JP2004088494A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for easily calculating a correction parameter used for correction processing to be applied to the acquired image data and improving the reproducibility of an image by a simple processing using the calculated correction parameter. <P>SOLUTION: A second color system converting section converts test image data of a Lab color system generated by a control section into test image data of CMYK color system, and a recording section records the converted image data on a recording sheet. A reading section reads the test image recorded on the recording sheet as test image data of an RGB color system, and a first color system converting section 32 converts the read image data into test image data of Lab color system. A correction parameter calculating section 34 calculates a correction parameter to be used for correction processing performed by a color correction section 33, by comparing the test image data subjected to the respective processing as described above with the test image data generated by the control section. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus that converts acquired image data into a different color system and records it on a recording sheet.
[0002]
[Prior art]
2. Description of the Related Art Digital color copiers that read a document image of a color display and record the obtained color image data on a recording sheet have become widespread. In such an apparatus, a document image is converted into, for example, RGB (R: red, G: (Green, B: blue) Acquired as color system image data. Further, the digital color copying machine performs a color system conversion process on the acquired RGB color system image data based on a conversion table generated by a predetermined mathematical formula, for example, CMYK (C: cyan, M: magenta). , Y: yellow, K: black) image data of a color system is generated, and the read image data is recorded on a recording sheet based on the image data of the CMYK color system.
Such digital color copying machines are required to correctly reproduce the color tone of a document image on a copy destination recording sheet, and some have a calibration function.
[0003]
The calibration function is a digital color copier that operates according to instructions from the user in order to reduce image quality deterioration due to image data acquisition processing, color system conversion processing, and image data recording processing. When the user operates the calibration function, the digital color copying machine executes a test image data generation processing program stored in advance in the digital color copying machine to execute test image data of the CMYK color system. Is generated, and the test image data is recorded on a recording sheet.
Further, the user places the recording sheet on which the test image is recorded on a document tray provided in a digital color copying machine and instructs image reading, and the digital color copying machine is placed on the document tray. The test image recorded on the recording sheet is read, and the read image data of the RGB color system is converted into image data of the CMYK color system.
[0004]
Therefore, the digital color copying machine compares the test image data acquired as described above with the test image data of the CMYK color system generated by itself, and based on the comparison result, reads the read image data during normal operation. Is calculated.
In addition, the digital color copying machine reflects the calculated correction parameter in a conversion table used for color system conversion processing in the digital color copying machine by a predetermined process.
[0005]
The calibration function as described above is executed at the time of initial setting of the digital color copying machine or when instructed by the user, whereby the correction parameters can be reflected in the conversion table used for the color system conversion processing. it can.
Also, by performing the color system conversion processing using this conversion table, it is possible to realize the color system conversion processing with the color adjustment, reduce the deterioration of the image quality due to various processing in the digital color copier, and The reproducibility of the color tone of the image on the recording sheet can be improved.
[0006]
[Problems to be solved by the invention]
However, there is no simple relationship between the RGB color system and the CMYK color system, and it is very difficult to sufficiently reflect the correction parameters calculated as described above in a conversion table used for color system conversion processing. For example, when the process of reflecting the calculated correction parameters in the conversion table is implemented by software, there is a problem that the program becomes enormous and complicated, and when the process is implemented by hardware, In addition, there is a problem that the circuit scale increases and the manufacturing cost increases.
[0007]
The present invention has been made in view of such circumstances, and for example, an L * a * b * (L *: brightness information, a *: red-green color information, b *: yellow-blue color information) table Test image data of a second color system including lightness information such as a color system (hereinafter referred to as a Lab color system) is generated, and the generated test image data and the test image data are converted to a third color system (for example, (CMYK color system) is converted to test image data, recorded on a recording sheet, the test image recorded on the recording sheet is read, and correction parameters are calculated based on the test image data converted to the second color system. By providing a configuration for performing a correction process based on the calculated correction parameters, the correction parameters can be easily calculated based on the image data in the same color system, and the image data in the second color system can be calculated. , To the calculated correction parameters Aims to brute correction process to provide an image forming apparatus is easy.
[0008]
Another object of the present invention is to provide a calibration function by providing storage means for storing test image data of the second color system and calculating correction parameters based on test image data read from the storage means. It is an object of the present invention to provide an image forming apparatus capable of performing each process on the test image data read from the storage unit when executing the above, and smoothly executing each process in the calibration function.
[0009]
Still another object of the present invention is to calculate a correction parameter based on brightness information included in test image data of the second color system, and to correct the acquired image data according to a function based on the calculated correction information-related correction parameter. By providing a configuration for performing the processing, it is possible to easily perform the calculation processing and the correction processing of the correction parameter, and to remove the variation of the color tone in the image data to be corrected, thereby reducing the deterioration of the image quality. Can be provided.
[0010]
[Means for Solving the Problems]
An image forming apparatus according to a first aspect of the present invention includes an image acquisition unit that acquires image data of a first color system, and a second table that includes brightness information, the image data of the first color system acquired by the image acquisition unit. First conversion means for converting the image data of the second color system converted by the first conversion means into image data of the third color system; Generating means for generating test image data of the second color system, wherein the image forming apparatus comprises: a recording means for recording the image data of the third color system converted by the second converting means on a recording sheet; The test image data and the test image data generated by the above are converted into the test image data of the third color system by the second conversion means, and are recorded on the recording sheet by the recording means, and the test recorded on the recording sheet is performed. An image is captured by the image acquisition means. Calculating means for calculating a correction parameter based on the test image data converted by the first converting means; and obtaining by the first converting means an image obtained by the image obtaining means based on the correction parameter calculated by the calculating means. Correction means for correcting the converted image data.
[0011]
In the case of the first invention, the image data of the first color system (for example, RGB color system) acquired by the image acquisition means is converted into an image of the second color system (for example, Lab color system) including the brightness information. Then, the image data of the second color system is converted into image data of a second color system (for example, YMCK color system) and recorded on a recording sheet.
Here, test image data of the second color system is generated, and the generated test image data and the test image data are converted into test image data of the third color system by the second conversion unit, and the test image data is generated by the recording unit. A correction parameter is calculated based on the test image recorded on the recording sheet, the test image recorded on the recording sheet acquired by the image acquisition unit and converted by the first conversion unit, and the correction parameter is calculated based on the calculated correction parameter. With the configuration for performing the correction process, the correction parameter can be easily calculated based on the image data in the same color system, and the calculated correction parameter can be calculated for the image data in the second color system. Since the correction processing based on the correction parameters is performed, it is not necessary to perform further processing on the correction parameters, and an image forming apparatus that can easily perform the correction processing can be realized.
[0012]
An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, further comprising a storage unit that stores the test image data of the second color system, wherein the generation unit performs the test that the storage unit stores. The image data is read out.
[0013]
According to the second aspect of the present invention, a storage unit for storing test image data of the second color system is provided, and a correction parameter is calculated based on the test image data read from the storage unit. At the time of execution, each process can be performed on the test image data read from the storage unit, and an image forming apparatus that smoothly executes each process in the calibration function can be realized.
[0014]
An image forming apparatus according to a third aspect of the present invention is the image forming apparatus according to the first or second aspect, wherein the calculating means calculates the correction parameter relating to brightness information included in the test image data of the second color system. The correction unit is configured to correct the image data obtained by the image obtaining unit and converted by the first conversion unit based on a function based on a correction parameter relating to the brightness information. And
[0015]
In the case of the third aspect, the correction parameter is calculated based on the brightness information included in the test image data of the second color system, and the correction processing is performed on the acquired image data according to a function based on the calculated correction parameter regarding the brightness information. By providing a configuration for performing the correction, it is possible to easily perform the correction parameter calculation processing and the correction processing, and to realize an image forming apparatus that removes a variation in color tone in image data to be corrected and reduces deterioration in image quality. be able to.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an image forming apparatus according to the present invention will be described in detail using a digital color copying machine as an embodiment thereof. FIG. 1 is a block diagram showing the configuration of a digital color copying machine according to the present invention. In FIG. 1, reference numeral 1 denotes a digital color copying machine.
The digital color copying machine 1 includes a control unit 10, a ROM 11, a RAM 12, a reading mechanism control unit 13, a CCD (image acquisition unit) 14, a display unit 16, an operation unit 17, a recording unit (recording unit) 18, and an image processing unit 3. , A memory management circuit 20, a second color system conversion unit (second conversion unit) 19, and the like.
The control unit 10 is specifically composed of a CPU (Central Processing Unit) and the like, and is connected to the above-mentioned hardware units of the digital color copying machine 1 via a system bus 21 to control them and In accordance with a computer program stored in the ROM 11, various software functions are executed.
[0017]
The ROM 11 stores various computer programs necessary for the operation of the digital color copying machine 1 of the present invention, and a test image data generation processing program for generating test image data used when executing the calibration function in the digital color copying machine 1. 11a is stored in advance.
The control unit 10 operates as a generation unit that generates test image data by executing the test image data generation processing program 11a, whereby the L component, the a component, and the b component of each pixel are each 8 bits. The test image data represented by the data is generated. The test image data is generated such that one of the L component, the a component, and the b component of each pixel changes linearly.
[0018]
The ROM 11 is used for a conversion processing program 11 b used in the color system conversion processing performed by the first color system conversion unit 32 in the image processing unit 3 and for the color system conversion processing performed by the second color system conversion unit 19. The conversion table 11c is stored.
The RAM 12 is configured by an SRAM, a flash memory, or the like, and temporarily stores data generated when the control unit 10 executes each program. If a flash memory is used as the RAM 12, the stored contents will not be lost even if the power is cut off due to a power failure, movement of the digital color copier 1, or the like.
[0019]
The display unit 16 is a display device such as a liquid crystal display (LCD), and displays the operation state of the digital color copying machine 1, image data read from the image memory 15 to be output, and the like.
The operation unit 17 includes various function keys necessary for operating the digital color copying machine 1, a calibration key 17a for setting a calibration mode for executing a calibration function when pressed by a user, and an instruction to execute a copy process. A start key 17b is provided. By using the touch panel type display unit 16, some or all of the various keys of the operation unit 17 can be substituted.
[0020]
A CCD (Charge Coupled Device) 14 operates as an image acquisition unit, reads a reflected light image from a document as an analog signal of a color system represented by RGB, and converts image data based on the read analog signal into an image processing unit 3. To enter.
The reading mechanism control unit 13 controls an operation of a transport mechanism that transports a document read by the CCD 14 and the like.
[0021]
The image processing unit 3, the memory management circuit 20, and the second color system conversion unit 19 are respectively connected via an image bus 22, and also connected to the image memory 15 via the image bus 22.
The image processing unit 3 has a configuration to be described later, performs a predetermined process on image data based on an analog signal acquired from the CCD 14, and converts the image data into Lab color system image data by the first color system conversion unit 32. Then, in accordance with an instruction from the memory management circuit 20, the image data is stored in the image memory 15 via the image bus 22.
[0022]
The image memory 15 is configured by a DRAM or the like, and stores image data acquired from the image processing unit 3 according to an instruction from the memory management circuit 20. In the present embodiment, the image data output from the image processing unit 3 is a multi-valued L-component, a-component, and b-component of each pixel represented by 8-bit data in the Lab color system. Image data.
The second color system conversion unit 19 acquires the image data stored in the image memory 15 according to the instruction from the memory management circuit 20, stores the image data in the ROM 11, and reads out the image data into the RAM 12 under the control of the control unit 10. An interpolation operation is performed based on the converted conversion table 11c, the image data is converted into, for example, image data of the CMYK color system and input to the recording unit 18.
The recording unit 18 is an electrophotographic printer device, and converts the image data that has been subjected to color system conversion by the second color system conversion unit 19 to be output as a hard copy into A3 portrait, B4 portrait, A4 portrait, B5 An optimum size is selected from recording paper or OHP (Over Head Projector) sheet of each size such as landscape and A5 landscape, and is recorded.
[0023]
FIG. 2 is a block diagram illustrating a configuration of the image processing unit 3. The image processing unit 3 includes an AFE (Analog Front End: analog front end) 30, a shading correction unit 31, and a first color system conversion unit ( A first conversion unit) 32, a color correction unit (correction unit) 33, a correction parameter calculation unit (calculation unit) 34, a switching unit 35, and the like.
The AFE 30 includes an amplifying circuit (not shown), a sample and hold circuit (not shown), an A / D (analog / digital) converter (not shown), and the like. The analog signal representing each of the component, the G component, and the B component is amplified to a predetermined magnitude by an amplifier circuit, and the amplified analog signal is sampled and held at a certain timing by a sample and hold circuit. The signal is converted into a digital signal by an A / D converter. In the present embodiment, the A / D converter outputs an 8-bit digital signal, and the image data output from the AFE 30 converts the R, G, and B components of each pixel into eight. This is multi-valued image data represented by bit data.
[0024]
Image data, which is a digital signal of the RGB color system generated by the AFE 30 as described above, is input to the shading correction unit 31.
The shading correction unit 31 corrects the input RGB color system image data to remove various types of distortion generated in the illumination system, the imaging system, and the imaging system of the CCD 14, and performs correction of the corrected RGB color system. The image data is input to the first color system conversion unit 32.
[0025]
The first color system conversion unit 32 controls the control unit 10 to execute the conversion processing program 11b read from the ROM 11 to the RAM 12 so that the acquired RGB color system image data can be easily handled in the correction process. For example, the image data is converted into Lab color system image data and input to the color correction unit 33 and the correction parameter calculation unit 34. By executing the conversion processing program 11b by the control unit 10, a matrix conversion process or the like is performed on the RGB color system image data to generate Lab color system image data.
Also in the Lab color system image data, each of the L component, the a component, and the b component of each pixel is represented by 8-bit data.
[0026]
When the calibration key 17a is pressed by the user and the calibration mode is set, the correction parameter calculation unit 34 converts the Lab color system image data input from the first color system conversion unit 32 into the control unit. 10 executes the test image data generation processing program 11a to compare with the test image data that has been generated in advance, thereby calculating correction parameters to be used for the correction processing performed by the color correction unit 33, and using the calculated correction parameters as color values. Input to the correction unit 33.
When the calibration mode is set, the color correction unit 33 stores the correction parameters obtained from the correction parameter calculation unit 34 in a register (not shown) provided therein, and the calibration key 17a is pressed. During normal operation, the Lab color system image data input by the first color system conversion unit 32 is corrected based on the correction parameters stored in the register in the calibration mode, and input to the switching unit 35. I do.
[0027]
The control unit 10 operates as a generation unit that generates test image data of the Lab color system by executing the test image data generation processing program 11 a stored in the ROM 11. The generated test image data and the image data of the Lab color system after the correction processing from the color correction unit 33 are input.
The switching unit 35 selects one of the image data based on the switching signal from the control unit 10 and causes the image memory 15 to store the selected image data via the image bus 22. Specifically, when the user presses the calibration key 17a, the generated test image data is stored in the image memory 15, and when the calibration key 17a is not pressed, that is, when the digital color copier is At the time of the normal operation 1, the image data acquired from the color correction unit 33 is stored in the image memory 15.
[0028]
As described above, when the acquired RGB color system image data is converted into, for example, CMYK color system image data and recorded on a recording sheet, the RGB color system image data is once subjected to correction processing. By converting the image data into Lab color system image data which is easy to handle and performing the correction process on the Lab color system image data, the reproducibility of the image can be improved by a simple correction process.
[0029]
Hereinafter, a processing procedure of the control unit 10 when the calibration function is executed by the digital color copying machine 1 having the above configuration will be described. FIG. 3 is a flowchart showing a calibration processing procedure by the digital color copying machine 1 according to the present invention.
The user performs an operation to execute the calibration function at the time of initial setting immediately after purchasing the digital color copying machine 1 and when the user feels that the reproducibility of an image output from the digital color copying machine 1 has deteriorated. The calibration key 17a provided in the unit 17 is turned on.
[0030]
When the calibration key 17a is turned on by the user (S1), the control unit 10 sets the hardware units of the digital color copying machine 1 to the calibration mode (S2). Specifically, a switching signal indicating the calibration mode is input to the correction parameter calculation unit 34 and the switching unit 35 provided in the image processing unit 3.
Next, the control unit 10 reads out the test image data generation processing program 11a stored in the ROM 11 to the RAM 12, and sequentially executes the program code included in the program, thereby displaying each pixel with 8-bit multi-valued data. The generated test image data of the Lab color system is generated (S3), and the generated test image data is input to the switching unit 35 of the image processing unit 3.
[0031]
When the calibration mode is set as described above, the switching unit 35 stores the test image data input by the control unit 10 in the image memory 15 via the image bus 22 in accordance with an instruction from the memory management circuit 20. . Further, the control unit 10 causes the memory management circuit 20 to input the test image data from the image memory 15 to the second color system conversion unit 19 via the image bus 22, and the second color system conversion unit 19 The test image data in the Lab color system is converted into test image data in the CMYK color system, and is recorded on the recording sheet as a test image by the recording unit 18 (S4).
The user places the recording sheet on which the test image is recorded as described above on a document tray (not shown) provided in the digital color copying machine 1, and turns on the start key 17b.
[0032]
When the start key 17b is turned on by the user (S5), the control unit 10 reads the test image recorded on the recording sheet on the document tray by the CCD 14 and acquires the test image data of the RGB color system (S6). ).
Further, the control unit 10 inputs the test image data acquired by the CCD 14 to the image processing unit 3, and sequentially processes the test image data by the AFE 30, the shading correction unit 31, and the first color system conversion unit 32, thereby obtaining the Lab. The image data is converted into color image-based test image data (S7), and the generated test image data is input to the correction parameter calculation unit 34.
[0033]
Next, the control unit 10 compares the Lab test image data generated in step S3 with the test image data converted in step S7 by the correction parameter calculation unit 34 of the image processing unit 3, and compares the comparison result with the Lab test image data. Based on this, a correction parameter is calculated (S8). The correction parameter is represented by, for example, an L component that is lightness information in the Lab color system, and the color correction unit 33 corrects the image data to be processed based on a linear function using the correction parameter as a proportional constant. By doing so, it is possible to further reduce the deterioration of the image quality.
The control unit 10 stores the correction parameters calculated by the correction parameter calculation unit 34 as described above in a predetermined register included in the color correction unit 33, thereby setting the correction parameters as correction parameters to be used for the correction process (S9). The calibration processing ends.
[0034]
As described above, by calculating the correction parameters in the Lab color system that is easy to handle in the correction processing and performing the correction processing based on the calculated correction parameters, the correction parameters can be calculated more easily, and The deterioration of the image quality can be reduced by a proper correction process.
In the above-described embodiment, the test image data generation processing program 11a stored in the ROM 11 in advance is stored, and the control unit 10 executes the program to generate the test image data of the Lab color system. Is generated, but the test image data itself used for the calibration process may be stored in advance. When the test image data itself is stored, it is desirable to reduce the memory capacity by compressing and storing the test image data.
[0035]
【The invention's effect】
In the case of the first invention, the image data of the first color system (for example, RGB color system) acquired by the image acquisition means is converted into an image of the second color system (for example, Lab color system) including the brightness information. Then, the image data of the second color system is converted into image data of a second color system (for example, YMCK color system) and recorded on a recording sheet.
Here, test image data of the second color system is generated, and the generated test image data and the test image data are converted into test image data of the third color system by the second conversion unit, and the test image data is generated by the recording unit. A correction parameter is calculated based on the test image recorded on the recording sheet, the test image recorded on the recording sheet acquired by the image acquisition unit and converted by the first conversion unit, and the correction parameter is calculated based on the calculated correction parameter. With the configuration for performing the correction process, the correction parameter can be easily calculated based on the image data in the same color system, and the calculated correction parameter can be calculated for the image data in the second color system. Since the correction process is performed based on the correction parameter, it is not necessary to further process the correction parameter, and the correction process can be easily performed.
[0036]
According to the second aspect of the present invention, a storage unit for storing test image data of the second color system is provided, and a correction parameter is calculated based on the test image data read from the storage unit. At the time of execution, each process can be performed on the test image data read from the storage unit, and each process in the calibration function can be smoothly performed.
[0037]
In the case of the third aspect, the correction parameter is calculated based on the brightness information included in the test image data of the second color system, and the correction processing is performed on the acquired image data according to a function based on the calculated correction parameter regarding the brightness information. With the configuration for performing the correction, the calculation processing and the correction processing of the correction parameter can be easily performed, and the variation of the color tone in the image data to be corrected can be removed, and the deterioration of the image quality can be reduced.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of a digital color copying machine according to the present invention.
FIG. 2 is a block diagram illustrating a configuration of an image processing unit.
FIG. 3 is a flowchart showing a calibration processing procedure by the digital color copying machine according to the present invention.
[Explanation of symbols]
1 Digital color copier
14. CCD (image acquisition means)
18 Recording unit (recording means)
19 Second color system conversion unit (second conversion unit)
3 Image processing unit
32 first color system conversion unit (first conversion unit)
33 color correction unit (correction means)
34 Correction Parameter Calculation Unit (Calculation Means)

Claims (3)

An image acquisition unit for acquiring image data of the first color system, and a first unit for converting the image data of the first color system acquired by the image acquisition unit into image data of a second color system including brightness information. Conversion means, second conversion means for converting the image data of the second color system converted by the first conversion means into image data of the third color system, and a third table converted by the second conversion means Recording means for recording color-based image data on a recording sheet, the image forming apparatus,
Generating means for generating test image data of the second color system;
The test image data generated by the generation unit and the test image data are converted into test image data of a third color system by the second conversion unit, and are recorded on a recording sheet by the recording unit, and are recorded on the recording sheet. Calculating means for calculating a correction parameter based on the test image data obtained by the obtained image by the image obtaining means and converted by the first converting means;
An image forming apparatus comprising: a correction unit configured to correct image data acquired by the image acquisition unit and converted by the first conversion unit based on the correction parameter calculated by the calculation unit. 2. The image according to claim 1, further comprising storage means for storing the test image data of the second color system, wherein the generation means reads out the test image data stored in the storage means. Forming equipment. The calculating means is configured to calculate the correction parameter related to brightness information included in the test image data of the second color system,
2. The image processing apparatus according to claim 1, wherein the correction unit corrects the image data obtained by the image obtaining unit and converted by the first conversion unit based on a function based on a correction parameter related to the brightness information. Or the image forming apparatus according to 2.

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