1. An image processing apparatus comprising: A first division unit configured to divide an input image into a plurality of tiles of a predetermined size; a second division unit configured to divide a tile of interest included in the plurality of tiles into a plurality of sub-tiles; an edge extraction unit configured to extract edges of each sub-tile; a determination unit configured to determine an attribute each of the sub-tiles based on a continuity, distribution, and a number of the extracted edges; a first decision unit configured to decide a total number of representative colors of each of the sub-tiles based on the determined attribute of each of the sub-tiles; a resolution conversion unit configured to convert the tile of interest into a lower-resolution tile; a generation unit configured to generate a histogram for pixels in the lower-resolution tile, the histogram indicating a relationship between each color of pixels and the number of pixels of that color in the lower-resolution tile; a second decision unit configured to decide the representative colors of each of the sub-tiles based on the generated histogram and the decided total number of representative colors in the sub-tile; and a conversion unit configured to convert the tile of interest into a tile in which colors of pixels comprise the decided representative colors.