Image forming apparatus and computer program product for performing color adjustment based on color shift and tendency for color shift over time

An image forming apparatus comprising:

• a processor configured to execute:
• an image forming section configured to periodically form a plurality of color calibration images which is used for color adjustment on a recording material;
• a color information obtaining section configured to obtain a first color information of a first color calibration image which is formed on the recording material at a first time and obtain a second color information of a second color calibration image which is formed on the recording material at a second time, the first color information and the second color information being obtained before color adjustment which is periodically performed;
• and
• a color adjusting section configured to:
• determine a first correction value based on a color shift from a reference value, based on the second color information that is obtained by the color information obtaining section;
• determine a temporal change value based on the first color information obtained at the first time and the second color information obtained at the second time, the temporal change value indicating a tendency of the color shift in relation to a change in time;
• determine a second corrected value based on the temporal change value;
• generate a third correction value generated by adding the first correction value and the second correction value;
• and
• perform color adjustment on an image formed by the image forming section based on the a third correction value, such that a difference between a color of an image which is supposed to be output and a color of an image which is output is adjusted based on both the color shift and the tendency of the color shift.