JPH10191075A - Color correction device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color correction device where the color is corrected to be a correct color by compensating a secular change in a characteristic of an output device in the case that a stored color image is outputted after an interval of a time and the processing for color correction is conducted in a short time. SOLUTION: Print data from a client device 10 is given to an expansion processing section 28, where the data are expanded in a printable form, its color is corrected by a reference correction section 42 in matching with a reference color space that provides a reference of a color characteristic of a printer 14, and the result of correction is stored in a storage device 30. In the case of printing out the image stored in the storage device 30, the color of the stored image is corrected by a color slurring correction section 46 and the resulting data are printed out by the printer 14. Since the color slurring correction section 46 applies correction independently of each primary color, the processing is conducted at a high speed. A monochromatic color conversion table group 48 referenced at the correction is calibrated in matching with a current status of the color characteristic of the printer 14 by a gradation characteristic revision section 58 or the like at any time, then the correction result by the color slurring correction section 46 is always in matching with the color characteristic of the printer 14.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a color correction technique for outputting a color image generated by a computer or the like in an appropriate color on an output device such as a printing device or a display device.

[0002]

2. Description of the Related Art When print data of a color image created by a computer is printed by a printing apparatus, color reproducibility becomes a problem. In image data created by a computer, a color is represented by a combination of density values of three primary colors, for example, R (red), G (green), and B (blue). In contrast, a printing apparatus generally expresses each color using four color materials (inks) of C (cyan), M (magenta), Y (yellow), and K (black). Incidentally, C, M, and Y are complementary colors of R, G, and B, respectively. Either the application on the computer side or the printing device performs a process of converting the RGB color expression into the CMYK color expression, so that the printing device can perform color printing. CM from RGB value
Conversion to the YK value can be performed using a complementary color relationship.

[0003] However, CMYK used in a printing apparatus is used.
Since the color materials (inks) of each primary color generally contain some other primary color components instead of the complete primary colors, if the RGB values were directly converted to CMYK values and printed, the colors intended by the creator would be different. May be printed in different colors.

[0004] The same can be said for a case where a computer creates data in which colors are expressed in CMYK values in advance and supplies the data to a printing apparatus. That is, C on the computer side
If color printing is performed using the MYK values as they are, the color materials of the printing apparatus may not be perfect primary colors, and may be output in different colors.

[0005] In order to prevent such a situation, a process called color correction is performed in the printing apparatus. When the original color image data supplied from the computer expresses a color in CMYK, the color correction correctly reproduces the color from the color values (C, M, Y, K) in the color space of the original color image data. Value in the color space of the printing device (C
', M', Y ', K'). In order to realize this, for example, for each color value (C, M, Y, K) in the color space of the original color image data, the color value (C ′, M ′) in the color space of the corresponding printing apparatus is used. , Y ', K
') Is used. Since the color material of each primary color includes a component of a primary color other than the primary color, for example, C ′
Cannot be determined from C alone, and C, M, Y, K
It is necessary to decide from four. Therefore, the conversion table is a multidimensional table that is searched from four combinations of C, M, Y, and K. Note that the original color image data is RG
When a color is represented by B, the color correction is performed based on the color values (R, G, B) of the original color image data and the corresponding color values (C ′, M ′, Y ′) in the color space of the printing apparatus. , K
'), Which can also be realized by a conversion table similar to the above.

[0006] This color correction is a very time-consuming process. That is, for example, in a case where both the original color image data and the printing apparatus express a color at a density level of 256 gradations (8 bits) per primary color, the conversion table indicates that 256 (C) in the color space of the original color image data × 256
For each combination of (M) × 256 (Y) × 256 (K), the corresponding CMYK value in the corresponding printing apparatus is registered. The conversion table is searched and corrected for each pixel of the original color image. Obtaining the value (conversion result) requires a considerable processing time. It is also conceivable to use a more coarse-grained conversion table and perform an interpolation operation on intermediate values. However, this is not an essential solution, and the interpolation operation requires essentially handling four variables (CMYK). It takes time because there is.

In recent years, as a description format of print data supplied from a computer to a printing apparatus, a page description language (PDL) has been widely used. The printing apparatus develops the PDL data into a bitmap image by using a mounted CPU and a dedicated interpreter program, and performs a printing process based on the bitmap image. However, this PDL data expansion process is a process that places a heavy burden on the CPU, and it takes an extremely long time especially for a color image. For this reason,
There is a use form in which an image that has been developed once is stored and reused. For example, in recent years, customers
A business form called a print shop, which receives manuscripts created using the P (Desktop Publishing) system in the form of PDL data and performs print processing, has appeared.
In this print shop, it is common practice to first proof print a small number of manuscript data received from a customer, obtain the approval of the customer by this proof printing, and then print the required number of copies. For this reason, the print shop saves the development results at the time of proof printing and, if the customer's approval is obtained by proof printing, performs the final printing using the saved development results. This saves time and the time required to transfer manuscript data.

However, when reprinting is performed using the developed result (bitmap image) stored as described above, the first printing and the reprinting are performed due to the aging of the mechanism of the printing apparatus. Therefore, there is a possibility that the color tone may be different even though printing is performed based on the same development result. The temporal change in the mechanism of the printing apparatus includes, for example, a change in the ink ejection amount due to nozzle clogging or the like in an inkjet printing apparatus. This problem occurs because the conversion table for color correction deviates from the color characteristics of the printing apparatus at the time of reprinting due to the temporal change of the printing apparatus.

As a technique for compensating such a change with time, there is a technique disclosed in, for example, JP-A-63-113568. In this conventional technique, a printing apparatus stores density pattern image data of each color as a reference. At any time, the density pattern image data is printed on a predetermined medium, the density pattern of the printing result is detected by a sensor, and the detected density pattern is compared with the stored reference density pattern data. By doing so, the parameters for color correction (that is, the conversion table for color correction) are adjusted. According to this technique, the conversion table for color correction can always be maintained in an appropriate state reflecting the color characteristics of the printing apparatus at that time, so that a change over time of the printing apparatus can be compensated. it can.

[0010]

As described above, the color correction process is also a heavy process requiring as much time as the rasterization process. When considering the efficiency of the process at the time of reprinting, the color correction process is not the same as the rasterization result. It is preferable that the result of performing color correction on the developed result be saved and reused. However,
The above-mentioned prior art is effective in a method of saving the development result of PDL data as it is, but cannot be applied to a method of saving a color correction result. That is, in the above-described conventional technology, either the development result before color correction is stored and the color correction is performed at the time of reprinting and printed, or the result of the color correction is stored and printed at the time of reprinting. It is. In the former case, it takes a very long time to perform color correction at the time of reprinting, and in the latter case, when there is an interval between the first printing and the reprinting, the color of the reprinted result is changed due to the aging of the printing apparatus. It may be different from the first printing.

Although the printing apparatus has been described above, this problem is not limited to the printing apparatus but is common to apparatuses for outputting a color image (for example, a display apparatus).

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem, and when the stored color image data is re-output after a certain time, the characteristics of the image output device change over time. It is an object of the present invention to provide a color correction apparatus which can output a correct color by compensating for the color correction and reduce the time required for color correction at the time of re-output.

[0013]

In order to achieve the above-mentioned object, a color correction apparatus according to the present invention comprises a color correction apparatus for correcting a color value of each pixel of an original color image to a color value dependent on an output device. Reference correction means for correcting the color value of each pixel of the original color image to a color value in a reference color space serving as a reference for the color characteristics of the output device; and A shift correcting unit that corrects a shift in a color value caused by a shift from a reference color space, wherein color values in the reference color space are independent for each primary color component based on correction data prepared for each primary color component. Deviation correction means for correcting to a color value in an actual color space of the output device, correction data calibrating means for calibrating the correction data, and the reference correcting means when storage of a color image is instructed. The result of the correction is stored in a predetermined storage device, and when output of the color image stored in the storage device is instructed, the color image is corrected by the shift correction unit and then output to the output device. Control means for supplying.

In this configuration, color correction is divided into two stages. The first step is to correct the color value of each pixel of the original color image data (for example, an image obtained by expanding the PDL as it is) supplied from a computer or the like to the color value in the reference color space of the output device. This is a process, which is executed by the reference correction means. Here, the reference color space is a so-called ideal color space that serves as a reference for the color characteristics of the output device. For example, the reference color space depends on the color material used by the output device (when the output device is a printing device, the color material corresponds to ink). Stipulated. The second stage is a process of correcting the color value of the reference color space to the color value of the actual color space of the output device. To adjust the color values to the current color characteristics of the output device. The processing of the second stage is performed by the deviation correcting means.

The first-stage correction is a conversion process between color spaces having completely different properties, that is, the color space of the original color image data and the color space of the output device. Is performed by a process using a multidimensional conversion table, such as the color correction in. Of course, a conversion operation expression may be used instead of the conversion table. The setting of the correction parameter of the reference correction means (for example, registration of the multidimensional conversion table, etc.) may be performed, for example, at the time of manufacturing the color correction device, and does not need to be changed thereafter.

If the color space of the output device completely matches the reference color space, the correction by the reference correction means alone is sufficient for color correction. Is deviated from the reference color space due to machine differences or changes over time. Correcting the deviation is the second-stage correction. The essential difference in the color tone due to the difference in the color material or the like has already been removed in the correction in the first step, and the deviation (difference) between the reference color space to be corrected in the second step and the actual color space is as follows. For example, each primary color component becomes darker or lighter than ideal due to a machine difference such as an ink ejection amount of an ink jet or a change with time. Therefore, the correction in the second stage can be performed by adjusting the density of each primary color component independently. Specifically, for example, a conversion table of a single color may be created for each primary color component, and conversion may be performed according to this conversion table. This single-color conversion table is
For example, it is a one-dimensional table in which values before conversion are associated with values before conversion for each primary color component, and the time required for retrieval is extremely short. Also, when performing interpolation calculations,
Since the interpolation operation expression is a one-variable expression, the operation process can be shortened.
As described above, the time required for the second-stage correction by the deviation correcting unit is much shorter than the time required for the first-stage correction by the reference correcting unit. It should be noted that such a single-color conversion table, a correction operation expression, and the like correspond to “correction data” in the claims.

Further, in this configuration, in order to cope with a change with time of the output device, a correction data calibrating means for forming correction data by the deviation correcting means is provided. That is, in the present configuration, the correction parameter in the reference correction unit is fixed, and only the correction data in the deviation correction unit is configured as needed to cope with a temporal change, a machine difference, and the like. Since the color value shift due to a change over time or a machine difference is a shift within a range that can be handled by the shift correcting means as described above, if the correction data of the shift correcting means is calibrated as needed, the shift is sufficiently large. Can be compensated for.

In this configuration, under the control of the control means, when the color image is stored, the correction result by the reference correction means is stored, and when the stored color image is output, the color image is shifted with respect to the color image. After the correction by the correction means, the power is supplied to the output device.

According to such a configuration, the stored color image data is the result of correction by the reference correction means, so that when re-outputting, only correction by the deviation correction means needs to be performed. Since the processing is much faster than the conventional color correction processing using a multidimensional conversion table, the re-output processing can be performed at a higher speed than the conventional method. In addition, by correcting the correction data of the deviation correction means as needed by the correction data correction means,
It is possible to always output a correct color by following the change over time of the output device.

In a preferred aspect of the present invention, the color correction device comprises:
The reference color space is connected to a plurality of common output devices,
A plurality of the shift correcting means are provided corresponding to each of the output devices.

In this embodiment, when the correction result of the reference correction means is output by the output device, the correction result is further corrected by the shift correction means corresponding to the output device and then output. According to this aspect, the portion of the machine difference of each output device can be compensated by the deviation correction means, so that a simple system configuration in which one reference correction means is shared by a plurality of output devices can be realized. it can. Further, the correction data correction means can be shared.

Further, a printing system according to the present invention is connected to a network, and includes a front-end processor having print data processing means for processing print data and generating image data for printing each page; And a back-end processor that is provided corresponding to one or more printing devices, and outputs image data of each page from the network to the corresponding printing device, wherein the front-end processor includes:
A color correction unit configured to correct a color value of each pixel of the original color image into a color value in a reference color space serving as a reference of a color characteristic of the printing apparatus; and A shift correction unit for correcting a shift of a color value caused by a shift of an actual color space of the apparatus from the reference color space, wherein a color in the reference color space is corrected based on correction data prepared for each primary color component. A shift correction unit that corrects a value to a color value in an actual color space of the printing apparatus that independently corresponds to each primary color component, and a correction data correction unit for correcting the correction data. When the storage is instructed, the correction result of the reference correction unit is stored in a predetermined storage device. When the printing of the image data stored in the storage device is instructed, the back-up is performed. And supplying to the printing apparatus corresponding after performing the correction by the deviation correcting means command processor.

According to this configuration, in a printing system including one front-end processor and one or more back-end processors, the same effect as the above-described configuration can be obtained. In this configuration, the front-end processor is provided with the reference correction unit, and each back-end processor is provided with the shift correction unit, thereby realizing a lean system configuration. The result of the color correction by the back-end processor is output from a printing device connected to the back-end processor.

Further, the image forming apparatus according to the present invention comprises an image reading means capable of reading a color image and a print data processing for developing print data inputted from a client device such as a computer to generate a print image. And an image forming apparatus having a common printing unit for printing the image obtained by the image reading unit and printing the image generated by the print data processing unit. Reading reference correction means for correcting the color value of a pixel to a color value in a reference color space serving as a reference for the color characteristics of the printing means; and the color of each pixel of an image generated by the print data processing means. Value, a printing reference correction unit for correcting the color to a color value in the reference color space,
A shift correction unit for correcting a shift in color values caused by a shift between the reference color space and an actual color space of the printing unit, wherein the reference color space is corrected based on correction data prepared for each primary color component. A deviation correction means for correcting the color value in each of the primary color components independently to a color value in an actual color space of the output device, a correction data correction means for correcting the correction data, and Saves the correction result obtained by the reading reference correction unit or the printing reference correction unit in a predetermined storage device, and when printing the image stored in the storage device, the image is stored in the storage device by the shift correction unit. And a control unit for performing color correction and then supplying the color correction to the printing unit.

This configuration relates to an apparatus such as a so-called multifunction machine having both functions of a copying machine and a printer. In this type of apparatus, a color space (or a color characteristic) may be used for an image supplied from a computer or the like and an image read from an image reading unit such as a scanner.
Therefore, it is necessary to independently perform color correction. With this configuration, both the image supplied from the computer or the like and the image supplied from the image reading unit are once corrected to the same common reference color space. For this reason, in this configuration, a printing reference correction unit and a reading reference correction unit are provided. Then, the printing apparatus prints the result obtained by correcting these correction results by the common deviation correction unit. The functions of the reference correction means and the deviation correction means themselves are basically the same as those of the other configurations described above. Also in this configuration, by correcting the correction data in the shift correction unit as needed by the correction data correction unit, it is possible to compensate for a change with time of the printing unit.

According to this configuration, both the print data supplied from the computer or the like and the image read by the image reading means are always output in an appropriate color while compensating for the aging of the printing means. Can be.

[0027]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of a printing system including a color correction device according to the present invention will be described below with reference to the drawings.

[First Embodiment] FIG. 1 is a diagram showing the overall configuration of a first embodiment of a printing system to which the present invention is applied. In FIG. 1, the printing system includes a printing device 14 that performs a mechanical process of printing on paper and a data format (for example, a bitmap image) that can be printed with print data transmitted from a client device 10 such as a personal computer. And a print control device 20 as a print server that converts the data into a print data and supplies the print data to the printing device 14.

In FIG. 1, PDL print data sent from a client device 10 such as a computer is:
It is transmitted to the print control device 20 via the network 12. In the print control device 20, the receiving unit 22 receives the print data. The control unit 24 is a unit that controls processing of the entire print control device 20. The user interface (hereinafter abbreviated as UI) unit 32 is a unit that displays management data and the like to the user or receives an instruction from the user. The control unit 24 controls the print data received by the reception unit 22 and the client device 10
The management data is extracted from the control information and the like transmitted according to the communication protocol from the server and registered in the job management unit 26, and the print data is transferred to the expansion processing unit 28. When an instruction to save print data is issued from the client device 10 or the like, the control unit 24 stores the PDL print data in the storage device 30 such as a hard disk device. Expansion processing unit 2
8 develops the print data received from the control unit 24 into a bitmap image. When the color expression in the print data is other than the CMYK system (for example, RGB or CIE)
, Etc.) are converted to the CMYK system color representation in this expansion processing. The data of the developed bitmap image is passed to the color correction mechanism 40 and color corrected according to the printing device 14.

Next, the color correction mechanism 40 in the present embodiment.
Will be described in detail.

In the color correction mechanism 40, the expansion processing unit 28
Is first corrected by the reference correction unit 42 in accordance with the color material (ink or the like) of the printing device 14. That is, the reference correction unit 42 refers to the multidimensional conversion table 44 and converts the color value of each pixel of the bitmap image into a color value of the reference color space of the printing device 14. The reference color space is a so-called ideal color space that serves as a reference for the color characteristics of the printing apparatus 14. For example, the printing apparatus 14 uses the color materials used in the printing apparatus 14 to perform printing processing in an ideal state in design. Refers to the color space of the image of the print result when the above is performed. Multidimensional conversion table 44
Are the color values (C, M, and C) in the color space of the developed bitmap image (that is, the color space assumed by the software that created the image in the client device 10).
Y, K) is a conversion table in which color values (C ′, M ′, Y ′, K ′) in the reference color space of the corresponding printing apparatus 14 are registered. The multidimensional conversion table 44 is searched by a combination of four values of C, M, Y, and K of the original bitmap image. The data to be registered in the multidimensional conversion table 44 may be roughened, and intermediate values may be obtained by interpolation. This multidimensional conversion table 44
Is common to the printing apparatuses 14 of the same model, and is connected to the printing apparatus 1 when the printing control apparatus 20 is manufactured.
4 is set according to the model. The correction result by the reference correction unit 42 is stored in the storage device 30. For example, when the instruction from the client device 10 is to expand and save the print data, the process of the print control device 20 ends at this stage.

On the other hand, if the instruction from the client device 10 is to store the print data after printing it, the correction result by the reference correction unit 42 is stored in the storage device 30 and further sent to the deviation correction unit 46. Passed. Deviation correction unit 4
A correction unit 6 corrects the correction result of the reference correction unit 42 by a deviation of a color value caused by a deviation between the reference color space assumed by the reference correction unit 42 and the actual color space of the printing apparatus 14. . The difference between the color space of the print data supplied from the client device 10 and the reference color space of the printing device 14 is that the assumed primary colors themselves are different (for example, the same CMY).
Even if the K system is adopted, the print data and the printing device 1
4 differs from the CMYK primary color itself in the “color”). However, the difference between the reference color space and the actual color space of the printing apparatus 14 is assumed by both of them. Since the primary colors are exactly the same, it is merely a difference in strength for each primary color component. Therefore, the shift correction unit 46 may perform color correction independently for each primary color component.

More specifically, the shift correction unit 46 performs a correction process with reference to the monochrome conversion table group 48. The monochrome conversion table group 48 includes a C conversion table 48a and an M conversion table 48, which are conversion tables for each primary color component of CMYK.
b, a Y conversion table 48c and a K conversion table 48d. Conversion tables 48a-48d for each primary color
In each of the primary colors, the gradation value in the reference color space and the gradation value in the actual color space are registered in association with each other. The shift correcting unit 46 searches the monochromatic conversion tables 48a to 48d for the respective primary colors for each pixel of the given image (that is, the correction result of the reference correcting unit 42), and stores the C, M, Y, and K Correction values are obtained respectively. That is, in order to obtain a correction value of, for example, cyan (C), a correction value corresponding to the gradation value of C of the target pixel of the given image may be retrieved from the C conversion table 48a. This correction result is adapted to the actual color space of the printing device 14.

When the color correction is completed for all the pixels by the shift correcting unit 46, the correction result is supplied to the printing device 14, and the printing device 14 prints the result on paper or the like. The print result has an appropriate color tone by the color correction by the color correction mechanism 40.

In order for the above-described color correction process to be appropriate, the single-color conversion table group 48 of the shift correction unit 46
However, it is necessary that the current color space accurately reflects the actual color space of the printing apparatus 14 at that time. For this reason, in the present embodiment, the calibration process of the single-color conversion table group 48 is performed as needed (periodically or before printing). Hereinafter, the calibration process will be described.

In the present embodiment, a calibration chart as shown in FIG. 6 is printed by the printing device 14, and calibration processing is performed based on the printing result of the calibration chart. As shown in FIG.
The calibration chart is 10 colors for each of the primary colors C, M, Y, and K.
It is composed of 10-step patches whose density changes from 10% to 100% in 10% steps. For example, 2 for each primary color
When 56 gradations are assigned, the gradation value is 2 at 10%.
5.5, and the gradation value is 255 at 100%. The print control device 20 stores the original data for printing such a calibration chart in the calibration data storage unit 50 as the calibration chart print data 52 described in PDL. In the calibration data storage unit 50, a correct value (target density value) of the density of each patch of the calibration chart is stored as target density value data 54.

When the user gives an instruction to calibrate the correction data from the UI unit 32, the control unit 24 converts the calibration chart print data 52 in the calibration data storage unit 50 into the expansion processing unit 2.
8 to perform a developing process. This development result is directly supplied to the printing device 14 without going through the color correction mechanism 40,
Printed on predetermined paper. Here, the reason why the color correction of the calibration chart is not performed is to know the actual capability of the printing apparatus 14 at that time. The printing result of this calibration chart is measured by a precise densitometer 16. That is, the densitometer 16 measures what density value each patch of the calibration chart has for each primary color. The result of this measurement is
It is input to the tone characteristic calculation unit 56 of the print control device 20.
The tone characteristic calculating section 56 calculates the density value of each patch based on the measurement result of the densitometer 16, and calculates tone characteristic data as shown in FIG. 7B for each primary color. obtain. In the gradation characteristic data, the ten-stage density value described in the calibration chart print data 52 is the
Reference numeral 4 indicates what density was actually printed. 7 (a) to 7 (d) including FIG. 7 (b).
Each graph corresponds to the printing device 14 capable of expressing 256 density levels.

When the gradation characteristic data of the printing device 14 is obtained in this manner, the gradation characteristic changing unit 58 compares the gradation characteristic data with the target density value data 54 based on the comparison.
The data of the conversion tables 48a to 48d for each single color is changed. FIG. 7A shows the contents of the target density value data 54. The gradation characteristic changing unit 58 calibrates the conversion table so that each input value is printed at the density indicated by the target density value. The specific processing contents of the gradation characteristic changing unit 58 will be described with reference to FIGS. FIG.
In (c), the data of the target density value is indicated by a point, and each point of the actually measured gradation characteristic data (FIG. 7B) is indicated by a broken line connecting a straight line (or a predetermined curve). ing. The processing procedure will be described using an example. In FIG. 7C, for example, while the target density value for the input value 77 is 0.4, only 0.35 is obtained in the actual gradation characteristic. It can be seen that the color became lighter. Therefore, the gradation characteristic changing unit 58 checks how many input values are necessary in the current gradation characteristic in order to achieve the density of 0.4 which is the target density value. As a result, as shown in FIG. 7C, it is understood that 102 is required as an input value in order to obtain a print result with a density of 0.4. Therefore,
The gradation characteristic changing unit 58 applies a correction value of 10
2 is associated. In this way, a correction value for realizing the target density value is obtained for each input value corresponding to the ten-step patch in the calibration chart. The relationship between the input value and the correction value is plotted at each point in FIG. The gradation characteristic changing unit 58 further interpolates between these points with a straight line or a predetermined curve to complete a correction curve (polyline) as shown in FIG. 7D. Then, the gradation characteristic changing unit 58 obtains correction values corresponding to each of the 256 levels of input values in the correction curve, and registers a set of these input values and correction values in the conversion tables 48a to 48d for each single color. . By performing such processing for each of C, M, Y, and K, the conversion table 48a for each single color is obtained.
To 48d are calibrated in a form corresponding to the current state of the color characteristics of the printing device 14.

By using the monochromatic conversion table group 48 calibrated in this way, the shift correcting section 46 can perform color correction suitable for the color characteristics of the printing apparatus 14. The print control device 20 supplies the image data of the correction result of the shift correction unit 46 to the printing device 14, and ends the processing. The printing device 14 prints the given image data on paper or the like.

It should be noted that even if there is a machine difference or a change over time in the printing apparatus 14, as long as there is no change in the color materials used, the color characteristic shift due to the difference or change is not strong or weak for each primary color component. It can be said that it depends on the degree. Therefore, only the calibration of the single-color conversion table group 48 described above can sufficiently compensate for machine differences and changes over time of the printing apparatus 14.

As described above, the client device 1
If the print data is supplied from 0 and an instruction to save the developed result even after printing is given, the correction result by the reference correction unit 42 is stored in the storage device 30 and the correction result is further corrected. The correction by the unit 46 is applied, and the double correction result is printed by the printing device 14.

When an instruction to discard the developed result is issued after printing is completed, the print control device 20 performs the same correction process as described above, executes the print process, and then temporarily stores it in the storage device 30. The stored bitmap image data is deleted, and the process ends.

The processing of the print control device 20 when the print data is supplied from the client device 10 has been described above. Next, the client device 10 or the UI unit 3
The case where printing of bitmap image data stored in the storage device 30 is instructed from 2 will be described.

As described above, the bitmap image data stored in the storage device 30 is
2, the color has been corrected so as to conform to the reference color space of the printing apparatus 14. When printing of such storage data is instructed from the client device 10 or the UI unit 32, the control unit 24 specifies the storage data via the job management unit 26, and shifts the storage unit 30 from the storage device 30.
Enter 6 The shift correcting unit 46 performs color correction of the stored data that has been input by using a single-color conversion table group 48 that is adjusted to the color characteristics of the printing device 14 at the current time by the calibration process, and compares the correction result with the printing device. 14 for printing. In this way, the stored data is always corrected and printed using the single-color conversion table group 48 adapted to the color characteristics of the printing device 14 at the time of reprinting. The color shift due to the temporal change of the printing apparatus 14 during the printing can be compensated, and the printing can be performed in almost the same color as the first printing even in the reprinting. In addition, since the correction by the shift correction unit 46 is performed for each primary color, it can be performed in an extremely short time.

As described above, in the present embodiment, when the bitmap image for printing is stored, the correction result of the reference correction unit 42 is stored, and when the stored bitmap image is printed, the correction result is stored. The bitmap image is printed after being corrected by the shift correction unit 46. Then, the conversion table used by the shift correction unit 46 is calibrated as needed, so as to cope with a temporal change in the color characteristics of the printing apparatus 14 or the like. According to such a configuration, when the stored image is reprinted, it is possible to always perform color correction after performing color correction in accordance with the color characteristics of the printing device 14 at the time of the reprinting, and furthermore, to reprint the image. Since color correction at the time of printing can be performed independently for each primary color, high-speed processing can be performed. Moreover, the calibration of the single-color conversion table in the present embodiment has an advantage that the processing time is much shorter than the case of calibrating a multi-dimensional conversion table as in the related art.

[Second Embodiment] FIG. 2 is a diagram showing the overall configuration of a printing system according to a second embodiment of the present invention. 2, the same reference numerals are given to the same or corresponding components as those in FIG. 1, and the detailed description is omitted.

This embodiment differs from the first embodiment in that a plurality of printing devices 14A and 14B are connected to a printing control device 20. Printing devices 14A and 1
4B is a printing apparatus of the same model that makes the reference color space equal. The printing control device 20 includes the printing devices 14A and 14B
Are the same as those in the first embodiment, except that the shift correction units 46A and 46B are provided correspondingly to In the present embodiment, the print control device 20 selects and operates the plurality of printing devices 14A and 14B as appropriate to perform the printing process. One print job is transferred to a plurality of printing devices 14A.
And 14B are also possible to print in parallel.

A problem that arises when a plurality of printing apparatuses are used is a difference in the color tone of the printing result of each printing apparatus. Even though they are the same model, there is a certain degree of personality (machine difference) between them, and the way they change over time also differs individually. Therefore, if no countermeasures are taken, a situation in which the color of the print result differs between one and the other even though the same image is printed will be caused.

On the other hand, in the present embodiment, such a machine difference and a difference of each machine with time are absorbed by the shift correcting units 46A and 46B, respectively. The calibration and functions of the shift correcting units 46A and 46B are the same as those of the shift correcting unit 46 of the first embodiment. As described in the first embodiment, if the color materials used are the same (this is the “primary color”).
Are the same), and the machine difference and the change over time here depend on the strength of each primary color, that is, the amount of each primary color. Therefore, the shift correction units 46A and 46B can correct the differences with high accuracy. . The single-color conversion table groups 48A and 48B used in the correction are calibrated as needed in the same manner as in the first embodiment according to the corresponding printing devices 14A and 14B.

Also in this embodiment, when storing an image for printing, the control unit 24 stores the correction result of the reference correction unit 42 in the storage device 30. Then, the storage device 30
When printing an image stored in the control unit 24,
Supplies the image taken out of the storage device 30 to the shift correction unit (46A or 46B) corresponding to the printing device (14A or 14B) designated by the user or the like, and performs color correction.

According to this embodiment, in a system in which a plurality of printing apparatuses are operated in parallel, the difference in color characteristics between the printing apparatuses and changes over time are compensated for, and printing is always performed regardless of which printing apparatus is used. It is possible to obtain a print result in which the colors match, and when reprinting an image that has been printed once after a while (even if a different printing device is used for the first printing), the same color as the first printing is used. Printing results can be obtained.

In the above, the printing devices 14A and 14A
Although B is the same model, this is not limited to the same model in a strict sense. For example, as in the case of printing devices of the same series, color materials to be used should be common and the reference color space should be set equal. The present embodiment is also effective for a case where a plurality of printing apparatuses capable of performing the above operations are operated in parallel.

When two or more printing apparatuses are to be connected, the print control apparatus 20 may be provided with a shift correction unit (single color conversion table) corresponding to each of the printing apparatuses.

Further, the shift correcting units 46A and 46B may be, for example, the same program in terms of mounting, and the above processing can be achieved by switching the unit conversion table group to be referred according to the printing apparatus to be used.

[Embodiment 3] FIG. 3 is a diagram showing the overall configuration of a printing system according to a third embodiment of the present invention.

This embodiment is an example in which the present invention is applied to a printing system of a front-end processor / back-end processor system separately proposed by the present applicant. This method is a so-called print server (print control device)
Is divided into two types of devices for each function. That is, in the example of FIG. 3, the PDL expansion function (so-called RI
P function) and a front-end processor (abbreviated as FEP) 120 having a job management function, and back-end processors (abbreviated as BEP) 130 and 14 for controlling a printing apparatus (so-called print engine) to perform a printing process.
0. The BEPs 130 and 140 are provided one for each of the printing devices 138 and 148. This method is intended to prevent an excessive load on the print server when a large number of printing apparatuses are connected, and to prevent a reduction in processing efficiency accompanying the load.

When the present invention is applied to a printing system of this type, a reference correction unit 124 is provided in the FEP 120 and each B
It is preferable to provide the EPs 130 and 140 with the shift correction units 134 respectively. The configuration and function of the reference correction unit 124 and the shift correction unit 134 are the same as those of the reference correction unit 42 of the first embodiment.
And the shift correction unit 46.

In FIG. 3, print data transmitted from the client device 100 is input to the FEP 120 via a network 110 such as a LAN. FEP12
At 0, the job processing unit 122 expands the print data into a printable format. In the FEP 120, data for job management is created and registered in a job management unit (not shown). The expansion result by the job processing unit 122 is
In the same manner as in the first embodiment, color correction is performed by the reference correction unit 124 so as to match the reference color space of the printing devices 138 and 148. In the present embodiment, as in the second embodiment, the printing devices 138 and 148 are the same type of printing devices that have the same reference color space. If the instruction from the client device 100 is merely expansion / storing, the reference correction unit 12
4 is stored in a storage device 12 such as a hard disk device.
6 is stored. In this embodiment, the storage device 136 can be provided for each BEP, and the FEP 120
If there is not enough space in the storage device 126 attached to
The image of the correction result of the reference correction unit 124 may be stored in a storage device attached to the BEP. In this case, FEP120
Stores and manages in which BEP the image is stored. When the instruction from the client device 100 is printing, the image data of the correction result of the reference correction unit 124 is
It is stored in the storage device 126 or the like, and a predetermined BEP
130, 140... FEP120 is
The printing device is selected based on a predetermined criterion, and the image data is transmitted to the BEP of the printing device 138, 148,... When the BEP 130 receives this, the image data is corrected by the shift correction unit 134,
The result of this correction is supplied to the printing device 138.

When printing of image data stored in the storage device 126 or the like is instructed from the client device 100 or the like, the FEP 120 transmits the image data based on the management information.
The storage device storing the designated image data is checked, the image data is taken out from the storage device, and sent to the designated BEP to perform the printing process. If no BEP (or printing device) is specified, the FEP 120 selects a transmission destination. If the image data for which printing has been instructed is stored in any of the BEP storage devices,
And a printing device connected to the same is efficient. In any case, BE that processes the image data
In P, the stored image data is corrected by the shift correction unit 134, and the correction result is supplied to the printing apparatus. Similar to the first embodiment, the correction processing in the shift correction unit 134 is an independent correction processing for each primary color using a single-color conversion table.

Each of the BEPs 130, 140,... Has a correction data calibrating mechanism 132 for calibrating the conversion tables in the shift correcting units 134,. ing. The correction data calibration mechanism 132 has functions equivalent to those of the calibration data storage unit 50, the gradation characteristic calculation unit 56, and the gradation characteristic change unit 58 in the first embodiment. When the calibration of the conversion table group is instructed, the correction data calibration mechanism 132 causes the printing device 138 to print a calibration chart, measures the printing result with the densitometer 133, and thereafter performs the same processing as described in the first embodiment. Calibrate the conversion tables by the method. Using the densitometer 133 as an external method, one densitometer 133
It is also possible to share with 130, 140.

As described above, also in the present embodiment, the same effects as in the above-described second embodiment can be obtained.

[Embodiment 4] FIG. 4 is an overall configuration diagram showing an embodiment of a system configuration using an apparatus having both functions of a printer and a copying machine, such as a so-called digital multifunction peripheral. In FIG. 4, the same reference numerals are given to the same or corresponding components as those in FIG. 1, and detailed description is omitted.

In this embodiment, the printing device 60 is of a type having both functions of a printer and a copier.
The printing device 60 includes an image reading unit 62 that reads a document placed on a platen, a reference correction unit 64 that performs color correction on the read result, and a print processing unit 66 that performs printing processing on paper.
have. Here, the reference correction unit 64 corresponds to the reference correction unit 42 of the print control device 20, and performs color correction from the color space of the image read by the image reading unit 62 to the reference color space of the print processing unit 66. Do. The processing by the reference correction unit 64 is performed using a multidimensional conversion table, for example, similarly to the processing by the reference correction unit 42. In the example of FIG. 4, the reference correction unit 64 does not perform the conversion of the color expression system. That is, the image reading section 62 converts the read image into RG
In the case of expressing in B, the reference correction unit 64 corrects it to an RGB value suitable for the reference color space of the print processing unit 66. Conversion of color representation system (for example, RGB to CMYK
Is performed by the printable data conversion unit 49 in the print control device 20. By adopting such a configuration, in the present embodiment, as the reference correction unit 64 of the printing apparatus 60, a color correction mechanism conventionally provided in this type (multifunction machine type) of the printing apparatus 60 is directly used as the reference correction unit. 64
Can be used as The print control device 20 of the present embodiment has the same configuration as the print control device 20 of the first embodiment, except for the printable data conversion unit 49. If the reference correction unit 64 converts the data to the color expression system, the printable data conversion unit 4 in the print control device 20 may be used.
9 becomes unnecessary.

In this embodiment, when an instruction to save an image read by the image reading unit 62 is given, the read image is subjected to color correction by the reference correction unit 64, and the correction result is output to the printable data conversion unit. At 49, the data is converted into printable CMYK data. The conversion result is given an identification number, registered as one job in the job management unit 26, and stored in the storage device 30.

FIG. 5 is a flowchart showing an overall process of the print control apparatus 20 according to the present embodiment. First, when the receiving unit 22 receives data from the client device 10 (S10), this data is registered as a job in the job management unit 26 (S12), and the expansion processing unit 28 can print a bitmap image or the like. The data is expanded to data (S14). The development result is color-corrected by the reference correction unit 42 so as to conform to the reference color space defined by the color material of the print processing unit 66 (S16). The printable data corrected by the reference correction unit 42 is stored in the storage device 30 (S18). Here, it is determined whether or not the instruction from the client device 10 is a print instruction (S20). If the instruction is not a print instruction, the process ends here. On the other hand, if it is a print instruction, the correction result of the reference correction unit 42 is further subjected to color correction for each primary color by the shift correction unit 46 (S22).
6 to perform a printing process (S24). And
It is determined whether the instruction from the client device 10 is an instruction to discard the printable data stored in the storage device 30 in S18 after printing or to save the printable data after printing (S26). ). In the case of discarding after printing, the printable data in the storage device 30 is deleted (S28), and the process ends. In the case of saving after printing, the processing is terminated without performing such deletion.

When the image is read by the image reading section 62 (S 30), the read image is transmitted to the printing device 60.
The color correction is performed by the reference correction unit 64 within the reference color space so as to conform to the reference color space of the print processing unit 66. Then, the result of the color correction is converted into printable data by the printable data conversion unit 49 of the print control device 20 (S32), registered in the job management unit 26 (S34), and stored in the storage device 30. It is stored (S18). Subsequent processing is performed by the client device 10
This is similar to the case where data is received from. In this embodiment, even when the printing device 60 is used as a copying machine, the read image is passed to the print control device 20, corrected by the shift correction unit 46, and then printed by the print processing unit 66.

Then, from the UI unit 32 or the like, the storage device 3
When the printing of the printable data stored in 0 is instructed (S40), the control unit 24 passes the designated printable data to the shift correction unit 46 to perform color correction (S2).
2) Thereafter, the same processing as when data is received from the client device 10 is performed.

In this embodiment, the client device 10
Is corrected by the reference correction unit 42 in accordance with the reference color space of the print processing unit 66, and the image read by the image reading unit 62 is printed by the reference correction unit 64 of the printing device 60. By performing correction in accordance with the reference color space of the processing unit 66, both can be treated as equivalent data. Therefore, the color shift due to the machine difference or the temporal change of the print processing unit 66 can be corrected by the common shift correction unit 46 regardless of the image originating from either the client device 10 or the image reading unit 62. it can.

As described above, according to the present embodiment, not only the print data supplied from the client device 10 but also the image read by the image reading unit 62 is stored and reprinted. It is possible to always obtain a print result having the same hue as the first print.

As a conventional technique for calibrating a color correction function in an image forming apparatus such as a copying machine, there is a technique disclosed in Japanese Patent Application Laid-Open No. 4-57573, for example. It is intended only for use as a copying machine in which printing is performed at the time of reading, and does not take into account any use in which a read image is stored and reprinted. Therefore, even if this prior art is applied as it is, the above-mentioned Japanese Patent Application Laid-Open No.
The same problem as in the case of JP-A-3-113568 remains. Further, this prior art does not consider at all how to handle an image read by an image reading apparatus and an image generated by a computer or the like in a unified manner.

In the embodiments described above, the example in which the device for outputting a color image is a printing device has been described. However, the present invention is not limited to the printing device, but may be a color display or the like.
The present invention is also applicable to other types of devices that output color images.

[0072]

As described above, according to the present invention, the color correction is performed in the first stage from the color space of the supplied original color image to the reference color space of the output device, and output from the reference color space. Divided into the second stage correction to the actual color space of the device,
When the image data is stored, the first-stage correction result is stored, and when the stored data is output, printing is performed only by the high-speed second-stage correction process. Can be performed at high speed. In addition, by correcting the correction data used in the correction in the second stage as needed, it is possible to always perform color correction that matches the current state of the color characteristics of the output device.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of an embodiment of a printing system to which the present invention is applied.

FIG. 2 is a diagram illustrating an overall configuration of another embodiment of a printing system to which the present invention has been applied.

FIG. 3 is a diagram illustrating an overall configuration of another embodiment of a printing system to which the present invention is applied.

FIG. 4 is a diagram illustrating an embodiment in which the present invention is applied to a system including a printing apparatus including an image reading unit.

FIG. 5 is a flowchart showing a processing procedure in the system of FIG. 4;

FIG. 6 is a diagram illustrating an example of a calibration chart.

FIG. 7 is a diagram for explaining processing of a gradation characteristic changing unit.

[Explanation of symbols]

10 client devices, 12 networks, 14
Printing device, 16 Densitometer, 20 Printing control device, 22
Receiving unit, 24 control unit, 26 job management unit, 28 expansion processing unit, 30 storage device, 32 user interface unit (UI unit), 40 color correction mechanism, 42 reference correction unit, 44 multidimensional conversion table, 46 shift correction unit , 4
8 single color conversion table group, 50 calibration data storage unit,
52 calibration chart print data, 54 target density value data, 56 gradation characteristic calculation unit, 58 gradation characteristic change unit.

Claims (4)

[Claims] 1. A color correction device for correcting a color value of each pixel of an original color image into a color value dependent on an output device, wherein the color value of each pixel of the original color image is converted into a color characteristic of the output device. Reference correction means for correcting a color value in a reference color space serving as a reference, and deviation correction means for correcting a deviation of a color value caused by deviation of an actual color space of the output device from the reference color space. Based on correction data prepared for each primary color component, a shift correction unit that independently corrects a color value in the reference color space to a color value in an actual color space of the output device for each primary color component; Correction data calibrating means for calibrating the correction data, and when the storage of the color image is instructed, the correction result by the reference correcting means is stored in a predetermined storage device, and stored in the storage device. Color correction apparatus characterized by and a control means for supplying to the output device after performing correction by the deviation correcting means with respect to the color image when it is instructed to output the color image. 2. The color correction device according to claim 1, wherein said plurality of output correction devices are connected to a plurality of output devices having a common reference color space, and each of said plurality of output devices is provided in correspondence with each of said output devices. A color correction device, characterized in that: 3. A front-end processor connected to a network and having print data processing means for processing print data and generating image data for printing each page; and one or more printing devices on the network. A back-end processor provided correspondingly and outputting image data of each page from the network to a corresponding printing device, wherein the front-end processor is configured to output the color of each pixel of the original color image. And a reference correction unit for correcting the value to a color value in a reference color space that is a reference of a color characteristic of each printing device, wherein the back-end processor is configured to: A shift correction unit for correcting a shift in a color value caused by a shift from a color space, and is provided for each primary color component. Deviation correction means for correcting the color value in the reference color space to the color value in the actual color space of the printing device corresponding independently for each primary color component based on the corrected data, and for correcting the correction data Correction data correction means, and when the image data is instructed to be stored, the correction result of the reference correction means is stored in a predetermined storage device, and printing of the image data stored in the storage device is performed. A printing system wherein, when instructed, the correction is made by the shift correction means of the back-end processor and then supplied to the corresponding printing device. 4. An image reading unit capable of reading a color image, a print data processing unit for expanding a print data input from a client device such as a computer to generate an image for printing, and acquiring the image by the image reading unit. And a common printing unit for printing the generated image and printing the image generated by the print data processing unit, wherein the color value of each pixel of the image obtained by the image reading unit is
Reading reference correction means for performing color correction to a color value in a reference color space which is a reference of the color characteristic of the printing means; and a color value of each pixel of the image generated by the print data processing means, the reference color A printing reference correction unit that performs color correction to a color value in a space, and a shift correction unit that corrects a shift in color value caused by a shift between the reference color space and an actual color space of the printing unit. Based on correction data prepared for each primary color component, a shift correction unit that independently corrects a color value in the reference color space to a color value in an actual color space of the output device for each primary color component; and Correction data calibrating means for calibrating, and when storing an image, a correction result by the reading reference correcting means or the printing reference correcting means is stored in a predetermined storage device, and is stored in the storage device. When printing the stored image, the image forming apparatus includes: control means for performing color correction on the image by the shift correcting means and supplying the corrected image to the printing means.