Image forming apparatus and method using density test patterns to adjust process parameters and subsequently update gradation correction data

An image forming apparatus that forms a color image by overlapping a plurality of colors, comprising:

• a scanner configured to read a document and generates image data;
• an image processing unit configured to correct gradation of the image data using gradation correction data and generate a gradation image of the image data with gradation after correction;
• a plurality of photoconductors corresponding to the plurality of colors;
• a plurality of charging units configured to electrically charge the plurality of photoconductors with a predetermined charged potential;
• a plurality of exposure units configured to expose the plurality of photoconductors with a predetermined exposure amount;
• a plurality of development units configured to develop the plurality of photoconductors with a predetermined development potential;
• a developer included in each of the plurality of the development units;
• a transfer body onto which images corresponding respectively to the plurality of colors formed on the plurality of photoconductors are transferred;
• a plurality of transfer units configured to transfer the images corresponding respectively to the plurality of colors from the plurality of photoconductors onto the transfer body;
• a sensor configured to detect a density of an image formed on the transfer body;
• a density adjusting unit configured to form a predetermined density test pattern on the transfer body and adjust process parameters including more than or equal to two among the charged potential, the exposure amount, the development potential, and a toner concentration of the developer such that a density of the density test pattern on the transfer body detected by the sensor falls within a predetermined range of a reference density;
• and
• a gradation adjusting unit configured to form a gradation test pattern having a plurality of gradation levels on the transfer body and update the gradation correction data such that a density for every gradation of the gradation test pattern on the transfer body detected by the sensor falls within a predetermined range of a reference gradation density acquired and stored beforehand,
• wherein the gradation adjusting unit updates the gradation correction data subsequently after the density adjusting unit adjusts the density of the density test pattern.