JP2004167947A - Color image forming apparatus and method of calibrating color density thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To comparatively readily perform calibration of a density without using a dedicated device. <P>SOLUTION: A printer 3 prints a calibration image data indicating a sample image having a plurality of gradations according to a designation of the calibration by each print head. The printer 3 detects the color density by scanning the sample image with a scanner head mounted on a carriage together with the print head. A host computer 1 or the printer 3 calculates a difference in density between a target value of the density in each gradation of each ink color and the measured value to obtain a density correction value of each gradation of each ink color. The density correction value for correcting the print density for image data to be printed is stored in a memory. The printer 3 corrects the print density of each color by the correction value when the image is printed thereafter. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color image forming apparatus using ink and a method for calibrating the color density of the apparatus.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, an image forming apparatus that handles color images, such as a color printer, handles a color image by dividing it into three images of R, G, and B images corresponding to so-called three primary colors of light. For example, a color printer converts the received RGB tone values into cyan (C), magenta (M>), and yellow (Y) tone values that can be handled by the printer, and then obtains the obtained CMY tone values. Accordingly, a color image is printed by attaching cyan, magenta, and yellow color inks on a print medium by various methods.
[0003]
However, even if the same RGB image data is supplied, the color expressed on the print medium may be slightly different depending on the type of the color printer. One cause of this is that, in a color printer, the manner in which the colors of cyan, magenta, and yellow are developed slightly differs depending on the model. Therefore, in the conventional color printer, density differences occur due to machine differences, aging, environmental changes, and the like. Therefore, calibration for correcting this density difference is required.
[0004]
Conventionally, a calibration method is performed by printing a yellow (Y), magenta (M), cyan (C) patch, or a patch obtained by adding a black (K) patch thereto, and performing a test print. The density of each patch of the obtained test print is measured by a densitometer, and the printer is calibrated based on the measurement result.
[0005]
[Problems to be solved by the invention]
However, the above-described conventional technique requires a densitometer for performing calibration and a special device for calculating a correction value, thereby increasing costs, and also requires a complicated manual operation by an operator.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of such a background, and an object of the present invention is to provide a color image forming apparatus capable of relatively easily performing density calibration without requiring a special apparatus, and a color density calibration apparatus. It is to provide a solution method.
[0007]
[Means for Solving the Problems]
A color density calibration method according to the present invention is a color density calibration method for a color image forming apparatus in which a scanner head for reading an image can be mounted on a carriage together with a plurality of ink color print heads. Printing image data for calibration representing a sample image of a plurality of gradations by each print head; scanning the printed sample image with the scanner head to detect color density; Calculating a density difference between a target value and a measured value of the density of each tone, obtaining a density correction value of each tone of each ink color; and the density correction value for correcting a print density based on image data to be printed. Is stored.
[0008]
Since the scanner head is mounted on the carriage together with the print head, after printing the calibration image data, the density of each part of the sample image can be read by the scanner head without discharging the printing paper. . Therefore, the calibration of the density can be performed relatively easily without requiring a special device.
[0009]
The calibration instruction may be output from the host computer in response to a user instruction, or may be received from the user in the color image forming apparatus.
[0010]
The calibration image data may be held in a host computer connected to the color image forming apparatus, or may be held in the color image forming apparatus.
[0011]
The calculation of the density difference may be performed by the host computer or the color image forming apparatus based on the measurement value returned from the color image forming apparatus.
[0012]
A printer driver according to the present invention is a printer driver having a color density calibration function for a color image forming apparatus capable of mounting a scanner head for reading an image on a carriage together with a plurality of ink color print heads. Displaying, on a monitor, a property screen including a button for accepting an application instruction, and performing a calibration that represents a sample image of a plurality of gradations by each print head with respect to the color image forming apparatus in response to an operation of the button by a user. Outputting a print instruction for image data for use; receiving a return of a measured value of color density obtained by scanning the sample image with the scanner head from the color image forming apparatus; and Calculate the density difference between the target value of the tone density and the measured value. Obtaining a density correction value for each gradation of each ink color, storing the density correction value, and correcting the density based on the density correction value when outputting image data to be printed. Is performed.
[0013]
A color image forming apparatus according to the present invention is a color image forming apparatus capable of mounting a scanner head for reading an image together with a plurality of ink color print heads on a carriage. Means for printing the calibration image data representing the following, means for scanning the printed sample image with the scanner head to detect the color density, and measuring the density value of each gradation of each ink color to the host computer. And means for returning to
[0014]
In this image forming apparatus, the host computer calculates the density difference and the density correction value.
[0015]
Another color image forming apparatus according to the present invention is a color image forming apparatus in which a scanner head for reading an image can be mounted on a carriage together with a plurality of ink color print heads, and means for holding image data for color density calibration, Means for printing the calibration image data representing a sample image of a plurality of gradations in response to a calibration instruction; means for scanning the printed sample image with the scanner head to detect color density; Means for calculating a density difference between a target value and a measured value of the density of each tone of each tone, and a density correction value for each tone of each ink color, and the density correction for correcting a print density based on image data to be printed. Means for storing a value.
[0016]
In this image forming apparatus, the image forming apparatus itself calculates the density difference and the density correction value.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0018]
FIG. 1 shows a schematic configuration of a system according to an embodiment of the present invention. A host computer 1 for creating an image, a monitor 2 for visually checking the created image, and a printer for receiving image data created by the host computer 1 and printing the received data on printing paper And 3. The printer 3 in the present embodiment will be described using an image forming apparatus of an ink jet recording system as an example.
[0019]
FIG. 2 shows a schematic internal configuration of the host computer 1 and the printer 3. The host computer 1 stores a control unit 5 such as a CPU, various programs used by the control unit 5, fixed data, image data to be printed, image data for calibration representing a sample image of a plurality of gradations, and the like. A storage unit 6 for performing the image output of the monitor 2 and the printer 3.
[0020]
The calibration image data is predetermined data for printing a test pattern of n gradations (n ≧ 2) for each of K, C, M, and Y. An image shown as an original image on the screen of the monitor 2 in FIG. 1 corresponds to a target print sample (assuming that the monitor is properly calibrated). Although the number of gradations is set to 3 in FIG. 1, a pattern of more gradations may actually be used. A pattern may be repeatedly printed so that the number of tone bars of each color also includes a plurality of bars, and a pattern portion of the same color and the same tone may be sampled a plurality of times to obtain an average value of density.
[0021]
On the other hand, the printer 3 receives image data from the image output driver 21 of the host computer 1 through the host interface (host I / F) 22. If the image data is compressed data, the image processing unit 23 decompresses the received image data, performs necessary image processing, and passes the image data to the engine controller 24. The engine controller 24 converts the image data received from the image processing unit 23 into a data string in which the nozzles of the print head are arranged, and passes the data to the head controller 26. The engine controller 24 is connected to a head controller 26 that controls ink ejection pulses and a motor controller 25 that drives a motor, and also arbitrates paper transport control (not shown). The head controller 26 generates an ink ejection pulse, forms an image on a sheet by printing it on a print head 28, and also generates an image sampling timing by the scanner head 27. Although the head controller 26 is illustrated as being outside the carriage 29, a part or all of the head controller 26 may be mounted on the carriage 29. The scanner head 27 is mounted on a carriage together with the print head, and reads an image as the carriage scans. By mounting the scanner head 27, the printer can be used as a scanner. In the present invention, such a scanner head is used for color density calibration.
[0022]
FIG. 3 shows the appearance of the scanner head 27. As shown in FIG. 3, the scanner head 27 according to the present embodiment includes a light source 32 that is covered with an outer shell (housing) 31 and irradiates light to a sheet, and a lens 33 that reads light reflected on the sheet surface. A filter unit 35 on which a color filter used for color reading is mounted, and sensors for converting the intensity of light input through the lens 33 and the filter unit 35 into a voltage are arranged in a line in the paper feeding direction. And a reading sensor unit 34. In the filter section 35, filter windows 35A, 35B and 35C are arranged in a line in the same direction as the sheet feeding direction, and R filters, G filters and B filters are respectively mounted.
[0023]
FIG. 4 shows a schematic configuration of a main part of a driving function related to scanning of the print head 28 and conveyance of the print paper. In the present embodiment, one of the five print heads (black 1, black 2, cyan, magenta, and yellow ink colors) mounted on the carriage (29 in FIG. 2) (black 1 in this example) Shows a case where the scanner head 27 can be replaced and attached. The mounting direction of the scanner head 27 is such that scanning for reading is performed in a direction along the sensor row of the reading sensor unit 34. The print head 28 and the scanner head 27 reciprocate in the head scanning direction together with the carriage in accordance with the driving of the main scanning motor 54. The printing paper 51 is conveyed in a paper feeding direction perpendicular to the head scanning direction according to the driving of the sub-scanning motor 55. The current position of the carriage (and, consequently, each print head and scanner head) in the head scanning direction is detected by a linear scale 52 and a regular slit or mark of the linear scale 52 by a linear scale sensor (not shown) also mounted on the carriage. This makes it possible to confirm. The current position of the printing paper 51 can be confirmed by a sensor (not shown) for detecting the leading edge of the paper, a rotary encoder (or a drive pulse counter) related to driving of the sub-scanning motor 55, and the like.
[0024]
FIG. 5 shows an example of a property screen of a printer driver which is a part of the image output driver 21 of the host computer 1. In the present embodiment, a calibration button 41 is provided in the property screen.
[0025]
FIG. 6 shows a flowchart of a first processing example in the present embodiment. This process is preferably executed after replacing the print head, after refilling the ink, after replacing the ink cartridge, or after a long period of non-use.
[0026]
When the calibration button 41 in the property screen is instructed (clicked) by the user on the host computer side (S11), the host computer notifies the printer side to enter the calibration mode, as well as the calibration image data and the calibration image data. The print instruction is transmitted to the printer (S12). At this time, if the printer holds calibration image data, it is not necessary to transmit the calibration image data from the host computer.
[0027]
The printer 3 receives the notification and the data, and prints the image data for calibration (S21). A sample image of this printing result is schematically shown on the printing paper 51 of FIGS. 1 and 4.
[0028]
After the printing, the printer rewound the paper on which the calibration image was printed without discharging the printing paper, and the paper was printed on the printing paper 51 by the scanner head 27 attached near the print head 28. The calibration image is read by the reading sensor unit 34, and the calibration image data (color density measurement data) of each color of K, C, M, and Y is converted into a digital signal (S22). At this time, since the calibration image is read by the scanner head 27 mounted on the same carriage as the print head without discharging the paper on which the calibration image is printed, the printing position of each gradation of each color is clearly specified. Can be read. Further, the digitized color density data of each color is returned to the host computer 1 again (S23).
[0029]
The host computer 1 receives the density measurement data of each color (S13), and calculates a color density difference of each color based on the data (S14). As shown in FIG. 1, the original image and the measured image may be arranged on the monitor 2 so that the user can visually check both. For example, when a measurement result as shown in FIG. 7 is obtained for a certain color, it is understood that the output density of the measurement color indicates a higher value than the target value of the original image. Therefore, for the color, it is necessary to set a color density correction value for the printer 3 in which the output density is corrected by the density difference ΔYi = | Y′i−Yi |. The number of points of the measured printer output data Xi corresponds to the number of gradations of each color of the calibration image. As described above, the same gradation of the same color may be read a plurality of times, and the average of the results may be output. Although the number of gradations of the calibration image illustrated in the figure is small, in practice, more gradations may be included in the calibration image to measure each gradation. The gray scale for which no measurement is performed can be obtained by interpolating the measurement results of the adjacent gray scales on both sides.
[0030]
The color density correction value of each color obtained in this way is set as a color density correction value in the image output driver 21 in the host computer 1. This correction value is stored in the host computer 1 in a non-volatile manner (S15), read out when the printer 3 is used, and used for the print density correction based on the image data. After the execution of the calibration, the printer 3 performs printing at an appropriate density.
[0031]
The density correction based on the correction value can be performed by a method of correcting the value of the image data itself or a method of adjusting the ink ejection amount based on the value of the image data without changing the value of the image data itself. There may be.
[0032]
In the processing of FIG. 6, the calculation of the color density difference and the storage of the correction value are performed on the host computer side, but the present invention is not limited to this. FIG. 8 shows a processing example in the case where the calculation of the color density difference and the storage of the correction value are performed on the printer side. That is, the calibration instruction and the printing instruction of the calibration image data are performed on the host computer side (S31, S32), the calibration image data is printed on the printer side (S41), and the sample image is scanned by the scanner head (S42). Thereafter, the printer calculates the color density difference of each gradation of each ink color (S43) and stores the correction value corresponding to this color density difference (S44). Thereafter, when an instruction to print image data is issued from the host computer, the printer performs print density correction based on the image data based on the correction value.
[0033]
FIG. 9 illustrates an example of processing in which a calibration instruction and a printing instruction of calibration image data are also performed on the printer side. The user issues a calibration instruction on the printer side by operating an operation unit (not shown) provided in the printer (S51). The calibration image data is held in a storage device (not shown) in the printer, and is read out and printed (S52). Subsequent processing steps S53, S54 and S55 are the same as steps S42, S43 and S44 in FIG.
[0034]
Although the preferred embodiment of the present invention has been described above, various modifications and changes other than those described above can be made.
[0035]
【The invention's effect】
According to the present invention, the use of the scanner head that can be mounted on the carriage together with the print head eliminates the need for a special device for performing color density calibration. Further, the user can automatically perform the printing and measurement of the pattern only by giving an instruction, so that the calibration can be easily performed.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a system according to an embodiment of the present invention.
FIG. 2 is a diagram showing a schematic internal configuration of a host computer and a printer of FIG. 1;
FIG. 3 is a diagram showing an external shape of a scanner head according to the embodiment of the present invention.
FIG. 4 is a diagram illustrating a schematic configuration of a main part of a drive function related to scanning of a print head and conveyance of a print sheet according to the embodiment of the invention.
FIG. 5 is a diagram illustrating an example of a property screen of a printer driver which is a part of an image output driver of a host computer according to the embodiment of the present invention.
FIG. 6 is a flowchart of a first processing example according to the embodiment of the present invention.
FIG. 7 is a graph showing a relationship between a measured value of a color density and a target value according to the embodiment of the present invention.
FIG. 8 is a flowchart illustrating a second processing example in a case where calculation of a color density difference and storage of a correction value are performed on the printer side in the embodiment of the present invention.
FIG. 9 is a flowchart illustrating an example of processing in which a calibration instruction and a printing instruction of calibration image data are also performed on the printer side in the embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Host computer 2 ... Monitor 3 ... Printer 22 ... Host I / F
23 image processing unit 24 engine controller 25 motor controller 26 head controller 27 scanner head 28 print head 29 carriage 41 calibration button

Claims (10)

A color density calibration method for a color image forming apparatus capable of mounting a scanner head for reading an image on a carriage together with a plurality of ink color print heads,
Printing a calibration image data representing a sample image of a plurality of gradations by each print head in response to the calibration instruction;
Scanning a printed sample image with the scanner head to detect color density;
Calculating a density difference between a target value and a measured value of the density of each tone of each ink color to obtain a density correction value of each tone of each ink color;
Storing the density correction value in order to correct the print density based on the image data to be printed. 2. The color density calibration method according to claim 1, wherein the calibration instruction is output from the host computer in response to a user instruction. 2. The color density calibration method according to claim 1, wherein the calibration instruction is received from a user in the color image forming apparatus. 2. The color density calibration method according to claim 1, wherein the calibration image data is held in a host computer connected to the color image forming apparatus. 2. The color density calibration method according to claim 1, wherein the calibration image data is held in the color image forming apparatus. 2. The color density calibration method according to claim 1, wherein the calculation of the density difference is performed by the host computer based on the measurement value returned from the color image forming apparatus. The color density calibration method according to claim 1, wherein the calculation of the density difference is performed by the color image forming apparatus. A printer driver having a color density calibration function for a color image forming apparatus capable of mounting a scanner head for reading an image on a carriage together with a plurality of ink color print heads,
Displaying on a monitor a property screen including a button for receiving a calibration instruction from a user;
Outputting, according to a user's operation of the button, a print instruction of calibration image data representing a sample image of a plurality of gradations by each print head to the color image forming apparatus;
From the color image forming apparatus, receiving a return of the measured value of the color density obtained by scanning the sample image with the scanner head,
Calculating a density difference between the target value of the density of each tone of each ink color and the measured value, and obtaining a density correction value of each tone of each ink color;
Storing the density correction value;
Correcting the density based on the density correction value when outputting the image data to be printed. In a color image forming apparatus capable of mounting a scanner head for reading an image on a carriage together with a print head of a plurality of ink colors,
Means for printing the calibration image data representing a sample image of a plurality of gradations in response to a calibration instruction from a host computer,
Means for detecting the color density by scanning the printed sample image with the scanner head,
Means for returning a measured value of the density of each gradation of each ink color to the host computer. In a color image forming apparatus capable of mounting a scanner head for reading an image on a carriage together with a print head of a plurality of ink colors,
Means for holding image data for color density calibration;
Means for printing the image data for calibration representing a sample image of a plurality of gradations according to a calibration instruction,
Means for detecting the color density by scanning the printed sample image with the scanner head,
Means for calculating a density difference between a target value and a measured value of the density of each tone of each ink color, and obtaining a density correction value of each tone of each ink color;
Means for storing the density correction value in order to correct the print density based on the image data to be printed.

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