Image forming apparatus and storage medium

A non-transitory computer readable storage medium storing a program causing a computer of an image forming apparatus comprising an image former that forms a measurement pattern on a recording medium to perform:

• acquiring image data obtained by reading a recording medium surface on which the measurement pattern is formed;
• and
• controlling the image former, wherein
• the program causes the computer to calculate gradation characteristics at positions of correction points arranged along a direction orthogonal to a conveyance direction of the recording medium on a basis of the acquired image data, and correct density unevenness of the measurement pattern in the direction orthogonal to the conveyance direction by correction values at the positions of the correction points calculated on the basis of the gradation characteristics, and
• the measurement pattern includes
• a first image having a maximum gradation value,
• second images that are adjacent to the first image on an upstream side in the conveyance direction and whose gradation values change stepwise and in ascending order in the conveyance direction, and
• third images that are adjacent to the first image on a downstream side in the conveyance direction and whose gradation values change stepwise and in descending order in the conveyance direction.