Calibration apparatus and method for calibrating image reading apparatus

A calibration apparatus includes a calibration section and a conversion section. The calibration section performs calibration with first and second image reading apparatuses which read in-line a color patch formed on paper by an image forming apparatus. The first image reading apparatus includes a first device which reads the color patch and outputs the reading result as a first signal. The second image reading apparatus includes a second device which reads the color patch and outputs the reading result as a second signal having a format different from a format of the first signal. The conversion section converts the first signal into an after-conversion first signal having the format of the second signal. The calibration section performs the calibration in such a way that an output value of the second signal is adjusted to an output value of the after-conversion first signal.

FIELD OF THE INVENTION

The present invention relates to a calibration apparatus and a method for calibrating an image reading apparatus.

DESCRIPTION OF THE RELATED ART

Conventionally, in the case where a color profile of an image forming apparatus is created, an image reading apparatus including a line sensor(s) which reads in full color, such as a CCD (Charge Coupled Device) and/or a CIS (Contact Image Sensor), is disposed in-line in order to increase productivity, and the line sensor reads a color chart constituted of a large number of colors formed on paper, so that automatic creation of a color profile is realized.

These line sensors, for example, have instrumental errors and deteriorate over time. Hence, output values of signals output by reading a color chart may be different depending on line sensors. Therefore, an image reading apparatus needs to be calibrated at the time of installation or regularly so as to obtain output values of a certain level.

However, in conventional calibration, it is necessary that an image forming apparatus forms a color patch on paper, an image reading apparatus thereof reads the color patch, a colorimeter performs colorimetry of the color patch on the output paper, and the image reading apparatus is calibrated in such a way that the reading result of the image reading apparatus is adjusted to the colorimetry result of the colorimeter. This reduces productivity of the image forming apparatus and increases labor costs.

As a method for calibrating an image reading apparatus without using a colorimeter, there is described, for example, in Japanese Patent Application Laid-Open Publication No. 2002-262007 (hereinafter “Patent Document 1”) creating a correction table to adjust an input image from a scanner as a calibration target to a reference image which is an input image from a specific scanner and calibrating the scanner as the calibration target on the basis of the created correction table.

The invention of Patent Document 1 uses a plurality of sensors which are the same type, for example, CCDs or a CCD and a CIS. The invention of Patent Document 1 corrects an instrumental error between these sensors. As described above, line sensors have instrumental errors. Hence, if no adjustment is performed on a line sensor at the time of installation, reliability of the sensor is unknown. That is, a line sensor cannot be used without adjustment, and therefore the specific scanner needs to be calibrated with a colorimeter so as to obtain output values of a certain level.

Considering that an image reading apparatus is disposed in-line, it is practically impossible to allow a printed calibration chart to pass on a paper conveyance path. That is, this type of image reading apparatus reads only images formed by an image forming apparatus provided with this image reading apparatus. It is possible that the image forming apparatus creates a calibration chart and the image reading apparatus is calibrated using this chart. However, color reproducibility of a calibration chart varies depending on image forming apparatuses. Therefore, in this case too, it is necessary that a colorimeter performs colorimetry of the calibration chart, which is formed by the image forming apparatus, for creation of a profile, and the image reading apparatus is calibrated on the basis of the created profile.

BRIEF SUMMARY OF THE INVENTION

Objects of the present invention include providing a calibration apparatus and a method for calibrating an image reading apparatus each of which calibrates an image reading apparatus without reducing productivity.

In order to achieve at least one of the objects, according to an aspect of the preset invention, there is provided a calibration apparatus including: a calibration section which performs calibration with a first image reading apparatus and a second image reading apparatus which read in-line a color patch formed on paper by an image forming apparatus which forms an image on paper; and an image signal conversion section, wherein the first image reading apparatus includes a first device which reads the color patch and outputs a result of the reading as a first signal, the second image reading apparatus includes a second device which reads the color patch and outputs a result of the reading as a second signal having a signal format different from a signal format of the first signal, the image signal conversion section converts the first signal into an after-conversion first signal having the signal format of the second signal, and the calibration section performs the calibration in such a way that an output value of the second signal is adjusted to an output value of the after-conversion first signal.

Preferably, in the calibration apparatus, the first device is constituted of a plurality of single-color sensors which read the color patch at different positions and output the first signals of different channels.

Preferably, in the calibration apparatus, the single-color sensors are constituted of: a first single-color sensor which emits red light to the color patch, receives the light reflected by the color patch, and outputs the first signal corresponding to an amount of the received light; a second single-color sensor which emits green light to the color patch, receives the light reflected by the color patch, and outputs the first signal corresponding to an amount of the received light; and a third single-color sensor which emits blue light to the color patch, receives the light reflected by the color patch, and outputs the first signal corresponding to an amount of the received light.

Preferably, in the calibration apparatus, the single-color sensors are disposed in a direction perpendicular to a conveyance direction of the paper, and the color patch is constituted of a color pattern having a length enough for the single-color sensors to read the color pattern simultaneously.

Preferably, in the calibration apparatus, the second device is constituted of a line sensor which reads the color patch in full color and outputs the result of the reading as the second signal which is a color signal.

Preferably, in the calibration apparatus, the color patch is constituted of color patterns of 228 colors conforming to IT8.7/2.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, an embodiment of the present invention is described with reference to the drawings. The scope of the present invention is not limited to the illustrated examples.

FIG. 1shows the functional configuration of an image forming apparatus100according to an embodiment of the present invention. The image forming apparatus100is an electrophotographic color image forming apparatus as a multifunction peripheral having a copier function, a scanner function and a printer function.

The image forming apparatus100includes, for example, as shown inFIG. 1, a control section10, an operation display section20, a scanner section30, an image forming section40, a first relay unit50, a second relay unit60, a storage section70and a communication section80which are connected to each other via a bus.

The control section10includes a CPU (Central Processing Unit), a ROM (Read Only Memory) and a RAM (Random Access Memory). In response to operation signals input from the operation display section20or instruction signals received through the communication section80, the CPU reads a system program and various process programs stored in the ROM, opens the read programs on the RAM and performs centralized control on the components of the image forming apparatus100according to the opened programs.

The operation display section20is constituted of an LCD (Liquid Crystal Display) and displays, on a display screen, various operation buttons, states of the apparatus, action states of each function and the like according to instructions of display signals input from the control section10. The display screen of the LCD is covered with a pressure sensitive (resistive film type) touch panel constituted of transparent electrodes arranged in a lattice. The operation display section20detects coordinates of points on the touch panel as voltage values, the points being pressed by a finger, a touch pen or the like, and outputs the detected position signals (i.e. the voltage values) as operation signals to the control section10. The operation display section20includes number buttons and various operation buttons such as a start button and outputs operation signals made by button operation to the control section10.

The scanner section30includes a scanner under a contact glass on which documents are placed and reads images of the documents. The scanner includes a light source, a CCD (Charge Coupled Device) image sensor and an A/D converter. The scanner reads images of the documents as RGB signals by forming images with reflected light of light emitted from the light source to illuminate and scan the documents and performing photoelectric conversion on the images formed of the reflected light and generates image data by performing A/D conversion on the read images.

The image forming section40forms and outputs images on paper with electrophotography on the basis of yellow (Y), magenta (M), cyan (C) and black (K) image data.

As shown inFIG. 2, the image forming section40includes, for Y, M, C and K, photosensitive drums41Y,41M,41C and41K, primary transfer rollers42Y,42M,42C and42K, an intermediate transfer belt43, a roller44, a resist roller45, a secondary transfer roller46, a fixing unit47and a paper feeding section48.

Here, image formation in the image forming section40is described.

The photosensitive drum41Y rotates, the surface thereof is charged by a charger (not shown), and a latent image of Y data is formed on the charged area by being exposed by a laser light source (not shown) or the like. Then, on the area where the latent image is formed, a yellow toner image is formed by a developing device (not shown). The yellow toner image is transferred to the intermediate transfer belt43by the photosensitive drum41Y and the primary transfer roller42Y pressing against each other. The yellow toner image is a yellow image corresponding to yellow image data of an output target. The toner not transferred to the intermediate transfer belt43is removed by a cleaner (not shown).

In the same way as the yellow toner image, each of magenta, cyan and black toner images is formed and transferred to the intermediate transfer belt43.

Rotation of the roller44and the primary transfer rollers42Y,42M,42C and42K rotates the intermediate transfer belt43, and the Y, M, C and K toner images are successively transferred to the intermediate transfer belt43, thereby being superposed thereon. The paper feeding section48includes a plurality of paper feeding trays and feeds paper housed in the paper feeding trays to the image forming section40. Rotation of the resist roller45carries the paper fed from the paper feeding trays of the paper feeding section48to the secondary transfer roller46.

As the resist roller45and the secondary transfer roller46rotate, the paper passes through a nip part formed by the secondary transfer roller46, so that the YMCK toner image on the intermediate transfer belt43is transferred to the paper. The paper to which the YMCK toner image is transferred passes through the fixing unit47. Pressurization and heating with the fixing unit47fixes the YMCK toner image to the paper, thereby forming a color image. The paper on which image formation has been performed is ejected to the first relay unit50.

In the case of double-sided printing, the paper, on one side of which image formation has been performed, is reversed by a double-side conveyance unit (not shown) for double-sided printing and carried to the secondary transfer roller46by the resist roller45so that image formation is performed on the other side on which image formation has not been performed yet.

The first relay unit50has a function to receive the paper ejected from the image forming section40and send the paper outside for further processing. The first relay unit50includes a single-color sensor unit50ain a route. The first relay unit50may have a finisher function to perform various processes such as a punching process, a folding process and a cutting process.

The single-color sensor unit50areads color patterns of a color patch formed on and fixed to paper by the image forming section40and outputs voltage values corresponding to the reading results to the control section10.

The control section10detects colors of the color patterns on the basis of the voltage values output from the single-color sensor unit50a.

FIGS. 3A and 3Bshow the schematic configuration of the single-color sensor unit50a.FIG. 3Ais an enlarged planar view of the single-color sensor unit50adisposed on a paper conveyance path C.

The single-color sensor unit50aincludes, as shown inFIG. 3A, a single-color sensor (R)51R, a single-color sensor (G)51G and a single-color sensor (B)51B arranged in a line parallel to a main-scanning direction of paper P at predetermined intervals. The arrangement of the single-color sensors is not limited to the one shown inFIG. 3A, and therefore they can be properly arranged. Insofar as the single-color sensor (R)51R, the single-color sensor (G)510and the single-color sensor (B)51B are arranged at different positions in the main-scanning direction, unlike the embodiment, it is unnecessary that they are arranged at the same position in a sub-scanning direction.

FIG. 3Bis a schematic side view of the single-color sensor (R)51R. The single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B have the same configuration, and therefore the schematic configuration of the single-color sensor (R)51R is described hereinafter and description of the schematic configurations of the other single-color sensors is omitted.

The single-color sensor (R)51R includes an LED (Light Emitting Diode)52R, a lens53R, a light receiving element54R, a white reference plate55R and a reference plate cover56R.

The LED52R is an emitter to emit red light. Note that the single-color sensor (G)51G includes an LED52G which is an emitter to emit green light, and the single-color sensor (B)51B includes an LED52B which is an emitter to emit blue light. The center wavelengths of the red light, green light and blue light emitted from the LEDs52R,52G and52B, respectively, are different from each other. The red light emitted from the LED52R is easily absorbed by cyan, the green light emitted from the LED52G is easily absorbed by magenta, and the blue light emitted from the LED52B is easily absorbed by yellow. That is, a color having a complementary color relationship with a luminescent color has a property to easily absorb light of the luminescent color. Note that black has a property to absorb light of any color. In the embodiment, LEDs are used as emitters. Alternatively, other types, such as EL (Electronic Luminescence), of light emitting elements may be used.

The lens53R condenses light emitted from the LED52R. The light receiving element54R is constituted of, for example, a photodiode, and converts the amount of light received into voltage values to output. The white reference plate55R is a reflective plate not to absorb but to reflect the light emitted from the LED52R and is used for shading correction. The reference plate cover56R prevents the white reference plate55R from being dirty with, for example, paper powder from paper when the white reference plate55R is not in use. The reference plate cover56R is displaced from a covering position to cover the white reference plate55R to an open position when the white reference plate55R is used.

The single-color sensor (R)51R thus configured emits light from the LED52to each color pattern of the color patch formed on the paper P, which is carried on the paper conveyance path C, when each color pattern passes through a measurement position DR, and receives the reflected light with the light receiving element54R through the lens53R. Then, the light receiving element54R outputs a voltage value corresponding to the amount of the reflected light to the control section10. On the basis of the voltage value, an output value from the single-color sensor (R)51R is determined. The single-color sensor (R)51R thus reads a color chart in the embodiment. The single-color sensor (G)51G and the single-color sensor (B)51B read the color chart in the same way as the single-color sensor (R)51R. For the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B, measurement positions DR, DG and DB are predetermined, respectively.

The second relay unit60has a function to receive the paper ejected from the first relay unit50and send the paper outside for further processing. The second relay unit60includes a line sensor unit60adisposed in the route. The second relay unit60may have a finisher function to perform various processes such as a punching process, a folding process and a cutting process. In the embodiment, the second relay unit60is provided in the image forming apparatus100by being optionally installed therein, but may be provided in the image forming apparatus100from the beginning.

The line sensor unit60aincludes, as shown inFIG. 4, a light source61which emits light to the paper P carried on the paper conveyance path C, at least one mirror62which reflects the light emitted from the light source61and reflected by the paper P in a predetermined direction, a lens63which condenses (forms images with) the light reflected by the mirror62, and a CCD64which receives the light condensed by the lens63.

As the light source61, for example, a LED (Light Emitting Diode), a CCFL (Cold Cathode Fluorescent Lamp) or a xenon lamp is used. The light source61extends in a direction (extending direction) perpendicular to a paper conveyance direction of the paper P. The length of the light source61in the extending direction is longer than the width of the paper P to be carried. Light L emitted from the light source61is reflected by the color patterns of the color patch formed on the paper P, is reflected by the mirror62, forms images with the lens63and then enters the CCD64. That is, the CCD64receives the light L reflected by the color patterns of the color patch, thereby performing scanning.

The CCD64is, what is called, a linear image sensor, and reads the entire image formed on the paper P carried on the paper conveyance path C by moving in relation to the paper P. The CCD64performs photoelectric conversion on the light L which has entered the CCD64, and on the basis thereof, the line sensor unit60adetermines a reflectance which is a ratio of the amount of light received by the CCD64(received-light amount) to the amount of light emitted from the light source61. Then, the line sensor unit60agenerates a signal corresponding to the reflectance and outputs the signal to the control section10. This signal is a signal which specifies gradations of R, G and B. This signal may be generated from the received-light amount obtained by photoelectric conversion. Alternatively, the line sensor unit60amay output information indicating the received-light amount obtained by photoelectric conversion to the control section10, and the control section10may obtain the reflectance from the information.

In the embodiment, the CCD64performs scanning away from paper, namely, in a noncontact manner. Alternatively, a contact optical reading apparatus such as a CIS may be used.

In the embodiment, the linear image sensor which reads images one-dimensionally is used. Alternatively, an area image sensor which reads images two-dimensionally may be used.

Further, a reference plate readable with the CCD64may be provided for shading correction.

The storage section70is constituted of a hard disk, a flash memory or the like and stores various data therein. The storage section70stores therein, for example, color patch image data and a calibration table described below.

The communication section80is constituted of a modem, a LAN (Local Area Network) adapter, a router, a TA (Terminal Adapter) or the like and controls communications between the image forming apparatus100and external apparatuses connected to a network N.

Next, an example of the color patch used in the embodiment is described.

A color patch R formed on paper P is, for example, constituted of color patterns of 228 colors conforming to IT8.7/2. More specifically, as shown inFIG. 5, on a sheet of paper P, belt-shaped color patterns of 11 colors each extending in a direction perpendicular to the paper conveyance direction are continuously formed in the paper conveyance direction, and this is performed for 21 sheets of the paper P each with other 11 colors, whereby the color patch R constituted of color patterns of 228 colors is formed. The length of the color patterns in the longitudinal direction (the direction perpendicular to the paper conveyance direction) is long enough for the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B to read each color pattern simultaneously. That is, the length of the color patterns is long enough for each color pattern to pass through the measurement positions DR, DG and DB simultaneously.

In the embodiment, the color patch R is constituted of color patterns of 228 colors conforming to IT8.7/2. However, the format and the number of colors of color patterns are arbitrary and not limited to those described above.

Next, a chart reading process performed by the control section10of the image forming apparatus100thus configured is described with reference toFIG. 6. The chart reading process is performed, for example, when a user operates the operation display section20to make an instruction to calibrate the line sensor unit60a.

First, the control section10performs a stabilization control process (Step S101). More specifically, the image forming section40forms a toner image(s) for adjustment on the intermediate transfer belt43. On the basis of process conditions of the image forming section40of the time and the amount of toners attached onto the intermediate transfer belt43detected by a sensor (not shown) disposed near the intermediate transfer belt43, the control section10adjusts the process conditions of the image forming section40such as charge potentials of the photosensitive drums41Y,41M,41C and41K, exposures of the laser light sources and development potentials of the developing devices. In addition, the image forming section40forms a gradational toner image, the gradations of which are expressed by screen processing, on the intermediate transfer belt43. The control section10calculates an engine gamma curve for area gradation by screen processing using measurement values of the toner image input from the sensor disposed near the intermediate transfer belt43. The engine gamma curve is a gamma correction curve obtained under the adjusted process conditions.

After performing the stabilization control process, the control section10performs a color patch data generating process to generate color patch image data to form the above-described color patch on paper P (Step S102).

Next, the control section10performs a color patch forming process to form the color patch on paper P on the basis of the generated color patch image data by controlling the image forming section40(Step S103).

Next, the control section10performs a single-color sensor reading process to read the color patch, which is formed on the paper P by the image forming section40, with the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B, the paper P being carried inside the first relay unit50, by controlling the single-color sensor unit50a(Step S104). At Step S104, the control section10obtains, for each color pattern, output values at a point of the color pattern while the color pattern passes through the measurement positions DR, DG and DB. The control section10stores the output values obtained from the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B, for example, in the RAM.

Next, the control section10performs a line sensor reading process to read the color patch on the paper P with the CCD64, the paper P being carried inside the second relay unit60, by controlling the line sensor unit60a(Step S105) and then ends the chart reading process. At Step S105, the control section10obtains, for each color pattern, output values about the entire belt-shaped color pattern. That is, the control section10obtains, for each color pattern, output values at multiple points of the color pattern. The control section10stores the output values obtained from the CCD64, for example, in the RAM.

Next, a calibration process is described with reference toFIG. 7. The calibration process is a process to be performed, for example, right after the above-described chart reading process is ended.

First, the control section10performs a single-color signal combining process (Step S201). With the single-color signal combining process, the output values of the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B obtained for each color pattern as described above are combined, thereby being converted into an image signal having the RGB format (color format).

The single-color signal combining process is described with reference toFIG. 8.

First, the control section10performs gain adjustment on the obtained output values (Step S301). More specifically, the control section10performs gain adjustment, for example, by referring to a gain adjustment table as shown inFIG. 9, the gain adjustment table being stored in the ROM, and multiplying each obtained output value by a coefficient for the type of the single-color sensor which has obtained the output value, namely, by a coefficient for the color of the output value.

Next, the control section10performs gamma correction on the gain-adjusted output values (Step S302). The control section10performs gamma correction, for example, by multiplying the gain-adjusted output values by a predetermined coefficient.

Next, the control section10combines the gain-adjusted and gamma-corrected output values (Step S303) and then ends the single-color signal combining process. More specifically, the control section10combines the output values obtained for each color pattern by the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B, thereby converting the output values into a signal which specifies gradations of R, G and B. Far more specifically, the control section10combines the output value of an R channel obtained from the single-color sensor (R)51R, the output value of a G channel obtained from the single-color sensor (G)51G and the output value of a B channel obtained from the single-color sensor (B)51B, thereby converting the output values into an RGB output value. Thus, the signals output from the single-color sensors are converted into a signal having the same signal format as the signals output from the CCD64.

Thus, the control section10functions as an image signal conversion section which converts first signals output from a first image reading apparatus into a signal (after-conversion first signal) having a signal format of a second signal(s).

After performing the single-color signal combining process in this way, the control section10performs a color signal correction process as shown inFIG. 7(Step S202). With the color signal correction process, the output values of the CCD64obtained as described above are corrected to create a calibration table described below.

The color signal correction process is described with reference toFIG. 10.

First, the control section10performs gamma correction on the obtained output values (Step S401). The control section10performs gamma correction, for example, by multiplying the output values obtained for each color pattern by a predetermined coefficient.

Next, the control section10performs an average value calculation process to obtain the average of the output values for each color pattern (Step S402) and then ends the color signal correction process. More specifically, the control section10obtains, for each color pattern, the average of the output values obtained as described above about the entire belt-shaped color pattern.

After performing the color signal correction process in this way, the control section10creates a calibration table as shown inFIG. 7(Step S203). More specifically, the control section10creates a calibration table to adjust the corrected output values (i.e. averages) output from the CCD64to the output values of the image signals having the RGB format output from the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B.

Thus, the control section10functions as a calibration section which performs calibration in such a way that the output values of second signals output from a second image reading apparatus are adjusted to the output values of after-conversion first signals obtained by the conversion with the image signal conversion section.

The control section10stores the created calibration table in the storage section70(Step S204) and then ends the calibration process.

As described above, according to the embodiment, the control section10performs calibration with the single-color sensor unit50aand the line sensor unit60awhich read in-line the color patch R formed on paper P by the image forming apparatus100which forms images on paper. The single-color sensor unit50ahas the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B which read the color patch R and output the reading results as first signals. The line sensor unit60ahas the CCD64which reads the color patch R and outputs the reading result(s) as a second signal(s) having a signal format different from a signal format of the first signals. The control section10converts the first signals output from the single-color sensor unit50ainto a signal (after-conversion first signal) having the signal format of the second signal. The control section10performs calibration in such a way that an output value of the second signal output from the line sensor unit60ais adjusted to an output value of the after-conversion first signal. Consequently, calibration can be performed in such a way that second signals are adjusted to first signals (after-conversion first signals) of an image reading apparatus which outputs signals having high reliability. Hence, calibration with a colorimeter is unnecessary, and therefore an image reading apparatus can be calibrated without reducing productivity. Further, for example, in the case where the second image reading apparatus is optionally installed in the image forming apparatus, the work time to install the second image reading apparatus can be shortened, and also the calibration work can be easily performed.

Further, according to the embodiment, the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B are single-color sensors which read the color patch R at their respective positions and output signals of their respective channels, thereby obtaining signals having high S/N (Signal to Noise ratio). Therefore, first signals having higher reliability can be obtained.

Further, according to the embodiment, the single-color sensors are: the single-color sensor (R)51R which emits red light to the color patch R, receives the light reflected by the color patch R, and outputs a signal corresponding to the amount of the received light; the single-color sensor (G)51G which emits green light to the color patch R, receives the light reflected by the color patch R, and outputs a signal corresponding to the amount of the received light; and the single-color sensor (B)51B which emits blue light to the color patch R, receives the light reflected by the color patch R, and outputs a signal corresponding to the amount of the received light. Therefore, first signals can be obtained with a simple method.

Further, according to the embodiment, the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B are disposed in the direction perpendicular to the paper conveyance direction. The color patch R is constituted of a color pattern(s) having a length enough for the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B to read the color pattern simultaneously. Therefore, an installation space for the single-color sensors can be small.

Further, according to the embodiment, the CCD64is a line sensor which reads the color patch R in full color and outputs the reading result(s) as a color signal(s). Therefore, a color profile can be properly created.

Further, according to the embodiment, the color patch R is constituted of color patterns of 228 colors conforming to IT8.7/2. Therefore, calibration can be properly performed.

The above embodiment is an example of the image forming apparatus of the present invention, and hence the present invention is not limited thereto. The detailed configurations and actions of the functional sections and the like which constitute the image forming apparatus can be appropriately modified.

Further, in the embodiment, the calibration table to adjust the output values output from the CCD64to the output values of the image signals having the RGB format output from the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B is created, and the CCD64is calibrated using this calibration table. Alternatively, the CCD64may be calibrated by matrix operation using the output values of the CCD64and the output values of the single-color sensor (R)51R, the single-color sensor (G)51G and the single-color sensor (B)51B.

Further, in the embodiment, with regard to the single-color sensors, one light receiving element is provided for one light source. Alternatively, one light receiving element may be provided for three light sources, whereby one light receiving element is shared between three light sources and the one light receiving element receives light from the three light sources.

Further, in the embodiment, a hard disk, a semiconductor nonvolatile memory or the like is used as a computer readable storage medium in which the programs to perform the processes are stored. However, this is not a limitation, and hence, for example, a portable storage medium such as a CD-ROM is also usable as the computer readable storage medium. Further, a carrier wave is usable as a medium to provide data of the programs to perform the processes via a communication line.

This application is based upon and claims the benefit of priority under 35 USC 119 of Japanese Patent Application No. 2014-004994 filed on Jan. 15, 2014, the entire disclosure of which, including the specification, claims, drawings and abstract, is incorporated herein by reference in its entirety.