Image forming method for increasing resolution in reverse mode

An image forming apparatus comprising: a resolution conversion unit configured to convert the resolution of a pixel provided by input image data; a gradation conversion unit configured to perform matrix conversion onto the pixel; and a writing unit configured to perform a write operation, wherein, in the normal mode, the gradation conversion unit performs matrix conversion onto the pixel with reference to the gradation conversion table for the normal mode, and the writing unit performs the write operation of the pixel in a normal order that is the order image data being input into the image forming apparatus, and in the reverse mode, the gradation conversion unit performs matrix conversion onto the pixel with reference to the gradation conversion table for the reverse mode, and the writing unit performs the write operation of the pixel in a reverse order opposite to the normal order.