IMAGE FORMATION APPARATUS

To provide a method of securing the number of patch images effective for density detection even when margins set at the front and rear sides of a detection region of the patch image are made to be narrower in comparison to a case of calculating the image density of the patch image by selecting only a detection result of a central region of the detection results of the patch image stored in storage means from a positional deviation amount of the patch image.SOLUTION: An image formation apparatus comprises: density detection means which detects the density of a patch image formed on image holding means over a plurality of spots; determination means which determines whether a plurality of detection results of the density detection means are within a threshold; and change means which changes the detection timing of the patch image by the density detection means or the formation position of the patch image on the image holding means when the determination results that the detection results are not within the threshold by the determination means exceed a predetermined number.SELECTED DRAWING: Figure 6 【課題】パッチ画像の位置ずれ量から格納手段に格納されたパッチ画像の検出結果のうち中央部領域の検出結果のみを選択してパッチ画像の画像濃度を算出する場合に比べ、パッチ画像の検出領域の前後に設定されるマージンを狭くした場合においても濃度検出に有効なパッチ画像の数を確保する方法を提供する。【解決手段】像保持手段に形成されるパッチ画像の濃度を複数箇所にわたり検知する濃度検知手段と、濃度検知手段の複数の検知結果が閾値以内か否かを判定する判定手段と、判定手段による閾値以内でないとの判定結果が予め定められた数を超えた場合、濃度検知手段によるパッチ画像の検知時期又は像保持手段へのパッチ画像の形成位置を変更する変更手段と、を備える。【選択図】図６