JP2019087795A - Image reading device, image forming apparatus, and color balance correction method - Google Patents

Abstract

To efficiently grasp and correct a variation in color balance characteristics in reading due to an individual difference and a change in light source characteristics in an image reading device, with a simple method regardless of the type of a white light source.SOLUTION: In an image forming apparatus, a control unit reads, with an image reading unit, a pattern image including patches having a plurality of gradations of reference colors to perform predetermined calculation by using R, G, B values of the patches in the acquired image data, and thereby calculates a color balance value when the patches are read by the image reading unit, calculates a feature quantity representing the color balance characteristics of the image reading unit on the basis of the calculated color balance value, and determines a parameter for correcting the color balance of the image data acquired by the image reading unit on the basis of the calculated feature quantity. The control unit corrects the color balance of the image data acquired by the image reading unit by using the determined parameter.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image reading apparatus, an image forming apparatus, and a color balance correction method.

  As a correction for reading variations in a scanner (image reading apparatus), there is a method of detecting and canceling variations in the intensity of each color of RGB for each element at the time of reading a white shading reference plate. This is a basic adjustment commonly called shading correction, in which (R, G, B) in the case of reading a predetermined white color is aligned with the reference white level (Rw, Gw, Bw). Here, Rw, Gw, and Bw are set to about 180 to 255 in the case of an 8-bit scanner. However, even if the reading level of the white document is always stable regardless of individual differences due to such correction, in the case of a chromatic document, the R, G, and so on of the reading system due to the dispersion of the white spectrum of the scanner light source. It is known that variations occur in the color balance of B.

  For example, in Japanese Patent Application Laid-Open Publication No. 2008-112501, in the white light emitting device, the color tone variation of the white light is adjusted by changing the YAG-based light emitter and the pigment to be mixed in the covering member according to the variation of It has been described that.

  Further, in Patent Document 2, in the image forming apparatus, an adjustment original for scanner C calibration provided in the image forming apparatus is scanned by a scanner to detect the B reflection amount from the patch for C calibration, and B reference data and B A technique is described that calculates the ratio to the gradation value according to the amount of reflection as the B correction value α, and corrects the fluctuation of the blue light amount of the white light source of the scanner.

  In addition, for example, the reading results of multiple colors by the scanner are collected in a dedicated chart, and the conversion matrix coefficients of (R, G, B) → (R, G, B) are individualized so as to minimize the average difference. It is also done to optimize the settings.

JP, 2004-119743, A JP 2017-46249 A

However, the technology described in Patent Document 1 is a technology of quality control in the manufacturing process of the white light source, and can not cope with the fluctuation of the light source characteristic accompanying the use of the product.
In addition, the technology described in Patent Document 2 is directed only to a white light source composed of a plurality of source light sources of a plurality of spectra, and is compatible with other white light sources such as fluorescent lamps and halogen lamps. Absent. Further, the patch to be read and the source light source to be adjusted are different depending on the types of a plurality of source light sources constituting the white light source. Therefore, it can not be applied widely and generally regardless of the type of white light source of the scanner.
In addition, since the above-described calibration adjustment original and dedicated chart are discolored by light and heat due to repeated irradiation of the light source, complicated color management is required, and correction accuracy sufficient to maintain the same reading accuracy as the initial one. It is difficult to keep the

  In the image forming apparatus that performs color printing, various adjustments are performed to stabilize the gradation of each color of C (cyan), M (magenta), Y (yellow), and K (black). In an apparatus having a scanner function, a method of outputting a pattern for adjustment and reading it with a scanner to grasp gradation characteristics to make correction to a more appropriate level is also widely performed. In order to carry out this accurately, it is necessary for the scanner reading characteristics to have small variations. However, in various scanner systems, for example, due to variations in the spectral sensitivity characteristics of the system including the white characteristics of the LED light source. Accordingly, the accuracy of grasping the gradation characteristics may deteriorate, and the correction of the gradation characteristics at the time of printing may be insufficient.

  An object of the present invention is to enable efficient grasping and correction of variations in color balance characteristics of reading due to individual differences and fluctuations such as light source characteristics in an image reading apparatus regardless of the type of white light source. It is.

In order to solve the above-mentioned subject, the image reading device of the invention according to claim 1 is
Image reading means for reading a color image and acquiring image data consisting of a plurality of read colors;
Performing predetermined calculations using values of the plurality of read colors in each patch of image data acquired by reading a pattern image including a plurality of gradations of at least one reference color by the image reading unit; And color balance value calculation means for calculating a color balance value when each of the patches is read by the image reading means.
Feature amount calculating means for calculating a feature amount representing a color balance characteristic of reading by the image reading means based on the color balance value calculated by the color balance value calculating means;
A determination unit configured to determine a parameter for correcting the color balance of the image data acquired by the image reading unit based on the feature amount calculated by the feature amount calculation unit;
A correction unit that corrects the color balance of the image data acquired by the image reading unit using the parameter determined by the determination unit;
Equipped with

In the invention described in claim 2, in the invention described in claim 1,
The plurality of read colors are red, green and blue,
The reference color includes at least one of cyan, magenta, yellow and black.

In the invention described in claim 3, in the invention described in claim 1 or 2,
The determination means determines the parameter based on a comparison between the feature amount calculated by the feature amount calculation means and a feature amount as a reference.

The image forming apparatus of the invention according to claim 4 is
The image reading apparatus according to any one of claims 1 to 3.
An image forming unit that forms an image on a sheet by using colorants of a plurality of reference colors including the reference color;
Equipped with

In the invention according to claim 5, in the invention according to claim 4,
The pattern image is an image output by the image forming unit.

In the invention according to claim 6, in the invention according to claim 5,
The parameter reading control of the gradation characteristic of the reference color of the image forming means by reading a pattern image including patches of plural gradations of at least one reference color outputted by the image forming means by the image reading means These parameters are used to convert the read data of each patch of the reference color acquired by the image reading unit into gradation values when correcting the γ curve to be performed.

In the invention according to claim 7, in the invention according to claim 5 or 6,
The parameter is for converting the image data to the plurality of reference colors in a copy function in which the image forming unit forms an image on a sheet based on image data acquired by reading the document by the image reading unit. Parameters used for

The invention according to claim 8 is
A color balance correction method in an image reading apparatus comprising an image reading unit for reading a color image and acquiring image data composed of a plurality of read colors, the method comprising:
Performing predetermined calculations using values of the plurality of read colors in each patch of image data acquired by reading a pattern image including a plurality of gradations of at least one reference color by the image reading unit; A color balance value calculating step of calculating a color balance value when each of the patches is read by the image reading unit;
A feature amount calculating step of calculating a feature amount representing a color balance characteristic of reading by the image reading unit based on the color balance value calculated in the color balance value calculating step;
A determination step of determining a parameter for correcting the color balance of the image data acquired by the image reading unit based on the feature amount calculated in the feature amount calculation step;
A correction step of correcting the color balance of the image data acquired by the image reading unit using the parameter determined in the determination step;
including.

  According to the present invention, it is possible to efficiently grasp and correct variation in color balance characteristics of reading due to individual differences and fluctuations such as light source characteristics in the image reading apparatus regardless of the type of white light source. It becomes.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus. FIG. 2 is a block diagram showing the main functional configuration of the image forming apparatus. It is a figure which shows an example of the general spectral characteristic of each part (a light source, a lens, CCD) which comprises a color scanner. It is a flowchart which shows the scanner correction | amendment process performed by the control part of FIG. Calculated from R, G, B values obtained by reading patches of each gradation of each reference color with a scanner of standard color balance characteristics (scanner standard product) and a scanner with shifted color balance characteristics (scanner A) It is the graph which plotted the color balance value (r, g). Calculated from R, G, B values obtained by reading patches of each gradation of each reference color with a scanner of standard color balance characteristics (scanner standard product) and a scanner with shifted color balance characteristics (scanner A) It is the graph which plotted the color balance value (Hue) with respect to G value. It is a figure which shows the example of data storage of a parameter determination table. It is a flowchart which shows the engine density correction process performed by the control part of FIG.

  Hereinafter, the present embodiment will be described in detail based on the drawings. However, the scope of the invention is not limited to the illustrated example.

  FIG. 1 is a view schematically showing an entire configuration of an image forming apparatus 1 according to an embodiment of the present invention. FIG. 2 is a block diagram showing the main functional configuration of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 shown in FIGS. 1 and 2 is an intermediate transfer type color image forming apparatus using an electrophotographic process technology. That is, the image forming apparatus 1 transfers the toner images of Y (yellow), M (magenta), C (cyan), and K (black) reference colors formed on the photosensitive drum 413 onto the intermediate transfer belt 421. After the toner images of four colors are superimposed on the intermediate transfer belt 421 (secondary transfer), a color image is formed by transfer (secondary transfer) on the sheet S.

  As shown in FIG. 2, the image forming apparatus 1 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a sheet conveyance unit 50, a fixing unit 60, a storage unit 70, a communication unit 80 and A control unit 100 is provided.

  The control unit 100 includes a central processing unit (CPU) 101, a read only memory (ROM) 102, a random access memory (RAM) 103, and the like. The CPU 101 reads out a program corresponding to the processing content from the ROM 102, develops it in the RAM 103, and cooperates with the developed program to centrally control the operation of each block of the image forming apparatus 1 shown in FIG.

The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a scanner 12 and the like.
The automatic document feeder 11 conveys the document D placed on the document tray by the conveyance mechanism to the scanner 12. The automatic document feeder 11 can continuously read the images (including both sides) of a large number of documents D placed on the document tray at once.

The scanner 12 is an image reading unit that reads a color image and acquires image data including an R (red) value, a G (green) value, and a B (blue) value. The scanner 12 includes a light source 12a, a lens 12b, a CCD (Charge Coupled Device) sensor 12c, etc., and the original D carried on the contact glass from the automatic original feeding device 11 or the original D placed on the contact glass The document image is read by optically scanning the document D and forming an image of the reflected light from the document D on the light receiving surface of the CCD sensor 12c to obtain image data. The image processing unit 30 applies predetermined image processing to the image data.
The scanner 12 and the control unit 100 realize the image reading apparatus of the present invention.
In the present embodiment, a white LED (Light Emitting Diode) is used as the light source 12a, but another white light source such as a fluorescent lamp or a halogen lamp may be used.

  The operation display unit 20 is configured of, for example, a liquid crystal display (LCD) with a touch panel, and functions as the display unit 21 and the operation unit 22. The display unit 21 displays various operation screens, image status display, operation status of each function, and the like according to a display control signal input from the control unit 100. The operation unit 22 includes various operation keys such as a ten key and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 100.

  The image processing unit 30 includes a circuit or the like that performs digital image processing according to settings on the input image data. For example, under the control of the control unit 100, the image processing unit 30 performs various types of image processing such as shading correction, color conversion, gradation correction, and compression processing. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 forms an image forming unit 41C, 41M, 41Y, 41K for forming an image with toner of each of the reference colors of C component, M component, Y component, and K component based on the image data subjected to image processing. , The intermediate transfer unit 42 and the like.

  The image forming units 41C, 41M, 41Y, and 41K for the C component, the M component, the Y component, and the K component have the same configuration. For convenience of illustration and description, common components are denoted by the same reference numerals, and when the components are distinguished, they are indicated by appending C, M, Y, or K to the reference. In FIG. 1, reference numerals are attached only to the components of the image forming unit 41Y for the Y component, and reference numerals of the components of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, an image density sensor 416, and the like. The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422, a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The surface of the photosensitive drum 413 is uniformly charged by the charging device 414, and a latent image is formed by scanning exposure by the exposure device 411, and the developing device 412 forms a latent image of any of C, M, Y, and K. The latent image is visualized by the adhesion of the toner. As a result, a toner image of a predetermined color is formed on the photosensitive drum 413. The toner image formed on the photosensitive drum 413 is sequentially transferred to a predetermined position on the rotating intermediate transfer belt 421 by the primary transfer roller 422. The transfer residual toner remaining on the surface of the photosensitive drum 413 after the primary transfer is removed by the drum cleaning device 415.

  The toner images of the respective colors transferred onto the intermediate transfer belt 421 are transferred by the secondary transfer roller 424 to the sheet S transported at a predetermined timing by the sheet transport unit 50 described later. Further, transfer residual toner remaining on the surface of the intermediate transfer belt 421 is removed by a belt cleaning device 426.

  The paper conveyance unit 50 includes a paper feed unit 51, a paper discharge unit 52, a conveyance path unit 53, and the like. In the three sheet feeding tray units 51a to 51c constituting the sheet feeding unit 51, sheets S (standard sheets and special sheets) identified based on basis weight, size and the like are stored for each preset type. . The conveyance path portion 53 has a plurality of conveyance roller pairs such as a registration roller pair 53a.

  The sheets S accommodated in the sheet feeding tray units 51 a to 51 c are fed one by one from the top and conveyed by the conveyance path unit 53 to the image forming unit 40. At this time, the inclination of the fed sheet S is corrected and the transport timing is adjusted by the registration roller unit in which the registration roller pair 53a is disposed. Then, in the image forming unit 40, the toner images of the intermediate transfer belt 421 are secondarily transferred collectively on one side of the sheet S, and the sheet S on which the toner image is transferred is conveyed toward the fixing unit 60.

The fixing unit 60 fixes the toner image on the sheet S by heating and pressing the sheet S on which the toner image has been secondarily transferred and conveyed at the fixing nip.
The fixed sheet S is discharged to the outside of the apparatus by the discharge unit 52 provided with a discharge roller 52a.

  The storage unit 70 is configured of, for example, a non-volatile semiconductor memory (so-called flash memory), a hard disk drive, or the like. The storage unit 70 stores various data including various setting information related to the image forming apparatus 1.

For example, the storage unit 70 stores a parameter determination table 701 (see FIGS. 7A to 7D) for determining a parameter according to the feature amount based on the color balance value in the scanner correction mode described later. There is.
The storage unit 70 further includes image data of a correction pattern image, a plurality of color conversion parameters (a plurality of engine density correction parameters, a plurality of copy parameters), a feature value calculated in the scanner correction mode, and a scanner correction mode. The type of color conversion parameter set in step (g), the γ curve used in tone correction, etc. are stored.

  The communication unit 80 includes, for example, a communication control card such as a LAN (Local Area Network) card, and communicates with an external apparatus (for example, a personal computer) connected to a communication network such as a LAN or WAN (Wide Area Network). Send and receive various data.

Next, the operation in the present embodiment will be described.
FIG. 3 is a diagram showing an example of general spectral characteristics of each part (light source, lens, CCD) constituting the color scanner. As shown in FIG. 3, each part constituting the color scanner has spectral characteristics, and the spectral sensitivity characteristic of the color scanner is (light source spectral characteristic) × (lens transmission (reflection) spectral characteristic) × (CCD spectral sensitivity) It is expressed by the integration of characteristics).
For example, in the light source, it is known that fluctuations such as a peak wavelength shift in the blue region of the spectrum particularly on the short wavelength side in the manufacturing process may occur due to lot differences in light source elements. Also in lenses and CCDs, variations in individual differences in manufacturing processes occur. Moreover, the characteristic of each part may change with use of a product. Such individual differences and changes in the characteristics of each part cause variations in the color balance of R, G, and B of image data acquired by reading with a color scanner, and image data of different values are obtained even if the same color is read. It will be acquired.

Therefore, the image forming apparatus 1 has a scanner correction mode for correcting the color balance of R, G, and B of the image data acquired by the scanner 12.
Here, in general, each reference color (C, M, Y, K) of the image forming apparatus is composed of one specific type of coloring material (coloring material), and it is unnecessary to use a predetermined recommended product. The reproduced colors of the printed image have a certain spectral reflection characteristic unless the color mixture is mixed and the process until fixing on the paper is not greatly changed. Although the spectral reflection characteristics fluctuate with the change of the color material amount and the R, G, B values acquired by the scanner 12 and their color balance characteristics also fluctuate, if the scanner characteristics are fixed, the fluctuation is a constant locus Varies along. In the scanner correction mode, using this fact, the R, G, B values obtained by scanning the patch of the appropriate reference color outputted by the image forming unit 40 with the scanner 12 and the color balance characteristics thereof should be grasped. Image data acquired by the scanner 12 according to the estimated color balance characteristics by simply estimating what kind of state the color balance characteristics of the reading by the scanner 12 (hereinafter referred to as the color balance characteristics of the scanner 12 are) Select parameters to correct the color balance of.

  FIG. 4 is a flowchart showing a scanner correction process performed in the scanner correction mode. The scanner correction process is executed by the cooperation of the control unit 100 and the program stored in the storage unit 70 when switching to the scanner correction mode is instructed by the operation unit 22.

First, the control unit 100 reads the image data of the correction pattern image stored in the storage unit 70, and causes the image forming unit 40 to form and output the correction pattern image on the sheet S (step S1).
Here, the correction pattern image is, for example, an image formed of patches of multiple gradations from the minimum gradation to the maximum gradation of each reference color (C, M, Y, K).

  Next, the control unit 100 reads the correction pattern image output in step S1 by the scanner 12 of the image reading unit 10, and acquires R, G, B values of each patch (step S2).

  Next, the control unit 100 calculates the color balance value of each patch from the R, G, and B values of each patch acquired in step S2 (step S3).

Here, the color balance value is a value obtained by performing a predetermined calculation using R, G, and B values acquired by reading each gradation of each reference color with a scanner. As the color balance value, for example, the chromaticity of (r, g) can be used. The r value and the g value can be obtained by the following (formula 1) and (formula 2).
r = R / (R + G + B) (Equation 1)
g = G / (R + G + B) (Equation 2)

5 (a) to 5 (d) are obtained by reading patches of each gradation of each reference color with a scanner of standard color balance characteristics (scanner standard product) and a scanner (scanner A) whose color balance characteristics are deviated. The color balance values (r, g) calculated from the R, G, B values are plotted. Fig. 5 (a) shows the color balance values (r, g) calculated by reading a black patch, (b) a cyan patch, (c) a magenta patch, and (d) a yellow patch. It is
As shown in FIGS. 5 (a) to 5 (d), the color balance values (r, g) move along a specific locus together with the density of the patch for each reference color, and the locus is the color balance of the scanner It can be seen that the shift is caused by the deviation of the characteristics, and the difference is smaller as the patch density is lower.

Also, the hue Hue may be used as the color balance value.
6 (a) to 6 (c) are obtained by reading a patch of each gradation of each reference color with a scanner of standard color balance characteristics (scanner standard product) and a scanner (scanner A) whose color balance characteristics are deviated. The color balance values (Hue) calculated from the R, G, B values are plotted against the G values. FIG. 6 (a) is a plot of values calculated by reading a cyan patch, (b) a magenta patch, and (c) a yellow patch. Among K, C, M, Y, and K, since the difference in color balance characteristics by the scanner is small, the description of k is omitted.
As shown in FIGS. 6 (a) to 6 (c), the color balance value (Hue) shifts along a specific locus together with the density of the patch for each color, and the locus is caused by the deviation of the color balance characteristic of the scanner. It turns out that it is shifting.

Although the difference in reading value may include the influence of variations in the paper used to output the correction pattern image, for example, for the blank standard paper (Rwstd, Gwstd, Bwstd), If (Rw, Gw, Bw) is different,
R → R * (Rwstd / Rw) (same for G and B)
The color balance value may be calculated after absorption as in FIG.

  Next, the control unit 100 calculates a feature amount representing the color balance characteristic of the scanner 12 (step S4).

For example, when the color balance value calculated in step S3 is (r, g), any one of the following (1) to (3) can be used as the feature amount.
(1) In the case of using the read result of the patch of Y The slope Sy of the linear approximation line of the plot of (r, g) of each gradation (refer to FIG. 5D) is used as the feature amount.
(2) In the case of using the reading result of the patch of M: A slope Sm of a linear approximate straight line of a plot (see FIG. 5C) of (r, g) having a g value of 0.200 or less is used as a feature value.
(3) In the case of using the reading result of the patch C: Obtain a regression curve of a plot (r, g) (see FIG. 5B) of a g value of 0.320 or less, and g value of the regression curve thus obtained = 0. An r value of 30 is used as a feature value.

  Also, for example, when the color balance value calculated in step S3 is the hue Hue, for example, the hue Hue at the G value (for example, G = 70 in the case of M) to be a reference of any of C, M, Y It calculates | requires by interpolation calculation, and makes this a feature-value.

  It is determined in advance which of the colors C, M, and Y the color balance value based on is a feature amount. For example, after assembling the scanner 12, a color balance value is calculated based on R, G, B values obtained by reading a plurality of gradation patches of each reference color by the scanner 12, and the color balance value of each reference color is calculated. Based on the color, it is determined which color-based color balance value is to be the feature.

  Next, the control unit 100 refers to the parameter determination table 701 and determines whether the comparison result of the calculated feature amount with the reference feature amount is different from the comparison result with the previously calculated feature amount with the reference feature amount ( Step S5). The reference feature value is a feature value that represents a color balance characteristic equivalent to that of a scanner standard product.

FIGS. 7A to 7D show examples of the parameter determination table 701 stored in the storage unit 70. FIG.
FIGS. 7A to 7C show examples of the parameter determination table 701 when the color balance value is (r, g). 7A shows an example where the feature amount of the color balance value is the slope Sy of (r, g) of Y, and FIG. 7B shows that the feature amount of the color balance value is M (r, g) FIG. 7C shows an example of the case where the feature amount of the color balance value is the r value when the g value of C is 0.30.
FIG. 7D shows an example of the parameter determination table 701 in the case where the color balance value is Hue and the feature amount of the color balance is Hue when the G value of M = 70. In FIG. 7 (d), when the feature amount exceeds the predetermined range, an abnormality warning is provided, but a feature amount range is also provided in which an abnormality warning is similarly issued even when the color balance value is (r, g). You may do it.
As shown in FIGS. 7A to 7D, the parameter determination table 701 is a value representing the comparison result between the range of feature amounts and the reference feature amount of the feature amounts of the feature amount range (the comparison result, A value representing whether or not there is a deviation from the reference feature amount) is stored in association with the type of color conversion parameter corresponding to the feature amount range.

  When it is determined that the comparison result of the calculated feature amount with the reference feature amount is the same as the comparison result with the reference feature amount of the feature amount calculated previously (step S5; NO), the control unit 100 proceeds to step S7. Do.

  If it is determined that the comparison result of the calculated feature amount with the reference feature amount is different from the comparison result with the previously calculated feature amount with the reference feature amount (step S5; YES), the control unit 100 determines the parameter determination table 701 The color conversion parameter to be used for correcting the color balance of the image data read by the scanner 12 is determined and set based on the comparison result of the calculated feature amount with the reference feature amount of the feature amount (step S6). Migrate to

  Here, the color conversion parameters include an engine density correction parameter and a copy parameter. Five types of parameters “−2” to “+2” are stored in the storage unit 70, respectively. The engine density correction parameter and the copy parameter are both passed to the image processing unit 30 for converting the R, G and B values of the image data read by the scanner 12 into C, M, Y and K tone values. Parameters (table showing the correspondence between R, G, B values and tone values of C, M, Y, K), but by performing color conversion using each parameter, a feature corresponding to each parameter The deviation of the color balance characteristic of the quantity range from the color balance characteristic of the scanner standard product is simultaneously corrected. Each parameter is obtained experimentally.

  The engine density correction parameters are C, M, and R, G, and B values obtained by reading, with the scanner 12, patches of each color of the correction pattern image output by the image forming unit 40 in engine density correction processing described later. It is a table (function) for converting into gradation values of Y and K. For example, it is composed of a plurality of one-dimensional curves indicating the relationship between R value and C tone value, G value and M tone value, B value and Y tone value, and G value and Y tone value. Be done.

  The copy parameters are tables (functions) for converting R, G, B values obtained by reading the original D by the scanner 12 into C, M, Y, K tone values. For example, the copy parameter is a table showing the relationship between the combination of R, G, B values (R, G, B) and the combination of C, M, Y, K tone values (C, M, Y, K) It is.

  In step S7, the control unit 100 stores the feature amount calculated this time in the storage unit 70 (step S7), and ends the scanner correction process.

Next, the engine concentration correction process will be described.
In the engine density correction process, the scanner 12 reads a pattern image including patches of plural gradations of a plurality of reference colors output by the image forming unit 40 and controls a gradation characteristic of the image forming unit 40 by using a γ curve. It is processing to correct.

  FIG. 8 is a flowchart showing the engine density correction process. The engine concentration correction process is executed by cooperation of the control unit 100 and the program stored in the storage unit 70 when switching to the engine concentration correction mode is instructed by the operation unit 22.

  First, the control unit 100 controls the image stabilization in the image forming unit 40 (step S11). For example, a patch is formed on the intermediate transfer belt 421 by the image forming unit 41 for each color of C, M, Y, and K, and the formed patch is read by the image density sensor 416. Make corrections etc.

  Next, the control unit 100 reads the image data of the correction pattern image stored in the storage unit 70, and causes the image forming unit 40 to form and output the correction pattern image on the sheet S (step S12).

  Next, the control unit 100 reads the correction pattern image by the scanner 12 of the image reading unit 10, and acquires R, G, B values of each patch (step S13).

  Next, the control unit 100 converts the R, G, B values into C, M, Y, K tone values using the engine density correction parameters set in the scanner correction mode (step S14). .

  Next, the control unit 100 reads C, M, Y, K tone values converted from R, G, B values obtained by reading the patches of the respective colors with the scanner 12, and the ideal values for the respective patches. The γ curves of C, M, Y and K colors are corrected from the correspondence relationship with C, M, Y and K (to be aimed) (step S15), and the engine density correction process is ended.

  Here, in general, since the engine density correction parameters are set according to the color balance characteristics of the standard scanner product, when individual differences and fluctuations occur in the color balance characteristics of the scanner, the read R, The G and B values can not be converted into appropriate C, M, Y and K tone values, and as a result, sufficient engine density correction accuracy can not be obtained. On the other hand, in the present embodiment, since the engine density correction parameter configured to correct the color balance of the image data read by the scanner 12 is set in the scanner correction mode, the color balance characteristic of the scanner is set. Even if individual differences and fluctuations occur, the read R, G, B values can be corrected and converted to appropriate C, M, Y, K tone values, and the correction accuracy of the engine density correction It can be improved. The γ curve corrected by the engine density correction process is used at the time of gradation correction in the image processing unit 30.

Next, copy processing will be described.
When a document D is set on the document tray of the automatic document feeder 11 and the start key of the operation unit 22 is pressed, the control unit 100 causes the document D to be transported by the automatic document feeder 11 to the platen glass At 12, the image of the document D is read to obtain image data (R, G, B).
Next, after the control unit 100 causes the image processing unit 30 to perform shading correction, the image data of R, G, B of the document D is C, M, Y using the copy parameters set in the scanner correction mode. , K image data is converted. Then, gradation correction is performed on the converted C, M, Y, K image data using a γ curve, and the image forming unit 40 forms an image on a sheet based on the image data after gradation correction.

  In the copying process of the present embodiment, color conversion is performed using an appropriate copying parameter (a parameter capable of correcting the color balance characteristic shift with the scanner standard simultaneously with the color conversion characteristic) according to the color balance characteristic of the scanner 12 As a result, the image quality of the original D can be reproduced more faithfully.

  As described above, in the image forming apparatus 1, even if there are individual differences or fluctuations in the color balance characteristics of the scanner 12, the reading error caused thereby can be reduced, and the correction accuracy of gradation correction and the accuracy of color reproduction in copying It is possible to improve the

  As described above, according to the image forming apparatus 1, the control unit 100 causes each of the patches of the image data acquired by reading the pattern image including the plurality of gradation patches of at least one reference color by the scanner 12. By performing predetermined calculations using R, G, B values, the color balance value when each patch is read by the scanner 12 is calculated, and the color balance characteristic of the scanner 12 is calculated based on the calculated color balance value. A characteristic amount to be expressed is calculated, and a parameter for correcting the color balance of the image data acquired by the scanner 12 is determined based on the calculated characteristic amount. Then, using the determined parameters, the color balance of the image data acquired by the scanner 12 is corrected.

  Therefore, even if there are individual differences or fluctuations in the color balance characteristic of the scanner 12, the reading error due to it can be reduced, and it becomes possible to improve the correction accuracy of gradation correction and the accuracy of color reproduction in copying. . Further, an image acquired by the scanner 12 based on the feature value of the color balance value calculated using the R, G, and B values in each patch of the image data acquired by reading the predetermined pattern image by the scanner 12 Since parameters for correcting the color balance of the data are determined and the color balance is corrected with the determined parameters, the variation of the color balance characteristic of reading due to the individual difference in the scanner 12 or the fluctuation of the light source characteristic Regardless of the type, it is possible to efficiently grasp and correct by a simple method.

  In addition, since the control unit 100 determines the parameters based on the comparison between the feature value calculated based on the color balance value and the reference feature value, the reading by individual differences and fluctuations of the light source characteristics and the like in the scanner 12 is performed. It becomes possible to grasp | ascertain efficiently the dispersion | variation in color balance characteristics by a simple method irrespective of the kind of white light source, and to determine the parameter according to the dispersion | variation in color balance characteristics.

  Further, since the pattern image read by the scanner 12 to determine the parameters is the image output by the image forming unit 40, the complicated color management of the pattern image becomes unnecessary as in the prior art.

  Further, as parameters for correcting the color balance of the image data acquired by the scanner 12, the pattern image including patches of plural gradations of a plurality of reference colors output by the image forming unit 40 is read by the scanner 12 It is a parameter used to convert the read data of each patch acquired by the scanner 12 into gradation values of a plurality of reference colors when correcting the γ curve that controls the gradation characteristics of the forming unit 40 . Therefore, even if individual differences or fluctuations occur in the color balance characteristics of the scanner 12, the read color balance characteristics of the R, G, B values are corrected to obtain appropriate C, M, Y, K tone values. Since conversion is possible, the correction accuracy of gradation correction can be improved.

  Further, the parameter for correcting the color balance of the image data acquired by the scanner 12 is a copy in which the image forming unit 40 forms an image on a sheet based on the image data acquired by reading the original D by the scanner 12 In function, it is a parameter used to convert image data acquired by the scanner 12 into a plurality of reference colors. Therefore, even if individual differences or fluctuations occur in the color balance characteristics of the scanner 12, the read color balance characteristics of the R, G, B values are corrected to obtain appropriate C, M, Y, K tone values. Since conversion is possible, the image quality of the original D can be reproduced more faithfully.

The above-described embodiment is a preferred example of the present invention, and the present invention is not limited to this.
For example, in the embodiment described above, the case where the image reading apparatus is provided in the image forming apparatus has been described as an example, but the image reading apparatus may be separate from the image forming apparatus. In the above embodiment, the function for correcting the color balance of the image data acquired by the image reading unit is provided as a parameter for converting the R, G, B values into C, M, Y, K gradation values. Although it has been described that it is described, it is also possible to separately provide a parameter (conversion table) for correcting the R, G and B values acquired by the image reading means to the R, G and B values of the scanner standard. Then, R, G, and R obtained by the image reading means based on the feature amounts calculated based on the color balance values of the R, G and B values obtained by reading the correction pattern image by the image reading means. Parameters for correcting the color balance of the B value may be determined.

  In the above embodiment, the correction pattern image used in the scanner correction mode is described as having patches of multiple gradations of C, M, Y, and K reference colors, but it corresponds to the feature amount. It is only necessary to provide patches of multiple gradations of at least one reference color. Also for the correction pattern image used in the engine density correction mode, patches of plural gradations of at least one reference color may be provided.

  Further, in the above embodiment, the chromaticity and the hue angle Hue of (r, g) are used as the color balance value, but the color balance value is not limited to these and, for example, general colors (Y, x, y) in CIE XYZ space widely known as degree coordinates, (L *, a *, b *) in CIELAB space, (H, L, S) in HLS space A degree equivalent value may be used.

  In the above embodiment, the range of the feature is divided into five steps, and the parameter corresponding to the feature is selected from the five steps. However, the range of the feature may be classified or prepared in advance. The number of parameters is not limited to this.

  In the above embodiment, the electrophotographic image forming apparatus is applied to the present invention. However, the present invention is applied to an image forming apparatus which forms an image on a sheet by another method such as an inkjet method. You may

  In the above description, an example using non-volatile memory, a hard disk or the like as a computer readable medium of the program according to the present invention has been disclosed, but the present invention is not limited to this example. As another computer readable medium, a portable recording medium such as a CD-ROM can be applied. In addition, carrier wave (carrier wave) is also applied as a medium for providing data of the program according to the present invention through a communication line.

  In addition, the detailed configuration and the detailed operation of the image forming apparatus can be appropriately modified without departing from the scope of the present invention.

Reference Signs List 1 image forming apparatus 100 control unit 10 image reading unit 11 automatic document feeder 12 scanner 20 operation display unit 30 image processing unit 40 image forming unit 412 developing device 110 developing roller 413 photosensitive drum 50 sheet conveyance unit 60 fixing unit 70 storage Unit 701 Parameter determination table 80 Communication unit

Claims (8)

Image reading means for reading a color image and acquiring image data consisting of a plurality of read colors;
Performing predetermined calculations using values of the plurality of read colors in each patch of image data acquired by reading a pattern image including a plurality of gradations of at least one reference color by the image reading unit; And color balance value calculation means for calculating a color balance value when each of the patches is read by the image reading means.
Feature amount calculating means for calculating a feature amount representing a color balance characteristic of reading by the image reading means based on the color balance value calculated by the color balance value calculating means;
A determination unit configured to determine a parameter for correcting the color balance of the image data acquired by the image reading unit based on the feature amount calculated by the feature amount calculation unit;
A correction unit that corrects the color balance of the image data acquired by the image reading unit using the parameter determined by the determination unit;
An image reading apparatus comprising: The plurality of read colors are red, green and blue,
The image reader according to claim 1, wherein the reference color includes at least one of cyan, magenta, yellow, and black.   The image reading apparatus according to claim 1, wherein the determination unit determines the parameter based on a comparison between the feature amount calculated by the feature amount calculation unit and a reference feature amount. The image reading apparatus according to any one of claims 1 to 3.
An image forming unit that forms an image on a sheet by using colorants of a plurality of reference colors including the reference color;
An image forming apparatus comprising:   The image forming apparatus according to claim 4, wherein the pattern image is an image output by the image forming unit.   The parameter reading control of the gradation characteristic of the reference color of the image forming means by reading a pattern image including patches of plural gradations of at least one reference color outputted by the image forming means by the image reading means The image forming apparatus according to claim 5, wherein the parameter is used to convert read data of each patch of the reference color acquired by the image reading unit into a gradation value when correcting a γ curve to be performed. .   The parameter is for converting the image data to the plurality of reference colors in a copy function in which the image forming unit forms an image on a sheet based on image data acquired by reading the document by the image reading unit. The image forming apparatus according to claim 5 or 6, which is a parameter used for the image forming apparatus. A color balance correction method in an image reading apparatus comprising an image reading unit for reading a color image and acquiring image data composed of a plurality of read colors, the method comprising:
Performing predetermined calculations using values of the plurality of read colors in each patch of image data acquired by reading a pattern image including a plurality of gradations of at least one reference color by the image reading unit; A color balance value calculating step of calculating a color balance value when each of the patches is read by the image reading unit;
A feature amount calculating step of calculating a feature amount representing a color balance characteristic of reading by the image reading unit based on the color balance value calculated in the color balance value calculating step;
A determination step of determining a parameter for correcting the color balance of the image data acquired by the image reading unit based on the feature amount calculated in the feature amount calculation step;
A correction step of correcting the color balance of the image data acquired by the image reading unit using the parameter determined in the determination step;
Color balance correction method including:

Images