1. An image processing apparatus comprising: an arrangement unit configured to arrange a plurality of images according to regions which are set in each of rows and columns of an output formation, the output formation having a row number of rows and a column number of columns; and an identification unit configured to identify a number of one or more unfilled regions, among the regions of the output formation, the unfilled regions being regions in which no images are arranged when the plurality of images are arranged according to the regions by the arrangement unit; wherein the row number of rows and the column number of columns of the output formation are based at least in part on the number of unfilled regions identified by the identification unit.