Image forming apparatus capable of performing accurate gradation correction

An image forming apparatus configured to form a toner image on an image bearing member according to image data, comprising:

• an image forming unit configured to form a gradation pattern on the image bearing member;
• a density detection unit configured to detect density of the gradation pattern formed by said image forming unit;
• a first calculation unit configured to calculate a first correction value for correcting gradation of the image data based on density of the gradation pattern, detected by said density detection unit;
• a second calculation unit configured to estimate a condition of toner with which said image forming unit forms a toner image on the image bearing member, and calculate a second correction value for correcting the gradation of the image data based on the estimated condition of toner;
• and
• a correction unit configured to correct density in a low density range of the toner image based on the first correction value, and correct density in a high density range of the toner image based on the second correction value.