gradation correction system if the range of the distribution of the degree of degradation is less than the predetermined value, the degree-of-degradation estimation unit includes a degree-of-degradation histogram generator configured to generate a histogram of the degree of degradation, and the range distribution of the degree of degradation is a range of a distribution of the histogram. a degree-of-degradation detector configured to detect, for each area including a pixel of interest of image data formed of pixel data including a plurality of color channels, a degree of degradation of an image indicating visibility of the area from a strength of the plurality of color channels; a degree-of-degradation estimation unit configured to estimate a distribution of the degree of degradation in the image; a correction system selector configured to select either a first gradation correction system or a second gradation correction system in accordance with the distribution of the degree of degradation; and a gradation correction unit configured to perform gradation correction of the image data based on either the selected first or second gradation correction system (110, 111), characterized in that the first gradation correction system is configured to perform adaptive gradation correction based on the degree of degradation of each area of the image data, and the second gradation correction system is configured to perform uniform gradation correction for entirety of the image, the correction system selector is configured to select the first gradation correction system if a range of a distribution of the degree of degradation is equal to or greater than a predetermined value, and select the second gradation correction system if the range of the distribution of the degree of degradation is less than the predetermined value, the degree-of-degradation estimation unit includes a degree-of-degradation histogram generator configured to generate a histogram of the degree of degradation, and the range distribution of the degree of degradation is a range of a distribution of the histogram.