An image processing apparatus includes a rendering unit, a reception unit, and a smoothing unit. The rendering unit executes rendering processing on page description language (PDL) data and generate bitmap data. The reception unit receives a setting of a rendering condition that is used in the rendering processing in order for the rendering unit to generate bitmap data in which a diagonal line, having a predetermined line width designated by the PDL data, is thicker than a horizontal line having the predetermined line width. The smoothing unit executes smoothing processing on the generated bitmap data. The smoothing unit executes smoothing processing of thickening the diagonal line within the bitmap data based on reception of the setting of the rendering condition by the reception unit, and the smoothing unit executes smoothing processing of thinning the diagonal line based on non-reception of the setting of the rendering condition by the reception unit.