An image forming apparatus includes a conversion unit, a correction unit, an image forming unit, a measurement unit, first, second, and third generation units, a reading unit, an input unit, and a determination unit. Image data of a color components indicating one pixel based on a multidimensional table is converted and then corrected based on one-dimensional tables corresponding to the color components. An image is formed on a sheet based on the corrected image data. A measuring image formed on the sheet is measured. The multidimensional table can be generated based on a multi-color first measuring image. The one-dimensional table can be generated based on a second measuring image. A pattern image formed on the sheet is read. The one-dimensional table can be generated based on a pattern image for each of the color components on the sheet. Input user instructions indicated how the one-dimensional table is generated.