1. An image forming apparatus that performs a rasterization of a thin graphic object, the image forming apparatus comprising: a controller including a processor and a memory storing instructions executed by the processor, wherein the controller acts as units comprising: (a) a correction unit configured to control, for the rasterization, whether or not to perform widening processing of widening a width of the thin graphic object, according to whether a setting of widening the thin graphic object is set to be enabled or disabled; and (b) a control unit configured to control, for the rasterization, whether to perform a first conversion complying with a first conversion rule on the thin graphic object for which the widening processing has been controlled to be performed by the correction unit or to perform a second conversion complying with a second conversion rule on the thin graphic object, in accordance with whether the setting of widening the thin graphic object is set to be enabled or disabled, wherein the rasterization corresponding to the first conversion rule fills or does not fill a pixel with color depending on a position of a boundary of the thin graphic object in the pixel, and wherein the rasterization corresponding to the second conversion rule fills a pixel with color in a case where the position of the boundary of the thin graphic object exists in the pixel.