Abstract: 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.

Abstract: 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.

Abstract: A high density detecting toner pattern is formed on a photosensitive body and a high density correction is effected by comparing a value detected by a reflection sensor with a high density reference value so as to maintain an image density at a specific level. An image density correcting section adopts a result of the preceding high density correction as the high density reference value, and compares the same with a result of a current high density correction. The image density correcting section effects the half-tone density correction only when a difference reaches or exceeds a preset difference reference value by forming a half-tone density detecting toner pattern on the photosensitive body and comparing a value detected by the reflection sensor with a half-tone reference value. Consequently, it has become possible to provide an image forming apparatus which can maintain a density output of an entire image at a specific level for any kind of images including solid, line, and half-tone, etc.

Abstract: A crystalline titanyl phthalocyanine having diffraction peaks at least at 7.4.degree., 9.4.degree., 9.7.degree. and 27.3.degree. of Bragg angle (20.+-.0.2.degree.) in X-ray diffraction pattern with a doublet peak at 9.4.degree. or 9.7.degree., one of the diffraction peaks at 9.4.degree. and 9.7.degree. being the maximum.