JP2011259227A - Wavelength calibration method, printing device, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily calibrate wavelength of light detected by a spectroscopic sensor for producing a color conversion LUT without using a special sensor.SOLUTION: A spectral reflectance 402 of a slave to be corrected and a spectral reflectance 401 of a master to be a reference are obtained. In a wavelength deviation search range 403 of the spectral reflectances 401 and 402, an intersection with a wavelength deviation detection line DL whose spectral reflectance is constant is obtained for each of the spectral reflectances 401 and 402. The wavelength detected by the spectral reflectance 401 is obtained from the intersection of the spectral reflectance 401 with the wavelength deviation detection line DL, and the pixel positions of light receiving elements of the spectral reflectance 402 from the intersection of the spectral reflectance 402 with the wavelength deviation detection line DL. Based on the relationship between the obtained pixel positions and the wavelength, a table showing the corresponding relationship between the pixel positions and wavelength of the slave is updated.

Description

  The present invention relates to a wavelength calibration method, a printing apparatus, and a computer program, and more particularly to use in a printing apparatus to calibrate the wavelength of light detected by a spectroscopic sensor for generating / updating a color conversion lookup table. Is preferred.

Conventionally, in a printing apparatus represented by a printer, a color conversion lookup table (hereinafter referred to as “LUT”) is used to output a desired color. The color conversion LUT includes an LUT used for calibration for keeping the printer in a certain state, an LUT used for color matching represented by an ICC profile, and the like.
Some recent printers have a spectral color sensor built into the printer engine. Such a printer prints color charts (hereinafter referred to as “patches”) such as IT87 / 3, for example, before execution of a print job or during execution of a print job, and patches it with a built-in spectral color sensor. The color is measured. Then, the result of the color measurement is fed back for generation of the color conversion LUT. As a result, color matching and printing color stabilization can be achieved by processing inside the printer without using an external colorimetric sensor.

In order to achieve color matching and print color stabilization with high accuracy, a spectral color sensor built in the printer is required to perform color measurement with high accuracy. Therefore, errors between sensor models and errors due to changes over time cannot be ignored. The error between sensor models includes “error between sensors of the same model (individual difference)” due to variations in the manufacturing of spectral color sensors, and “difference between sensors of different models” due to differences in optical conditions (geometry) between sensors. There is an "error difference". Among these, an error between sensors of the same model becomes a problem particularly in a printer equipped with a plurality of spectral color sensors. That is, there is a problem that even if the same color is measured by a plurality of spectral color sensors, the output value of each individual is different. In addition, an error due to a change with time causes a problem in that the sensor optical system changes due to the distortion of the sensor body or the thermal expansion of the diffraction grating, resulting in deviation from the past output state.
For these reasons, there is a need for a technique for reducing errors between spectral color sensor models and errors due to changes over time. Further, the error between sensor models is roughly divided into two types in terms of spectral reflectance. One is the spectral axis deviation (horizontal axis deviation), and the other is the spectral reflectance axis deviation (vertical axis deviation). FIG. 9 conceptually shows an example of a shift δ between the wavelength axes of the first spectral reflectance 901 and the second spectral reflectance 902.

Normally, when calibrating the wavelength axis of such a spectral color sensor, the wavelength axis shift of the spectral reflectance (hereinafter referred to as “ (Referred to as “wavelength shift”). However, “error between sensors of the same model” that cannot be removed by factory adjustment remains in the spectral color sensor. In addition, if a product is shipped with a spectral color sensor installed in the printer, it will be necessary to remove the spectral color sensor once and adjust it again at the factory when correcting for changes over time. End up.
Therefore, in Patent Document 1, the spectral color sensor itself can calibrate the wavelength by providing an LED monochromatic light source for wavelength calibration inside the spectral color sensor. Based on the absolute amount of the bright line of the LED single-color light source for wavelength calibration, the wavelength axis of the plurality of spectral color sensors is matched to correct individual differences and temporal changes of the spectral color sensors.
Further, as a wavelength calibration algorithm for a spectral color sensor, the following conventional techniques can be cited.
In Patent Document 2, two spectral reflectances (reference spectrum and correction target spectrum) are compared, and the shift amount of the wavelength of the spectral color sensor is calculated using an optimization method. In Patent Document 3, attention is paid to an inclined region of two spectral reflectances (a reference spectrum and a correction target spectrum), and a correction coefficient in each inclined region is calculated using the inclination in the inclined region.

JP 2008-185565 A JP-A-8-15134 JP 2006-214968 A

However, in the technique described in Patent Document 1, since it is necessary to have a light source different from a normal light source, the configuration of the spectral color sensor is complicated and the cost of the spectral color sensor is increased.
Further, in the technique described in Patent Document 2, since the two spectral reflectances are optimized in the entire wavelength region, the spectral reflectance wavelength is changed when there is a spectral reflectance axial shift (vertical axis shift). It is difficult to correct with high accuracy. Furthermore, the technique described in Patent Document 2 is complicated in calculation and lacks simplicity.
Further, the technique described in Patent Document 3 has a problem that it is easily affected by noise in each inclined region of the spectral reflectance.
The present invention has been made in view of the above problems, and the wavelength of light detected by a spectroscopic sensor for generating a color conversion LUT used for outputting a desired color in a printing apparatus is specially determined. The object is to calibrate accurately and easily without using a sensor.

  The wavelength calibration method of the present invention includes a first spectral reflectance derivation step for deriving a first spectral reflectance based on a result of color measurement of a wavelength calibration sample by a first spectral sensor serving as a reference, A second spectral reflectance derivation step for deriving a second spectral reflectance based on a result of color measurement of the wavelength calibration sample by the target second spectral sensor; the first spectral reflectance; A wavelength shift detection step for detecting a shift in wavelength between the first spectral reflectance and the second spectral reflectance in a predetermined inclined region of the second spectral reflectance; A wavelength shift correction step of correcting a wavelength shift of the second spectral reflectivity with respect to the first spectral reflectivity based on a wavelength shift between the first spectral reflectivity and the second spectral reflectivity; It is characterized by having.

  According to the present invention, the first spectral reflectance based on the result of colorimetry by the first spectroscopic sensor serving as a reference, and the second spectrum based on the result of colorimetry by the second spectroscopic sensor to be calibrated. A wavelength shift in a predetermined region where the reflectance is inclined is detected. Based on the wavelength shift, the wavelength shift of the second spectral reflectance with respect to the first spectral reflectance is corrected. Therefore, the wavelength of light detected by the spectroscopic sensor for generating and updating the color conversion lookup table used for outputting a desired color in the printing apparatus can be accurately and easily without using a special sensor. Can be calibrated.

2 is a diagram illustrating a configuration of a printer apparatus. FIG. It is a flowchart explaining the wavelength calibration sequence of 2nd Embodiment. It is a figure which shows a mode that a spectral color sensor measures a color of a patch. It is a figure which shows a spectral reflectance. It is a flowchart explaining a wavelength calibration process (wavelength calibration algorithm). It is a figure explaining the method to detect the wavelength shift of a spectral reflectance. It is a figure which shows a polynomial approximation curve. It is a flowchart explaining the wavelength calibration sequence of 2nd Embodiment. It is a figure which shows the shift | offset | difference of the wavelength axis with two spectral reflectances.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
First, a first embodiment of the present invention will be described.
"Overview"
In the present embodiment, a case will be described in which individual differences between two spectral color sensors built in an electrophotographic printer, particularly a shift in wavelength axis, are corrected. In the present embodiment, one of the two spectral color sensors is a master and the other is a slave, and processing for adjusting the spectral reflectance (correction target) of the slave to the spectral reflectance (reference) of the master is performed. Hereinafter, the configuration of the printer, the wavelength calibration sequence of the spectral color sensor, and the details of the wavelength calibration algorithm will be described in this order.

"Printer Configuration"
FIG. 1 is a block diagram illustrating an example of the configuration of a printer apparatus according to the present embodiment.
The functional parts of the printer apparatus 1 are roughly divided into a controller unit 11 and an engine unit 12.
The controller unit 11 includes a color matching unit 111, a calibration unit 112, a calibration LUT generation unit 113, and a color matching LUT generation unit 114. The controller unit 11 has various other functional parts related to image processing. Here, description of components not directly related to the present embodiment is omitted.

  The color matching unit 111 performs color adjustment using a color matching LUT 1111 typified by an ICC profile. The color matching LUT generation unit 114 generates a color matching LUT 1111 using the colorimetric value 1232. The calibration unit 112 performs image correction (calibration) for keeping the printing state constant by using a calibration LUT 1121 typified by a one-dimensional LUT for each CMYK. The calibration LUT generation unit 113 generates a calibration LUT 1121 using the colorimetric values 1232. In this embodiment, the color matching LUT 1111 and the calibration LUT 1121 are color conversion lookup tables.

On the other hand, the engine unit 12 includes a fixing unit 121, spectral color sensors 122 a and 122 b, and a sensor signal processing unit 123. In addition, the engine unit 12 includes various functional parts for forming an image on a medium such as paper. Here, description of components that are not directly related to the present embodiment is omitted.
The fixing unit 121 includes a roller, a belt, and a heat source such as a halogen heater, and melts and fixes the toner to the medium by heat and pressure. The two spectral color sensors 122a and 122b are installed in the transport path from the fixing unit 121 to the paper discharge port, and measure the color of the patch on the transported medium. In the present embodiment, it is assumed that the two spectral color sensors 122a and 122b are arranged side by side in the horizontal direction (direction along the paper surface) perpendicular to the conveyance direction of the medium (paper). . Colorimetric data from each of the spectral color sensors 122 a and 122 b is sent to the sensor signal processing unit 123. The sensor signal processing unit 123 converts the color measurement data into a color measurement value 1232 (for example, CIE L * a * b *). In the sensor signal processing unit 123, the wavelength calibration unit 1231 performs wavelength calibration processing based on a wavelength calibration algorithm described later. The colorimetric value 1232 in which the wavelength shift is corrected by this wavelength calibration processing is transmitted to the calibration LUT generation unit 113 and the color matching LUT generation unit 114.

The printer apparatus 1 according to the present embodiment outputs a calibration patch to a medium (paper) before execution of a print job or during execution of a print job, and performs colorimetry using built-in spectral color sensors 122a and 122b. Then, the printer apparatus 1 creates / updates the calibration LUT 1121 based on the measured color value. This keeps the color reproducibility constant. In addition, the printer device 1 according to the present embodiment outputs a color matching patch to a medium (paper) before executing a print job, and performs colorimetry using the built-in spectral color sensors 122a and 122b. Then, the printer apparatus 1 creates and updates the color matching LUT 1111 based on the colorimetric values. This absorbs the color difference between the printer devices.
The reason why two spectral color sensors 122 are installed in the printer apparatus 1 is to reduce the color measurement time by the spectral color sensor 122 and to reduce the number of sheets output from the printer apparatus 1. is there. However, the number of spectral color sensors 122 mounted on the printer apparatus 1 is not limited to two, and may be one or three or more.
Further, the update timing of the calibration LUT 1121 and the color matching LUT 1111 can be determined based on preset contents. For example, each time a print job is received, the calibration LUT 1121 and the color matching LUT 1111 can be updated.

A wavelength shift correction process described later is a process performed before calibration and color matching, and is performed for the purpose of improving the colorimetric accuracy of the spectral color sensors 122a and 122b. In the wavelength shift correction process of the present embodiment, a wavelength calibration patch is printed separately from the above-described LUT creation patch (calibration patch, color matching patch), and based on the result of the color measurement, It detects and corrects the wavelength shift of the spectral reflectance.
Note that the wavelength calibration processing may be performed using the color measurement result of the LUT creation patch without preparing a patch for wavelength calibration.

"Wavelength calibration sequence"
A wavelength calibration sequence of the spectral color sensors 122a and 122b in the present embodiment will be described. In the present embodiment, minute errors remaining between the individual spectral color sensors 122a and 122b in the wavelength calibration process are reduced.
FIG. 2 is a flowchart for explaining an example of a wavelength calibration sequence in the present embodiment.
First, in step S201, the printer apparatus 1 prints a wavelength calibration patch. Since the spectral reflectance gradient region is used in the algorithm described later, the spectral reflectance of the wavelength calibration patch measured by the spectral color sensors 122a and 122b needs to have a steep gradient. Therefore, for example, it is preferable to use a high saturation patch (a high saturation color patch) as the wavelength calibration patch.

Further, in the present embodiment, a plurality of wavelength calibration patches are printed on the same medium (paper), and from the wavelength shift of the slope region (rising region or falling region) of the spectral reflectance of each wavelength calibration patch, A wavelength correction amount in an arbitrary wavelength region is calculated. Therefore, in order to correct the wavelength deviation with high accuracy, it is necessary to detect the wavelength deviation in a wide wavelength range. Therefore, each inclined area needs to be dispersed over all wavelengths supported by the printer apparatus 1.
FIG. 3 is a diagram conceptually illustrating an example of a state in which the spectral color sensors 122a and 122b perform color measurement on the wavelength calibration patches 301a to 301d. FIG. 4 is a diagram illustrating an example of spectral reflectances 401 and 402 obtained from color measurement results of the wavelength calibration patches 301a to 301d by the spectral color sensors 122a and 122b.

  Here, as shown in FIGS. 3 and 4, wavelength calibration patches 301 a, 301 b, 301 c, where the spectral reflectances 401 and 402 are steep, are near 400 nm, 500 nm, 550 nm, and 600 nm, respectively. 301d is used. Then, the four wavelength calibration patches 301a to 301d printed on the paper 302 conveyed in the conveyance direction T are measured along the color measurement lines 303a and 303b. Then, a predetermined region of the inclined regions of the spectral reflectances 401 and 402 obtained from the color measurement result is used as the wavelength shift search range 403a to 403d. By doing so, it is possible to detect a wavelength shift in a wide wavelength range of 400 nm to 600 nm. Further, when the color of the toner patch is measured, an inclined region is obtained in the spectral reflectance in the wavelength regions (400 nm, 500 nm, 550 nm, and 600 nm) as shown in FIG. 4 depending on the mixing ratio of each color of CMYK. For this reason, the four wavelength calibration patches 301a to 301d from which these inclined regions are obtained are used here.

Returning to the description of FIG. 2, in step S202, the spectral color sensors 122a and 122b measure the color of the wavelength calibration patches 301a to 301d printed in step S201 and conveyed to the colorimetric positions of the spectral color sensors 122a and 122b. . At this time, as shown in FIG. 3, two spectral color sensors 122a and 122b measure the same wavelength calibration patch 301 simultaneously. The color of the patch is measured by the number of inclined regions used for detecting the wavelength shift. In the example shown in FIGS. 3 and 4, the number of patches is four.
Next, in step S203, the wavelength calibration unit 1231 calibrates the wavelength of the spectral color sensor 122b (wavelength calibration process) based on the colorimetric value (spectral reflectance) obtained in step S202. Here, of the two spectral color sensors 122a and 122b, one spectral color sensor 122a is a master, and the other spectral color sensor 122b is a slave. Then, processing is performed to match the spectral reflectance 402 (correction target) obtained from the slave colorimetric result with the spectral reflectance 401 (reference spectrum) obtained from the master colorimetric result. In this embodiment, the following wavelength calibration algorithm is used for this processing.

"Wavelength calibration algorithm"
FIG. 5 is a flowchart for explaining an example of the wavelength calibration process (wavelength calibration algorithm) in step S203.
First, in step S501, the wavelength calibration unit 1231 performs initial parameter settings. Here, the total number N of the slope regions of the spectral reflectances 401 and 402 to be detected is set to 4, and the slope count n is set to 1. The inclination count n represents the number of detected inclination areas.

Next, in step S502, the wavelength calibration unit 1231 detects a wavelength shift in the inclined region of the spectral reflectances 401 and 402 based on the color measurement result obtained in step S202.
Here, the relationship between the pixel position of the light receiving element of the spectral color sensor 122 and the wavelength of light detected by the light receiving element will be described. In general, in a spectral color sensor, reflected light from a measurement object is decomposed for each wavelength by a diffraction grating and then detected by a light receiving element (line sensor). Since the wavelength of the light detected by the light receiving element is different for each pixel of the light receiving element, a table indicating the correspondence between the pixel position (pixel number) and the detected wavelength is required. This table defines the wavelength axis (horizontal axis) of spectral reflectance. Therefore, it is possible to correct the wavelength axis shift (wavelength shift) by changing this table. Therefore, in the wavelength calibration algorithm of the present embodiment, the wavelength shift is corrected by re-creating and updating the table of the spectral color sensor 122b serving as a slave.

FIG. 6 is a diagram for explaining an example of a method for detecting the wavelength shift of the spectral reflectance 402 of the spectral color sensor 122b. In FIG. 6, as illustrated in FIG. 6A, a case where a wavelength shift of the spectral reflectance 402 c is detected will be described as an example. Here, FIG. 6B is a diagram illustrating intersections between the spectral reflectance 402c of the spectral color sensor 122b serving as a slave and the wavelength shift detection lines DL1 to DL5. On the other hand, FIG. 6C is a diagram illustrating intersections between the spectral reflectance 401c of the spectral color sensor 122a serving as a master and the wavelength shift detection lines DL1 to DL5.
As shown in FIG. 6A, the slope region (wavelength shift search range 403c) to be used may be a region near the center of the slope region with less waveform rounding.

  In step S502, the wavelength calibration unit 1231 determines a wavelength shift detection line DL (Detect Line) having a constant spectral reflectance so as to pass through the inclined region, and detects the wavelength shift on the wavelength shift detection line DL. To do. First, the wavelength calibration unit 1231 sets the wavelength shift detection line DL as shown in FIG. In the example shown in FIG. 6, the wavelength calibration unit 1231 sets five wavelength shift detection lines DL1 to DL5 for the spectral reflectances 401c and 402c. Next, the wavelength calibration unit 1231 calculates the intersection between the master and slave spectral reflectances 401 and 402 and the wavelength shift detection line DL. Note that the spectral reflectances 401 and 402 are actually discrete. For this reason, the wavelength calibration unit 1231 performs necessary data interpolation processing using the obtained spectral reflectances 401 and 402 data, and determines the intersection between the spectral reflectances 401 and 402 and the wavelength shift detection line DL. Ask.

  Next, as shown in FIG. 6B, the wavelength calibration unit 1231 calculates the pixel position from the intersection of the slave spectral reflectance 402 and the wavelength shift detection line DL. Further, as shown in FIG. 6C, the wavelength calibration unit 1231 calculates the wavelength detected by the light receiving element from the intersection of the master spectral reflectance 401 and the wavelength shift detection line DL. Then, the wavelength calibration unit 1231 associates the calculated pixel position with the wavelength on a one-to-one basis. Such processing is repeated for all the wavelength shift detection lines DL1 to DL5. The above operation calculates the correspondence between the pixel position and the wavelength when it is assumed that there is no master wavelength deviation on the wavelength deviation detection line DL. Here, the wavelength shift of the slave in the inclined region is detected by performing the process of step S502.

  In step S503, the wavelength calibration unit 1231 determines whether the tilt count n is less than the total number N of tilt regions of the spectral reflectances 401 and 402 to be detected. As a result of this determination, if the tilt count n is less than the total number N of tilt regions, the process proceeds to step S504, and the wavelength calibration unit 1231 adds 1 to the tilt count n and returns to step S502. Then, the wavelength shift of the slave in the tilt region (wavelength shift search range 403) corresponding to the tilt count n is detected. In the example shown in FIGS. 3 and 4, the process of step S502 is performed four times.

On the other hand, when the tilt count n has reached the total number N of tilted regions, since the detection of slave wavelength shifts in all tilted regions (wavelength shift search range 403) has been completed, the process proceeds to the next step S505. .
In step S505, the wavelength calibration unit 1231 calculates the wavelength at an arbitrary pixel based on the wavelength shift detected in the processing in steps S501 to S604. Specifically, the wavelength calibration unit 1231 calculates the relationship between an arbitrary pixel position and wavelength from the “correspondence relationship between pixel position and wavelength” obtained in step S502. In the example shown in FIGS. 3, 4, and 6, the number of plots indicating the correspondence between the pixel position and the wavelength is 5 for one inclined region (wavelength shift search range 403), that is, 20 (= 4 × 5) Obtained. Therefore, in this embodiment, the wavelength calibration unit 1231 calculates a polynomial approximate curve from the 20 plots using a method such as a least square method. FIG. 7 is a diagram illustrating an example of a polynomial approximation curve 701 calculated from a plot indicating the correspondence between the pixel position and the wavelength. As a result, a relationship between an arbitrary pixel position and a wavelength at which the wavelength shift error is minimized can be obtained. By doing so, the relationship between the arbitrary pixel position of the slave light receiving element and the wavelength when it is assumed that there is no wavelength deviation in the spectral reflectance 401 of the master is obtained. By performing the processing in step 605 as described above, the wavelength shift of the slave at an arbitrary wavelength is corrected.

  In step S506, the wavelength calibration unit 1231 can correct the slave wavelength shift by replacing the table indicating the correspondence between the pixel position and the wavelength obtained in step S505 with an existing table.

As described above, in this embodiment, the spectral reflectance 402 of the slave (spectral color sensor 122b) to be corrected for the wavelength axis of the spectral reflectance and the spectral reflectance 401 of the master (spectral color sensor 122a) serving as a reference. And get. Then, in the inclined region (wavelength deviation search range 403) of the spectral reflectances 401 and 402, the intersections with the wavelength deviation detection lines DL1 to DL5 having a constant spectral reflectance are obtained for the spectral reflectances 401 and 402, respectively. And the wavelength detected by the spectral reflectance 401 is calculated | required from the intersection of the spectral reflectance 401 and the wavelength shift detection lines DL1-DL5. Further, the pixel position of the light receiving element having the spectral reflectance 402 is obtained from the intersection between the spectral reflectance 402 and the wavelength shift detection lines DL1 to DL5. Then, from the obtained pixel position and wavelength, a polynomial approximate curve 701 indicating the relationship between the pixel position and wavelength in the spectral color sensor 122b is obtained, and the contents of the table indicating the correspondence between the slave pixel position and wavelength are updated ( Or generation). Therefore, the wavelength shift of the slave relative to the master can be accurately corrected without using a special sensor or performing complicated processing, and measurement errors between spectral color sensors of the same model can be reduced. . In addition, it is difficult to be affected by the deviation of the spectral reflectance axis (vertical axis) of the spectral reflectances 401 and 402, and it is difficult to be affected by noise in the inclined regions of the individual spectral reflectances 401 and 402, so that high correction accuracy is achieved. The wavelength can be calibrated with.
The above wavelength calibration processing is performed by the signal processing module inside the spectral color sensor 122, but may be performed by other arithmetic modules. The above wavelength calibration processing algorithm shows an example, and other methods may be used as long as they do not depart from the present invention.

  In the present embodiment, for example, the wavelength calibration unit 1231 (step S502) realizes an example of a first spectral reflectance derivation unit, a second spectral reflectance derivation unit, and a wavelength shift detection unit. Further, for example, an example of a wavelength shift correction unit is realized by the wavelength calibration unit 1231 (steps S505 and S506). The calibration LUT generation unit 113 and the color matching LUT generation unit 114 realize an example of a color conversion lookup table generation / update unit. Further, for example, an example of a wavelength calibration sample is realized by the wavelength calibration patch 301. For example, the spectral reflectance 401 realizes an example of the first spectral reflectance, and the spectral reflectance 402 realizes an example of the second spectral reflectance. Further, for example, the spectral color sensor 122a realizes an example of a first spectral sensor serving as a reference, and the spectral color sensor 122b realizes an example of a second spectral sensor to be calibrated.

(Second Embodiment)
Next, a second embodiment of the present invention will be described. In the first embodiment, correction of individual differences between the two spectral color sensors 122a and 122b built in the printer apparatus 1 (correction of the shift of the wavelength axis of the spectral reflectance) is performed, and the spectral reflectance 401 of the spectral color sensor 122a is corrected. As an example, the case where the above process is performed is described. On the other hand, in the present embodiment, the spectral reflectance obtained from the colorimetric values of each spectral color sensor built in the printer device is changed to the spectral reflectance obtained from the colorimetric values of the reference colorimeter outside the printer device. In accordance with the above, the shift of the spectral reflectance wavelength axis is corrected. As described above, the present embodiment and the first embodiment are mainly different in the portion relating to the reference spectral reflectance. Therefore, in the description of the present embodiment, the same portions as those in the first embodiment are denoted by the same reference numerals as those in FIGS.

FIG. 8 is a flowchart for explaining an example of a wavelength calibration sequence in the present embodiment.
First, in step S901, the printer apparatus prints wavelength calibration patches 301a to 301d.
In step S902, the spectral color sensors 122a and 122b measure the color of the wavelength calibration patches 301a to 301d printed in step S201 and conveyed to the colorimetric positions of the spectral color sensors 122a and 122b. The processes in steps S801 and S902 are the same as those in steps S201 and 302 in FIG.

Next, in step S903, the wavelength calibration patches 301a to 301d output from the printer apparatus are measured by a reference colorimeter (a spectral color sensor included in the printer apparatus) separate from the printer apparatus. The wavelength calibration patches 301a to 301d are the same as those used in step S902.
Here, in the case of the spectral color sensor 122 built in the printer apparatus, the spectral reflectance is obtained by processing the raw data from the spectral color sensor 122 in the sensor signal processing unit 123. On the other hand, in the case of an external reference colorimeter, the spectral reflectance can be directly obtained by using attached PC application software or the like.

  Next, in step S904, the wavelength calibration unit corrects the wavelength shift of the spectral color sensors 122a and 122b based on the colorimetric values (spectral reflectance) obtained by the processing in steps S902 and S903. In this embodiment, an external reference colorimeter is used as a master, and spectral color sensors 122a and 122b are used as slaves. The spectral reflectance obtained from the colorimetric values obtained from the external reference colorimeter is used as a reference spectrum, and the spectral reflectance obtained from the colorimetric values obtained from the spectral color sensors 122a and 122b is used as a correction target. Then, for each of the spectral reflectances obtained from the colorimetric values of the spectral color sensors 122a and 122b, wavelength calibration processing is performed to match the spectral reflectances obtained from the colorimetric values obtained from the external reference colorimeter. The details of the wavelength calibration process are the same as the wavelength calibration process of the first embodiment (see FIG. 5). However, the processing of the flowchart of FIG. 5 is performed for each of the spectral reflectances obtained from the colorimetric values of the spectral color sensors 122a and 122b.

As a result of the wavelength calibration process, the wavelength shift between the spectral reflectances 401 and 402 of the spectral color sensors 122a and 122b and the spectral reflectance of the external reference colorimeter is corrected. Therefore, the wavelength axes of the spectral reflectances 401 and 402 of the spectral color sensors 122a and 122b can be matched with the wavelength axis of the spectral reflectance of the reference colorimeter. Thereby, in addition to the effect demonstrated by 1st Embodiment, the following effect is acquired. That is, the spectral reflectance of an external reference colorimeter can be used as a reference. It is also possible to correct the wavelength shift due to the temporal change of the spectral color sensors 122a and 122b. In addition, since the absolute value of the wavelength axis can be adjusted, it is possible to correct the wavelength shift uniformly among different types of printer apparatuses. Further, even when both of the spectral reflectances 401 and 402 of the two spectral color sensors 122a and 122b built in the printer device cause a wavelength shift, the wavelength shift can be corrected.
Also in this embodiment, various modifications described in the first embodiment can be employed.
In this embodiment, for example, an example of a spectral color sensor that is a reference is realized by a reference colorimeter (a spectral color sensor included in the reference colorimeter), and an example of a spectral color sensor that is a calibration target by the spectral color sensors 122a and 122b. Is realized.

(Third embodiment)
Next, a third embodiment of the present invention will be described. In the first and second embodiments, the wavelength calibration patch 301 output from the printer device is measured by the spectral color sensor 122 built in the printer device or an external colorimetric reference machine, and the spectral reflectance to be corrected is measured. The wavelength shift was corrected by aligning the wavelength axis with the reference spectral reflectance. However, patches measured by the spectral color sensor 122 or an external color measurement reference machine have errors due to in-plane unevenness. Therefore, in this embodiment, instead of printing the wavelength calibration patch 301, a wavelength calibration standard chart (wavelength calibration chart) compensated for color stability is transported into the printer apparatus and the color is measured. As described above, the present embodiment is different from the first and second embodiments in the portion related to the patch to be used. Therefore, in the description of the present embodiment, the same parts as those in the first and second embodiments are denoted by the same reference numerals as those in FIGS.

The wavelength calibration sequence of the present invention performs the following processing instead of steps S201 and S901 in FIGS. That is, the printer device captures the wavelength calibration standard chart. At this time, the printer apparatus stops the operation of the fixing device when the wavelength calibration standard chart is being conveyed so that the wavelength calibration standard chart is not subjected to the heat of the fixing device (fixing unit 121), or for wavelength calibration. For example, the standard chart may pass through a path that does not pass through the fixing unit.
As described above, in this embodiment, it is possible to correct the wavelength shift with higher accuracy than in the first and second embodiments by using the wavelength calibration standard chart.
In the present embodiment, for example, an example of a wavelength calibration sample is realized by a wavelength calibration standard chart.

  The above-described embodiments are merely examples of implementation in carrying out the present invention, and the technical scope of the present invention should not be construed in a limited manner. That is, the present invention can be implemented in various forms without departing from the technical idea or the main features thereof.

(Other examples)
The present invention is also realized by executing the following processing. That is, first, software (computer program) for realizing the functions of the above embodiments is supplied to a system or apparatus via a network or various storage media. Then, the computer (or CPU, MPU, etc.) of the system or apparatus reads and executes the computer program.

  1 Printer device, 122 spectral color sensor, 1231 wavelength calibration unit

The wavelength calibration method of the present invention is based on the result of color measurement of a plurality of wavelength calibration samples formed on a medium by a first spectroscopic sensor serving as a reference . Based on a result of color measurement of a plurality of wavelength calibration samples formed on the medium by a first spectral reflectance derivation step for deriving a spectral reflectance and a second spectral sensor to be calibrated, A second spectral reflectance derivation step for deriving a second spectral reflectance for each of the plurality of wavelength calibration samples, and the first spectral reflectance and the second spectral reflectance for each of the plurality of wavelength calibration samples. A specifying step of specifying an inclined region inclined with a rate, and the first spectral reflectance and the second passing through the inclined region specified by the specifying step for each of the plurality of wavelength calibration samples. Minutes A definition step of defining a plurality of detection lines for detecting the wavelength shift of the reflectance, for each of the plurality of wavelength calibration sample, along the plurality of detection lines defined by said definition step, the first spectral A wavelength shift detection step for detecting a shift in wavelength between the reflectance and the second spectral reflectance, and a second spectral sensor based on a plurality of wavelength shifts detected in the wavelength shift detection step. spectral reflectances colorimetry, have a, a wavelength shift correction step of correcting the deviation of the wavelength for the spectral reflectances colorimetry by the first spectral sensor, the wavelength deviation detecting step, the first The wavelength detected by the light receiving element of the first spectroscopic sensor is obtained from the intersection between the spectral reflectance of the first spectral sensor and the plurality of detection lines, and the intersection between the second spectral reflectance and the plurality of detection lines. From The position of the pixel of the light receiving element of the second spectroscopic sensor is obtained, the relationship between the obtained wavelength and the position of the pixel is derived for each of the plurality of wavelength calibration samples, and the wavelength deviation detection step includes the wavelength deviation detection step. The spectral reflectance measured by the second spectroscopic sensor is measured by the first spectroscopic sensor based on the relationship between the wavelength and the pixel position for each of the plurality of wavelength calibration samples. It is characterized by correcting a shift in wavelength with respect to the spectral reflectance to be colored .

According to the present invention, the wavelength of light detected by the spectral sensor for generating and updating a color conversion lookup table used for outputting a desired color printing apparatus, using a special sensor Can be calibrated accurately and easily.

Claims (18)

A first spectral reflectance derivation step for deriving the first spectral reflectance based on the result of color measurement of the wavelength calibration sample by the first spectral sensor serving as a reference;
A second spectral reflectance derivation step for deriving a second spectral reflectance based on a result of color measurement of the wavelength calibration sample by the second spectral sensor to be calibrated;
Detection of a shift in wavelength between the first spectral reflectance and the second spectral reflectance in a predetermined inclined region of the first spectral reflectance and the second spectral reflectance. A wavelength shift detecting step,
Wavelength shift correction for correcting a wavelength shift of the second spectral reflectance with respect to the first spectral reflectance based on a wavelength shift between the first spectral reflectance and the second spectral reflectance. A wavelength calibration method comprising the steps of:   The wavelength shift correction step acquires the wavelengths corresponding to a plurality of spectral reflectances from the first spectral reflectance, and the first corresponding to the plurality of spectral reflectances from the second spectral reflectance. The position of the pixel of the light receiving element of the second spectroscopic sensor is acquired, and the relationship between the position of the pixel of the light receiving element of the second spectroscopic sensor and the wavelength is derived based on the relationship between the acquired wavelength and the position of the pixel. The wavelength calibration method according to claim 1, wherein a wavelength shift of the second spectral reflectance with respect to the first spectral reflectance is corrected.   The wavelength shift correction step derives a polynomial approximation curve indicating a relationship between the wavelength of the light receiving element of the second spectroscopic sensor and the wavelength based on the acquired wavelength and the position of the pixel. The wavelength calibration method according to claim 2. The first spectral reflectance derivation step derives a first spectral reflectance based on a result of color measurement of a plurality of wavelength calibration samples by a first spectral sensor as a reference,
The second spectral reflectance derivation step derives a second spectral reflectance based on a result of colorimetry of the plurality of wavelength calibration samples by the second spectral sensor to be calibrated. The wavelength calibration method according to any one of claims 1 to 3.   The first spectroscopic sensor serving as the reference and the second spectroscopic sensor serving as the calibration target are both spectroscopic sensors of the same model mounted on a printing apparatus. The wavelength calibration method according to claim 1. The first spectroscopic sensor serving as the reference is a spectroscopic sensor provided in a reference colorimeter different from the printing apparatus,
The wavelength calibration method according to claim 1, wherein the second spectral sensor to be calibrated is a spectral sensor mounted on a printing apparatus.   The wavelength calibration method according to claim 1, wherein the wavelength calibration sample is a patch printed by a printing apparatus or a wavelength calibration chart.   The wavelength calibration method according to claim 7, wherein the patch is a high-saturation color in which the slope of the region where the spectral reflectance is inclined is steep. First spectral reflectance deriving means for deriving the first spectral reflectance based on the result of color measurement of the wavelength calibration sample by the first spectral sensor serving as a reference;
Second spectral reflectance derivation means for deriving a second spectral reflectance based on the result of color measurement of the wavelength calibration sample by the second spectral sensor to be calibrated;
Detection of a shift in wavelength between the first spectral reflectance and the second spectral reflectance in a predetermined inclined region of the first spectral reflectance and the second spectral reflectance. A wavelength shift detecting means,
Wavelength shift correction for correcting a wavelength shift of the second spectral reflectance with respect to the first spectral reflectance based on a wavelength shift between the first spectral reflectance and the second spectral reflectance. Means,
And a color conversion lookup table generation / updating unit that generates or updates a color conversion lookup table based on the second spectral reflectance corrected for the wavelength shift.   The wavelength shift correction step acquires the wavelengths corresponding to a plurality of spectral reflectances from the first spectral reflectance, and the first corresponding to the plurality of spectral reflectances from the second spectral reflectance. The position of the pixel of the light receiving element of the second spectroscopic sensor is acquired, and the relationship between the position of the pixel of the light receiving element of the second spectroscopic sensor and the wavelength is derived based on the relationship between the acquired wavelength and the position of the pixel. The printing apparatus according to claim 9, wherein a wavelength shift of the second spectral reflectance with respect to the first spectral reflectance is corrected.   The wavelength shift correction step derives a polynomial approximation curve indicating a relationship between the wavelength of the light receiving element of the second spectroscopic sensor and the wavelength based on the acquired wavelength and the position of the pixel. The printing apparatus according to claim 10. The first spectral reflectance derivation step derives a first spectral reflectance based on a result of color measurement of a plurality of wavelength calibration samples by a first spectral sensor as a reference,
The second spectral reflectance derivation step derives a second spectral reflectance based on a result of colorimetry of the plurality of wavelength calibration samples by the second spectral sensor to be calibrated. The printing apparatus according to any one of claims 9 to 11.   The printing apparatus according to claim 9, comprising both the first spectroscopic sensor serving as the reference and the second spectroscopic sensor serving as the calibration target. A second spectroscopic sensor to be calibrated,
The printing apparatus according to claim 9, wherein the first spectroscopic sensor serving as a reference is a spectroscopic sensor provided in an external reference colorimeter.   The printing apparatus according to claim 9, wherein the wavelength calibration sample is a patch printed by the printing apparatus or a standard chart for wavelength calibration.   The printing apparatus according to claim 15, wherein the patch is a high-saturation color in which a slope of a region where the spectral reflectance is inclined is steep. The wavelength calibration sample is a standard chart for wavelength calibration,
In order to perform color measurement by the spectral reflectance, the wavelength calibration standard chart is transported in a state where the operation of the fixing device is stopped, and the wavelength calibration is performed in order to perform color measurement by the spectral reflectance. 16. The printing apparatus according to claim 15, further comprising: a means for conveying the standard chart without passing through the fixing device. A first spectral reflectance derivation step for deriving the first spectral reflectance based on the result of color measurement of the wavelength calibration sample by the first spectral sensor serving as a reference;
A second spectral reflectance derivation step for deriving a second spectral reflectance based on a result of color measurement of the wavelength calibration sample by the second spectral sensor to be calibrated;
Detection of a shift in wavelength between the first spectral reflectance and the second spectral reflectance in a predetermined inclined region of the first spectral reflectance and the second spectral reflectance. A wavelength shift detecting step,
Wavelength shift correction for correcting a wavelength shift of the second spectral reflectance with respect to the first spectral reflectance based on a wavelength shift between the first spectral reflectance and the second spectral reflectance. A computer program that causes a computer to execute the process.

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