1. An image processing apparatus comprising: a region analysis unit configured to generate a plurality of quantized regions by integrating regions that are included in an input multivalued image and have similar colors and to determine connected components included in each of the generated quantized regions, and to obtain region information of the connected components, the region information including attribute information, positional information, color information and surrounding relationship information of the connected components; and a character portion filling unit configured to acquire the quantized regions adjacent to a connected component having a character attribute based on the region information, and to determine a color used for filling the connected component having the character attribute based on a count number, the attribute information and the color information of the acquired quantized regions, and to execute processing for filling the connected component having the character attribute based on the determined color, wherein the character portion filling unit is configured to change, based on the count number and the attribute information of the acquired quantized regions, a method for determining the color used for filling the connected component having the character attribute.