US Patent 7466464 Image forming apparatus and image forming method

A gradation pattern is printed, the gradation pattern is corrected with a gamma correction table TO based on a result in which the printed gradation pattern is read, the corrected gradation pattern is printed on a photosensitive drum or the like, and a measured density of the printed gradation pattern in S4 is stored as a reference value of density DR. Thereafter, without user's operation, at a set automatic timing, the read gradation pattern P is corrected with the gamma correction table TO and printed on the photosensitive drum or the like, density deviation ΔD between a measured density D of the printed gradation pattern in S6 and the reference value of density DR is determined, and the latest gamma correction table T is generated and updated on the basis of the density deviation ΔD. Consequently, high-quality image formation can be automatically performed.