Data processing device and image forming apparatus

A data processing device comprising:

• a first acquisition processing portion configured to acquire, respectively from a first specific area and a second specific area that align in a sub scanning direction on a color image that is formed based on image data, a first position and a second position in a main scanning direction, the first position and the second position being respectively positions of pixels of a first color and a second color formed on a plurality of image carriers that rotate;
• a second acquisition processing portion configured to acquire, from a third specific area having a second specific length in the sub scanning direction on the color image, a plurality of third positions of a plurality of pixels of the first color in the main scanning direction, the second specific length being larger than a first specific length that is a length in a peripheral direction of each of the image carriers;
• a first derivation processing portion configured to, based on the plurality of third positions, derive a first color shift amount that indicates an amount of shifting of pixels of the first color in the main scanning direction in the third specific area;
• and
• a second derivation processing portion configured to, based on the first position, the second position, and the first color shift amount, derive a second color shift amount that indicates an amount of shifting between the first color and the second color in the main scanning direction in the first specific area.