JP2009010571A - Device for forming image, and method and program for preparing gamma correction data - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily acquire gamma correction data in a short time even when a device itself for forming an image does not have a function detecting gamma characteristics. <P>SOLUTION: A device for forming an image has a printing means 12 printing a first chart when gamma characteristics are under a normal state while printing a second chart when gamma characteristics are under a state different from the normal state, a scanner 13 reading the first chart and the second chart and an image analyzing means 14 extracting RGB data at every chart on the basis of image data read by the scanner 13. The device for forming the image further has a calibration means 15 computing a gamma characteristic value on the basis of each RGB data, computing a correction value (a gamma correction data) required for approximating the gamma characteristic value of the second chart to that of the first chart and correcting a gamma correction table by using the gamma correction data. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that creates data for correcting input / output characteristics (gamma characteristics), a gamma correction data creation method that is a data creation method, and a gamma correction data creation method. The present invention relates to a gamma correction data creation program, and more particularly to an image forming apparatus, a gamma correction data creation method, and a gamma correction data creation program for creating a data table for correcting a gamma characteristic and creating a stable high quality image quality.

In a device (image forming apparatus) that outputs an image typified by a printer or the like, density (gamma) control is performed.
The gamma characteristic is one of the factors that greatly affect the image quality, and its stability is desired. However, it can be said that the gamma characteristic is in a stable state at the time of shipment when the machine quality is stable, but the stability of the gamma characteristic is lost depending on the frequency of use by the user (change with time). Such a breakdown of the gamma characteristic almost inevitably occurs, and it is difficult to maintain a good state at the time of shipment. Therefore, various techniques for correcting the broken gamma characteristic and restoring it to a good state have been proposed.

For example, an environment detection unit that detects relative humidity and temperature in the image forming apparatus as an operating environment state, an environment correction value is selected based on the detected operating environment state, and the selected environment correction value and developer are selected. A target permeability calculating means for calculating a target permeability based on the environmental correction value in the operating environment state at the time of replacement, the target permeability calculating means when the selected environmental correction value and developer are exchanged When the difference value with the environmental correction value in the operating environment state is greater than the difference between the output value of the permeability sensor and the output value of the permeability sensor in the operating environment state when the developer is replaced, In some cases, instead of the environmental correction value, the target magnetic permeability is calculated using the output value of the magnetic permeability sensor and the output value of the magnetic permeability sensor in the operating environment when the developer is replaced (for example, Patent Document 1). Ether.).
According to this technique, when the ambient environment changes, the charging characteristics of the developer are prevented from changing, and the toner density is prevented from changing. Based on the environmental conditions, the developer color, and the toner density information, the developer In consideration of the environmental characteristics of each color, correction control that approximates the actual measurement value is performed, so that a color image with good quality can be obtained.

As another technique, for example, first gamma correction information stored in the image forming apparatus and second gamma correction information input to the image forming apparatus are integrated to generate integrated gamma correction information. An image processing method for performing gamma correction on image data based on the integrated gamma correction information, wherein the first output value of the first gamma correction information matches the first input value of the second gamma correction information If the two match, the first output value of the second gamma correction information is set as the first output value of the integrated gamma correction information, and then the first input value of the second gamma correction information Is used to determine whether there is a match with the second output value of the first gamma correction information.If they do not match, the second input value of the second gamma correction information is used to The first gun that did not match in the judgment There is the presence or absence of coincidence between the first output value of the correction information that and a determining step (for example, see Patent Document 2.).
According to this method, the gamma correction for obtaining the gradation desired by the user and the gamma correction according to the characteristics of the image output device can be realized without causing a significant increase in memory capacity and processing amount. .

Further, as another technique, there is provided an image forming apparatus that includes a total amount regulating unit that regulates the total amount of toner accompanying printing, and that forms a color image of CMYK four colors, so that the total amount regulating unit does not perform the regulation of the total amount of toner. In addition, there is a gamma correction unit that performs gamma correction processing for each color of CMYK (see, for example, Patent Document 3).
According to such a technique, it is possible to keep a gamma correction value for each color of CMYK constant, and to prevent color misregistration that occurs by regulating the total amount of toner.
Japanese Patent No. 3693547 Japanese Patent No. 3810620 JP 2006-154532 A

However, the techniques described in Patent Documents 1 to 3 cannot be realized unless the above-described functions are provided to the image forming apparatus. That is, a user who does not have an image forming apparatus having such a function cannot perform gamma correction described in Patent Documents 1 to 3.
As a method for detecting the gamma characteristic, a method using a colorimeter is generally known, but this method takes a considerable time. For this reason, there has been a demand for a proposal of a technique that can easily obtain gamma correction data in a short time.

  The present invention is considered in view of the above circumstances, and even if the image forming apparatus itself does not have a function of detecting the gamma characteristic, the gamma correction data is obtained by performing the detection easily in a short time. An object of the present invention is to provide an image forming apparatus, a gamma correction data creation method, and a gamma correction data creation program.

  In order to achieve this object, the image forming apparatus of the present invention is an image forming apparatus that creates data for correcting the gamma characteristic, and prints the first chart when the gamma characteristic is normal. Printing means for printing the second chart when the gamma characteristic is different from the normal state, a scanner for reading the first chart and the second chart, and RGB for each chart based on the image data read by the scanner Based on image analysis means for extracting data and each RGB data, a gamma characteristic value obtained by quantifying the gamma characteristic for each chart is calculated, and the gamma characteristic value of the second chart is approximated to the gamma characteristic value of the first chart. The gamma correction data is calculated as the gamma correction data, and the gamma correction table is read from the storage means. A configuration equipped with a calibration means for correcting the Ma correction table.

  The gamma correction data creation method of the present invention is a gamma correction data creation method for creating data for correcting gamma characteristics, and prints the first chart when the gamma characteristics are normal, When the chart is in a different state from the normal state, the second chart is printed, the first chart and the second chart are read by the scanner, the RGB data is extracted for each chart, and each chart is based on each RGB data. Calculate the gamma characteristic value obtained by quantifying the gamma characteristic, calculate the correction value necessary to approximate the gamma characteristic value of the second chart to the gamma characteristic value of the first chart, and calculate the gamma correction data from the storage means. This is a method of reading a table and correcting the gamma correction table using gamma correction data.

  The gamma correction data creation program of the present invention is a gamma correction data creation program for causing an image forming apparatus to execute processing for creating data for correcting gamma characteristics, and when the gamma characteristics are in a normal state. The first printing process for printing the first chart, the second printing process for printing the second chart when the gamma characteristic is different from the normal state, and the chart reading for reading the first chart and the second chart by the scanner. RGB data extraction process for extracting RGB data for each chart based on the processing and image data read by this chart reading process, and a gamma characteristic value obtained by quantifying the gamma characteristics for each chart based on each RGB data And calculate the correction value necessary to approximate the gamma characteristic value of the second chart to the gamma characteristic value of the first chart. Calculated as comma correction data, reads the gamma correction table from the storage means, there a calibration process to correct the gamma correction table as the configuration to be executed by the image forming apparatus by using the gamma correction data.

  As described above, according to the present invention, the characteristic at the time of printing is grasped using the scanner and the gamma correction data is calculated. Even if the image forming apparatus itself does not have, the gamma correction data can be created in a short time and easily. Thereby, even a commercially available image forming apparatus can correct the gamma correction table.

  Hereinafter, preferred embodiments of an image forming apparatus, a gamma correction data creation method, and a gamma correction data creation program according to the present invention will be described with reference to the drawings.

[Image forming apparatus]
First, the configuration of the image forming apparatus of this embodiment will be described with reference to FIG.
FIG. 1 is a block diagram illustrating a configuration of the image forming apparatus according to the present exemplary embodiment.
The image forming apparatus according to the present embodiment is a computer that operates under program control. As shown in the figure, the storage unit 11, the printing unit 12, the scanner 13, the image analysis unit 14, and the calibration unit 15 are used. And have.

The storage means 11 has an RGB value (PWV) obtained when the paper white is read by the scanner 13, a Cyan RGB value (CMV), a Magenta RGB value (MMV), a Yellow RGB value (YMV), a Black Save RGB values (BMV).
The storage unit 11 stores image data and a bitmap file obtained when a color chart (1), (2) described later is scanned by the scanner 13. RGB values can be extracted from this bitmap file.

Further, the storage means 11 includes color chart (1), (2) design data, gamma correction table, gamma correction data, averaged RGB values (for each patch, for each area), overall noise removal data ALL_RGB, Noise removal data Area * _RGB for each area, RGB value FP for noise removal patch, number of patches for noise removal FP_num, RGB value EFP * for noise removal patch for each area, number of noise removal patches for each area EFP Data relating to a gamma correction data creation method such as * _mun, area correction value Area * _C_RGB, data relating to normalization processing, gamma characteristic values, F (x), H (x), G (x), and the like are stored.
The storage unit 11 stores a program for executing various functions of the image forming apparatus 10 according to the present exemplary embodiment.

The printing unit 12 executes a printing process. In particular, the printing unit 12 prints the color charts (1) and (2). Also outputs a gamma correction table.
The scanner 13 reads the content printed on the paper. In particular, the scanner 13 scans the color charts (1) and (2).

The image analysis unit 14 analyzes the image read by the scanner 13 to generate a bitmap file (bitmap data), and stores it in the storage unit 11. In addition, the image analysis unit 14 extracts RGB values from the bitmap file.
The calibration means 15 executes the processing of step 22 and step 23 shown in FIG. 3 and the processing of step 30 to step 36 shown in FIG. 4 (processing 4-1 to processing 10 described later, calibration processing).

[Gamma correction data creation method]
Next, the operation (gamma correction data creation method) of the image forming apparatus of this embodiment will be described with reference to FIGS.
2 to 4 are flowcharts illustrating the operation of the image forming apparatus according to the present exemplary embodiment. FIG. 2 illustrates a processing procedure until RGB values are extracted for each chart. FIG. 3 illustrates the extracted RGB values. The processing procedure until the gamma correction table is used for correction and output, and FIG. 4 shows the detailed processing procedure for calibration.

[1] Process 0-1: Design Value Measurement First, a paper on which nothing is printed is scanned by the scanner 13, and RGB values are examined from the image data obtained by this scan. The RGB value at this time is set to PWV (measurement of paper scanner spectroscopy, step 10 in FIG. 2).
Next, the scanner 13 scans the print chart with the maximum amount of CMYK toners, and examines the RGB values at this time.
Specifically, the printing chart with the maximum amount of cyan toner is scanned to obtain the RGB value CMV at this time. Similarly, the Magenta print chart is scanned to obtain the RGB value MMV. Then, the yellow print chart is scanned to obtain the RGB value YMV. Further, the Black print chart is scanned to obtain the RGB value BMV (measurement of the scanner spectrum of Cy / Mg / Ye / Bk, step 10).

The design values obtained by the measurement of the scanner spectroscopy are listed below.
Design value Paper white: PWV (Formula 1-1)
Cyan: CMV (Formula 1-2)
Magenta: MMV (Formula 1-3)
Yellow: YMV (Formula 1-4)
Black: BMV (Formula 1-5)

[2] Process 0-2: Color chart design A color chart for measuring gamma characteristics is designed.
The color chart is designed for each of Bk, Cy, Mg, and Ye.
By printing these designed Bk, Cy, Mg, and Ye color charts on the paper, 4 sheets each for the color chart (1) and 4 sheets for the color chart (2). A total of 8 characteristic sheets are completed.
The color chart printed when the gamma characteristic is normal is “color chart (1)”, and the color chart printed when the gamma characteristic is changed from normal (changed with time) is “ Color chart (2) ".
For example, a plurality of Bk color charts may be printed. In this case, the places where 65 points of patches (described later) are applied may all be the same or different. A method of calculating and averaging the RGB values of the patches of the plurality of printed characteristic sheets to obtain gamma correction data is also possible. Thereby, highly accurate area correction values and gamma correction data can be obtained.

  As shown in FIG. 5, a predetermined number of patches 110 are printed on a single characteristic sheet in the vertical and horizontal directions. Note that a total of 375 patches, 15 in the vertical direction and 25 in the horizontal direction, can be printed on the characteristic sheet 100 of this embodiment, as shown in FIG. However, there are parts that are not printed.

The plurality of patches 110 are divided into those constituting the edge frame 120 and those constituting the area 130.
The edge frame 120 is on a line connecting the midpoints of a plurality of patches 110 located on the outer edge (outer peripheral part) and two opposite sides of the four sides of the quadrangle formed as the outer peripheral part. It is composed of the ones that are located (the middle crosspiece) (when there are four areas 130).
In the characteristic sheet 100 shown in FIG. 5, the edge frame 120 is composed of 111 patches 110.

A fixed amount of toner (50% toner in this embodiment) is adhered to the edge frame 120. That is, in the characteristic sheet 100 shown in FIG. 5, all of the 111 patches are attached with 50% toner. In the case of the Bk characteristic sheet, 50% Bk toner is adhered. In the case of a Cy characteristic sheet, Cy 50% toner is adhered.
In this way, by attaching a constant amount of toner to the entire edge frame 120, it is possible to see the amount of change in RGB value depending on the position on the paper. This is because even with the same color value, the density changes depending on the printing position due to device noise. That is, by observing the density variation of the color value of the edge frame 120 and reflecting the variation amount depending on the position on the 65-point patch, device noise and the like can be reduced.

  The area 130 is a portion surrounded by the edge frame 120. The area 130 is divided into a plurality (four in this embodiment) (areas 131 to 134). And the edge frame 120 is formed in the outer side of each area 131-134 so that these areas 131-134 may be enclosed (refer FIG. 7).

In the area 130, a predetermined number of patches 110 having different color values are printed. In this embodiment, 65 points of toner are hit at random positions. For example, in the case of the Bk characteristic sheet 100, 65 Bk toners are applied. In the case of the Cy characteristic sheet 100, 65 points of Cy toner are applied.
“65 points” is 65 points when the color values 0 to 255 are divided at equal intervals. That is, 256 is the maximum number that can be taken as a color value, and is a number (65) obtained by adding 1 to a number (64) obtained by dividing the number by a whole number (1/4).

In the present embodiment, the number of color values of the patches 110 printed in the area 130 is “65 points”, but the number is not limited to 65 points, and any number smaller than the maximum number that can be taken as the color values is used. The number of
Here, taking all 256 points is optimal, but there is a problem that it takes a long measurement time. Therefore, in this embodiment, 65 points smaller than 256 points are taken, and then a gamma characteristic value is calculated. Then, the increase process of the gamma characteristic value is performed with the maximum number (256) as the upper limit.

Further, in the present embodiment, the color value of the patch 110 is obtained by dividing the maximum number (256) that can be taken as the color value at equal intervals. However, the color value is not limited to this. Can be divided at equal intervals. For example, one predetermined value (10) in the maximum range (256) that can be taken as color values, another predetermined value (250), and an interval between these one predetermined value and another predetermined value ( 20), the segment values (30, 50,..., 210, 230) can be used as the color values of the patch 110 printed in the area 130.
Also in this case, the measurement time can be shortened by performing point increase processing later.

Further, not all 65 points need be hit in one area 130, and each area 130 may be hit with each point.
Further, it is not necessary that 65 points / 4 = about 16 points of toner be applied to one area 130, and there may be deviation such that there are only 12 points or 25 points depending on the area 130.

Furthermore, in addition to printing 65 patches 110 having different color values, a predetermined number of patches 110 having the same color value can also be printed. In this case, the RGB data of a predetermined number of patches 110 having the same color value are averaged later. Thereby, the accuracy of gamma correction can be increased.
In this way, patches 110 with different (or the same) color values are printed in the area 130, but the unprinted portion is blank (paper color).

[3] Process 1: Printing Color Chart (1) When the gamma characteristic is normal (when the machine is stable and the gamma characteristic is optimal), a color chart as shown in FIG. 5 is printed (first printing process, Step 11). The color chart (1) output at this time outputs the color chart in a form that can express the gamma characteristics of each CMYK channel without performing color conversion or the like (output as designed from CMYK to CMYK).
At this time, in order not to depend on the engine characteristics, it is better to randomly arrange the patches of the chart and generate the patch of the same color value a plurality of times.

[4] Processing 2: Printing of color chart (2) When the gamma characteristic is different from the normal state (when the gamma characteristic is changed due to changes over time, etc.), a color chart as shown in FIG. 5 is output. (Second printing process, step 12). This printed color chart is referred to as a color chart (2). Note that it is preferable to use the same paper to be output in the processing 1 and the processing 2.

[5] Process 3-1: Scan of each color chart The color chart (1) is scanned by the scanner 13 of the image forming apparatus 10 (chart reading process, step 13). Similarly, the scanner 13 scans the color chart (2) (chart reading process, step 14).

[6] Process 3-2: Storage of Image Data, Extraction of RGB Values The image analysis unit 14 analyzes the image data obtained by the scan of the process 3-1, and stores it as a bitmap file in the storage unit of the image forming apparatus 10. 11 to save. Then, the image analysis means 14 extracts RGB data from the bitmap file (RGB data extraction process, step 15).
These image data storage and RGB value extraction are performed for both the color chart (1) and the color chart (2).

[7] Process 3-3: Reading Gamma Correction Table The calibration unit 15 reads the gamma correction table data set in the image forming apparatus 10 from the storage unit 11 (step 20 in FIG. 3).

[8] Process 3-4: Reading of RGB Data The calibration means 15 reads RGB values (RGB data) extracted from the bitmap file of the color chart (1) and (2) read by the scanner 13 (step) 21).

[9] Process 4-1: Calculation of area correction value The RGB value read in process 3-4 is brought into a state where the area correction value can be calculated (step 22).
Specifically, first, the RGB values of the patch 110 output at 50% to the edge frame 120 for noise removal are calculated, and these RGB values are averaged. This averaged data is called “edge frame RGB data”.

Next, as shown in FIG. 7, the plurality of patches 110 constituting the edge frame 120 are divided for each area 130. That is, the plurality of patches 110 printed so as to surround the outside of the first area 131 are set as the first area edge frame patches 111. Similarly, a plurality of patches 110 printed so as to surround the outside of the second area 132 are referred to as second area edge frame patches 112. The third area 133 is the third area edge frame patch 113. Further, the fourth area 134 is a fourth area edge frame patch 114.
Then, RGB data is calculated for each patch 110, an average value of the RGB data is calculated for each of the first area edge frame patch 111 to the fourth area edge frame patch 114, and this is referred to as area-specific RGB data. To do.

Further, the difference between the edge frame RGB data and the area-specific RGB data is calculated as area-specific correction data.
Then, the RGB data of the patch 110 printed in the area 130 is corrected using the area-specific correction data.

Here, the calculation of the RGB data of each patch 110 is performed by averaging the RGB values of each patch 110 of the image scanned in the process 3-1 for several pixels. At this time, by generating the same color value a plurality of times, the color patches of the respective color values can be averaged. The numerical values at this time are RGB channels 0-255.
The RGB value calculation method of each patch 110 is performed by averaging pixels within a predetermined range in the patch 110 as shown in FIG.
The predetermined range can be a square range near the center of one patch 110 as shown in FIG. That is, the RGB values of each pixel within this square range are averaged. Note that the number of pixels of each patch 110 is determined by the resolution.

The noise removal data for each area 130 can be calculated by the following equation.
Noise removal data:
(ALL_RGB): ΣFP / (FP_num) (Formula 2-1)
(Area1_RGB): ΣEFP1 / (EFP1_num) (Equation 2-2)
(Area2_RGB): ΣEFP2 / (EFP2_num) (Equation 2-3)
(Area3_RGB): ΣEFP3 / (EFP3_num) (Equation 2-4)
(Area4_RGB): ΣEFP4 / (EFP4_num) (Equation 2-5)

The meaning of each variable in these formulas 2-1 to 2-5 is as follows.
Overall noise removal data (edge frame RGB data): ALL_RGB
Noise removal data for area 1 (RGB data by area): Area1_RGB
Area 2 noise removal data (Area-specific RGB data): Area2_RGB
Noise removal data for area 3 (RGB data by area): Area3_RGB
Noise removal data for area 4 (RGB data by area): Area4_RGB

RGB value of noise removal patch: FP
Number of patches for noise removal: FP_num
RGB value of patch for noise removal in each area: EFP1, EFP2, EFP3, EFP4
Number of noise reduction patches in each area: EFP1_mun, EFP2_mun, EFP3_mun, EFP4_mun

Here, FP_num is the number of patches 110 constituting the edge frame 120, and is 111 in the chart shown in FIG.
EFP1_mun or the like is the number of patches surrounding one area 130 among the patches constituting the edge frame 120, and is 38 for each area in the chart shown in FIG.

An RGB value that must be corrected in each area 130 is defined as an area correction value.
The area correction value can be calculated by the following formula.
Area correction value (area-specific correction data):
(Area1_C_RGB): (ALL_RGB)-(Area1_RGB) (Equation 3-1)
(Area2_C_RGB) :( ALL_RGB)-(Area2_RGB) (Equation 3-2)
(Area3_C_RGB) :( ALL_RGB)-(Area3_RGB) (Equation 3-3)
(Area4_C_RGB) :( ALL_RGB)-(Area4_RGB) (Equation 3-4)
The calculation is performed using an area correction value (RGB value) of each area added for each area to the finally scanned RGB value.

[10] Process 5: Replace RGB data with a predetermined one channel of RGB data having gamma characteristics corresponding to CMYK toners In process 4, the RGB values of the color charts (1) and (2) were averaged. Based on this data, a process of replacing the RGB data with a predetermined one channel of RGB data having gamma characteristics corresponding to CMYK toners is performed.
The second chart is drawn using CMYK toner, and when the chart is read by the scanner 13, values are calculated using RGB data.
Here, the numerical value of Red is used as the Gamma characteristic of Cyan. In addition, as the numerical value of Magenta, Green is used as the numerical value of Yellow and Yellow, and Green data is used as the numerical value of Black.
This is because the relationship depending on the input / output characteristics of the C, M, Y, K and R, G, B channels is generally known.

Note that FIGS. 8 to 11 show a summary of this relationship obtained by experimenting with two models.
In each graph, the horizontal axis indicates C, M, Y, and K color values, and the vertical axis indicates RGB values.
In each figure, “RG” refers to the numerical value of the optimum gamma characteristic (ReferenceGamma), and “CG” refers to the numerical value of the gamma characteristic (CurrentGamma) that has collapsed due to changes over time or the like.
Of the two models tested, one is a model that obtains RG and the other is a model that obtains CG.

[11] Processing 6: Normalization processing Normalization processing is performed on the C, M, Y, K channel data of the color charts (1) and (2) averaged in processing 5 (step 23 (calibration processing). ), Step 30 to step 31 in FIG.
Normalization generally refers to a process of making data easier to use by transforming data based on a certain rule.
In this embodiment, normalization refers to transformation so that each C, M, Y, K channel data (color value) can be expressed in the range of 0-1.
As values used for the normalization process, there are a numerical value calculated in the process 5 and a value designed in the process 0-1.

The calculation formula is as follows.
Normalization processing
CyanValue = (Cr-CMV) / (PWV-CMV) (Formula 4-1)
MagentaValue = (Mg-CMV) / (PWV-MMV) (Formula 4-2)
YellowValue = (Yb-CMV) / (PWV-YMV) (Formula 4-3)
BlackValue = (Bg-CMV) / (PWV-BMV) (Formula 4-4)

In these equations 4-1 to 4-4, the numerical values calculated in the process 5 are defined as follows.
Cyan: Cr
Magenta: Mg
Yellow: Yb
Black: Bg

[12] Process 7: Calculation of Gamma Characteristic Value Using the numerical values of the color charts (1) and (2) normalized in process 6, the image quality due to changes with time is calibrated (step 32).
Here, the following calculation is performed on the numerical values of the color charts (1) and (2) calculated in the process 6.

Gamma characteristic value (sensor value)
CyanValue '= 1-CyanValue (Formula 5-1)
MagentaValue '= 1-MagentaValue (Formula 5-2)
YellowValue '= 1-YellowValue (Formula 5-3)
BlackValue '= 1-BlackValue (Formula 5-4)

[13] Process 8: Point increase process 256 points (gradation) are predicted from the gamma characteristic of 65 points (gradation) and points are increased (point increase processing, step 33).
As a point increasing method at this time, for example, a generally known nonlinear regression equation or a prediction equation such as a spline can be used.
The non-linear regression equation is a method of obtaining a non-linear (formula including high-order terms) regression equation and adding points from a curve represented by the regression equation.
A spline prediction formula (spline interpolation) is a method that uses several representative points of a curve as control points, and based on the coordinates of these control points, the entire curve or between control points is smooth. A method of connecting (interpolating). In this spline, several continuous control points are taken out and a polynomial (prediction formula) of a curve passing through those control points is obtained. Here, mathematically, the coefficient of the polynomial is determined so that the differential coefficient of the curve connecting the end points is continuous at the end points.

In this point increase processing, processing is performed so as to increase monotonously.
The monotonic increase means that f (x ₁ ) <f (x ₂ ) is satisfied if x ₁ <x ₂ . This monotonic increase can include satisfying f (x ₁ ) ≦ f (x ₂ ) if x ₁ ≦ x ₂ .
As a result, the number of points can be increased to 256 points while substantially maintaining the curve obtained at 65 points.

[14] Process 9: Correction of gamma characteristic The gamma characteristic destroyed by the change with time is brought close to the optimum gamma characteristic.
Specifically, in the example of FIG. 11, CG is brought close to the gamma characteristic of RG.
Note that a gamma correction table is required to correct the CG shown in FIG.

If the curve of the gamma characteristic of RG is F (x), F (x) is an R, G, B value, and x is a C, M, Y, K value. Similarly, if the curve of the gamma characteristic of CG is H (x), H (x) is an R, G, B value, and x is a C, M, Y, K value.
The relationship between F (x) and x of the curve F (x) is exchanged (step 34). F (x) is a C, M, Y, K value, and x is an R, G, B value.
Further, a function F (H (x)) is created (step 35). The numerical value calculated at this time is a numerical value for converting CG read by the scanner into RG.

[15] Process 10: Correction of Gamma Correction Table The value (function) of the gamma correction value (gamma correction table) used for printing is G (x). Data G (F (H (x))) in which the gamma correction table G (x) at this time is F (H (x)) is the optimum gamma correction value (gamma correction table) at that time (step 36).
The curves of F (x) and H (x) are shown in FIG. 12 (i), and the curve of F (H (x)) is shown in FIG. 12 (ii). Further, F (x), H (x), and G (F (H (x))) are shown in FIG. It can be seen from FIG. 13 that the gamma characteristic changed with time has approached the optimum gamma characteristic.
Processes 6 to 10 are referred to as calibration processes. Further, G (F (H (x))) is referred to as gamma correction data.

[16] Processing 11: Output of Gamma Correction Table The corrected gamma correction table is set in the image forming apparatus 10 (stored in the storage unit 11). The gamma correction table is printed out by the printing means 12 (step 24 in FIG. 3).
Even if the engine characteristics deteriorate, it is possible to provide a high-quality image by mounting the gamma correction table created in processing 10 on the image forming apparatus.

[Gamma correction data creation program]
Next, a gamma correction data creation program will be described.
The gamma correction data creation function (function for executing the gamma correction data creation method) of the computer (image forming apparatus) in each of the above embodiments is the gamma correction data stored in the storage means (for example, ROM or hard disk). Realized by the creation program.

The gamma correction data creation program is read by a computer control means (CPU or the like), and sends commands to various components of the computer to perform predetermined processing, for example, design value measurement processing, color chart design processing, color chart Printing processing, color chart scanning, image data saving processing, RGB value extraction processing, gamma correction table reading processing, RGB data reading processing, area correction value calculation processing, replacement processing from RGB data to CMYK data Normalization processing, gamma characteristic value calculation processing, point increase processing, gamma characteristic correction processing, and the like are performed.
As a result, the gamma correction data creation function is realized by the cooperation of the gamma correction data creation program as software and each component of the computer (image forming apparatus) as hardware resources.

Note that a gamma correction data creation program for realizing the gamma correction data creation function is stored in a computer ROM, hard disk, or the like, as well as a computer-readable recording medium such as an external storage device and a portable recording medium. Can be stored.
The external storage device is a memory expansion device that incorporates a storage medium such as a CD-ROM and is externally connected to the gamma correction data creation device. On the other hand, the portable recording medium is a recording medium that can be mounted on a recording medium driving device (drive device) and is portable, and refers to, for example, a flexible disk, a memory card, a magneto-optical disk, and the like.

The program recorded on the recording medium is loaded into the RAM of the computer and executed by the CPU (control means). By this execution, the function of the above-described gamma correction data creation apparatus of the present embodiment is realized.
Furthermore, when loading a gamma correction data creation program by a computer, the gamma correction data creation program held by another computer can be downloaded to its own RAM or external storage device using a communication line. The downloaded gamma correction data creation program is also executed by the CPU, and realizes the gamma correction data creation function of the gamma correction data creation apparatus of this embodiment.

As described above, according to the image forming apparatus, the gamma correction data creation method, and the gamma correction data creation program of the present embodiment, the machine characteristics that change with time can be recalibrated to the optimum gamma characteristics each time. As a result, high quality image quality can be provided.
In particular, gamma correction can be performed in a short time and easily even if the image forming apparatus does not have the functions described in Patent Documents 1 to 3 described above.
Further, since the characteristic sheet is provided with an edge frame, gamma correction calculation can be performed after removing noise of a device such as a scanner or a printer.

The preferred embodiments of the image forming apparatus, gamma correction data creation method, and gamma correction data creation program of the present invention have been described above. However, the image forming apparatus, gamma correction data creation method, and gamma correction data creation program according to the present invention are described above. It is needless to say that various modifications can be made within the scope of the present invention.
For example, in the above-described embodiments, the image forming apparatus is simply used. However, the image forming apparatus includes a printer (copier), a copier, a facsimile machine, a scanner, and a digital composite apparatus.
The printer includes printers having various printer methods such as an ink jet printer, a sublimation type thermal transfer printer, a dot impact printer, an ink jet printer, a laser printer, and a melt type thermal transfer printer.

  Since the present invention is an invention related to correction of gamma characteristics, it can be used in apparatuses and devices that perform correction of gamma characteristics.

1 is a block diagram illustrating a configuration of an image forming apparatus of the present invention. It is a flowchart which shows the operation | movement procedure of the gamma correction data creation method in the Example of this invention. It is a flowchart which shows the operation | movement procedure of the gamma correction data creation method in the Example of this invention. It is a flowchart which shows the operation | movement procedure of the gamma correction data creation method in the Example of this invention. It is a front view which shows the structural example of a characteristic sheet. It is a front view of a characteristic sheet for explaining averaging of RGB values in each patch. It is a front view of the characteristic sheet for demonstrating calculation of the data for noise removal. It is a graph which shows the gamma characteristic of Cyan-Red. It is a graph which shows the gamma characteristic of Yellow-Blue. It is a graph which shows the gamma characteristic of Magenta-Green. It is a graph which shows the gamma characteristic of Black-Green. It is a graph which shows a gamma characteristic when F (x) and H (x) are converted into F (H (x)). It is a graph which shows the optimal gamma characteristic (RG), the gamma characteristic (CG) destroyed by the time-dependent change, and the gamma correction data G (x).

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Memory | storage means 12 Printing means 13 Scanner 14 Image analysis means 15 Calibration means 100 Characteristic sheet (color chart)
110 Patch 120 Edge frame 130 (131-134) Area

Claims (11)

An image forming apparatus for creating data for correcting gamma characteristics,
Printing means for printing the first chart when the gamma characteristic is normal and printing the second chart when the gamma characteristic is different from the normal state;
A scanner for reading the first chart and the second chart;
Based on the image data read by the scanner, image analysis means for extracting RGB data for each chart;
Based on the RGB data, a gamma characteristic value obtained by quantifying the gamma characteristic for each chart is calculated, and a correction value necessary to approximate the gamma characteristic value of the second chart to the gamma characteristic value of the first chart An image forming apparatus, comprising: a calibration unit that calculates gamma correction data by reading a gamma correction table from a storage unit and corrects the gamma correction table using the gamma correction data. The first chart and / or the second chart are:
One or more areas printed with a predetermined number of patches having different color values;
An edge frame on which a plurality of patches having a constant amount of toner are printed,
The image forming apparatus according to claim 1, wherein the edge frame is printed so as to surround each of the areas. The number of color values of patches printed in the area is less than the maximum number that can be taken as this color value,
The image forming apparatus according to claim 2, wherein when the gamma characteristic value is calculated, the gamma characteristic value is increased with the maximum number as an upper limit. The color value of the patch printed in the area is one predetermined value in the range that can be taken as this color value, another predetermined value, and an interval between these one predetermined value and another predetermined value. The image forming apparatus according to claim 3, further comprising: each division value when divided into two. The image forming apparatus according to claim 2, wherein a predetermined number of patches having the same color value are printed in the area, and the RGB data of the patches are averaged. Calculate RGB data for each of the plurality of patches constituting the edge frame, and calculate an average value of the calculated RGB data as edge frame RGB data,
The RGB data is calculated for each of the patches printed so as to surround the outside of one area among the plurality of patches constituting the edge frame, and the average value of the calculated RGB data is calculated. RGB data by area
The difference between the edge frame RGB data and the area-specific RGB data is calculated as area-specific correction data,
The image forming apparatus according to claim 2, wherein the correction data for each area is used to correct RGB data of a patch printed in the area. The RGB data of the first chart and the RGB data of the second chart are respectively replaced with predetermined one channel of RGB data having a gamma characteristic corresponding to CMYK toner,
Normalize the CMYK data for each of these charts,
The image forming apparatus according to claim 1, wherein the gamma characteristic value is calculated for each of the charts using the normalized CMYK data. A gamma correction data creation method for creating data for correcting gamma characteristics,
Print the first chart when the gamma characteristic is normal,
Print the second chart when the gamma characteristic is different from the normal state,
Read the first chart and the second chart with a scanner, extract RGB data for each chart,
Based on each of the RGB data, a gamma characteristic value obtained by quantifying the gamma characteristic for each chart is calculated,
A correction value necessary to approximate the gamma characteristic value of the second chart to the gamma characteristic value of the first chart is calculated as gamma correction data;
A gamma correction data generation method, comprising: reading a gamma correction table from a storage unit; and correcting the gamma correction table using the gamma correction data. The first chart and / or the second chart are:
One or more areas printed with a predetermined number of patches having different color values;
An edge frame on which a plurality of patches having a constant amount of toner are printed,
The gamma correction data creation method according to claim 8, wherein the edge frame is printed so as to surround each of the areas. A gamma correction data creation program for causing an image forming apparatus to execute processing for creating data for correcting gamma characteristics,
A first printing process for printing a first chart when the gamma characteristic is normal;
A second printing process for printing the second chart when the gamma characteristic is different from the normal state;
A chart reading process in which the scanner reads the first chart and the second chart;
RGB data extraction processing for extracting RGB data for each chart based on the image data read by this chart reading processing;
Based on the RGB data, a gamma characteristic value obtained by quantifying the gamma characteristic for each chart is calculated, and a correction value necessary to approximate the gamma characteristic value of the second chart to the gamma characteristic value of the first chart Is calculated as gamma correction data, a gamma correction table is read from the storage means, and a calibration process for correcting the gamma correction table using the gamma correction data is executed by the image forming apparatus. Data creation program. The first chart and / or the second chart are:
One or more areas printed with a predetermined number of patches having different color values;
An edge frame on which a plurality of patches having a constant amount of toner are printed,
The gamma correction data creation program according to claim 10, wherein the border frame is printed so as to surround each of the areas.