Abstract: An image printing system includes a print engine and a sensing system. The print engine is configured to print a marking material image on a image bearing surface. The sensing system includes a plurality of illuminators, a modulator, a sensor, and a demodulator. Each illuminator is configured to simultaneously emit a light beam at the marking material image on the image bearing surface, thereby producing reflectance from the marking material image at least in a first direction. The modulator is configured to modulate an intensity characteristic of each of the light beams emitted by the illuminators such that each light beam has a different modulated waveform characteristic, where the waveform characteristic includes at least frequency. The sensor is configured to detect the reflectance from the plurality of light beams in the first direction and output a reflectance signal.

Abstract: An image forming apparatus capable of identifying the amount of reflected light from any portion of an image carrier in a short time. A sensor detects reflected light from an intermediate transfer belt. A CPU performs pattern matching between the amount of reflected light from the belt corresponding to one rotation thereof and the amount of reflected light from a specific portion of the belt to thereby identify a first circumferential location of the specific portion and a second circumferential location of a toner patch formed on the belt. The CPU calculates toner patch density based on the amount of reflected light from the toner patch and the amount of reflected light from the belt in the second circumferential location. The density of a toner image to be formed on the belt is controlled according to the calculated toner patch density.

Abstract: An image forming apparatus which is capable of decreasing the failure rate by improving a photocatalytic material and utilization efficiency thereof, and by decomposing substances that cannot be completely removed with a cleaning member or by not causing the substances to adhere. A light emitting unit irradiates an object to be irradiated with light. A light receiving unit receives reflected light from the irradiated object. A protection sheet containing a photocatalytic material is disposed so as to cover the light emitting unit and light receiving unit. The light emitting unit emits light of a wavelength range adapted to a bandgap width of the protection sheet, and the light receiving unit has sensitivity in a wavelength range of light emitted from the light emitting unit.

Abstract: A toner image height measurement apparatus capable of accurately measuring heights of toner images of respective colors with a relatively simple construction and without being affected by toner colors. With motion of an image carrier, there occurs a change in reflection light amount detected by a photodiode of the height measurement apparatus in timing when laser light having been irradiated onto the image carrier starts to be irradiated onto or intercepted by a toner image and in timing when the laser light having been irradiated onto the toner image starts to be irradiated onto the image carrier. Based on a principle that these timings vary according to a toner image height, the height measurement apparatus detects the timing when the reflection light amount changes by a predetermined amount, thereby detecting the toner image height.

Abstract: Failures of respective light emitting elements are detected without printing on a sheet.

Abstract: An image forming apparatus includes a sensor having a light emitting section for irradiating a detection area and a light receiving section for outputting a light sensitive signal indicative of the amount of the light received from the detection area. A sensor adjustment section adjusts the sensitivity of the sensor by varying the set value of an adjustable characteristic value associated with the sensitivity, based on explorative measurement of the adjustable characteristic value corresponding to a predetermined reference level of the light sensitive signal. If an estimation section estimates that the amount of a leakage current generated on the light receiving section is larger than a reference amount, a mitigation section mitigates the influence of the leakage current on the explorative measurement, by at least one of adjustment of the light receiving section for reduction of the leakage current and modification of the predetermined reference level.

Abstract: In a reflective optical sensor in an image forming apparatus, an output from each N number of light-receiving elements (N?3), obtained when M number of light-emitting elements (M?3) included in a light-emitting unit emit detecting light, is separated into an amount of specularly reflected light and an amount of diffusely reflected light. The toner density of a pattern, which is formed on a supporting member in the image forming apparatus, is calculated based on a sum of the amounts of specularly reflected light and a sum of the amounts of diffusely reflected light.

Abstract: An image forming apparatus includes a toner image forming device configured to form a toner image on an image conveying member, a detector configured to optically detect a density of the toner image on the image conveying member, a controller configured to control an image forming condition of the toner image forming device based on an output of the detector, a shutter configured to open and close an optical window of the detector, wherein the image forming apparatus is operable in a cleaning mode of the shutter in which an opening and closing movement of the shutter is repeatedly executed.

Abstract: This invention provides an image forming apparatus capable of outputting, without using any special device, an image which is free from changes in density and tint even upon crisscross rotation and exhibits good proportion of a small character. To accomplish this, the pulse width of a laser emission signal is controlled at 16 levels for one dot at 600 dpi, controlling an actual image in the main scanning direction. When adjusting vertical and horizontal line widths, patch data are created by rotating an anisotropic pattern through 0° and 90° (S1 in FIG. 5). Then, a reader/scanner (15) reads each patch as density data (S2 in FIG. 5). A pulse width, that is, line width correction value at which the densities of the patch patterns rotated through 0° and 90° become equal to each other is obtained (S3 in FIG. 5).

Abstract: An image forming apparatus is provided having a mechanism that toner density of a toner image is automatically adjusted based on a toner patch. In an image forming apparatus including a document conveying section, a document reading section, an image forming section, a sheet discharging section, a sheet feeding section, a patch density detecting section, and a toner density adjusting section for adjusting density of a toner image depending on a result detected by the patch density detecting section, there are further provided a patch forming section for forming a toner patch, an operation detecting section for detecting an operating state of the patch density detecting section, and a patch printing section for printing the toner patch in response to such a result detected by the operation detecting section that the patch density detecting section does not properly operate, thereby adjusting the toner density based on the patch image.

Abstract: An image-forming device has an image-forming unit, a toner density detection unit, a reflective shutter, a storage unit, and a control unit. The control unit calculates a correction value for correcting the output value to control an image-forming unit according to the correction value. The image-forming unit forms a reference toner image on the image-carrying member. The toner density detection unit receives a reflected light beam from the reflective shutter positioned at the shielding position to generate a first output value, the first output value being stored in the storage unit. The toner density detection unit receives another reflected light beam from the reference toner image to generate a second output value when the reflective shutter is positioned at the retracted position, the second output value being stored in the storage unit. The control unit calculates a ratio of the second value and the first value and then calculates the correction value based on the ratio.

Abstract: An optical sensor includes a light-emitting element for directing light to an image, a light-receiving element for receiving light reflected by the image, a normal detection optical path for allowing the light emitted by the light-emitting element and the light reflected from the image to follow a normal detection optical path during normal operation, a calibration reflecting plate disposed inside the optical sensor for reflecting light from the light-emitting element when sensitivity is calibrated, a calibration optical path for allowing the light emitted by the light-emitting element to follow a calibration optical path to the light-receiving element when the emitted light is reflected by the calibration reflecting plate, and a first optical function element disposed in the calibration optical path and switchable between a light permeating state, in which the light passes therethrough, and a light intercepting state, in which the light is blocked, when voltage is applied.

Abstract: A toner-concentration controller includes a controller configured to control a toner supply amount in accordance with a detection result of a toner-concentration of two-component toner, and a sensor unit configured to detect the toner-concentration of two-component toner. The sensor unit includes a correction mechanism to correct an output signal of the sensor unit by changing an external-input voltage, based on relationship data between an output voltage change of the sensor unit and a toner-concentration of unused developer, to control the toner supply amount when the toner-concentration of the two-component toner deviates a predetermined amount from the toner-concentration of the unused developer. The sensor unit is configured to detect the toner-concentration of the unused developer from unused two-component toner based on a change in the external-input voltage.

Abstract: A toner patch sensor for use in an image forming device may be operated in different modes according to the color of the patch being sensed. The toner patch sensor may include a detector and a source adapted to transmit light that is reflected off a toner patch and towards the detector. The detected light may be specular and/or diffuse. A controller may selectively change the amount of one or both of the specular and diffuse light received by the detector. The source may include separate emitters for the specular and diffuse light, with the controller selectably turning off one of the emitters or selectably adjusting a ratio of illumination power between the emitters. Alternatively, the source may include a single emitter and an optical element to split light between specular light and diffuse light. Diffuse light may be blocked when sensing black toner patches.

Abstract: An image forming apparatus that can provide a quality image in a stable manner without lowering the productivity. A reference image forming unit forms reference images on a transfer member. A plurality of sensing units detect densities of the formed reference images. A control unit adjusts respective output values from the plurality of sensing units according to a difference between the output values from the plurality of sensing units. The control unit performs error processing according to the difference between the output values from the plurality of sensing units when the control unit adjusts the output values from the plurality of sensing units.

Abstract: A toner density detection apparatus has a sensor unit and a controller. The sensor unit irradiates a toner patch formed on an image carrier with light, splits the light reflected by the toner patch into first and second light components, receives the first and second light components, and outputs first and second light reception signals. The controller causes an analog/digital converter to convert, based on a reference voltage, the output first and second light reception signals into first and second digital data, and detects the density of the toner patch based on the first and second digital data. The toner density detection apparatus adjusts the toner density detection value based on a comparison between a first reference value stored in advance and the first digital data, and a comparison between a second reference value stored in advance and the second digital data.

Abstract: An image density control device includes a first detecting unit that detects a light amount of first specular reflected light which is reflected from a surface of an image carrier, a second detecting unit that detects a light amount of first diffuse reflected light which is reflected from an image on the surface of the image carrier, a surface change information acquiring unit that acquires a surface change information which shows changes with time, and a control unit that corrects the light amount of the first specular reflected light by using the surface change information to a light amount of second specular reflected light, and controls the density of the image by using the light amount of the first diffuse reflected light and the light amount of the second specular reflected light.

Abstract: Aspects of the disclosure provide a method for improving performance of a raster output scanner (ROS) system with a reduced cost. The method can include identifying a current mirror facet of a motor polygon assembly (MPA) including multiple mirror facets that each mirror facet has a reflectivity characteristic, determining a driving signal based on the reflectivity characteristic of the current mirror facet and a performance characteristic of a light source, and driving the light source based on the driving signal to emit light that is reflected by the MPA onto a photoreceptor.

Abstract: A toner amount measuring unit irradiates a toner image formed on an image carrying member with light, and an image capturing unit captures an image of a reflected waveform according to light reflected by the toner image. Then, an amount of applied toner is calculated based on the peak position or peak height of the reflected waveform in accordance with information associated with the density of the toner image to be formed.

Abstract: An image forming apparatus includes: an image forming unit for forming a correcting image for correcting gradations of an output image, on a bearing body; a sensor for measuring reflected light quantity of the correcting image formed on the bearing body; a gradation correcting unit for correcting the gradations of the output image, based on a measurement result of the measured reflected light quantity of the correcting image; and a timing correcting unit for detecting a shift of measurement timing, based on the measurement result by the sensor, and for correcting the detected shift of the measurement timing.

Abstract: A developer unit used in xerographic printing retains a mixture of at least a first colorant and a second colorant. An illuminator directs toward at least a portion of the mixture a first light of one color, a second light of a second color, and a third light substantially outside of a visible range. A photosensor records a first reflectance signal based on light reflected from the mixture substantially in a visible range, and a second reflectance signal based on light reflected from the mixture substantially outside a visible range. The signals can be used to maintain the mixture at the desired total color and other properties.

Abstract: An image printing system includes a print engine and a sensing system. The print engine is configured to print a marking material image on a image bearing surface. The sensing system includes a plurality of illuminators, a modulator, a sensor, and a demodulator. Each illuminator is configured to simultaneously emit a light beam at the marking material image on the image bearing surface, thereby producing reflectance from the marking material image at least in a first direction. The modulator is configured to modulate an intensity characteristic of each of the light beams emitted by the illuminators such that each light beam has a different modulated waveform characteristic, where the waveform characteristic includes at least frequency. The sensor is configured to detect the reflectance from the plurality of light beams in the first direction and output a reflectance signal.

Abstract: A method is provided for decoupling the control of dot gain and optical density in electrophotographic based printing by varying the exposure level for each dot in an image.

Abstract: An image forming apparatus includes a toner image forming device, a toner image conveyer unit, a control device, and a moving device. The toner image conveyer unit includes a toner image conveyer, a supporting member that detachably supports the toner image conveyer, and a detecting member that detects a toner image on the toner image conveyer. The toner image conveyer unit is movable between a first position where the toner image is formed on the toner image conveyer and a second position where the toner image conveyer is attached to or detached from the supporting member. The moving device moves the detecting member located at a position to detect the toner image, away from the toner image conveyer supported by the supporting member, in conjunction with an operation to move the toner image conveyer unit from the first position to the second position.

Abstract: A plurality of chambers are adapted to accommodate a plurality of cartridges each containing toner to be used for printing. A mode changer is operable to change an operation mode of the printing apparatus in accordance with a combination of respective colors of toner in the cartridges accommodated in the chambers. A first detector is operable to detect a residual amount of toner in each of the cartridges. A second detector is operable to detect the respective colors of toner in the cartridges when the operation mode is changed. A controller is operable to generate an image data including a plurality of first identifiers each indicative of the residual amount of toner in one of the cartridges and a plurality of second identifiers each indicative of one of the colors of toner and associated with one of the first identifiers. A display is adapted to display the image data.

Abstract: An image forming apparatus includes a pattern forming unit which forms a light amount adjustment pattern on an image carrier belt, a light amount control unit which controls the amount of light irradiating the image carrier belt and pattern, a detection sensor which detects reflected light amounts from the image carrier belt and pattern with respect to the irradiating light amount and stores the detection results in a storage unit, a calculation unit which calculates the correspondence between the irradiating light amount and the reflected light amounts from the image carrier belt and pattern on the basis of the detection results and stores the calculation results in the storage unit, and a light amount decision unit which decides, on the basis of the calculation results, a light amount at which the difference between the reflected light amounts from the image carrier belt and pattern exhibits a value set in advance.

Abstract: An image forming apparatus includes an image carrying member to carry a toner image, a drive device to drive the image carrying member, a cleaning member to slide in contact with the image carrying member so as to remove toner remaining on the image carrying member after transferring the toner image onto a sheet from the image carrying member, and a controller, so as to perform a reverse rotation to rotate and stop the image carrying member in a reverse direction of a forward direction at time of image formation and then perform a forward operation to rotate and stop the image carrying member in the forward direction, to control the drive device on the basis of a use amount of the image carrying member.

Abstract: A toner density is calculated from outputs of light-receiving elements based on a difference between a reflection property of a supporting member and a reflection property of a toner pattern. Light-emitting elements aligned in one direction that is inclined to a sub-direction emit a detection light in such a manner that a distance between adjacent spots falling on the supporting member in a second direction is equal to or smaller than a width of the toner pattern in the second direction. The light-receiving elements receive a reflected light reflected from the supporting member and/or the toner pattern. The light-receiving elements are aligned, opposed to the supporting member, in a one direction corresponding to the light-emitting elements.

Abstract: An electrophotographic image formation device comprises an image transfer unit (including an image transfer member) attached to a main body in a detachable manner, a density detecting unit including a detector unit and thereby detecting density of a developing agent transferred to the image transfer member, a protective cover which protects the density detecting unit not detecting the density by covering the detector unit, first and second reflecting parts (differing in reflectivity) formed in a part of the protective cover facing the detector unit, and a shifting unit which places the protective cover at a first position (with the first reflecting part facing the detector unit) when the image transfer unit has been attached to the main body while placing the protective cover at a second position (with the second reflecting part facing the detector unit) when the image transfer unit has not been attached to the main body.

Abstract: An amount of toner transfer on a reference pattern is calculated by using an optical detecting unit that detects both regular reflection light and diffuse reflection light from a detection target simultaneously, based on a relative ratio between a value obtained by subtracting a result of multiplying a “diffuse reflection output” by a “minimum value of a ratio between a regular reflection output and the diffuse reflection output” from the “regular reflection output” of the density detection reference pattern, and a value obtained by subtracting a result of multiplying the “diffuse reflection output” by a “minimum value of a ratio between the regular reflection output and the diffuse reflection output” from the “regular reflection output” in the background of a transfer belt or an intermediate transfer body.

Abstract: A belt includes a surface layer and an underlayer. An interface between the surface layer and the underlayer is roughened to irregularly reflect incident light.

Abstract: An image forming method includes detecting a toner degradation state by detecting an image density on an electrostatic latent image carrier with high sensitivity and low cost. The degraded toner is processed based on the detected information, so that the waste toner can be reduced and a good image can be obtained. An image density of an image that is transferred with a predetermined reference electric field is detected in a first detecting step. An image density of an image that is transferred with an electric field that is smaller or greater than the reference electric field is detected in a second detecting step. A processing step of processing the degraded toner is performed on the basis of the image density detected by each of the detecting steps.

Abstract: An image forming apparatus capable of setting a criterion individually for respective image forming apparatuses, which is used in determining whether or not a developer is properly supplied to a developing unit, thereby stabilizing a developer toner density. With a shutter member closed, reflection light from a reflection sheet is received by a toner density detection sensor, and an output voltage is stored in a memory. After the shutter member is opened, reflection light from a developing sleeve is received by the sensor, and an output voltage is stored in the memory. If an amount of change in voltage per unit toner density calculated based on the output voltages does not fall within a predetermined range, an operation of a main unit of the image forming apparatus is stopped. If the amount of voltage change falls within the predetermined range, the amount of voltage change is stored in the memory.

Abstract: It is determined whether a low density area in which pixels having density less than a predetermined density exist in succession is included in an image signal or not, and if the low density area exists, an image is formed by irradiating the laser light in a first condition for a pixel to be interested in each pixel area within the low density area and irradiating the laser light in a second condition being different from the first condition for other pixels in the pixel area. In this way, it is possible to improve reproducibility of a highlight area in a high resolution image and improve reproducibility of characters and line images or the like.

Abstract: An image-forming apparatus sets a DAC output voltage 1602, a VI conversion5 current ID 1603, and a laser current IL 1604 using a correction profile 1601, and performs density nonuniformity correction that addresses various factors contributing to density nonuniformity.

Abstract: An enhanced toner area coverage (ETAC) sensor may be calibrated to adjust for changes in LED intensity by determining a functional relationship between specular developed mass per unit area (DMA) values and diffuse readings obtained from the sensor. Specular and diffuse readings are obtained from an ETAC sensor that senses reflected light from toner patches generated with incrementally increasing densities on the photoreceptor belt. The specular readings in a particular range and their corresponding diffuse readings are selected for the calibration computations. Reflected ratios are computed from the specular readings and used to determine specular DMAs. The specular DMAs and selected diffuse readings define a set of points for which a functional relationship is determined.

Abstract: An image forming apparatus includes a toner image forming device configured to form a toner image on an image conveying member, a detector configured to optically detect a density of the toner image on the image conveying member, a controller configured to control an image forming condition of the toner image forming device based on an output of the detector, a shutter configured to open and close an optical window of the detector, wherein the image forming apparatus is operable in a cleaning mode of the shutter in which an opening and closing movement of the shutter is repeatedly executed.

Abstract: The change in an output voltage when a control voltage is changed is calculated, and the change in the control voltage divided by the calculated change in the output voltage is defined as a sensitivity coefficient. The sensitivity coefficient is recalculated for each predetermined time interval or whenever a predetermined condition is satisfied, and the control voltage is corrected based on the recalculated sensitivity coefficient. Example of the predetermined condition include the time of start-up of the apparatus, the time at which the accumulated number of printed sheets reaches a predetermined number, and the time of carrying out process control.

Abstract: An image forming apparatus is constituted by a dark color image forming station for forming an image with such a toner of recording materials having the same hue and different lightness as has a lower lightness; a light color image forming station for forming an image with such a toner of the recording materials having the same hue and different lightness as has a higher lightness; and a control portion for effecting control so that an image to be emphasized by partly disappearing or by relatively and partly decreasing in density is formable substantially only with the toner having the higher lightness.

Abstract: A method for measuring an amount of toner on a recording medium that can accurately measure the toner amount. Information on the recording medium to which the toner is fixed is acquired. The toner fixed to the recording medium is irradiated with laser light. A light intensity distribution of reflected light of the laser light is detected. The amount of the toner on the recording medium is calculated on the basis of the acquired recording medium information and the detected light intensity distribution.

Abstract: An image forming apparatus includes an image forming unit configured to form a plurality of toner images on an image carrier, an optical detector configured to detect reflection light from the toner image, and dedicated to detect infrared rays and near-infrared rays, and a controller configured to perform a predetermined control using a detection results of the optical detector. Gradation pattern that is comprised of a plurality of toner patches formed in the image forming unit with an image forming condition to have different adhesive amounts, and is formed of at least two colors, and detection values detected by the optical detector are used for the predetermined control.

Abstract: An optical sensor detects at least one of a toner image and a toner adhesion amount per unit area based on a change of an optical characteristic on a surface of an endless belt member. A control unit performs a predetermined process based on a detection result obtained by the optical sensor. A sensor moving unit moves the optical sensor between a first position in opposite to a belt supporting area in which the endless belt member is supported by a supporting roller and a second position that is different from the first position. The detection result is obtained by the optical sensor when the optical sensor is placed at the first position by the sensor moving unit.

Abstract: An image forming apparatus comprising: an image bearing member; a toner image forming means forming a toner image on the image bearing member, using light toners, and dark toners which have a same hue as that of the light toners and are darker than the light toners; a transfer means which electrostatically transfers a toner image on the image bearing member onto a recording material; and an adjusting means which adjusts the toner image forming means so that a rate between the dark toners and the light toners included in a toner image with predetermined density on the image bearing member is changed according to the roughness of a surface of the recording material onto which the toner image on the image bearing member is transferred.

Abstract: An apparatus prohibits an unfair copying of a document by forming a latent image region and a background region on the document in a manner that prevents detection of their existence. The apparatus has a controller that detects background region densities and latent image region densities. The controller extracts only a background region density, which enables a special dot pattern to be detected when copying the image of the document. The controller also extracts only a latent image region density, at which a dot image corresponding to the dots constituting the latent image region is not formed on a copy when copying the image of the document. The controller then derives the background region densities and the latent image region density matching with the background region density.

Abstract: An image-forming device has an image-forming unit, a toner density detection unit, a reflective shutter, a storage unit, and a control unit. The image-forming unit forms a toner image on an image-carrying member. The toner density detection unit detects a toner density of the toner image, the toner density detection unit having a light-emitting element for emitting a light beam to the image-carrying member, and a light-receiving element for receiving the light beam to produce an output value based on an intensity of the received light beam. The reflective shutter is provided between the toner density detection unit and the image-carrying member to be movable between a shielding position and a retracted position. The storage unit stores the output value of the toner density detection unit. The control unit calculates a correction value for correcting the output value to control an image-forming unit according to the correction value.

Abstract: An image processing apparatus which makes it possible to correct the image density of a target color in real time and maintain highly accurate image density characteristics over a long term. In a first control, the output of a laser driver is controlled such that the gradation of an image signal coincides with that of an image to be recorded on a sheet. The density level of a developed patch to be formed on a photosensitive drum is set to a different value on a toner color-by-toner color basis. In a second control, the output from the laser driver is controlled such that the density of the developed patch coincides with a reference density. An LUT generated in the first control is corrected according to the difference between the density of the developed patch and the reference density.

Abstract: An image processing apparatus, according to the present invention can include a forming portion capable of forming a mark on a bearing member, a light projecting portion capable of irradiating a light onto the bearing member, a light receiving portion capable of receiving a reflection light from the bearing member and from the mark, and outputs a received light signal in accordance with the received light amount, a judging portion capable of judging the existence or non-existence of a mark on the bearing member based on the received light signal, an evaluating portion capable of evaluating a reflection state of the bearing member and an adjusting portion capable of adjusting a light receiving sensitivity of the light receiving portion at a time of a judgment by the judging portion, in accordance with an evaluation of the evaluating portion.

Abstract: A mark detector optically detecting a scale having multiple marks formed successively at predetermined intervals along the moving direction of an endless belt member, and outputting an electrical signal corresponding to the presence or absence of the marks when the endless belt member moves is disclosed. The mark detector includes a light illumination part configured to illuminate the light illumination surface of the endless belt member on which surface the scale is formed with parallel light rays; a light receiving part configured to receive reflected light from the light illumination surface; and a variation prevention part configured to prevent a variation of the light illumination surface. The variation prevention part includes a holding member configured to hold the endless belt member in the vicinity of the light illumination surface movably in the moving direction from the exterior surface side and the interior surface side of the endless belt member.

Abstract: A method for calibrating a toner concentration sensor may include obtaining a zero % TC reading from the toner concentration sensor using a carrier material, determining an estimated TC intercept, and adjusting the toner concentration sensor based on the estimated TC intercept. An apparatus for calibrating a toner concentration sensor may include a toner concentration sensor that detects toner concentration of a developer mix in a developer cartridge and a toner concentration sensor controller that applies calibration to the toner concentration sensor. The toner concentration sensor controller mat include a toner concentration sensor reading section that obtains a zero % TC reading of the toner concentration sensor based on the carrier material, a toner concentration sensor correcting section that determines an estimated TC intercept, and an adjusting section that determines for the calibration for the toner concentration sensor based on the estimated TC intercept.

Abstract: In an image forming apparatus of the present invention, an allowable temperature range of a fixing unit is divided into a plurality of fixing temperature ranges, and image data conversion ? tables respectively suitable for the divided fixing temperature ranges are prepared. A fixing temperature of the fixing unit is measured during image forming. A ? table suitable for the measured fixing temperature can be selected and used. Consequently, even when a reduction in fixing temperature within the allowable temperature range is caused in the fixing unit in the case of continuously outputting color images at a high speed, the resulting change in tint of output images can be reduced.