1. An image processing apparatus comprising: a region segmentation unit configured to divide an input image into a plurality of regions, wherein the input image is not outline data; a selection unit configured to determine whether each of the regions is suitable for thinning processing and configured to select outlining processing to be executed based on a result of the determination; an outlining unit configured to generate outline data for each of the regions using the outlining processing selected by the selection unit; and an outputting unit configured to output outline data generated by the outlining unit, wherein the outlining processing selected by the selection unit includes first outlining processing of generating outline data based on a contour of an object included in each of the regions and second outlining processing of generating outline data based on the object which is included in each of the regions and which has been subjected to the thinning processing, and wherein the selection unit determines whether regions having a drawing attribute among the regions are suitable for thinning processing for individual regions and when the determination is affirmative, the second outlining processing is selected and when the determination is negative, the first outlining processing is selected.