An image processing apparatus performing a rasterization process with a scanline method interprets a received printing job and generates objects. In an objecting combining process, the reception objects are spooled, the generated objects are interpreted, and it is subsequently determined whether or not the objects are vertically long objects to be combined into a single object. If the objects are determined to be the vertically long objects, an object combining process is performed to render the vertically long objects respectively in a longitudinal direction to form the single object.