JP2021024139A - Printer, gradation correction device, gradation correction program, and gradation correction method - Google Patents

Abstract

To obtain a printed matter that has appearance intended by a user without requiring the user's confirmation with a simple configuration.SOLUTION: A printer determines whether or not the variation of image information acquired by an acquisition unit with respect to reference image information is within a prescribed variation range, and performs control so as to output a printed matter as it is when the variation is within the prescribed variation range. On the other hand, the printer performs control so as to discard the printed matter when the variation is outside the prescribed variation range. In one example, the printer comprises: an output tray to which the printed matter for output is output; and a purge tray to which the printed matter for discarding is output. The printer outputs the printed matter to the output tray when the variation is within the prescribed variation range, and outputs the printed matter to the purge tray when the variation is outside the prescribed variation range.SELECTED DRAWING: Figure 12

Description

Embodiments of the present invention relate to a printing device, a gradation correction device, a gradation correction program, and a gradation correction method.

Digital printing devices such as electrophotographic and inkjet methods, which are premised on mass printing, are required to have stable output colors in continuous output of hundreds or thousands of sheets. In particular, stable management of reproduced colors is important in use cases where similar manuscripts with slightly replaced content are repeated every few pages, or in use cases where distributed printing is performed at multiple locations.

On the other hand, unlike full-scale commercial printing, the operating environment in which these digital printing machines are used is not always strictly controlled in many cases. In addition, load fluctuations due to mixed printing of various document types are large, and the amount of toner and ink supplied and machine conditions change from moment to moment.

Therefore, in order to strictly control the output color to some extent, it is necessary to frequently stop the machine and perform calibration. However, if such a calibration operation is performed frequently, problems such as waste paper, job stoppage, and increase in work man-hours occur.

Here, Patent Document 1 (Japanese Unexamined Patent Publication No. 2004-251996) discloses a printing system that realizes stable color reproducibility and prevents interruption of printing processing for calibration processing. Further, Patent Document 2 (Japanese Unexamined Patent Publication No. 2006-21401) describes a test chart and a reference so that the output image does not differ due to a change in the state of the internal mechanism over time in an image output device such as a color printer. An image output device with a calibration function that visually evaluates a chart and performs calibration based on the evaluation result is disclosed.

However, in the conventional printing apparatus, if the density of the engine fluctuates after the calibration is performed, the color intended by the user and the color of the printed matter still deviate from each other. It is also possible to suppress the density fluctuation of this engine by feedback control, but in this case, if the feedback control is deviated, printed matter of a different color will be output, and in the end, the user will change the color of the printed matter. It is necessary to confirm.

Further, in the case of the printing system of Patent Document 1, there is a problem that the system becomes complicated, and in the case of the image output device with a calibration function of Patent Document 2, there is a problem that the user needs to confirm the color.

The present invention has been made in view of the above-mentioned problems, and is a printing device and gradation that can obtain a printed matter having an appearance intended by the user with a simple configuration without requiring confirmation by the user. An object of the present invention is to provide a correction device, a gradation correction program, and a gradation correction method.

In order to solve the above-mentioned problems and achieve the object, in the present invention, the acquisition unit for acquiring the image information of the printed matter and the fluctuation amount of the acquired image information with respect to the reference image information are within a predetermined fluctuation range. A discriminant unit that determines whether or not there is a fluctuation amount, and if the fluctuation amount is within a predetermined fluctuation range, the output is controlled, and if the fluctuation amount is outside the predetermined fluctuation range, the printed matter is discarded. It has an output control unit.

According to the present invention, there is an effect that a printed matter having an appearance intended by a user can be obtained with a simple configuration without requiring confirmation by the user.

FIG. 1 is a diagram showing a system configuration of the image forming system of the embodiment. FIG. 2 is a block diagram of an image forming apparatus provided in the image forming system of the embodiment. FIG. 3 is a cross-sectional view of a laser printer which is an example of an image forming apparatus provided in the image forming system of the embodiment. FIG. 4 is a diagram showing a characteristic tendency of the concentration distribution. FIG. 5 is a flowchart showing a flow of processing for extracting a color measurement region. FIG. 6 is a diagram showing the relationship between the colorimetric region and the segment. FIG. 7 is a diagram showing an example of weighting in the equation (6). FIG. 8 is a processing flowchart for calculating the TRC correction amount. FIG. 9 is a diagram showing TRC before and after correction. FIG. 10 is a functional block diagram corresponding to an output control operation in the image forming system of the embodiment. FIG. 11 is a flowchart showing a simplified flow of the correction curve calculation operation of the TRC correction amount determining unit of the image forming system of the embodiment. FIG. 12 is a flowchart showing the flow of the gradation correction operation and the output control operation of the image forming system of the embodiment.

Hereinafter, an image forming system according to an embodiment will be described as an example.

(Overview)
The image forming system of the embodiment corrects the gradation for each segment divided in the main scanning direction, suppresses the density fluctuation in the main scanning direction, and enables appropriate correction of the reproduced color (gradation). Correction operation).

Further, the image forming system of the embodiment measures the initial fluctuation of the printed matter to be printed first, confirms that the fluctuation is within a preset allowable value, and performs gradation correction to correct the fluctuation portion. Do. Then, if the printed matter to be printed subsequently has a color variation within a set range rather than the initial variation, the printed matter is output to the output tray as a printed matter, and if the color variation exceeds the set range, the printed matter is purged from the purge tray ( Output to the waste tray) (output control operation). As a result, only the printed matter within the set color variation can be output.

Since the user recognizes the reproduction color only in the printed matter output to the output tray, the user recognizes the reproduction color of the printed matter output in the output tray as the reproduction color desired by himself / herself. Therefore, it is possible to eliminate the work of checking the color of the printed matter.

Hereinafter, the image forming system of the embodiment will be described in the order of system configuration, gradation correction operation, and output control operation.

(System configuration)
FIG. 1 is a diagram showing a system configuration of the image forming system of the embodiment. As shown in FIG. 1, the image forming system includes a user's personal computer device (user PC) 1, a network 2, a server device 7, and an image forming device 8.

The image forming apparatus 8 includes an image processing unit 3 that expands and processes original data input via the network 2, an electrophotographic printer engine 4 that executes printing, and an engine control unit 9 that controls the printer engine. It also has an image inspection unit 5 that inspects the output image 6 from the printer engine 4 in-line before output.

The image processing unit 3 is composed of software and an expansion board on a PC separate from the printer engine 4, and also has an independent user interface. The image inspection unit 5 is provided with an RGB line sensor (R: red, G: green, B: blue) and a paper feed mechanism, and is a scanner device capable of measuring an image on a surface.

One or more user PCs 1 connected on the network 2 transmit image data and a print request to the image forming apparatus 8. Further, the server device 7 stores information necessary for color conversion required by the image processing unit 3.

Normally, the manuscript data requested to be printed from the user PC1 is a bitmap, text or graphic drawing command whose color is specified in RGB or CMYK (C: cyan, M: magenta, Y: yellow, K: key plate or black). Is transmitted to the image processing unit 3 in a data format including. The image processing unit 3 performs predetermined image processing such as development of drawing instructions and color processing on the original data, and converts the original data into a signal form that can be processed by the printer engine 4. The printer engine 4 recognizes the original data in the converted signal form and prints an image or the like on the paper.

(Configuration and operation of image forming apparatus)
FIG. 2 is a block diagram of the image forming apparatus 8. In FIG. 2, image processing related to drawing commands and text expansion is omitted in order to avoid complicated explanations. Further, the user manuscript will be described as image data assuming specific printing device characteristics (for example, Japan Color 2001 Coated) such as RGB or CMYK.

The original color Lab conversion 10, LabCMYK conversion 11, CMYKLab conversion 13, scanner color Lab conversions 15 and 18, and Lab scanner color conversion 14 shown in FIG. 2 require basic data called a color profile for each color space conversion. (As such a color profile, an ICC profile defined by ICC (International Color Consortium) is widely known).

Among these color profiles, the color profile required for the original color Lab conversion 10 is the one attached to the original data, or the one prepared as a default is used. Further, the color profiles required for the scanner color Lab conversions 15 and 18 and the Lab scanner color conversion 14 are fixedly set in advance in the image processing unit 3 and the image inspection unit 5.

On the other hand, the color profiles required for the LabCMYK conversion 11 and the CMYKLab conversion 13 have different color reproduction characteristics depending on the paper set in the printer engine 4, and therefore, an appropriate color selected prior to the start of the printing operation. A profile (hereinafter referred to as a paper profile) is downloaded from the server device 7 and set. The selection of the paper profile by the user is performed via the user interface (not shown) of the user PC 1 or the image processing unit 3.

Under such a color profile setting, the user manuscript described in RGB, CMYK, etc. is first subjected to the manuscript color Lab conversion 10 to have a Lab value which is a device-independent color value (docLab in FIG. 2). ) Is converted. The LabCMYK conversion 11 converts the docLab into 8-bit digital values of each color of the basic color CMYK of the printer engine 4. By default, the user gradation conversion 12 outputs the CMYK value as it is without changing it (PrnCMYK in FIG. 2).

These color conversions are processed at the same time as the vector data and font expansion, and the CMYK data output as a result is output as bitmap data. The image data developed as a bitmap of CMYK values in this way is temporarily stored in the storage device (disk) 22 for each print document. The CMYK image data held in the storage device 22 is also used for color measurement area detection, which will be described later.

The image forming unit 23 forms (prints) an image on the designated paper based on the CMYK bitmap image data. The gradation correction unit 16 includes n gradation reproduction corrections (TRC: Tone Reproduction Correction) for each of the colors C, M, Y, and K (n = 16 in the example described later), and CMYK using these. Correct each value. Usually, the gradation reproduction correction is provided by a function or a LUT (Lookup Table). In the following description, the description will proceed assuming that the LUT is provided as an example, but it may be provided by software with a representative value and a function by interpolation. In the following, the gradation reproduction correction will be simply referred to as TRC or gradation correction curve.

Here, for example, for cyan data in which the pixel position in the main scanning direction is x and the pixel value is c, the TRC for cyan is f (n, c), c = 0,1,2,. .. , 255, the truncated value obtained by dividing the number of pixels in the main scanning direction by 16 is Nw, n = [x / Nw + 0.5], s = [x / Nw + 0.5] -n.

とする。ただし、記号［ｘ］は、ｘを超えない最小の整数を表すガウス記号である。その他Ｍ，Ｙ，Ｋの各色に対しても同様である。

And. However, the symbol [x] is a Gaussian symbol representing the smallest integer not exceeding x. The same applies to the other colors M, Y, and K.

In addition to linear interpolation, a smooth interpolation method such as polynomial interpolation or spline interpolation may be used.

The gradation processing unit 17 converts the color values sent in 8 bits for each of the C, M, Y, and K colors into the number of gradations that the printer engine 4 can express with one dot by the area gradation method or error diffusion. Convert using the method. The printer engine 4 forms an output image 6 on paper based on a CMYK signal whose gradation number is converted by the gradation processing unit 17.

On the other hand, the CMYK value (prnCMYK) input to the image forming unit 23 is returned to the Lab value (prnLab in FIG. 2) again by the CMYKLab conversion 13. The CMYKLab conversion 13 is a model that simulates the reproduced color of the output image 6 output by the image forming unit 23 as a Lab value.

Basically, the simulated Lab value (prn-Lab) and the measured value (mesCol) of the output image 6 scanned by the image inspection unit 5 are converted into a Lab value by the scanner Lab conversion 18. (MesLab) is used by the TRC correction amount determining unit 19 to correct the TRC set in the gradation correction unit 16.

The ideal scanner provided in the image inspection unit 5 is a multi-band scanner capable of measuring spectrophotometrically more than a general RGB scanner. However, if the color gamut of the image inspection unit 5 cannot cover the entire color gamut of the printer engine 4 due to mounting convenience and cost, the Lab scanner color conversion 14 and the scanner Lab conversion 15 are used. It becomes necessary to further compress the prnLab into the color gamut of the image inspection unit 5. In FIG. 2, the CMYKLab conversion 13, the Lab scanner conversion 14, and the scanner Lab conversion 15 constitute the reproduction color model unit 21.

As a result, the print color prnLab simulated by the reproduction color model unit 21 is converted (generated) into the target color targetLab to be measured by the image inspection unit 5.

In the TRC correction amount determination unit 19, the target color, the targetLab, the measured value mesLab actually obtained from the image inspection unit 5, the prnCMYK, which is the input value to the gradation correction unit 16, and the engine control unit 9 The TRC correction amount (δc, δm, δy, δk) is determined for each segment based on the engine information of (details will be described later).

(Printer engine configuration and operation)
As an example, a laser printer can be used as the printer engine 4. FIG. 3A is a cross-sectional view of a main part of the laser printer. First, the configuration and operation of the developing unit 60k will be described. The photoconductor drum 50k rotates in the direction of arrow A in FIG. This rotation position is detected by a rotation detector 57 provided at the end of the photoconductor drum 50k. First, the charger 52 applies a uniform charge to the surface of the photoconductor drum 50k cleaned by the cleaning roller 51 with respect to the photoconductor drum 50k. Next, the laser beam 55 irradiated from the laser unit 53 scans the surface of the photoconductor drum 50 while blinking according to the signal of the exposure control device 10, thereby forming an electrostatic latent image on the photoconductor drum 50. ..

At this time, the scanning direction of the laser beam 55 is the main scanning direction, and the rotation direction A of the photoconductor drum 50k is the sub-scanning direction. The formed electrostatic latent image is developed by black (K) toner charged to the opposite potential supplied by the developing roller 54 to become a toner image. The developed toner image is transferred to the intermediate transfer belt 61.

The configurations of the developing units 60c, 60m, and 60y are also the same, forming toner images of cyan (C), magenta (M), and yellow (Y), respectively, and sequentially superimposing and transferring them on the intermediate transfer belt 61.

The transfer roller 58 collectively transfers the toner images of C, M, Y, and K stacked on the intermediate transfer belt 61 onto the paper conveyed from the right side on the paper transfer path 59. The fuser 56 heat-presses the toner image on the paper to fix it on the paper surface.

Since the mechanism of density fluctuation generation does not depend on the developing unit, the developing unit 60k will be described as an example in the following description. Each photoconductor drum 50k in the series of processes described above is usually positioned by strict control, but due to variations within the control accuracy of the parts, the drum rotation axis 66 and the drum central axis 65 are aligned with FIG. A minute eccentricity as shown in b) is generated (in FIG. 3B, it is exaggerated for explanation).

If the photoconductor drum 50k has the above-mentioned eccentricity, the development gap (not shown) with the developing roller 54 causes periodic fluctuation. This is one of the major factors of the periodic density fluctuation of the output image.

In the example of FIG. 3B, since the rotation axis intersection 67a at the left end of the drum and the rotation axis intersection 67b at the right end are on opposite sides with respect to the drum center axis 65, the density fluctuation on the image as a printing result is , Both ends of the image (with respect to the main scanning direction) are out of phase.

In many cases, the photoconductor drum 50k is eccentric with respect to the drum rotation axis 66 in the same direction, and the density fluctuations at both ends of the image are often in phase, but if not so extreme, both ends of the image. The phase of concentration fluctuation may be different.

Further, as a finer eccentric mode, as shown in FIG. 3C, there is a bending mode in which the photoconductor drum 50k is slightly curved with respect to the drum central axis 65. In this case, since the distribution of the development gap in the main scanning direction (65 directions of the drum center axis) at each rotation position is not linear, higher-order density unevenness occurs in the main scanning direction.

Further, even if the photoconductor drum is not eccentric, the rotation axis of the photoconductor drum 50k and the rotation axis of the developing roller 54 cannot be adjusted completely in parallel. Therefore, when a minute gap gradient is generated in the developing gap in the main scanning direction. There is also.

In the case of the density gradient in the main scanning direction caused by such a development gap gradient, the gradient in a specific density range (for example, solid density) can be eliminated by adjusting the exposure intensity distribution of the laser beam in the main scanning direction. it can. However, even in this case, since the depth and diameter of the potential of the spot exposed by the laser beam also change, the thickness of each dot to be developed, the so-called dot gain, changes, and as a result, the main scanning direction. There will be variations in the way the gradation characteristics of the laser are changed.

FIG. 4A is a graph showing a characteristic tendency of the concentration distribution in the main scanning direction. The horizontal axis is the position in the main scanning direction, and the vertical axis is the concentration of any of CMYK (for example, cyan). However, for convenience of explanation, the amplitude of the concentration distribution is exaggerated. The solid line is an example of the density distribution at the initial stage of printing, and the broken line is the change in density distribution in printing of several tens of pages. In this example, it is a change that occurs when the large density distribution near the arrows A and B, which was initially caused by the bias of the toner density in the developing device, is gradually relaxed as printing is continued. In particular, the density gradually decreases in the arrow A portion, and conversely, the density gradually increases in the arrow B portion, so that the tendency of increasing or decreasing the density is reversed at the adjacent main scanning positions. In this case, if the same correction is applied to the B portion based on the color measurement of the A portion, the error of the B portion will be further increased.

FIG. 4B is a graph showing a characteristic tendency of the concentration distribution in the sub-scanning direction. The horizontal axis represents the sub-scanning position of the print output over 5 pages with one coordinate axis including the space between papers that are not actually printed, based on the writing of the 1st page, and the vertical axis is the density. ..

The characteristic of the density fluctuation in the sub-scanning direction consists of the periodic fluctuation as shown by the solid line and the random fluctuation superimposed on it on the gentle density drift over several pages as shown by the broken line. ..

Such periodic fluctuations of several centimeters to several tens of centimeters often occur in synchronization with the photoconductor drum 50 or the developing roller 54. FIG. 4B is estimated from the colorimetric values indicated by the black circles because the period of density fluctuation indicated by the downward triangular mark and the sampling period indicated by the upward arrow are slightly different. This is an example in which the drift amount (dashed line) is overestimated than the actual drift amount (broken line).

In the present embodiment, the influence of the gradual periodic fluctuation of several cm to several tens of cm is examined except for the tendency of the concentration distribution in the main scanning direction and the random fluctuation and the periodic fluctuation of a very short cycle on the order of several mm. By avoiding it, the effect of drift (concentration fluctuation) over several pages is corrected.

(Gradation correction operation)
(TRC correction amount determination algorithm)
Next, the TRC correction amount determination algorithm by the TRC correction amount determination unit 19 will be described. First, FIG. 5 shows a processing flowchart for extracting a color measurement area of a CMYK bitmap-ized user document stored in a storage device to be printed prior to the main processing.

In step S100 of FIG. 5, one page of CMYK bitmap image data of the original data to be printed is read from the storage device 22 into the page buffer.

Next, in step S101, a color measurement region to be color-measured is extracted from the image data. As a specific extraction method, for example, a method of extracting a plurality of small regions having a high flatness and a gradual change of a fixed size (for example, 41 × 41 pixels at 400 dpi) as disclosed in Patent Document 1 is used. ..

At this time, the extracted color measurement region is described by the center coordinates (x, y) of each pixel. x is the position in the main scanning direction, and y is the position in the sub-scanning direction (paper feed direction). In this example, the main scanning direction is evenly divided into 16 segments, and is expressed as (xij, yij) according to the segment number to which x belongs. Here, i = 1, 2, ... .. , 16 are segment numbers, j = 1, 2, ... .. .. , Ni are sample numbers for each segment belonging to the segment corresponding to the segment number i. Of course, the number of segments is set to 16 here, but in reality, an appropriate number of divisions is selected according to the output device to be applied.

(Relationship between colorimetric area and segment)
FIG. 6 is a diagram for explaining the relationship between the colorimetric region and the segment (xij, yij). FIG. 6 shows the relationship between the output image 6 and the segment and the color measurement area. As an example, in this example, the region of the output image 6 is divided into 16 segments from the first segment to the 16th segment. In FIG. 6, for convenience of explanation, the segment number is shown at the top of the segment (the segment number is not actually printed). Further, for the sake of simplicity, the extracted colorimetric regions are illustrated by square frames only in the 7th segment 32 and the 12th segment 33. The center coordinates of the colorimetric region are numbered for each segment in the order of appearance in the sub-scanning direction and in the ascending order of the y-coordinate. For example, in the 7th segment, the center coordinate 34 of the colorimetric region 35 detected first is described as (x7,1, y7,1).

In addition, since the use case assumed here is the stabilization management of the reproduced color in printing in which the same type of original is repeated, the sample of the colorimetric region to be extracted is one or more as the repetition unit. It straddles the page of. Therefore, the sub-scanning coordinates y are described as continuous coordinates including the space between papers whose origin is the writing position of the first page, with the number of repeated pages as a group. Since "the sub-scanning coordinate y is a set of the number of pages to be repeated", this repetition unit is t.

If the colorimetric extraction for the print cycle page is not completed in step S102 (step S102: Yes), the process from step S100 is repeated, and if the colorimetric extraction for the print cycle page is completed, the process is performed. It ends (step S102: No).

Next, the colorimetric region of the i-segment {(xij, yij)} j = 1, 2,. .. .. , A method of determining the TRC correction amount based on the colorimetric value of Ni will be described. The method of calculating the TRC correction amount from the colorimetric value in the colorimetric region is almost the same as that of Patent Document 1. That is, the colorimetric region (
The prnCMYK values in FIG. 2 corresponding to (xij, yij) are set to (cij, mij, yij, ki).
j), the targetLab value,

離散化された時刻ｔにおけるｍｅｓＬａｂ値を、

The mesLab value at the discretized time t,

とするとき、第ｉセグメントの測色値に対する評価関数Ｊｉを、

Then, the evaluation function Ji for the colorimetric value of the i-segment is

とし、Ｊｉを最小化する

And minimize Ji

を時刻ｔにおける第ｉセグメントのＴＲＣ補正量とする。

Is the TRC correction amount of the i-th segment at time t.

The evaluation function (2) is the TRC correction amount.

に関する評価関数である。

Evaluation function for.

は、要素数２５６の１次元配列であり、（２）式の第１項が、ｍｅｓＬａｂ値の補正後の線形近似による予測値とｔａｒｇｅｔＬａｂの誤差を評価する主要な項、第２項が、曲線としての、

Is a one-dimensional array with 256 elements, the first term of Eq. (2) is the main term for evaluating the error between the predicted value by linear approximation after correction of the mesLab value and the targetLab, and the second term is the curve. As,

それぞれの曲率を押さえるために追加された項、第３項が、補正量そのものの大きさを押さえるための項である。

The term added to suppress each curvature and the third term are terms for suppressing the magnitude of the correction amount itself.

However, the value corresponding to the input values 0 and 255 of each δ is set to 0. Further, α and β are positive constants determined in advance based on experiments so that the entire system is stable, and Dj is a CMYK → Lab function formed by the color reproduction model unit 21 in (cj, mj, yj, kj). Jacobian matrix,

である。特に、スキャナ色域が十分で、ＣＭＹＫＬａｂ変換１３のカラープロファイルが、ＩＣＣプロファイル（ＩＳＯ１５０７６−１：２００５）に規定されているような、ＣＭＹＫ入力Ｌａｂ出力の多次元ＬＵＴで実装されている場合には、実装されている多次元ＬＵＴの（ｃｉｊ，ｍｉｊ，ｙｉｊ，ｋｉｊ）に最も近い配列要素で、Ｊａｃｏｂｉ行列Ｄｊを代用することが可能である。

Is. In particular, when the scanner color gamut is sufficient and the color profile of the CMYKLab conversion 13 is implemented by a multidimensional LUT of the CMYK input Lab output as defined in the ICC profile (ISO15076-1: 2005). , The Jacobi matrix Dj can be substituted with the array element closest to (cij, mij, yij, kij) of the implemented multidimensional LUT.

In this way, by dividing the main scanning direction into a plurality of segments and applying feedback for each segment, the problem of the difference in the tendency of the density fluctuation for each main scanning position is solved, but on the other hand, the segments are divided. As a result, there are segments in which it is difficult to secure a color measurement region, and due to the bias of the color scheme for each segment, an extreme difference in TRC occurs between the segments, which causes a problem that a pseudo contour is likely to be generated at the segment boundary.

To alleviate this problem, first based on the colorimetric values in the colorimetric area of all segments,

により、

By

を最小化する全体補正量を、

The total correction amount that minimizes

と置いて、基準ＴＲＣ補正量とし、先の（２）式のＪｉに、この基準ＴＲＣ補正量からの差を抑制する項を追加した。

As a reference TRC correction amount, a term for suppressing the difference from the reference TRC correction amount was added to Ji in the above equation (2).

これにより、測色領域の少ない（又は存在しない）セグメントでも、全体的なＴＲＣ変動に追随した補正が行われるため、ＴＲＣ補正量が不安定になることを抑制でき、また、セグメント間のＴＲＣ補正量の極端な乖離を防止できる。

As a result, even in segments with a small (or non-existent) color measurement region, correction is performed according to the overall TRC fluctuation, so that it is possible to suppress the TRC correction amount from becoming unstable, and TRC correction between segments Extreme divergence in quantity can be prevented.

If the color measurement region is insufficient in the entire page, it is easy to provide an unstable avoidance means that does not perform TRC correction. The problem here is that the difference in the color distribution sampled in the colorimetric region between the segments causes a large gap in the correction direction between the adjacent segments.

For example, if the i-th segment has a color measurement area sufficient to correct the cyan gradation, but a small amount of cyan around a specific gradation is not used in the i + 1 segment, the i-segment The color in the vicinity of the i + 1 segment of the above is pulled by the gradation error of cyan in the i + 1 segment due to the interpolation between the segments of the TRC (Equation (1)), causing a problem that color unevenness occurs. The above-mentioned measures are means for avoiding such a problem.

In the above method, the total correction amount by the entire color measurement area is used as the reference TRC correction amount, and the difference from the correction amount is suppressed. However, when the color measurement area is sufficient, it is better than using the entire color measurement area. If the segment is limited to a segment close to the segment of interest to some extent, the followability to the non-uniformity of the TRC change in the main scanning direction is improved.

In that case, first, the weight of each segment with respect to the i-th segment is weighted with with to extend the above equation.

により、

By

を決定することで、セグメント間のＴＲＣ補正量の極端な乖離を防止できる。

By determining, it is possible to prevent an extreme deviation of the TRC correction amount between the segments.

Here, an example of the weight wir is shown in FIG. In FIG. 7, the distribution of the weighting coefficient vir corresponding to the 1st, 8th, and 16th segments is shown by a solid line in an easy-to-understand manner, and the weight distribution related to the other segments is shown by a broken line. Therefore, for example, for the first segment, the curves w1 and r shown by the solid line at the left end are weighted and determined by the equation (6).

を基準ＴＲＣ補正量として、（７）式から第１セグメントのＴＲＣ補正量

Is the reference TRC correction amount, and the TRC correction amount of the first segment from Eq. (7)

を決定する。

To decide.

As a result, the TRC correction amount of the first segment can be determined in the color measurement region from the first segment to the fourth segment. The same applies to other segments.

In equations (6) and (7), a two-step processing procedure is taken in which the reference TRC correction amount is calculated for each segment and then the TRC correction amount in the segment is calculated, following the concept of equations (4) and (5). However, if there is no large deviation in the fluctuation tendency between the segments, the calculation load can be reduced by using the reference TRC correction amount of each segment according to the equation (6) as it is as the TRC correction amount of that segment.

(TRC correction amount calculation process)
FIG. 8 is a flowchart showing the flow of the TRC correction amount calculation process. First, steps S201 and S202 are executed for each segment number i = 1 to 16.

In step S201, the smallest integer s in which the sum of the number of colorimetric regions Ni from the i−s segment to the i + s segment exceeds the predetermined reference value No is searched in order from 0, centering on the i segment. To do. Although not shown, if the search range exceeds all segments, the search ends there.

In step S202, the weighting coefficient of the equation (6) is determined by the equation shown in step S202 based on the s determined in step S201. Here, a uniform weight is simply given.

Next, the processes of steps S203 and S204 are executed for each segment number i = 1 to 16 using the obtained weighting coefficient. In step S203, the reference TRC correction amount is determined from the equation (6), and in step S204, the TRC correction amount corresponding to the segment is determined by using the reference TRC correction amount and the color measurement value of the color measurement area in the segment. ..

The explanation of the flowchart of FIG. 8 is an example of another method for determining the weighting coefficient wrj in the equation (6). In the case of the example of FIG. 8, the value taken by wrj is only {0,1}, and the range of the neighboring segments sufficient for the number of colorimetric regions to reach the reference value No by adding the neighboring segments to the center of the attention segment. give. The reference TRC correction amount for determining the TRC correction amount of each segment by the equation (7) is determined within the range of the peripheral segment including the attention segment limited by this.

In relation to FIG. 2, the prnCMYK data is image data for each printed document, and the TRC correction amount determination unit 19 determines the center coordinates (xij, yij) of the color measurement region based on this data. The reference TRC correction amount is determined from the CMYK value (prnCMYK) in the color measurement region and the target Lab value (tagetLab) according to the equation (6).

Here, since the prnCMYK value and the targetLab value are page data, the center value (xij, yij) of the color measurement area is used as an index for referring to the value in the color measurement area. The determined correction amount is associated with the corresponding segment number (id in FIG. 2) and sent to the gradation correction unit 16.

Finally, in step S205, the TRC correction amount obtained for each segment is added to the TRC of the gradation correction unit 16 to complete the TRC correction.

(Relationship of TRC before and after correction)
FIG. 9 is a diagram showing the relationship of TRC before and after the correction in the gradation correction of cyan. In FIG. 9, the horizontal axis is the cyan input gradation value vc (in the equation (4), etc., it is represented by ci, j, etc. in association with the colorimetric region), and the vertical axis is the cyan output gradation value V'. As c, an example of the correspondence between input and output is shown. The solid line 31 is the cyan gradation correction curve (TRC) before correction, the broken line 30 is the TRC after correction, and the amount of change δc (vc) from the solid line 31 to the broken line 30 is the TRC correction amount.

By the TRC correction for each segment described above, even if the density fluctuation tendency differs depending on the pixel position in the main scanning direction as described in FIG. 4A, the TRC correction suitable for each segment is applied. Therefore, the density fluctuation between pages is properly corrected.

However, if the evaluation method of the colorimetric region as described above is used as it is, there remains a problem that the periodic fluctuation and the drift in the sub-scanning direction as described in FIG. 4B are not separated. In order to avoid this, it is necessary to understand the relationship between the phase of the main periodic fluctuations and the colorimetric region.

The period in which the same color measurement region is sampled and the phase of the period fluctuation in the main sub-scanning direction determined by the mechanical system can be adjusted to some extent by adjusting the space between the papers in FIG. 4B in advance. .. For example, when the fluctuation period of the maximum amplitude is 180 mm for all CMYK colors, the phase of the 90 ° density amplitude is shifted for each sampling by adjusting the paper spacing so that the sampling period of the same color measurement area is 270 mm. The color measurement value can be obtained.

Therefore, in this case, by buffering the colorimetric values between several pages and averaging the colorimetric values in the combined colorimetric area for each even page, the effect of the maximum periodic fluctuation on the colorimetric values Is excluded. Alternatively, when the paper spacing is adjusted so that the sampling period is 300 mm, a colorimetric value with a phase shift of 60 ° density amplitude can be obtained for each sampling, so the colorimetric value for each page that is a multiple of 3 can be obtained. It may be combined and averaged. Similarly, an adjustment that cancels out one periodic fluctuation by averaging the number of color-measured sheets to some extent is realized in combination with the adjustment of the paper spacing.

(Effect of gradation correction processing)
As described above, the image forming system of the embodiment has the imprinting performance in the main scanning direction when performing TRC control that minimizes the color difference from the target color based on the color measurement value of the output image. Good feedback control can be realized even when the fluctuation pattern varies, or when the fluctuation cycle in the sub-scanning direction and the sampling cycle interfere with each other. In addition, it is possible to realize control that keeps optimally approximating the target color given by the color profile while executing the print job.

Further, since the image forming system of the embodiment performs the color difference comparison in a region suitable for the color difference evaluation in advance, it is possible to prevent the inconvenience that the color difference evaluation value becomes unstable due to the image structure. Further, it is possible to prevent the inconvenience that tone jump occurs between the segments because the corrected TRC is remarkably deviated from the difference in the color range distributed in the extraction region depending on the segment. In particular, stable correction is possible even if there are segments with a small extraction area.

Further, since the image forming system of the embodiment can give priority to matching of segments close to each other, it is possible to perform matching between segments particularly suitable for a situation with high non-uniformity in the main scanning direction. In addition, it is possible to fine-tune the TRC according to the user's preference.

Further, the image forming system of the embodiment can stably control only gentle drift fluctuations without being interfered with by periodic fluctuations in the sub-scanning direction. Further, by acquiring the color profile from the server device, the reproduction color control can be flexibly performed even when the color reproduction characteristics differ remarkably depending on the print medium. The present invention is suitable for color management of image output devices such as printers, copiers, and printing machines.

(Output control operation)
Next, the output control operation in the image forming system of the embodiment will be described. FIG. 10 is a block diagram corresponding to an output control operation in the image forming system of the embodiment. As shown in FIG. 10, the inspection unit 5 shown in FIG. 1 reads and controls the inline scanner 80 so as to acquire an image of a printed matter (output paper) output from the printer engine 4 (reading control unit 81 ( It has an example of an acquisition unit). Further, the inspection unit 5 switches and controls the output switching mechanism 90 (an example of the switching mechanism) so as to switch the printed matter to the purge tray 91 or the output tray 92 based on the reading result of the inline scanner 80 and output the printed matter. It has a control unit 85. The tray switching control unit 85 is an example of a discriminating unit and a switching control unit.

Further, in FIG. 10, the TRC correction amount determination unit 19 includes a comparison color variation calculation unit 82, a correction curve calculation unit 83, and a master generation unit 84. The flowchart of FIG. 11 shows a simplified flow of the correction curve calculation operation of the TRC correction amount determination unit 19. In step S301, the reading control unit 81 reads and controls the in-line scanner 80 so as to acquire an image of the printed matter (output paper) output from the printer engine 4.

The master generation unit 84 stores a master image as a reference for gradation. In step S302, the comparative color variation calculation unit 82 compares the image read by the in-line scanner 80 with the master image stored in the master generation unit 84, and calculates the color variation amount (initial variation value). .. Then, in step S303, the correction curve calculation unit 83 calculates the correction curve based on the calculation result of the color variation, and sets it in the TRC correction amount determination unit 16 of the printer engine 4.

In other words, the TRC correction amount determining unit 19 has the target color targetLab, the measured value mesLab actually obtained from the image inspection unit 5 side, and the gradation correction unit 16 as described in the gradation correction operation described above. The TRC correction amount (δc, δm, δy, δk) is determined for each segment based on the prnCMYK which is the input value to and the engine information from the engine control unit 9, and the TRC correction of the printer engine 4 is performed. It is set in the amount determination unit 16. As a result, it is possible to realize control that keeps optimally approximating the target color given by the color profile.

In this example, the comparative color variation calculation unit 82 will be described as detecting the color variation between the image read by the inline scanner 80 and the master image stored in the master generation unit 84. In addition to color, appearance-related fluctuations other than color, such as "brightness" or "brightness", may be detected.

FIG. 12 is a flowchart showing the flow of the output control operation following the gradation correction operation. A print job until the printing of one or a plurality of sheets designated by the user is completed is regarded as one print job, and the process of the flowchart of FIG. 12 is executed for each print job.

The gradation correction operation described above and the output control operation described below are executed by the control unit 25 shown in FIG. 1 based on the gradation correction program stored in the storage unit 26. The processing of steps S401 to S405 of the flowchart of FIG. 12 is the same as the processing of steps S301 to S303 of the flowchart of FIG. First, the reading control unit 81 controls the in-line scanner 80 so as to read the image of the printed matter (output paper) output from the printer engine 4 (step S401).

The reading control unit 81 controls the in-line scanner 80 so as to read printed matter for a plurality of pages. The calculation of the color variation (initial variation value) described below is performed based on the image information of the printed matter for a plurality of pages.

Next, a master image that serves as a tone reference is stored in the master generation unit 84 that corresponds to a part of the storage area of the storage unit 26. The comparative color variation calculation unit 82 compares the image read by the in-line scanner 80 with the master image stored in the master generation unit 84, and calculates the color variation (initial variation value) (step S402, Step S403). Then, the correction curve calculation unit 83 calculates the gradation correction amount (correction curve) based on the calculation result of the color variation (step S404), and sends it to the TRC correction amount determination unit 16 of the printer engine 4 (step S405). ). As described above, this makes it possible to realize control that keeps optimally approximating the target color given by the color profile.

Next, in the tray switching control unit 85, the gradation of the image read by the inline scanner 80 is a gradation within a predetermined range based on the gradation of the master image stored in the master generation unit 84. Whether or not it is determined (step S406).

When the gradation of the image read by the in-line scanner 80 is within a predetermined range based on the gradation of the master image stored in the master generation unit 84, the tray switching control unit 85 sets the tray switching control unit 85. The output switching mechanism 90 is controlled so that the printed matter is output from the normal output tray 92 (step S407).

On the other hand, when the gradation of the image read by the inline scanner 80 is a gradation outside the predetermined range based on the gradation of the master image stored in the master generation unit 84, the tray is switched. The control unit 85 controls the output switching mechanism 90 so that the printed matter is discarded in the purge tray 91, which is a tray for disposal (step S408). The purge tray 91 may be provided close to the output tray 92, or may be provided as a tray for accumulating in the image forming apparatus 8 so that the paper is not discharged to the outside.

(Effect of output control)
In this way, the initial fluctuation of the printed matter to be printed first is measured, it is confirmed that the fluctuation is within the preset allowable value, and the gradation correction for correcting the fluctuation portion is performed, and then printing is performed. If the printed matter has a color variation within a set range of the initial variation, it is output to the output tray 92, and if the color variation is unacceptable, it is discarded in the purge tray 91. As a result, only the printed matter within the set color variation can be obtained (the printed matter having the appearance such as the color intended by the user can be obtained).

Then, the user can reproduce the color of the printed matter of the image forming apparatus 8. Since there is no choice but to visually recognize only the printed matter output from the output tray 92, and the color reproduction of the printed matter output from the output tray 92 can only be considered as the desired color reproduction, as a result, the color of the printed matter is confirmed. It is possible to eliminate the act of doing.

Further, such output control determines whether or not the color variation of the printed matter is within a predetermined range, and based on the determination result, the printed matter is switched to the purge tray 91 or the output tray 92 and output. As described above, it can be realized by a simple configuration in which the tray switching control unit 85 for switching and controlling the output switching mechanism 90 is provided.

Finally, the embodiments described above are presented as an example and are not intended to limit the scope of the invention. This novel embodiment can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the gist of the invention.

For example, in the description of the above-described embodiment, it is determined that each function of the read control unit 81 to the tray switching control unit 85 is realized by software based on the gradation correction program. However, all or part of the read control unit 81 to the tray switching control unit 85 may be realized by hardware such as an IC (Integrated Circuit).

That is, each of the above-mentioned functions can be realized by one or a plurality of processing circuits. A "processing circuit" is a processor programmed to perform each function by software, such as a processor implemented by an electronic circuit, or an ASIC (Application Specific Integrated Circuit) designed to execute each of the above-mentioned functions. , DSP (Digital Signal Processor), FPGA (Field Programmable Gate Array) or devices such as conventional circuit modules.

Further, the gradation correction program may be provided by recording the file information in an installable format or an executable format on a recording medium readable by a computer device such as a CD-ROM or a flexible disk (FD). Further, the gradation correction program may be provided by recording on a recording medium readable by a computer device such as a CD-R, a DVD (Digital Versatile Disk), a Blu-ray (registered trademark) disc, or a semiconductor memory. Further, the gradation correction program may be provided in the form of being installed via a network such as the Internet. Further, the gradation correction program may be provided by incorporating it into a ROM or the like in the device in advance.

Moreover, the embodiment and the modification of each embodiment are included in the scope and gist of the invention, and are included in the scope of the invention described in the claims and the equivalent scope thereof.

1 User PC
2 Network 3 Image processing unit 4 Printer engine 5 Image inspection unit 6 Output image 7 Server device 8 Image forming device 9 Engine control unit 10 Original color Lab conversion unit 11 LabCMYK conversion unit 12 User gradation conversion unit 13 CMYKLab conversion unit 14 Lab scanner Color conversion unit 15 Scanner color Lab conversion unit 16 Gradation correction unit 17 Gradation processing unit 18 Scanner color Lab conversion unit 19 TRC correction amount determination unit 25 Control unit 26 Storage unit 80 In-line scanner 81 Reading control unit 82 Comparison color fluctuation calculation unit 83 Correction curve calculation unit 84 Master generation unit 85 Tray switching control unit 90 Output switching mechanism 91 Purge tray 92 Output tray

Japanese Unexamined Patent Publication No. 2004-251996 Japanese Unexamined Patent Publication No. 2006-21401

Claims (13)

An acquisition unit that acquires image information of printed matter,
A discriminating unit that determines whether or not the fluctuation amount of the acquired image information with respect to the reference image information is within a predetermined fluctuation range.
A printing apparatus having an output control unit that controls output of printed matter when the fluctuation amount is within a predetermined fluctuation range, and discards and controls printed matter when the fluctuation amount is outside the predetermined fluctuation range. An output tray from which printed matter for output is output, and
A purge tray that outputs printed matter for disposal,
A switching mechanism for switching the printed matter to the output tray or the purge tray and outputting the printed matter is provided.
When the fluctuation amount is within the predetermined fluctuation range, the output control unit switches and controls the switching mechanism so as to output the printed matter to the output tray, and the fluctuation amount is outside the predetermined fluctuation range. The printing apparatus according to claim 1, wherein the switching mechanism is switched and controlled so as to output printed matter to the purge tray. A gradation correction unit that corrects the input gradation value of the image information requested for printing to the output gradation value based on the gradation correction curve,
An image forming unit that forms an image on a predetermined medium based on the corrected output gradation value,
Using the color measurement value of the image formed on the predetermined medium and the target color generated based on the image information, a plurality of main scanning directions orthogonal to the sub-scanning direction of the paper feed of the image forming unit are set. A determination unit for determining the correction amount of the gradation correction curve for each segment divided into segments is further provided.
The determination unit determines for each segment the correction amount that minimizes a predetermined evaluation function based on the colorimetric value and the target color.
The printing apparatus according to claim 1 or 2, wherein the gradation correction unit corrects the gradation correction curve for each segment according to the determined correction amount for each segment. The printing apparatus according to claim 3, wherein the predetermined evaluation function is weighted according to the segment. A measuring unit for measuring the colorimetric value of the image formed on the predetermined medium is further provided.
Claim 3 or claim 4 is characterized in that the measuring unit divides an image formed on the predetermined medium into a plurality of segments and measures a colorimetric value using a predetermined region in the divided segments as a measurement region. The printing apparatus described in. The printing apparatus according to any one of claims 3 to 5, further comprising a user gradation correction unit for fine adjustment by the user. By averaging the sample periods of the measurement region over a plurality of pages in the segment in opposite phases, an averaging unit that cancels out the main concentration period fluctuations that occur in the sub-scanning direction of the image forming unit is further added. The printing apparatus according to claim 5, wherein the printing apparatus is provided. A gradation correction unit that corrects the input gradation value of the image information requested for printing to the output gradation value based on the gradation correction curve,
An image printing unit that prints an image on a predetermined medium based on the corrected output gradation value,
An acquisition unit that acquires image information of printed matter on which an image is printed,
A discriminating unit that determines whether or not the fluctuation amount of the acquired image information with respect to the reference image information is within a predetermined fluctuation range.
A floor having an output control unit that controls the output of the printed matter when the fluctuation amount is within the predetermined fluctuation range, and discards the printed matter when the fluctuation amount is outside the predetermined fluctuation range. Key correction device. When the fluctuation amount is within a predetermined fluctuation range, the output control unit switches and controls a switching mechanism so as to output the printed matter to the output tray from which the printed matter for output is output, and the fluctuation amount is controlled. The gradation correction device according to claim 8, wherein the switching mechanism is switched and controlled so that the printed matter is output to the purge tray from which the printed matter for disposal is output when the fluctuation range is out of the predetermined fluctuation range. Computer,
A gradation correction unit that corrects the input gradation value of the image information requested for printing to the output gradation value based on the gradation correction curve,
An image printing unit that prints an image on a predetermined medium based on the corrected output gradation value,
An acquisition unit that acquires image information of printed matter on which an image is printed,
A discriminating unit that determines whether or not the fluctuation amount of the acquired image information with respect to the reference image information is within a predetermined fluctuation range.
When the fluctuation amount is within the predetermined fluctuation range, the printed matter is output-controlled, and when the fluctuation amount is outside the predetermined fluctuation range, the printed matter is to function as an output control unit for disposal control. A gradation correction program characterized by. When the fluctuation amount is within a predetermined fluctuation range, the output control unit switches and controls a switching mechanism so as to output the printed matter to the output tray from which the printed matter for output is output, and the fluctuation amount is controlled. The gradation correction program according to claim 10, wherein the switching mechanism is switched and controlled so that the printed matter is output to the purge tray from which the printed matter for disposal is output when the fluctuation range is out of the predetermined fluctuation range. A gradation correction step that corrects the input gradation value of the image information requested for printing to the output gradation value based on the gradation correction curve, and
An image printing unit that prints an image on a predetermined medium based on the corrected output gradation value,
The acquisition step to acquire the image information of the printed matter on which the image is printed, and
A determination step for determining whether or not the fluctuation amount of the acquired image information with respect to the reference image information is within a predetermined fluctuation range, and
When the fluctuation amount is within the predetermined fluctuation range, the output control of the printed matter is controlled, and when the fluctuation amount is outside the predetermined fluctuation range, the printed matter is discarded and controlled.
Gradation correction method having. In the output control step, when the fluctuation amount is within a predetermined fluctuation range, the switching mechanism is switched and controlled so that the printed matter is output to the output tray from which the printed matter for output is output, and the fluctuation amount is controlled. The gradation correction method according to claim 12, wherein the switching mechanism is switched and controlled so that the printed matter is output to the purge tray from which the printed matter for disposal is output when the fluctuation range is out of the predetermined fluctuation range.

Images