An image forming apparatus includes an optical sensor for detecting an image formed on an intermediate transfer belt. The optical sensor includes first and second light emitting diodes (LEDs) and first and second photodiodes (PDs). The first and second LEDs irradiate an optical-axis center point of an intermediate transfer belt. The first PD is arranged at a position at which an optical axis of specularly reflected light of light emitted from the second LED and an optical axis along which specularly reflected light of light emitted from the first LED is received form a first angle. The second PD is arranged at a position at which the optical axis of the specularly reflected light of the light emitted from the second LED and an optical axis along which diffused reflected light of the light emitted from the second LED is received form a second angle different from the first angle.

A method for correcting cross-track position errors in a digital printing system having a linear printhead includes printing a test target including a plurality of alignment marks. A data processing system is used to automatically analyze a captured image of the printed test target to determine a measured position for each of the alignment marks. The measured positions for the alignment marks is compared to reference positions to determine measured cross-track position errors. A cross-track position correction function is determined responsive to the measured position errors, wherein the cross-track position correction function specifies cross-track position corrections to be applied as a function of cross-track position. A corrected digital image is determined by resampling the image lines of a digital image responsive to the cross-track position correction function.

An image forming apparatus includes a photosensitive drum, a developing device, a transfer unit, an image sensor configured to detect a toner image on the transfer unit, and a processor. The processor is configured to determine whether the remaining amount of toner in a toner cartridge has decreased to a predetermined level or below. The processor is configured to carry out an image quality stabilization process when the remaining amount of toner is above the predetermined level. The image quality stabilization process being based on a detection result from the image sensor detecting a test pattern formed on the transfer unit. The processor is further configured to perform print process without performing an image stabilization process, without carrying out the image quality stabilization process.

An image forming apparatus includes a first sensor configured to measure a measurement image on a first photoreceptor, a second sensor configured to measure a measurement image on an intermediate transfer member, and a controller. The controller controls the first image forming unit to form first measurement images, wherein the first measurement images are formed along a rotation direction of the first photoreceptor, and controls the first sensor to measure the first measurement images on the first photoreceptor. The controller further controls the first image forming unit and the second image forming unit to form a plurality of measurement images while a rotation speed of the first photoreceptor is being controlled based on a measurement result of the first sensor, wherein the plurality of measurement images is formed along the predetermined direction of the intermediate transfer member.

A printer includes a first printing unit responsible for one of preceding printing and subsequent printing that are to be performed on one sheet in overprinting, an other of the preceding printing and the subsequent printing being performed by a second printing unit; and a base-printing controller that causes the first printing unit to print a base for printing by the second printing unit in an operation of forming a test pattern for registration between the preceding printing and the subsequent printing on the sheet.

An image forming apparatus includes a transfer belt, a plurality of endless rotational bodies, an image forming device, a pattern sensor, and processing circuitry. The image forming device forms correction patterns including a first pattern as a straight line pattern orthogonal to a conveyance direction of the correction patterns and a second pattern as one of a straight line pattern orthogonal to and an oblique line pattern inclined with respect to the conveyance direction. The processing circuitry causes the image forming device to form the correction patterns using a correction value such that the second pattern included in one correction pattern on the transfer belt is same in color and shape as the second pattern included in at least one correction pattern of a preceding correction pattern and a following correction pattern in the conveyance direction with respect to the one correction pattern.

An image forming apparatus includes an image forming device, an image position detector, and an image density detector. The image forming device forms an image on a surface of a recording medium. The image position detector detects a position of the image. The image density detector detects a density of the image. The image forming device forms a position detection image on a surface of a first recording medium. The image position detector detects a position of the position detection image on the surface of the first recording medium. The image forming device forms a density detection image on a second recording medium. The image density detector detects a density of the density detection image on the surface of the second recording medium.

An image forming apparatus comprises a first temperature detector to detect a temperature of a first portion of an optical scanning device in a printer. The first portion is proximate to a heat generating element in the optical scanning device. A second temperature detector is provided to detect a temperature of a second portion of the optical scanning device, which is farther from the heat generating element than the first portion. A controller is configured to perform alignment control for correcting a color positional shift of the printer when either a detected temperature change of the first portion is greater than or equal to a first threshold value or a detected temperature change of the second portion is greater than or equal to a second threshold value.

An image forming apparatus includes image forming devices, image output devices, an endless conveyor, a transfer device, holders, a detector, and circuitry. The image forming devices include image bearers. The image output devices form latent images on the image bearers. The image forming devices form visible images from the latent images. The transfer device transfers the visible images onto the endless conveyor that conveys the visible images in an image conveyance direction. The holders hold the image forming devices interchangeable at holding positions aligned in the image conveyance direction. The detector detects the visible images. The circuitry compares a first visible image of the visible images formed at a specific holding position of the holding positions with a second visible image of the visible images formed at another holding position of the holding positions on the endless conveyor, to correct misalignment between the first and second visible images.

An image forming apparatus is configured to calculate an estimated value of a color misregistration amount based on a first estimation expression when a temperature of an exposure device is under a temperature increasing state. The image forming apparatus is configured to calculate the estimated value of the color misregistration amount based on the first estimation expression when the temperature of the exposure device is under the temperature decreasing state and the exposure device is not in a thermally-deformed state. The image forming apparatus is configured to calculate the estimated value of the color misregistration amount based on a second estimation expression when the temperature of the exposure device is in the temperature decreasing state and the exposure device is in the thermally-deformed state. The image forming apparatus is configured to correct color misregistration based on the calculated estimated value.