An image processing apparatus which applies processing to image data encoded by an encoding method that encodes image data by holding, for each block including the predetermined number of pixels, color information and color layout information included in that block, the apparatus comprises: a detection unit configured to detect a region including successive pixels having identical color information, the number of pixels of which is larger than a predetermined value, using the color information and the color layout information in the encoded image data; and a conversion unit configured to convert color information of a pixel corresponding to a predetermined position in the region, and layout information of a block including the pixel at the predetermined position, of a plurality of blocks including the region detected by the detection unit.