An image processing apparatus includes the following elements. An image data obtaining unit obtains image data. A sampling unit samples the image data. A statistic value determining unit determines a statistic value based on statistic information in a histogram with respect to a grayscale value of image data that is obtained by performing rough quantization and linear interpolation on the sampled image data. A correction-amount determining unit determines a correction amount to be used for image processing based on the statistic value. An image processing unit performs the image processing according to the correction amount.