Image forming apparatus

An image forming apparatus comprising:

• a storing section to store predetermined information,
• an image forming section to form a measurement image on a sheet to output a measurement chart, and
• a control section to receive inputs of a plurality of pieces of density information respectively indicating densities at a plurality of positions of the measurement image formed on the sheet, to calculate a correction value corresponding to each of the positions based on the input density information, to store in the storing section at least one calculated correction value in association with an output condition including a screen condition indicating a content of a screen processing at the time of outputting the measurement chart, to determine the output condition of the input image data, to read the correction value corresponding to the determined output condition from the storing section, and to correct the input image data based on the read correction value, wherein
• the image forming section forms an image on the sheet based on the corrected image data, and
• when no correction value corresponding to the screen condition of the input image data is stored in the storing section, the control section inhibits the correction corresponding to the input image data from being executed.