An image processing apparatus comprising: an image information acquisition unit (111, 258) configured to acquire an average brightness of image data and a cumulative frequency distribution of pixels related to a gradation of the image data; a conversion range determination unit (112, 259) configured to acquire a conversion threshold value from the average brightness based on a set relationship, and determine a gradation conversion range in which the gradation of the image data is to be converted based on the gradation at which a cumulative frequency corresponds to the conversion threshold value in the cumulative frequency distribution; and a gradation conversion unit (116, 262) configured to convert the gradation of the image data in the gradation conversion range so that the gradation of the image data is increased by making an output gradation value greater than an input gradation value and a difference between the output gradation value and the input gradation value equal to a gradation conversion amount at a center of the gradation conversion range, when the shine appearance is to be emphasized, and decreased by making the output gradation value less than the input gradation value and the difference between the output gradation value and the input gradation value equal to the gradation conversion amount at the center of the gradation conversion range, when the shine appearance is to be reduced, wherein slopes of the curved lines representing the relationships between the input gradation values and the respective output gradation values are set in a manner such that the slopes continuously change across the entire gradation areas without being discontinuously changed in the boundaries between the gradation conversion ranges and the other gradation ranges. an image information acquisition unit (111, 258) configured to acquire an average brightness of image data and a cumulative frequency distribution of pixels related to a gradation of the image data; a conversion range determination unit (112, 259) configured to acquire a conversion threshold value from the average brightness based on a set relationship, and determine a gradation conversion range in which the gradation of the image data is to be converted based on the gradation at which a cumulative frequency corresponds to the conversion threshold value in the cumulative frequency distribution; and a gradation conversion unit (116, 262) configured to convert the gradation of the image data in the gradation conversion range so that the gradation of the image data is increased by making an output gradation value greater than an input gradation value and a difference between the output gradation value and the input gradation value equal to a gradation conversion amount at a center of the gradation conversion range, when the shine appearance is to be emphasized, and decreased by making the output gradation value less than the input gradation value and the difference between the output gradation value and the input gradation value equal to the gradation conversion amount at the center of the gradation conversion range, when the shine appearance is to be reduced, wherein slopes of the curved lines representing the relationships between the input gradation values and the respective output gradation values are set in a manner such that the slopes continuously change across the entire gradation areas without being discontinuously changed in the boundaries between the gradation conversion ranges and the other gradation ranges.