An image forming apparatus and a printing control terminal apparatus include an input unit to receive printing data, a rendering unit to transform the printing data into bitmap data, an image processor to determine whether the bitmap data includes a transparency pattern and if it is determined that the bitmap data includes the transparency pattern, perform smoothing processing with respect to the bitmap data; and an output unit to output the bitmap data processed by the image processor. Accordingly, an image quality of printing data including a transparency pattern can be improved. In addition, an image forming method includes receiving image data including a plurality of pixels, determining whether an area of pixels is a patterned area including a pattern, determining the patterned area is transparent when the pattern of the patterned area matches a pre-stored pattern, performing a smoothing process on the patterned area, and printing the image data after performing the smoothing.