Patent ID: 7432494

Claim:
A color image forming apparatus comprising: image forming units configured to form images of different colors on an image carrier; a plurality of detectors configured to output detection signals; and a controller configured to receive the detection signals, wherein the image forming units are configured to form test marks of different colors on the image carrier in a conveying direction thereof at predetermined intervals, the test marks include linear position displacement detecting test marks, and density detecting test marks that include an area having a predetermined density and are adjacent to the linear position displacement detecting test marks, wherein the density detecting test marks correspond to the linear position displacement detecting test marks, and the linear position displacement testing marks are a part of the corresponding density detecting test marks, wherein the plurality of detectors are configured to detect the test marks and to output the detection signals based upon the detection of the test marks, and wherein the controller is configured to perform a detection operation for detecting position displacements of the linear position displacement detecting test marks in a scanning direction of the image carrier and to perform a detection operation for detecting densities of the density detecting test marks, based on the detection signals output from the plurality of detectors.