Image forming apparatus, image forming method, and image forming system that ensure reduction of color unevenness and recording medium therefor

An image forming apparatus includes a table generating unit. The table generating unit determines whether a target-value Voronoi region and a measured-value Voronoi region are identical or not. The table generating unit sets an output color value associated with a print position where the target-value Voronoi region and the measured-value Voronoi region are identical in the second color conversion table as the output color value associated with a specific input color value in the first color conversion table. The table generating unit sets the output color value associated with the print position where the target-value Voronoi region and the measured-value Voronoi region are different in the second color conversion table as a color value that is a color value in the hue plane and is different from the output color value associated with the specific input color value in the first color conversion table.

INCORPORATION BY REFERENCE

This application is based upon, and claims the benefit of priority from, corresponding Japanese Patent Application No. 2016-108182 filed in the Japan Patent Office on May 31, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND

A typical image forming apparatus such as a multi-function peripheral (MFP) prints with color unevenness depending on print positions in every image forming apparatus, even when an image is printed based on an input image with a single color value. There is known a technique for reducing such color unevenness.

SUMMARY

An image forming apparatus according to one aspect of the disclosure includes a central processing unit (CPU), a print device, a color-measurement device, and a storage device. The print device executes printing on a recording medium. The color-measurement device measures a color value at each print position in the recording medium printed by the print device. The storage device stores an image forming program. The CPU executes the image forming program to function as a color conversion unit and a table generating unit. The color conversion unit converts an input image into an output image for printing by the print device using a color conversion table. The table generating unit generates a second color conversion table based on a first color conversion table. The first color conversion table is the color conversion table that defines a correspondence relationship between input color values as color values of a colorimetric system of the input image and output color values as color values of a colorimetric system of the output image with respect to a specific count of colors. The second color conversion table is the color conversion table that defines a correspondence relationship between the print positions and the output color values corresponding to a specific input color value as one of the input color values. When the color conversion unit converts the input image all over a surface of which is constituted of only the specific input color value into the output image using the first color conversion table, the table generating unit determines whether a target-value Voronoi region and a measured-value Voronoi region are identical or not at each of the print positions in the recording medium printed by the print device, in a Voronoi diagram in a hue plane of the specific input color value that includes a generatrix corresponding to a definition color defined in the first color conversion table. The target-value Voronoi region is a Voronoi region that includes the specific input color value. The measured-value Voronoi region is a Voronoi region that includes a measured value as a color value measured by the color-measurement device. The table generating unit sets the output color value associated with the print position where the target-value Voronoi region and the measured-value Voronoi region are identical in the second color conversion table as the output color value associated with the specific input color value in the first color conversion table. The table generating unit sets the output color value associated with the print position where the target-value Voronoi region and the measured-value Voronoi region are different in the second color conversion table as a color value that is a color value in the hue plane and is different from the output color value associated with the specific input color value in the first color conversion table.

DETAILED DESCRIPTION

The following describes one embodiment of the disclosure referring to the accompanying drawings.

First, a description will be given of a configuration of a multi-function peripheral (MFP) as an image forming apparatus according to the embodiment.

FIG. 1illustrates a block diagram illustrating a configuration of an MFP10according to the embodiment.

As illustrated inFIG. 1, the MFP10includes an operation unit11, a display12, a scanner13, a printer14, a fax communication unit15, a communication unit16, a storage unit17, and a control unit18. The operation unit11is an input device such as a button with which the user inputs various kinds of operations. The display12is a display device such as a liquid crystal display (LCD) that displays various kinds of information. The scanner13is a reading device that reads an image from a document. The printer14is a print device that executes printing on a recording medium such as a paper sheet. The fax communication unit15is a fax device that performs fax communication with an external facsimile device (not illustrated) via a communication line such as a dial-up line. The communication unit16is a communication device that communicates with an external device via a network such as a local area network (LAN) or the Internet, or directly communicates with an external device by wired communication or wireless communication without a network. The storage unit17is a storage device such as a semiconductor memory and a hard disk drive (HDD). The control unit18controls the entire MFP10.

The scanner13constitutes a color-measurement device that measures a color value at each print position in a recording medium printed by the printer14.

The storage unit17stores an image forming program17aexecuted by the control unit18. The image forming program17amay be installed into the MFP10at production stage of the MFP10, may be additionally installed into the MFP10from a storage medium such as a SD card, or a universal serial bus (USB) memory, or may be additionally installed into the MFP10from a network.

The storage unit17stores an RGB-to-Lab-to-CMYK table17bas a first color conversion table that defines a correspondence relationship between a color value of an RGB colorimetric system as a colorimetric system of an input image, namely an RGB value, a color value of a Lab colorimetric system as a colorimetric system that is independent of a device, namely a Lab value, and a color value of a CMYK colorimetric system as a colorimetric system of an output image for printing by the printer14, namely a CMYK value, with respect to a specific number of colors.

The storage unit17stores an RGB-to-Lab table17cthat defines a correspondence relationship between the color value of the RGB colorimetric system as the colorimetric system of an image read by the scanner13, namely the RGB value and the color value of the Lab colorimetric system as the colorimetric system that is independent of a device, namely the Lab value, with respect to a specific number of colors.

The storage unit17can store a CMYK table17das a second color conversion table that defines a correspondence relationship between a print position and a CMYK value corresponding to a specific RGB value, for each RGB value.

The storage unit17can store a Voronoi diagram17e,which will be described later, for each specific hue.

The storage unit17can store a Delaunay diagram17f,which will be described later, for each specific hue.

The control unit18includes, for example, a Central Processing Unit (CPU), a read-only memory (ROM) that stores programs and various data, and a random-access memory (RAM) that is used as a work area of the CPU. The CPU executes the program stored in the ROM or the storage unit17.

By executing the image forming program17astored in the storage unit17, the control unit18functions as a color conversion unit18athat converts an input image into an output image for printing by the printer14using the RGB-to-Lab-to-CMYK table17bor the CMYK table17d,and a table generating unit18bthat generates the CMYK table17dbased on the RGB-to-Lab-to-CMYK table17b.

Next, a description will be given of operations of the MFP10.

First, a description will be given of the operations of the MFP10when generating a Voronoi diagram and a Delaunay triangle for each hue.

Instructing a start of generation of the Voronoi diagram and the Delaunay triangle for each hue via the operation unit11causes the control unit18to execute the operations illustrated inFIG. 2by executing the image forming program17a.

FIG. 2illustrates the operations of the MFP10when generating the Voronoi diagram and the Delaunay triangle for each hue.

As illustrated inFIG. 2, the table generating unit18btargets a specific hue in the RGB-to-Lab-to-CMYK table17b(Step S101).

The table generating unit18b,of the Lab values in the RGB-to-Lab-to-CMYK table17b,extracts the Lab value of the hue targeted at Step S101(Step S102).

The table generating unit18bgenerates a Voronoi diagram40(seeFIG. 3) using the Lab values extracted at Step S102as generatrices (Step S103).

The Voronoi diagram is a diagram that partitions a closest space from each generatrix, which is present in space, using a hyperplane such as a line and a surface. That is, the Voronoi diagram can be defined as a set of Voronoi regions {V(p1), V(p2), . . . , V(pn)} with respect to a finite subset P={p1, p2, . . . , pn} within a metric space. Here, the Voronoi region is a region V(pi) constituted of the following Formula 1 with respect to a distance function d. In the formula shown in Formula 1, d(p, pi) is a distance between a point p and a point pi, and d(p, pj) is a distance between a point p and a point pj.
V(pi)={p|d(p,pi)≤d(p,pj),i≠j}Formula 1

The Voronoi diagram has, for example, the following features: a Voronoi side is a perpendicular bisector of adjacent generatrices; and a Voronoi seed is a center of a circle that passes through three adjacent generatrices.

FIG. 3illustrates one example of the Voronoi diagram40generated at Step S103.

As illustrated inFIG. 3, the Voronoi diagram40includes generatrices41, Voronoi regions42that each include the generatrix41, Voronoi sides43that partition the Voronoi regions42, and Voronoi seeds44that are intersection points between the Voronoi sides43.

As illustrated inFIG. 2, after the process of Step S103, the table generating unit18bgenerates a Delaunay diagram50(seeFIG. 4) that corresponds to the Voronoi diagram40generated at Step S103(Step S104).

The Delaunay diagram is a diagram that connects the generatrices of the Voronoi regions adjacent with one another in the Voronoi diagram.

FIG. 4illustrates one example of the Delaunay diagram50generated at Step S104.

As illustrated inFIG. 4, the Delaunay diagram50includes Delaunay points51, which are identical to the generatrices41(seeFIG. 3) in the Voronoi diagram40(seeFIG. 3), and Delaunay sides52that connect the Delaunay points51to one another. The Delaunay diagram50is formed by a Delaunay triangle53that is formed by three Delaunay sides52.

As illustrated inFIG. 2, after the process of Step S104, the table generating unit18bstores the Voronoi diagram40generated at Step S103and the Delaunay diagram50generated at Step S104in the storage unit17, as the Voronoi diagram17eand the Delaunay diagram17fof the hue targeted at Step S101(Step S105).

Subsequently, the table generating unit18bdetermines whether all hues in the RGB-to-Lab-to-CMYK table17bare targeted or not (Step S106).

When determining that the hue that has not yet been targeted is present at Step S106, the table generating unit18bexecutes the process of Step S101.

When determining that all the hues have been targeted at Step S106, the table generating unit18bterminates the operations illustrated inFIG. 2.

When already storing the Voronoi diagram17eand the Delaunay diagram17ffor each of all the hues in the RGB-to-Lab-to-CMYK table17bin the storage unit17, the MFP10does not have to execute the operations illustrated inFIG. 2. Here, the Voronoi diagram17eand the Delaunay diagram17ffor each of all the hues in the RGB-to-Lab-to-CMYK table17bmay be generated outside the MFP10and stored in the storage unit17of the MFP10. For example, the Voronoi diagram17eand the Delaunay diagram17ffor each of all the hues in the RGB-to-Lab-to-CMYK table17bmay be stored in the storage unit17of the MFP10from an external device of the MFP10together with the RGB-to-Lab-to-CMYK table17b.

Next, a description will be given of operations of the MFP10when measuring color values at print positions of a printed matter all over the surface of which is printed with only a color value of a correction target.

Instructing a start of measurement of the color values at the print positions of the printed matter, all over the surface of which is printed with only the color value of the correction target, via the operation unit11causes the control unit18to execute the operations illustrated inFIG. 5, by executing the image forming program17a.

FIG. 5illustrates operations of the MFP10when measuring the color value by the print position of the printed matter, all over the surface of which is printed with only the color value of the correction target.

As illustrated inFIG. 5, the table generating unit18bdisplays a correction-target-color-value accepting screen60(seeFIG. 6) for accepting the color value of the correction target on the display12(Step S131).

FIG. 6illustrates one example of the correction-target-color-value accepting screen60.

The correction-target-color-value accepting screen60illustrated inFIG. 6includes: a spin box61for accepting a R value of the color value of the correction target; a spin box62for accepting a G value of the color value of the correction target; a spin box63for accepting a B value of the color value of the correction target; an OK button64for accepting the color value designated by the spin boxes61to63; and a cancel button65for terminating the acceptance of the color value designated by the spin boxes61to63. The spin boxes61to63each ensure input of integers from zero to255.

As illustrated inFIG. 5, after the process of Step S131, the table generating unit18bdetermines whether the cancel button65is pressed or not (Step S132).

When determining that the cancel button65is pressed at Step S132, the table generating unit18bterminates the operations illustrated inFIG. 5.

When determining that the cancel button65is not pressed at Step S132, the table generating unit18bdetermines whether the OK button64is pressed or not (Step S133).

When determining that the OK button64is not pressed at Step S133, the table generating unit18bexecutes the process of Step S132.

When determining that the OK button64is pressed at Step S133, the table generating unit18baccepts the color value designated by the spin boxes61to63at the time when the table generating unit18bdetermines that the OK button64is pressed (Step S134).

Subsequently, the table generating unit18bgenerates an input image for printing all over the surface of the recording medium with the color value accepted at Step S134(Step S135).

Subsequently, the color conversion unit18aconverts the input image generated at Step S135into an output image using the RGB-to-Lab-to-CMYK table17b(Step S136) and then executes printing based on the output image generated at Step S136with the printer14(Step S137).

Then, after setting the printed matter, which has been printed at Step S137, to the scanner13, a user can instruct the MFP10to continue the process from the operation unit11.

Consequently, the table generating unit18breads the printed matter with the scanner13(Step S138), and then obtains “the RGB value at each print position” based on the image read by the scanner13at Step S138(Step S139).

Subsequently, after obtaining “the Lab value at each print position” by converting the RGB value obtained at Step S139into the Lab value using the RGB-to-Lab table17c(Step S140), the table generating unit18bstores “the Lab value at each print position” obtained at Step S140in the storage unit17(Step S141), and then terminates the operations illustrated inFIG. 5.

Next, a description will be given of operations of the MFP10when generating the CMYK table17drelative to a specific RGB value.

Instructing a start of generation of the CMYK table17drelative to the specific RGB value via the operation unit11causes the control unit18to execute the operations illustrated inFIGS. 7 and 8by executing the image forming program17a.

FIG. 7illustrates a part of operations of the MFP10when generating the CMYK table17drelative to the specific RGB value.FIG. 8illustrates a part that is a part of operations of the MFP10when generating the CMYK table17drelative to the specific RGB value and is different from the part illustrated inFIG. 7.

As illustrated inFIGS. 7 and 8, the table generating unit18bdisplays the correction-target-color-value accepting screen60(seeFIG. 6) on the display12(Step S161).

Subsequently, after the process of Step S161, the table generating unit18bdetermines whether the cancel button65is pressed or not (Step S162).

When determining that the cancel button65is pressed at Step S162, the table generating unit18bterminates the operations illustrated inFIG. 5.

When determining that the cancel button65is not pressed at Step S162, the table generating unit18bdetermines whether the OK button64is pressed or not (Step S163).

When determining that the OK button64is not pressed at Step S163, the table generating unit18bexecutes the process of Step S162.

When determining that the OK button64is pressed at Step S163, the table generating unit18baccepts the color value designated by the spin boxes61to63at the time when the table generating unit18bdetermines that the OK button64is pressed (Step S164).

Subsequently, the table generating unit18bidentifies the Lab value (hereinafter referred to as a “target value”) associated with the RGB value (hereinafter referred to as a “target RGB value”) accepted at Step S164as a definition color in the RGB-to-Lab-to-CMYK table17b(Step S165), identifies the Voronoi diagram17eassociated with the hue of the identified target value (Step S166), and then identifies the Voronoi region (hereinafter referred to as a “target-value Voronoi region”) in which the target value is included as the generatrix in the identified Voronoi diagram17e(Step S167).

Subsequently, the table generating unit18btargets a specific print position that is printable on the recording medium by the printer14(Step S168).

Subsequently, the table generating unit18bobtains the Lab value (hereinafter referred to as a “measured value”) corresponding to the print position of the current target based on the “Lab value at each print position” stored by the operations illustrated inFIG. 5relative to the target RGB value (Step S169).

Subsequently, in the Voronoi diagram17eidentified at Step S166, the table generating unit18bidentifies the Voronoi region (hereinafter referred to as a “measured-value Voronoi region”) in which the measured value obtained at Step S169is included (Step S170).

Subsequently, the table generating unit18bdetermines whether the target-value Voronoi region and the measured-value Voronoi region are identical or not (Step S171).

When determining that the target-value Voronoi region and the measured-value Voronoi region are identical at Step S171, the table generating unit18bstores the target RGB value as the RGB value corresponding to the print position of the current target (Step S172).

FIG. 9illustrates one example of the Voronoi diagram40when the target-value Voronoi region and the measured-value Voronoi region are identical.

InFIG. 9, the Voronoi region42in which a generatrix41A as the target value is included, namely the target-value Voronoi region, and the Voronoi region42in which a measured value45is included, namely the measured-value Voronoi region are identical.

As illustrated inFIGS. 7 and 8, when determining that the target-value Voronoi region and the measured-value Voronoi region are not identical at Step S171, the table generating unit18bdetermines whether the measured value is present inside of any of two Delaunay triangles that have vertices of the target value, namely the generatrix of the target-value Voronoi region, and the generatrix of the measured-value Voronoi region or not (Step S173).

FIG. 10Aillustrates one example of the Delaunay diagram50that indicates the measured value when the measured value is present inside the Delaunay triangles that have vertices of the target value and the generatrix of the measured-value Voronoi region.FIG. 10Billustrates one example of the Delaunay diagram50that indicates the measured value when the measured value is not present inside the Delaunay triangles that have vertices of the target value and the generatrix of the measured-value Voronoi region.

InFIGS. 10A to 10B, the Delaunay triangles that have the vertices of the target value and the generatrix of the measured-value Voronoi region are illustrated with half-tone dot meshing.

InFIG. 10A, the measured value45is present inside one of the two Delaunay triangles53that have the vertices of the generatrix41A as the target value and the generatrix41of the measured-value Voronoi region, namely the Voronoi region42that includes the measured value45.

InFIG. 10B, the measured value45is not present inside any one of the two Delaunay triangles53that have the vertices of the generatrix41A as the target value and the generatrix41of the measured-value Voronoi region, namely the Voronoi region42that includes the measured value45.

As illustrated inFIGS. 7 and 8, when determining that the measured value is present inside at Step S173, the table generating unit18bcalculates a distance L1between the target value and the generatrix of the measured-value Voronoi region (Step S174), and then calculates a correction distance by doubling the distance L1calculated at Step S174(Step S175).

FIG. 11illustrates one example of the Voronoi diagram40that indicates the distance between the target value and the generatrix of the measured-value Voronoi region.

InFIG. 11, the distance L1is a distance between the generatrix41A as the target value and the generatrix41of the measured-value Voronoi region, namely the Voronoi region42that includes the measured value45.

As illustrated inFIGS. 7 and 8, when determining that the measured value is not present inside at Step S173, the table generating unit18bcalculates the distance L1between the target value and the generatrix of the measured-value Voronoi region (Step S176), calculates a distance L2between the measured value45of the measured-value Voronoi region and an inner center54aof the Delaunay triangle that includes the measured value (Step S177), and then calculates the correction distance by totaling two times of the distance L1calculated at Step S176and the distance L2calculated at Step S177(Step S178). The distance L2is also referred to as a distance calculated by a second criterion.

FIG. 12Aillustrates one example of the Voronoi diagram40that indicates the distance between the target value and the generatrix of the measured-value Voronoi region.FIG. 12Billustrates one example of the Delaunay diagram50that indicates the distance between the measured value45of the measured-value Voronoi region and the inner center54aof the Delaunay triangle that includes the measured value.

InFIG. 12A, the distance L1is a distance between the generatrix41A as the target value and the generatrix41of the measured-value Voronoi region, namely the Voronoi region42that includes the measured value45.

InFIG. 12B, the distance L2is a distance between the measured value45of the measured-value Voronoi region, namely the Voronoi region42that includes the measured value45and a center of an inscribed circle54of the Delaunay triangle53that includes the measured value45, namely the inner center54a.

As illustrated inFIGS. 7 and 8, after the process of Step S175or the process of Step S178, the table generating unit18bidentifies a point of a position of the correction distance on the target value side (an opposite side of the measured value with respect to the target value) from the measured value as a correction point, on a straight line passing through the target value and the measured value (Step S179).

FIG. 13Aillustrates one example of the Voronoi diagram40that indicates the correction point when the measured value is present inside the Delaunay triangle that has the vertices of the target value and the generatrix of the measured-value Voronoi region.FIG. 13Billustrates one example of the Voronoi diagram40that indicates the correction point when the measured value is not present inside the Delaunay triangle that has the vertices of the target value and the generatrix of the measured-value Voronoi region.

InFIG. 13A, a correction point46is a point of the position of the correction distance (2×L1) on the generatrix41A side from the measured value45, on the straight line passing the generatrix41A as the target value and the measured value45. The correction distance is also referred to as a distance calculated by a first criterion.

InFIG. 13B, the correction point46is a point of the position of the correction distance (2×L1+L2) on the generatrix41A side from the measured value45, on the straight line passing through the generatrix41A as the target value and the measured value45.

As illustrated inFIGS. 7 and 8, after the process of Step S179, the table generating unit18bconverts the Lab value of the correction point identified at Step S179into the RGB value by interpolation calculation based on the RGB-to-Lab-to-CMYK table17b(Step S180).

Subsequently, the table generating unit18bstores the RGB value obtained at Step S180as the RGB value that corresponds to the print position of the current target (Step S181).

After the process of Step S172or S181, the table generating unit18bdetermines whether all the print positions, which are printable on a recording medium by the printer14, are targeted or not (Step S182).

When determining that the print position that is not yet targeted is present at Step S182, the table generating unit18bexecutes the process of Step S168for the print position that is not yet targeted.

When determining that all the print positions, which are printable on the recording medium by the printer14, are targeted at Step S182, the table generating unit18bgenerates the CMYK table17drelative to the target RGB value by converting the “RGB value corresponding to the print position” stored at Step S172or S181into the CMYK value based on the RGB-to-Lab-to-CMYK table17b(Step S183).

Subsequently, the table generating unit18bstores the CMYK table17dgenerated at Step S183in the storage unit17(Step S184) and then terminates the operations illustrated inFIGS. 7 and 8.

Next, a description will be given of operations of the MFP10when execution of printing based on an input image is instructed.

FIG. 14illustrates the operations of the MFP10when execution of printing based on the input image is instructed.

As illustrated inFIG. 14, the color conversion unit18adetermines whether the input image is an input image having a single color value or not (Step S201).

When determining that the input image is an input image having a single color value at Step S201, the color conversion unit18adetermines whether the CMYK table17dof the color value included in the input image is stored in the storage unit17or not (Step S202).

When determining that the input image is not an input image having a single color value at Step S201, or when determining that the CMYK table17dof the color value included in the input image is not stored in the storage unit17at Step S202, the color conversion unit18aconverts the input image into the output image using the RGB-to-Lab-to-CMYK table17b(Step S203).

When determining that the CMYK table17dof the color value included in the input image is stored in the storage unit17at Step S202, the color conversion unit18aconverts the input image into the output image using the CMYK table17dof the color value included in the input image (Step S204).

After the process of Step S203or Step S204, the color conversion unit18aexecutes the print job based on the output image generated at Step S203or Step S204with the printer14(Step S205), and then terminates the operations illustrated inFIG. 14.

As described above, the MFP10sets an output color value in the CMYK table17d,which defines the correspondence relationship between the print position and the output color value that corresponds to the specific input color value, as the color value in the hue plane that includes the specific input color value (Steps S172, S181and S183). Thus, this ensures the reduced color unevenness depending on the print positions by correcting not only lightness but also saturation with respect to the output color value. Consequently, the MFP10ensures the improved ability of reducing color unevenness by the print position in a print job based on an input image having a single color value.

Generating the CMYK table17dusing the Voronoi diagram enables the MFP10to reduce a calculation amount required for generating the CMYK table17d.Generating the CMYK table17dusing the Delaunay diagram enables the MFP10to further reduce a calculation amount required for generating the CMYK table17d.Consequently, the MFP10enables generating the CMYK table17dat high speed.

When the target-value Voronoi region and the measured-value Voronoi region are different (NO at Step S171), the MFP10calculates the distance between the output color value when the measured value is present inside any of the two Delaunay triangles that have the vertices of the specific input color value and the generatrix of the measured-value Voronoi region (YES at Step S173), and the measured value simply using the measured value indirectly (Steps S174to S175). Consequently, this enables the MFP10to generate the CMYK table17dat high speed.

When the target-value Voronoi region and the measured-value Voronoi region are different (NO at Step S171), the MFP10calculates the distance between the output color value when the measured value is present outside both of the two Delaunay triangles that have the vertices of the specific input color value and the generatrix of the measured-value Voronoi region (NO at Step S173), and the measured value simply using the measured value indirectly (Steps S176to S178). Consequently, this enables the MFP10to generate the CMYK table17dat high speed.

While in the embodiment the processes inFIG. 5and the processes inFIGS. 7 and 8are separately executed, the MFP10may execute the processes inFIG. 5and the processes inFIGS. 7 and 8as a series of processes. When the MFP10executes the processes inFIG. 5and the processes inFIGS. 7 and 8as a series of processes, it is only necessary that only any one of the processes of Steps S131to S134in the processes inFIG. 5and the processes of Steps S161to S164in the processes inFIGS. 7 and 8is executed.

While in the embodiment the Voronoi diagrams and the Delaunay diagrams for all the hue planes are prepared, the MFP10may, for example, after the process at Step S134, prepare the Voronoi diagram and the Delaunay diagram of the hue plane where the color value accepted at Step S134is present.

While in the embodiment the MFP10executes all the processes, a part of the processes may be executed by an apparatus other than the MFP10. For example, a color-measurement device that measures the color value at each print position in the recording medium printed by the printer14may be a device outside the MFP10not the scanner13. That is, the MFP10and a color-measurement device outside the MFP10may constitute an image forming system.

While the image forming apparatus of the disclosure is an MFP in the embodiment, an image forming apparatus other than an MFP, such as a printer-only machine or a copy-only machine, may be employed.