IMAGE PROCESSING APPARATUS, IMAGE PROCESSING METHOD AND COMPUTER-READABLE MEDIUM

An image processing apparatus which performs boundary line extraction for raster image data, comprises: a detection unit configured to detect a color region formed from a plurality of pixels having an 8-neighbor connection in the image data; a determination unit configured to determine whether the 8-neighbor connection in the color region detected by the detection unit is to be modified to a 4-neighbor connection, in accordance with a connection state of pixels connected by the 8-neighbor connection and pixels surrounding the pixels connected by the 8-neighbor connection; a modification unit configured to modify the 8-neighbor connection in the color region, a modification of which is determined by the determination unit, by converting a pixel value of a pixel neighboring the pixels connected by the 8-neighbor connection; and an extraction unit configured to extract a boundary line from image data modified by the modification unit.