Image forming apparatus and method for forming images for carrying out development using a light toner and a dark toner having substantially the same hue

An image forming apparatus configured to form an image corresponding to an input signal which is less than or equal to a predetermined value using a light toner, and to form an image corresponding to an input signal which is more than the predetermined value using the light toner and a dark toner, the light toner and the dark toner having a same hue and a density of the dark toner being higher than that of the light toner, the image forming apparatus comprising:

• an image forming unit configured to form an image on a recording material using the light toner or the dark toner;
• a control unit configured to cause the image forming unit to form a pattern having a gradation on the recording material;
• a reading unit configured to read the pattern on the recording material;
• a detecting unit configured to detect a density of the pattern based on the result of the reading unit;
• a determining unit configured to determine whether a density difference between a reference density and a density of an image only with the light toner based on an input signal corresponding to the predetermined value exists;
• a correcting unit configured to correct a slope of a characteristic of image density detected by the detection, so that the density difference equals zero, the correcting unit corrects the slope on an input signal to a zero level as a base point;
• and
• an updating unit configured to update a gradation correcting date to correct a gradation characteristic of an image formed only with the light toner based on the result of correction by the correcting unit.