1. An image processing apparatus comprising: an area dividing part configured to divide an input image produced by an image pickup system into plural provisional areas, to obtain in each provisional area an evaluation value by using a response function of the image pickup system, and to determine whether or not a difference between the evaluation values of two provisional areas adjacent to each other is not less than a threshold to set the provisional areas whose obtained evaluation values are mutually different as divided image areas; and a processing part configured to perform image processing on the divided image areas by using response functions different for the respective divided image areas to produce an output image whose definition is higher than that of the input image, wherein area dividing part is configured to repeatedly divide the input image and determine whether or not the difference between the evaluation values of two provisional areas adjacent to each other is not less than a threshold until the input image is divided into provisional areas where the difference between the evaluation values is less than the threshold.