An image forming apparatus includes: an image data generation unit configured to write at least one of image data for print output and image data for confirmation display based on intermediate data on an object included in print data and store the image data in a buffer; an intermediate data generation unit configured to generate the intermediate data based on comparing a resolution or gradation of a target object with an output resolution or output gradation that is defined based on a size of the buffer, adjusting a resolution to either the resolution of the target object or the output resolution and adjusting gradation to either the gradation of the target object or the output gradation; a printing unit configured to print using the image data for print output; and a display unit configured to display a print preview.