1. An image forming apparatus comprising: a first determination unit configured to determine a type of an object contained in input data; a second determination unit configured to determine, in a case where the type of the object contained in the input data is determined by said first determination unit to be a text type or a graphic type, whether or not an amount of colorant of a specified color exceeds a first colorant amount when the specified color contained in the input data has been rasterized; a conversion unit configured to convert, when it is determined by said second determination unit that the amount of colorant of the specified color exceeds the first colorant amount, the specified color into a color with an amount of colorant that falls within the first colorant amount; a rasterizing unit configured to rasterize the text type or graphic type object contained in the input data with a color converted or not converted by said conversion unit, and rasterize an image type object contained in the input data without determination by said second determination unit and conversion by said conversion unit; and a processing unit configured to set, i) when the type of the object rasterized by said rasterizing unit is the graphic type and a fine line correction mode is not selected based on a user operation, an amount of colorant of the graphic type object to the first colorant amount, ii) when the type of the object rasterized by said rasterizing unit is the graphic type and a fine line correction mode is selected based on a user operation, an amount of colorant of the graphic type object to the second colorant amount which is smaller than the first colorant amount, and iii) when the type of the object rasterized by said rasterizing unit is the text or image type, an amount of colorant of the text or image type object to the first colorant amount independent of whether or not the fine line correction mode is selected based on the user operation.