JP2012191459A - Image processing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which a pseudo contour, gradation inversion, or the like is caused if a correction amount is too large when color tint correction processing is performed using an LUT in an electrophotographic device.SOLUTION: It is determined whether to update a target based on a degree of deviation between a colorimetric value and the target in color tint correction, and a user is urged to re-register a target.

Description

  The present invention relates to an image processing apparatus and an image processing method for creating an image processing parameter for correcting a color of a printer, and a program for creating an image processing parameter.

  In recent years, the performance of electrophotographic apparatuses has improved, and machines that have achieved image quality equivalent to that of printing machines have appeared. However, due to the instability specific to electrophotography, the problem remains that the amount of color variation is larger than that of a printing press. Therefore, various calibration techniques are installed in the conventional electrophotographic apparatus.

  First, there is a calibration technique for creating a one-dimensional tone correction LUT (Look Up Table) corresponding to cyan, magenta, yellow, and black toners in order to correct primary colors. The LUT is a table indicating output data corresponding to input data divided at specific intervals, and can express non-linear characteristics that cannot be expressed by arithmetic expressions. Further, as a method of correcting the color mixture of red, green, blue, black, etc., there is a method of correcting by paying attention to an ICC profile based on the provisions of ICC (International Color Consortium). There has been proposed a technique for correcting a color difference of mixed colors by correcting a multidimensional LUT called a destination profile in an ICC profile. As these correction methods, a chart created from color data to be corrected is output by a printer and measured by a scanner or a colorimeter. A method of correcting the LUT using the difference between the color measurement result and the target is generally used.

  However, when the paper used for correction is different from the paper for which the target is set, there is a problem that appropriate color correction cannot be performed. This is the case where the user performs correction using paper having low whiteness, such as recycled paper. In view of this, a method has been proposed in which a plurality of targets corresponding to the printing paper are provided and correction is performed by determining an appropriate target at the time of correction (for example, see Patent Document 1). If an appropriate target is not found, the user is warned to that effect. This makes it possible to correct the color appropriately regardless of the type of paper.

JP 2008-066923 A

  However, the characteristics of the scanner used as a colorimeter at the time of correction are not uniform. This point will be described with reference to FIG. FIG. 2 is a diagram conceptually showing variations in scan data in a certain color space. There is a paper target 201. The target 201 can obtain an ideal center value by obtaining an average value from scan data of a plurality of scanners. On the other hand, when the chart is actually read by some scanners, the colorimetric values are the colorimetric values (circled number 1 shown in the figure) 202 and the colorimetric values (circled number 2 shown in the figure). It varies like 203. This is mainly due to lot variations of parts constituting the scanner and differences in assembly accuracy. The variation in the initial scan data is considered to be a substantially uniform variation range 205 from the target 201 as shown by the dotted line in FIG. However, when the state of the device changes greatly due to secular change, it can be considered that the colorimetric value (circled number 3 shown in the figure) 204 greatly deviates from the target 201. If the ideal target 201 registered in advance is always used, especially when performing mixed color correction, the color space (multidimensional) of the secondary color or higher is corrected nonlinearly, so that the correction amount increases, so that gradation There is a problem of greatly reducing the performance.

Image forming means for outputting a plurality of color patches;
Colorimetric means for colorimetrically measuring the output color patch;
A difference calculating means for calculating a difference between the colorimetric value obtained by the colorimetric means and a target corresponding to the colorimetric value;
Using the difference obtained by the difference calculation means and a predetermined threshold value, a difference determination means for determining whether the target needs to be updated; and
A process selection means for selecting a subsequent process based on the determination result of the difference determination means;
A target registration unit for registering a target based on a determination result of the difference determination unit or (and) a result of the process selection unit;
An image processing apparatus comprising: a tint correction execution unit configured to perform tint correction using the colorimetric value and the target based on a result of the difference determination unit or (and) the processing selection unit.

  According to the present invention, it is possible not only to cope with the media type at the time of correction, but also to have an optimum target for each device, and it is possible to perform color correction while maintaining gradation, especially in color mixing. Further, by urging the user with an appropriate timing for registering the target, it is possible to perform color correction that always maintains gradation.

1 is a configuration diagram of an image forming apparatus to which a first embodiment is applied. It is a conceptual diagram which shows the specific example of a subject. It is a flowchart of the process sequence in 1st Embodiment. It is a flowchart of the process sequence in 2nd Embodiment. It is an example of UI which arouses target re-registration. It is a conceptual diagram showing distribution of the data before target re-registration. It is a conceptual diagram showing distribution of the data after target re-registration. This is an example of a LUT. FIG. 7 is a diagram illustrating the correspondence between the timing of color correction and the data in FIG. 6. It is a conceptual diagram of the prediction control in 2nd Embodiment.

Example 1
The best mode for carrying out the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram of the minimum configuration necessary for realizing the present embodiment.

  In the figure, reference numeral 100 denotes an image forming apparatus. A control unit 101 of the image forming apparatus 100 includes an apparatus control unit 102 that controls the image forming apparatus and an image processing unit 103 that optimizes image data. Furthermore, the control unit 101 includes a color stabilization control unit 104 that performs processing for device color stabilization. The control unit 101 processes image data using a CPU (Central Processing Unit) 108 and a RAM (Random Access Memory) 109 and stores the image data in the storage unit 110 or outputs an image from the image output unit 106. The image reading unit 105 scans an image, and the scanned image data is processed by the control unit 101 and stored in the RAM 109 or the storage unit 110, or the image is output from the image output unit 106. Examples of the image reading unit include a scanner and a colorimeter.

  A UI (User Interface) 107 notifies the control unit 101 of various settings at the time of image processing, and the image processing unit 103 processes image data based on the notified setting. Alternatively, various settings of the UI 107 are stored in the storage unit 110 through the device control unit 102, and the image processing unit 103 and the color stabilization control unit 104 read the stored setting values and process the image data. The image output unit 106 outputs the image data processed by the control unit 101 to a recording device such as a printer or a monitor. The storage unit 110 stores parameters for controlling the apparatus, parameters for color stabilization control, an application for realizing the present embodiment, chart data, a target 201, an OS, and the like.

  The above is the minimum necessary configuration. If necessary, a data input unit such as a network interface or a scanner, a server computer connected to the image forming apparatus 100, or the like may be added. Further, a configuration necessary when considering the entire image forming apparatus can be added.

  Here, the color stabilization control in the present proposal and its purpose will be described by taking correction of mixed colors as an example. One of the purposes of color stabilization control in electrophotography that is unstable compared to a printing press is to absorb variations such as a color difference from the previous day and a color difference from a few days ago. The target 201 is indispensable in the stabilization control for keeping the color of the output product constant. If there is an ideal target 201 and it can be matched to the ideal target 201 in any state, there is an advantage that an image can be always output with a stable and accurate color. On the other hand, there is a risk of causing false contours and gradation inversion when trying to match an ideal target despite the large correction amount. FIG. 7 shows a two-dimensional LUT as an example. For example, the x-axis is the first color component value in a certain color space, the y-axis is the second color component value, and each grid point is the first and second color components that are output for certain input data Holds the value. Reference numeral 701 denotes an uncorrected LUT, and the output values of each grid point data have smooth gradation characteristics at equal intervals. Reference numeral 702 denotes a corrected LUT, and correcting the LUT results in a distorted lattice point interval, which may deteriorate gradation. As a method of correcting the color mixture, it is possible to change the destination profile of the ICC profile, or create a four-dimensional LUT for converting from CMYK to CMYK and perform correction after processing the ICC profile.

  The color stabilization control according to the present proposal will be described with reference to FIGS. FIG. 8 is a diagram showing the flow of time and the timings t0 to t4 of the color stabilization control. For the color stabilization control, the target 201, the colorimetric value 310 read from the correction chart, and the difference value 800 between the colorimetric value 310 and the target 201 are used, and the colorimetric value 310 is transferred to the target 201 so that the difference value 800 becomes smaller. Stabilize the color by moving closer.

  FIG. 6A conceptually shows the target 201 and the colorimetric value 310 at the timings t0, t1, t2, t3, and t4. Reference numeral 605 denotes an allowable range in which color stabilization control can be performed without degrading gradation. First, an ideal target 201 is set at t0. The colorimetric value A 601 at t 1 has a small difference A 801 from the target 201 and is within the correction allowable range 605. The same applies to the colorimetric value B602 and the difference B802 at t2. At t3, the difference C803 between the colorimetric value C603 and the target 201 exceeds the correction allowable range 605, and there is a high risk of deterioration of gradation. Therefore, the colorimetric value C603 is newly registered as a target (circled number 1 shown in the figure) 606 without correction, so that it becomes a new target for subsequent color stabilization. As shown in FIG. 6B, since the state at t3 is targeted at t4, the difference D804 between the target (circled number 1 shown in the figure) 606 and the colorimetric value D604 becomes sufficiently small, and the floor Correction can be performed without deteriorating the tonality. As described above, by updating the target 201 in the mixed color tint stabilization control, the tint can be stabilized in a short period of time.

  FIG. 3 is a flow showing the processing flow of the present embodiment. A control program (not shown) that realizes the present embodiment is stored in the storage unit 110, loaded into the RAM 109, and executed by the CPU 108. It is assumed that the target 201, chart data (not shown), and various threshold values required in this embodiment are stored in the storage unit 110.

  The proposed method will be described along the flowchart of FIG. When the UI 107 receives a color correction execution instruction from the user, the color stabilization control unit 104 outputs a color correction chart from the image output unit 106 in S301. The chart is composed of a plurality of colors used for color correction and may be a patch having a size that can be measured. The color stabilization control unit 104 reads the chart data stored in the storage unit 110 and the image processing unit 103 generates a chart. In step S <b> 302, the image reading unit 105 scans the output chart, and stores the read colorimetric value 310 in the RAM 109. In this case, the colorimetric value 310 may be the RGB value itself read by the image reading unit 105, or may be a value converted into L * a * b * value of CIELAB color space or other PCS (Profile Connection Space) data. . Any color space data that is optimal for use in the subsequent processing may be used. In step S <b> 303, the color stabilization control unit 104 reads the target 201 and the correction allowable amount 311 from the storage unit 110, calculates the colorimetric value 310 from the RAM 109, calculates the difference value 800, and stores the result in the RAM 109.

  As the difference value 800, for example, the colorimetric values 310 of all patches in the chart and the color difference ΔE between the targets 201 are calculated. ΔE is represented, for example, by the Euclidean distance of the L * a * b * value. In S <b> 304, the color stabilization control unit 104 reads the difference value 800 from the RAM 109 and compares it with the correction allowable amount 311 read from the storage unit 110. The correction allowable amount 311 is, for example, the color difference ΔE between the colorimetric value 310 and the target 201. When the difference value 800 is larger than the allowable correction amount 311 in S304, it is determined that new target registration is necessary, and in S305, the color stabilization control unit 104 urges target registration. If the difference value 800 is smaller than the allowable correction amount 311, it is determined that new target registration is unnecessary, and calibration is executed in S <b> 307.

  The determination method of S304 is a method that excludes a tolerable object if there is at least one patch that exceeds the allowable correction amount 311, a method that excludes a tolerable object if there is a patch that exceeds the allowable correction amount 311 above a certain threshold, and the like. Can be considered. Alternatively, when the difference value 800 and the correction allowable amount 311 are the sum of the difference values 800 of all patches or the average value of the difference values 800 of all patches, the determination is made by comparing the difference value 800 and the correction allowable amount 311. Yes.

  In the target registration awakening S 305, the color stabilization control unit 104 reads out the message stored in the storage unit 110 and displays it on the UI 107 to call up the target registration to the user. FIG. 5 shows an example of a message screen 500 displayed on the UI 107. The message screen 500 has a “Yes” button 501 for selecting target registration and a “No” button 502 for selecting no registration. In step S <b> 306, the UI 107 receives an instruction on whether to perform target registration from the user, and notifies the color stabilization control unit 104 of the instruction result via the control unit 101. When the “Yes” button 501 is pressed in S306, the color stabilization control unit 104 receives an instruction through the control unit 101, and performs target registration in S309. The target 201 to be registered is the colorimetric value 310 stored in the RAM 109, and the color stabilization control unit 104 stores the colorimetric value 310 as a new target 201 in the storage unit 110. At this time, the old target 201 may be overwritten or additionally stored as a new target. In the case of adding as a new target, after the “Yes” button 501 is pressed, the screen may change to a registration screen so that the target can be named.

  When the “NO” button 502 is pressed in S306, the color stabilization control unit 104 receives an instruction through the control unit 101, and executes color correction in S307. The color correction method is as described above. Any other color correction method is not limited as long as the same effect can be obtained. After executing the color correction S307, the color stabilization control unit 104 confirms with the user whether or not to register the target as the next and subsequent targets in S308, and receives the user's instruction result via the control unit 101. When it is instructed to perform target update in S308, target registration S309 is performed, and the process ends. If it is instructed not to update the target, the process is terminated.

  As described above, it is determined whether to deteriorate the gradation by executing the color correction on the registered target, and if it is determined to deteriorate, the user is prompted to re-register the target. To do. As a result, it is possible to avoid a situation in which the gradation is deteriorated as an adverse effect of the color stabilization control.

(Example 2)
Here, only the parts different from the first embodiment will be described. In the present embodiment, unlike the first embodiment, when a color correction execution instruction is received, the degree of divergence between the current state and the target 201 is predicted, and target registration is triggered based on predictive control.

  FIG. 4 is a flow showing the processing flow of the present embodiment.

  When the UI 107 receives a color correction execution instruction from the user, in S400, the color stabilization control unit 104 calculates a predicted value 402 of the current state from the log data 401 stored in the storage unit 110, and the RAM 109 Save to In step S <b> 303, the color stabilization control unit 104 reads the predicted value 402 stored in the RAM 109 and the target 201 stored in the storage unit 110, and calculates a difference value 800 as in the first embodiment. When the difference value 800 is larger than the allowable correction amount 311 in S304, it is determined that new target registration is necessary, and in S305, the color stabilization control unit 104 urges target registration. When the “Yes” button 501 is pressed in S306, the color stabilization control unit 104 receives an instruction through the control unit 101, and registers the predicted value 402 calculated in S400 as a target. Thereby, target registration can be performed without bothering the user. Alternatively, chart output and chart reading are performed and the target is registered. When the “No” button 502 is pressed in S306, the color stabilization control unit 104 receives an instruction through the control unit 101, outputs a chart in S401, reads a chart in S402, and executes color correction in S403. Note that the processes of S401, S402, and S403 are the same as the processes of S301, S302, and S307, respectively.

  The predicted value calculation S400 will be described in detail. FIG. 9 is a conceptual diagram of predictive control, in which the horizontal axis represents time, and the vertical axis represents the degree of colorimetric value deviation ΔE with the target 201 as a reference. The color stabilization control unit 104 executes color correction at timings t1, t2, t3, and t4, and calculates the differences A, B, C, and D at that time. In this embodiment, in order to perform prediction, the colorimetric value 310 or the difference value 800 when the color correction is performed is stored in the storage unit 110 as the log data 401. At the same time, the date and time of correction is also stored in association with the log data 401. The color stabilization control unit 104 calculates a predicted value 900 at t5 from the log data. Since the predicted value 900 exceeds the allowable correction amount 311 at the time t5, the predicted value 900 is determined not to be allowable.

  When target re-registration is executed at t5, a target (circled number 2 shown in the figure) 901 is stored in the storage unit 110 as a new target 201. The predicted value 900 at t6 is calculated using the previous log. Since the predicted value 900 at t6 is close to the new target (circled number 2 shown in the figure) 901, the color correction is executed, and the difference value 800 is stored as the log data 401.

  As described above, by predicting the state of the image forming apparatus 100 using the log data 401, it is possible to know the state of the apparatus before execution, and therefore, when the target 201 needs to be re-registered, the burden on the user Can be reduced.

100 Image forming device
107 UI
109 RAM
110 Memory
104 Color stabilization control unit
201 target
310 Colorimetric value
605 Correction tolerance
800 Difference value

Claims (26)

Image forming means for outputting a plurality of color patches;
Colorimetric means for colorimetrically measuring the output color patch;
A difference calculating means for calculating a difference between the colorimetric value obtained by the colorimetric means and a target corresponding to the colorimetric value;
Using the difference obtained by the difference calculation means and a predetermined threshold value, a difference determination means for determining whether the target needs to be updated; and
A process selection means for selecting a subsequent process based on the determination result of the difference determination means;
A target registration unit for registering a target based on a determination result of the difference determination unit or (and) a result of the process selection unit;
An image processing apparatus comprising: a tint correction execution unit configured to perform tint correction using the colorimetric value and the target based on a result of the difference determination unit or (and) the processing selection unit. The image processing apparatus according to claim 1, wherein the color measuring unit is an image reading device or a color measuring device. The image processing apparatus according to claim 1, wherein the difference calculation unit calculates a difference for each patch and calculates a statistical value of the difference as necessary. The image processing apparatus according to claim 3, wherein the statistical value of the difference is an average value or total value of differences for each patch, or other statistical values. The image processing apparatus according to claim 1, wherein the threshold value used by the difference determination unit is a threshold value that determines an upper limit value of the difference. The image processing apparatus according to claim 1, wherein the threshold used by the difference determination unit is a threshold that defines an upper limit of the number of difference values exceeding a certain level. The image processing apparatus according to claim 1, wherein the process selection unit determines whether to perform target registration. 2. The target registration unit according to claim 1, wherein the target registration unit registers a target when the difference determination unit determines that the target needs to be updated and the selection unit determines to perform target registration. 3. Image processing apparatus. The image processing apparatus according to claim 8, wherein the target registration unit registers the colorimetric value as a target. The image processing apparatus according to claim 1, wherein the color correction unit performs a color correction process when the difference determination unit determines that the target update is unnecessary. The color correction unit performs a color correction process when the difference determination unit determines that the target needs to be updated and the selection unit determines not to register the target. The image processing apparatus according to claim 1. The image processing apparatus according to claim 1, wherein the color correction unit performs color correction using the colorimetric value and the target. A predicting means for calculating predicted values of a plurality of color patches used at the time of color correction execution;
A difference calculation means for calculating a difference between a prediction value obtained by the prediction means and a target corresponding to the prediction value;
Using the difference obtained by the difference calculation means and a predetermined threshold value, a difference determination means for determining whether the target needs to be updated; and
A process selection means for selecting a subsequent process based on the determination result of the difference determination means;
A target registration unit for registering a target based on a determination result of the difference determination unit or (and) a result of the process selection unit;
An image forming unit that outputs a plurality of color patches based on the result of the difference determination unit or (and) the processing selection unit;
Colorimetric means for colorimetrically measuring the output color patch;
Color correction execution means for executing color correction using the colorimetric value obtained by the color measurement means and the target; and
An image processing apparatus comprising log storage means for storing various data at the time of color correction execution as a log. The image processing apparatus according to claim 13, wherein the prediction unit predicts a value of patch data using a saved log. The image processing apparatus according to claim 13, wherein the difference calculating unit calculates a difference for each patch and calculates a statistical value of the difference as necessary. The image processing apparatus according to claim 13, wherein the statistical value of the difference is an average value or total value of differences for each patch, or other statistical values. The image processing apparatus according to claim 13, wherein the threshold value used by the difference determination unit is a threshold value that determines an upper limit value of the difference. The image processing apparatus according to claim 13, wherein the threshold value used by the difference determination unit is a threshold value that defines an upper limit of the number of difference values exceeding a certain level. The image processing apparatus according to claim 13, wherein the process selection unit determines whether to perform target registration. The target registration unit registers a target when the difference determination unit determines that the target needs to be updated and the selection unit determines to perform target registration. Image processing apparatus. The image processing apparatus according to claim 13, wherein the target registration unit registers the predicted value as a target. The image forming unit outputs a chart when it is determined that the target needs to be updated by the difference determination unit and when it is determined that the target registration is not performed by the selection unit. The image processing apparatus described. The image processing apparatus according to claim 13, wherein the image forming unit outputs a chart when the difference determination unit determines that the target update is unnecessary. The image processing apparatus according to claim 13, wherein the color measuring unit is an image reading device or a color measuring device. The color correction unit performs a color correction process when the difference determination unit determines that the target needs to be updated and the selection unit determines not to register the target. The image processing apparatus according to claim 13. The image processing apparatus according to claim 13, wherein the color correction unit performs color correction using the colorimetric value and the target.