1. An image processing apparatus comprising: a region analysis unit configured to generate a quantized region by integrating regions that are included in an input multivalued image and have similar colors and to determine an attribute of a connected component included in the generated quantized region; and a character portion filling unit configured to determine a color used for filling a connected component that has been determined by the region analysis unit to have a character attribute and to execute processing for filling the connected component that has been determined to have the character attribute, wherein the character portion filling unit is configured to change a method for determining the color used for filling based on the quantized region existing adjacent to the connected component determined to have the character attribute.