Before replacement of constituent parts of an image density sensor or of
other image forming units, the image density of a formed test toner patch
image is detected by the image density sensor and conditions for image
formation are controlled. After replacement of the constituent parts, the
image density sensor detects the image density of a test toner patch image
which is formed based on the controlled conditions for image formation.
The optical output and/or the optical sensitivity is adjusted so that a
detected value becomes a predetermined reference value, to calibrate the
image density sensor. With this image formation controlling method, the
image density sensor can be calibrated easily and precisely, the image
density of a toner pattern image can be held proper and a stable
high-quality image can be obtained.
