Provided here are toner sets and image forming apparatus and methods for the formation of a bright image with excellent brightness and concealability. A toner set according to an embodiment comprises a first toner which is stored in a first container and comprises a plurality of first toner particles containing a first bright pigment and a first binder resin, and a second toner which is stored in a second container and comprises a plurality of second toner particles containing a second bright pigment and a second binder resin, wherein the second toner has a larger volume average particle diameter than the first toner.

An image forming apparatus is configured to determine that a toner container was replaced during power off in a case where identification information acquired from a toner container and identification information stored in a nonvolatile memory do not match each other when power is turned on. In a case where the replaced toner container does not satisfy a replacement condition and does not contain a black toner, the image forming apparatus permits the execution of printing in a monochrome print mode, and suspends the execution of printing in the color print mode.

An image forming unit of an image forming apparatus includes a developing device and a toner replenishing unit that replenishes the developing device with toner. The toner replenishing unit includes an upper toner container, a lower toner container, a toner conveyance unit, and a replenishment control unit. The upper toner container and the lower toner container are disposed adjacently to each other in a vertical direction in an apparatus body. When the upper toner container becomes empty, the replenishment control unit controls the toner replenishing unit so as to replenish the developing device with the toner from the lower toner container.

An image forming apparatus includes an intermediate transferor to rotate in a predetermined rotation direction, a plurality of image bearers disposed along the intermediate transferor to bear latent images, a plurality of developing devices to develop the latent images, a plurality of developer containers to contain developers, and a plurality of conveyance paths each corresponding to a respective one of the plurality of developing devices and a respective one of the plurality of developer containers to supply the developers to the plurality of developing devices respectively. An arrangement of the plurality of developing devices in the predetermined rotation direction is configured to be changed without changing an arrangement of the plurality of developer containers. A layout of the plurality of conveyance paths is configured to be changed without changing connections between a supply source and a supply destination of the plurality of conveyance paths.

A charge roller includes, in a surface thereof, recesses that have sizes that are equivalent to or larger than a volume average particle diameter of a toner accommodated in a developing unit and that are capable of collecting the toner retransferred to a photosensitive drum.

In an image forming apparatus which includes a plurality of image forming units each including an image bearing member, a contact charging member, and a developer bearing member for forming toner of normal polarity, and which, in a printing operation, applies a charging bias having a first direction, in a cleaning operation, applies a charging bias having a second direction, and recovers residual toner remaining on the image bearing member without used for printing by the developer bearing member, before performing the cleaning operation, when successively performing the printing operation on a plurality of recording materials including a first recording material and a second recording material, which is used for printing following the first recording material, the charging voltage larger in absolute value in the printing operation for the second recording material than in the printing operation for the first recording material is applied.

An image forming apparatus includes a controller configured to control a first image forming unit such that while a plurality of images are being sequentially formed, a first pattern image is formed in a first sheet-to-sheet area between a first black image and a second black image among the plurality of images on a first photosensitive body, and control the second image forming unit such that while the plurality of images is being sequentially formed, a second pattern image are formed in a second sheet-to-sheet area between a first color image and a second color image among the plurality of images on a second photosensitive body. The first sheet-to-sheet area in a case where the first pattern image is formed without the second pattern image being formed is narrower than the first sheet-to-sheet area in a case where the first pattern image and the second pattern image are formed.

An image forming unit of an image forming apparatus includes a developing device and a toner replenishing unit that replenishes the developing device with toner. The toner replenishing unit includes an upper toner container, a lower toner container, a toner conveyance unit, and a replenishment control unit. The upper toner container and the lower toner container are disposed adjacently to each other in a vertical direction in an apparatus body. When the upper toner container becomes empty, the replenishment control unit controls the toner replenishing unit so as to replenish the developing device with the toner from the lower toner container.

Provided is an image forming apparatus, which is configured to determine that a toner container was replaced during power off in a case where identification information acquired from a toner container and identification information stored in a nonvolatile memory do not match each other when power is turned on. In a case where the replaced toner container does not satisfy a replacement condition and does not contain a black toner, the image forming apparatus permits the execution of printing in a monochrome print mode, and suspends the execution of printing in the color print mode.

According to one embodiment, there is provided an image forming apparatus including an image forming unit and a controller. The image forming unit is able to execute a first image formation processing using a first color material and a second image formation processing using a second color material. The controller performs image quality stabilizing processing for the first image formation processing using second color material.