To compensate a streak defect in an image formed by an image forming device.

A compensation pattern including a plurality of gray level portions and a plurality of fiducial marks is used. Each of the gray level portions 412 to 418 has a gray level different from the other gray level portions and extends along the cross-process direction, and are spaced form each other along the process direction 440 such that a gap is provided between each pair of adjacent gray level portions. The fiducial marks 430 are arranged before (431) and after (433) the plurality of gray level portions 412 to 418 along the process direction 440. The compensation pattern is used for determining a difference between an actual gray level and an intended gray level at a cross-process-direction image-forming device pixel location in the image.