Patent ID: 7852532

Claim:
An image forming apparatus comprising: an outputting section to output a chart which comprises a gradation pattern in a low-density area, the gradation pattern including patches, each of the patches having a density; a reading section to read-in the density of each of the patches for obtaining an input-output characteristics; a calculating section to calculate an adjusting value to adjust the output in the low-density area of a low-density correction curve, wherein the low-density correction curve has output values corresponding only to input values of not greater than a half of maximum input value of a gradation correction curve; and an output adjusting section to conduct an adjustment of an output in the low-density area based on a the gradation correction curve for totally correcting gradation characteristics, and on the low-density correction curve including the adjusting value as a parameter, wherein the calculating section extracts, from the input-output characteristics, a referential input value corresponding to an input value where a color density starts to rise in a gradation of the low-density area, receives a target input value regarding the input value where the color density starts to rise, and calculates an offset value to adjust the output in the low-density area as the adjusting value, so as to satisfy a relation of: B′+C′=B+C; where B′ represents an output value when the referential input value is inputted to the gradation correction curve, C′ represents an output value when the referential input value is inputted to the low-density correction curve before applying the adjusting value, B represents an output value when the target input value is inputted to the gradation correction curve, and C represents an output value when the target input value is inputted to the low-density correction curve after applying the adjusting value.