An example method of controlling the concentration of a printing substance is provided. A layer of printing substance is received on a printing substance receiving member, and a parameter indicative of a current concentration of non-volatile material in the printing substance is measured. The current concentration is compared to a predetermined target concentration. Based on the comparison, a concentration adjustment is determined. The adjustment comprises at least one of (i) an adjustment to a pressure applied to the printing substance receiving member by a pressurizing member, and (ii) an adjustment to a voltage applied to the pressurizing member. The concentration of the printing substance is controlled based on the determination.

An image forming apparatus includes a latent image forming portion configured to form a latent image on an image bearing member; a developing device including a container configured to store toner and a developing member configured to supply the toner to the latent image formed on the image bearing member to form a toner image; an environment sensor configured to detect environmental information related to an environment in which the developing device is placed; and a controller configured to control switching between a first mode and a second mode, in which a number of prints per unit time is less than that in the first mode. The controller is configured to perform switching from the first mode to the second mode based on an update value obtained by adding or subtracting over time an index value weighted in accordance with the environmental information detected by the environment sensor.

Downtime relating to formation and detection of a detection image is reduced. An image forming apparatus includes a controller configured to calculate a first conversion unit to convert a gradation of input image data so that density output for the input image data becomes a first density output characteristic based on a first detection result of the detection image detected by a density sensor in a first mode. The controller generates a second conversion unit to convert the gradation of the input image data so that the density output for the input image data becomes a second density output characteristic in a second mode based on the detection result in the first mode and correction information, and further updates the correction information based on a second detection result of the detection image detected by the density sensor in the second mode and the first detection result.

An image forming apparatus includes an image forming section, a controller, and storage. The storage stores therein a coverage rate of a past image specified by a past print job. The controller includes a determining section and a first calculating section. When a new print job is received, the determining section determines whether or not to perform a running-in operation by comparing a coverage rate of a new image specified by the new print job to the coverage rate of the past image stored in the storage. The first calculating section calculates an amount of toner to be supplied from a developing section to a photosensitive drum based on the coverage rate of the new image. The running-in operation is to supply the toner in the amount calculated by the first calculating section from the developing section to the photosensitive drum before the new image is formed on a sheet.

A method of printing images in a liquid electrophotographic printer is provided. In an example, the method comprises measuring at least one current associated with an image development unit of the liquid electrophotographic printer. A first time at which a peak occurs in the measured current is determined; the first time indicates that a printing substance is transferred from a point on a developer roller of the image development unit to a photo imaging member of the liquid electrophotographic printer at a first location within the image development unit. A second time at which said point on the developer roller is expected to contact the cleaner roller within the image development unit is calculated and, at the second time, a voltage applied to the cleaner roller is controlled to reduce the potential difference between the cleaner roller and the developer roller.

Method and devices for calibrating optical density reflective color fluids to be deposited on substrate are disclosed. Some methods comprise depositing a quantity of a keying color fluid on a first region of the substrate; applying a voltage level to a reflective color fluid application device; depositing, in response to the voltage level applied, a quantity of reflective color fluid on the first region of the substrate and on a second region of the substrate; performing reflectance measurements of the first region and of the second region; performing optical density calculations as a function of the reflectance measurements; varying the voltage level applied to the reflective color fluid application device in response to said optical density calculation until the optical density calculation is within a calibrated range of optical densities.

In an example of a printing system, the amount of a printing fluid that is transferred from a developer unit onto an imaging plate is varied in order to alter the optical density of an area covered by the printing fluid.

An example printing system for printing liquid ink has a developer device to transfer ink to an image plate of the printing system. The developer device has an ink inlet to receive ink from an ink reservoir of the printing system; a developer roller to transfer ink to the image plate, a motor to rotate the developer roller, and an ink sensor to detect arrival of ink at the developer device. The printing system is configured to start the motor in response to the ink sensor detecting arrival of ink at the developer device.

An image forming apparatus includes a latent image forming portion configured to form a latent image on an image bearing member; a developing device including a container configured to store toner and a developing member configured to supply the toner to the latent image formed on the image bearing member to form a toner image; an environment sensor configured to detect environmental information related to an environment in which the developing device is placed; and a controller configured to control switching between a first mode and a second mode, in which a number of prints per unit time is less than that in the first mode. The controller is configured to perform switching from the first mode to the second mode based on an update value obtained by adding or subtracting over time an index value weighted in accordance with the environmental information detected by the environment sensor.

An example printer comprises an impression cylinder arranged to receive an impression medium thereon and an intermediate transfer member arranged to transfer printing fluid onto a substrate received on the impression medium. The printer further comprises an image sensor arranged to sense an accumulation of printing fluid on the impression medium as sensor data and a controller. The controller is configured to determine, based on the sensor data, an accumulation level of the printing fluid on the impression medium and determine if the accumulation level meets a threshold.