JP2016015675A - Color chart, image evaluation device, image evaluation method, and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color chart, image evaluation device, image evaluation method, and image forming apparatus with which unevenness in density in main scanning and a variation in density over time can be eliminated, and the number of prints of the color chart can be reduced, and thereby a time required for an adjustment process can be reduced and paper loss can be reduced.SOLUTION: There is provided a color chart 100 for measuring a plurality of color patches on the color chart 100 printed by an image forming apparatus 50 and detecting a variation in density over time of the image forming apparatus from differences from target colors and differences from past measurement results, where a patch column arranged in the sub scanning direction X is arranged shifted in the sub scanning direction X from a patch column adjacent in the main scanning direction Y by a preset amount of shift.

Description

  The present invention relates to a color chart, an image evaluation apparatus, an image evaluation method, and an image forming apparatus used in an image forming apparatus such as a copying machine, a printer, and a facsimile machine.

In recent years, image forming apparatuses such as copying machines, printers, and facsimiles form an unfixed toner image by an image forming process such as electrophotographic recording, electrostatic recording, and magnetic recording, and transfer this to a recording medium for fixing processing. Then, image formation is performed.
In such an image forming apparatus such as an electrophotographic system, a predetermined color chart is periodically printed and output in a main printing process for forming an image on a recording medium. Each color patch constituting the obtained color chart is measured, and main scanning density unevenness (density change in the main scanning direction Y) and temporal density fluctuation are calculated from the color measurement result constituting the image information to stabilize the image. Yes.
For example, an example of a program that functions as a parameter generation function unit that generates gradation correction parameters for correcting gradation values of image data by comparing gradation image reading data and gradation image data with a known reading value is patented It is disclosed in Document 1. Here, a patch row in which the gradation value of a single color gradually changes together with the gradation image data is arranged substantially in parallel with the main scanning direction Y, and this is used for mechanical density unevenness in the sub-scanning direction X. The effect is suppressed.

Further, Patent Document 2 discloses an example of an image forming apparatus in which a color measurement chart for measuring the color reproduction characteristics of the image forming apparatus is arranged in the sub-scanning direction X. The color measurement chart discloses a program that has control patches arranged in different phases on the same column, and thereby detects periodic color fluctuations.
Further, an example of an image processing apparatus and program for measuring color patches at a plurality of main scanning positions to form color charts in order to improve the correction accuracy of main scanning color unevenness correction in the image plane Is disclosed in Patent Document 3. Here, after generating conversion characteristics for correcting color unevenness at a plurality of main scanning positions, a color chart is formed with the output color obtained by the conversion characteristics, and the main scanning position is determined according to the color difference between the colorimetric value and the target color. Accordingly, the main scanning color unevenness is corrected, and this process is repeated until it becomes less than the allowable value.

  By the way, an image forming apparatus such as a printer or a copying machine forms an image in a certain direction (main scanning direction Y) on a recording medium (medium) that is an image forming target while forming an image in a line or a band shape, and a direction orthogonal to this ( By sending the recording medium in the sub-scanning direction X), a planar image is formed on the recording medium. At this time, in the sub-scanning direction X, periodic density fluctuations having a period of about several tens to several hundreds of millimeters occur due to eccentricity of shafts such as rollers and gears in the image forming apparatus.

Specifically, the photosensitive drum in a series of processes is usually positioned by strict management. However, a minute eccentricity as shown in FIG. This occurs (in FIG. 7A, it is exaggerated for explanation).
If the photosensitive drum 100k has the eccentricity as described above, a periodic variation occurs in a developing gap (not shown) generated between the opposingly arranged developing roller (not shown). This is one of the major factors of the periodic density fluctuation of the output image.
In the example of FIG. 7A, the leftmost axis intersection 67a and the rightmost axis intersection 67b of the displaced center axis 66k of the photosensitive drum 100k are opposite to the reference center axis 65k. The resulting density variation on the image is in antiphase at both ends of the image (with respect to the main scanning direction Y).

  In many cases, the photosensitive drum 100k is eccentric in the same direction with respect to the reference central axis 65k, and the density fluctuations at both ends of the image are often in the same phase. The phase of density fluctuation at both ends may be different. Further, as a finer eccentric mode, as shown in FIG. 7B, there is a bending mode in which the photosensitive drum 100k is slightly curved with respect to the central axis 65k. In this case, the distribution of the development gap in the main scanning direction Y (in the direction of the central axis 65k) at each rotational position is not linear, and therefore higher-order density unevenness occurs in the main scanning direction Y.

Further, in addition to this, density fluctuations with time occur due to environmental factors such as temperature and humidity, and changes with time in the state of color materials such as ink and toner.
Further, in the main scanning direction Y, a relatively stable main scanning density unevenness is caused mainly due to non-uniformity of the developing portion.
Since the main scanning density unevenness is relatively stable, it is desirable to make regular adjustments. For example, a predetermined color chart is printed in the previous process of the printing process, and correction information for each color and density is created in a plurality of main scanning areas along with the measured image information, and this is reflected in the printing process. Thus, the influence of the main scanning density unevenness is reduced. (An example of this is disclosed in Patent Document 3)

In addition, the density fluctuation over time is relatively stable in the range where the number of printed sheets is small, so this is also affected by measuring the characteristics in the previous process of the printing process and processing the image data to correct it. Can be reduced. For example, in Patent Document 1, a predetermined color chart including a plurality of gradations is printed, measured, and gradation correction parameters are generated.
Here, it is difficult to improve periodic density fluctuations by regular adjustment. Further, since the above-described main scanning density unevenness and temporal density fluctuation are superimposed as errors in the measurement process when adjusting this, there is a problem that the accuracy of adjustment is lowered. Therefore, for example, in Patent Document 2, in order to reduce the influence of periodic density fluctuations superimposed on the color chart, a plurality of patch rows arranged in different phases are provided in the sub-scanning direction X of the color chart. Is disclosed.

However, since any color chart is discarded as waste paper after measurement, there is a need to reduce the number of printed color charts in order to reduce the environmental burden. For this purpose, it is necessary to arrange as many color patches as possible on one sheet of paper. However, the size of each color patch is determined to be the minimum size corresponding to the color measuring device used in the measurement process, and thereby the minimum value of the arrangement pitch of the color patches is also determined. Generally, the minimum value of the color patch size is about 5 to 10 mm in consideration of the influence of halftone screening of a printed image.
On the other hand, the number of colors to be included in the color chart is that cyan (C), magenta (M), yellow (Y), and black (K) color patches having a plurality of gradations are arranged in a plurality of main scanning areas. It is necessary to put in.
Further, in order to reduce the influence of periodic density fluctuations, a plurality of color patches having the same color and density are arranged in different positions in the sub-scanning direction X in the plurality of main scanning areas, and this effect is obtained by using an averaging effect. Reduce.

Here, as disclosed in Patent Document 2, when an integer multiple of the period of the above-described periodic density fluctuation and an integer multiple of the arrangement pitch of the color patches on the color chart are close to each other, In some cases, it becomes impossible to distinguish by sampling), and error reduction due to the averaging effect may not work well. Since the period and magnitude of the periodic density fluctuation (color fluctuation) depend on the image forming apparatus, the period that appears is different for each model or individual. For this reason, the arrangement pitch of the color charts corresponding to all image forming apparatuses cannot be uniquely determined. Further, when the color patch arrangement pitch of the color chart is increased in order to reduce the influence of aliasing, the number of color patches arranged on one color chart is reduced.
The present invention reduces the influence of periodic density fluctuations in measuring main scanning density unevenness and temporal density fluctuations, while reducing the number of printed color charts used for this purpose, thereby reducing the time and loss of the adjustment process. It is an object to provide a color chart, an image evaluation apparatus, an image evaluation method, and an image forming apparatus that can reduce paper.

  In order to solve the above-described problem, a color chart according to claim 1 of the present invention measures a plurality of color patches on a color chart printed by an image forming apparatus, and measures a difference from a target color or a past measurement. A color chart for detecting density variation with time of the image forming apparatus from the difference from the result, and patch rows arranged in the sub-scanning direction X are set in advance from patch rows adjacent in the main scanning direction Y. It is characterized by being displaced in the sub-scanning direction X by the amount of deviation.

  According to the present invention, periodic density fluctuations in the sub-scanning direction (temporal density fluctuations) and aliasing are avoided, and a sufficient averaging effect is obtained, so that the influence of periodic density fluctuations can be reduced, and color By measuring the color of the color patch on the chart, it is possible to detect the density variation with time of the image forming apparatus with high accuracy.

It is a block diagram which shows the example of the color chart which concerns on one Embodiment of this invention. It is a schematic sectional drawing of the image forming apparatus which prints the color chart shown in FIG. 1, and performs image evaluation. FIG. 2 is a schematic diagram illustrating a network connection configuration including the image forming apparatus illustrated in FIG. 1. FIG. 2 is a schematic block diagram of image processing performed by a management PC deployed in a network including the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a flow of image processing performed by a management PC deployed in a network including the image forming apparatus illustrated in FIG. 1. 3 is a flowchart of an image evaluation control process performed by a management PC deployed in a network including the image forming apparatus illustrated in FIG. 1. It is a perspective view of the photoconductive drum as a reference example, (a) is eccentric explanatory drawing, (b) is curved explanatory drawing.

  Next, an embodiment according to the present invention will be described with reference to the drawings. Note that, in each drawing and each embodiment, the same member or a member having the same function is basically denoted by the same reference numeral, and redundant description is appropriately omitted.

In this embodiment, the color chart printed by the electrophotographic image forming apparatus has the following characteristics. In short, the patch rows arranged in the sub-scanning direction X of the color chart are shifted from the patch rows adjacent in the main scanning direction Y by a shift amount specified in the sub-scanning direction X. This makes it possible to change the interval between a plurality of apparent color patches having the same color and density without reducing the number of patches. Further, it is possible to provide a color chart that can reduce the influence of main scanning density unevenness (periodic density fluctuation), measure the color patch color on the color chart with high accuracy, and detect the density fluctuation with time of the image forming apparatus. It is.
Here, the color chart of FIG. 1 (first embodiment) and the image forming apparatus (fourth embodiment) for printing the color chart will be described in order. In addition, an image evaluation apparatus that is a functional unit of the management PC 41 used in a network (system configuration) including the image forming apparatus, and an image evaluation method performed therein will be described as second and third embodiments.

First, a color chart (first embodiment) printed on a paper Sp for use in detection of a change in density over time of an image forming apparatus (fourth embodiment) 50 described later will be described.
FIG. 1 is a schematic diagram of a color chart 100 according to the first embodiment.
A plurality of color patches are arranged on the color chart 100 and function as colorimetric patches. Here, a plurality of patch rows arranged in the conveyance direction of the paper Sp is referred to as a patch row in the sub-scanning direction X. The scanning direction of the laser beam 7 orthogonal to the transport direction of the paper Sp is the main scanning direction Y, and an area including a plurality of patch rows is called a main scanning area.
Next, display characteristics of the color chart 100 according to the first embodiment will be described.
In the first embodiment, in the sub-scanning direction X, 16 color patches with a width of 10 mm are arranged with an interval of 2 mm for 210 mm of A4 short. Although the lower side of the figure is omitted in the main scanning direction Y, 24 color patches having a width of 10 mm are arranged at an interval of 2 mm with respect to 297 mm of A4 length. In addition, one main scanning area is constituted by four patch rows. Therefore, the color chart 100 has a total of six main scanning areas.

The symbols described in each color patch indicate color patch areas of “C” for cyan, “M” for magenta, “Y” for yellow, and “K” for black. Further, the subscripts “1” to “4” in the color patch are the number of shade steps, which indicate gradation, and are divided into four steps here. Here, “1” indicates a color patch having a first density of 100%, “2” indicates a second density of 70%, “3” indicates a third density of 40%, and “4” indicates a fourth density of 20%.
The density and the number of densities of each color patch included in the color chart (first embodiment) 100 illustrated in FIG. 1 are described as an example, but the density and the number of densities of each color patch are not limited thereto.
That is, any density and number of densities may be used according to the characteristics of the image forming apparatus using the color chart 100 and the density to be managed.
Further, the size of the color chart 100, the size of the color patches, and the number of color patches in the patch row are not limited to the numerical values of the color chart (first embodiment) 100 shown in FIG. For example, when a paper having a large size in the sub-scanning direction X is used, for example, the size of the color chart is A3 paper, the number of color charts that can be placed in each patch row can be increased. Furthermore, the number of color charts that can be placed in each patch row can also be increased by reducing the size of the color patch within a colorimetric range. In this case, for example, variations in the density of the same color may be increased. Arbitrary color patches such as mixed colors may be added.

Next, the misalignment characteristics of the color chart 100 according to the first embodiment will be described.
In the color chart (first embodiment) 100 shown in FIG. 1, all types (four colors) of colors to be measured are included in each patch row.
Each patch array arranged in the sub-scanning direction X is shifted from the patch array adjacent in the main-scanning direction Y (adjacent to each other) in the sub-scanning direction X by a predetermined shift amount δ. ing.
Accordingly, there are four color patches of the same color and density in the main scanning region (in FIG. 1) composed of four patch rows, and the average value is calculated to obtain a periodic pattern in the sub-scanning direction X. To reduce the effects of various density fluctuations.

Here, in the color chart (first embodiment) 100 shown in FIG. 1, it has been described that all kinds of colors to be measured are included in one patch row, but the present invention is not limited to this.
Further, the order described in the first embodiment is not limited. What is important is that each main scanning area includes a plurality of color patches having the same color and the same density, and these patches are distributed substantially evenly in the sub-scanning direction X, so that the influence of periodic density fluctuations is obtained by the averaging effect. It is arranged to reduce.
For example, even if the arrangement of the color patches in one patch row is set at random, a plurality of color patches of the same color and the same density are arranged substantially uniformly in the sub-scanning direction X within one main scanning region. It only has to be. In addition, here, each patch row is characterized by being shifted in the sub-scanning direction X with respect to the adjacent patch row.

In consideration of the fact that the printing range in the sub-scanning direction X of the color chart 100 is limited due to the paper Sp and the image forming apparatus, the shift amount δ is preferably smaller than the color patch arrangement pitch. Here, the shift amount δ is set to 3 mm.
In the color chart 100 shown in FIG. 1, since a shift amount δ is given to a plurality of patch rows, the accumulated amount exceeds the print range in the sub-scanning direction X (for example, exceeds the area of the four patch rows that are the main operation areas). ) Wrap each time. It is desirable that the color patch that exceeds the printing range is folded in the sub-scanning direction X and moved to the opposite side. In particular, it is desirable to turn back when the accumulated shift amount exceeds the color patch arrangement pitch. Thereby, the decrease in the number of color patches on the color chart can be minimized.

Specifically, in the color chart 100 shown in FIG. 1, when attention is paid to the interval p1 in the sub-scanning direction X of four “C1” patches with 100% cyan, they are 51 (= 40 + 8 + 3), 51, and 51 mm, respectively. Here, it is assumed that the color patches in FIG. 1 are arranged with a width of 10 mm in the sub-scanning direction X and an interval of each color patch in the sub-scanning direction X of 2 mm. Here, if there is no deviation amount, the intervals p0 in the sub-scanning direction X of the four patches are 48 (= 40 + 8), 48, and 48 mm, respectively, so that the apparent pitch is increased by 3 mm here. . In addition, the interval p2 of the “M1” patch is 39 (= 30 + 6 + 3), and the interval “p1” of the “M1” patch is 51 and 51 mm, which is an unequal interval. Has changed.
Therefore, by arranging each patch row so as to be shifted from the adjacent patch row in the sub-scanning direction X, the apparent arrangement interval of patches of the same color and density can be changed without changing the basic arrangement pitch. be able to.
As a result, aliasing with periodic density fluctuations in the sub-scanning direction X caused by the image forming apparatus is avoided, and this influence is reduced by the averaging effect, and then main scanning density unevenness and temporal density fluctuations are obtained. Thus, the state of the image forming apparatus can be grasped.
According to the color chart of the first embodiment, the patch row arranged in the sub-scanning direction X of the color chart 100 is shifted from the patch row adjacent in the main scanning direction Y by the shift amount specified in the sub-scanning direction X. Deploy.
Thus, by changing the patch arrangement pitch on the color chart, it is possible to change the interval between a plurality of apparent color patches having the same color and density without reducing the number of patches.
For this reason, occurrence of periodic density fluctuations and aliasing in the sub-scanning direction X is avoided, and a sufficient averaging effect is obtained. In addition, the influence of periodic density fluctuations can be reduced, and the color patch color on the color chart is measured with high accuracy, so that the temporal density fluctuations of the image forming apparatus can be detected with high precision.
In addition, by reducing the number of printed color charts, the overall printing time can be reduced and the environmental load can be reduced.

Next, an image forming apparatus 50 (fourth embodiment) for printing the color chart 100 and a network (system configuration) including the image forming apparatus 50 will be described prior to the second and third embodiments.
The image forming apparatus 50 (fourth embodiment) shown in FIG. 2 is connected to the network 43 via the management PC 41 as shown in FIG.
The management PC 41 also functions as an image processing apparatus and an image evaluation apparatus. The document data sent from another user's PC 40 connected to the same network 43 is subjected to a predetermined image processing process, and then image formation is performed. Transfer to device 50. The management PC 41 is connected with a color measurement device 42 as a color measurement means used for calibration of gradation characteristics of the image forming apparatus 50 and measurement of color reproduction characteristics. Here, calibration refers to measuring the deviation of the device using a standard device or the like, or adjusting it to a correct value in order to obtain a standard value with a measuring device.

Next, the developing unit 60k included in the image forming apparatus 50 that is a laser printer will be described with reference to FIG.
The photosensitive drum 1k included in the developing unit 60k rotates in the direction of arrow A in FIG. On the other hand, the charger 52 first applies a uniform charge to the surface of the photosensitive drum 1k cleaned by the cleaning roller 51. Next, the laser beam 7 emitted from the laser unit 53 scans the surface of the photosensitive drum 1k while blinking in accordance with a signal from the exposure control device 10, thereby forming an electrostatic latent image on the photosensitive drum 1k.
The scanning direction of the laser beam 7 at this time is the main scanning direction Y, and the rotation direction A of the photosensitive drum 1k is the sub-scanning direction X.

  The formed electrostatic latent image is developed with 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 configuration of the developing units 60c, 60m, and 60y is the same. Cyan (C), magenta (M), and yellow (Y) toner images are formed and transferred onto the intermediate transfer belt 61 in succession.

The transfer roller 55 collectively transfers the C, M, Y, and K toner images superimposed on the intermediate transfer belt 61 onto the continuous paper 59 supplied from the paper feed stacker 57, and the fixing device 56 heat-presses the toner images. To fix it on the paper surface. The paper on which the image is formed by the above image forming process is discharged to the lower paper discharge stacker 58.
Here, in the image forming apparatus 50 of the present embodiment, a color measuring device 42, a paper discharge branch device 81, and an upper paper discharge stacker 82 are added between the fixing device 56 and the lower paper discharge stacker 58.
The image forming apparatus 50 receives the image information of the color chart 100 in which the sub-scanning position of the patch row generated by the management PC 41 is shifted as will be described later, generates the color chart 100 on the paper Sp, and outputs the lower sheet stacker. 58.
The recording medium sheet that has passed through the fixing device 56 of the image forming apparatus 50 is colorimetrically measured by the colorimetric device 42 for all the color patches of the color chart 100.

  Specifically, the color measuring device 42 is a device in which a plurality of color measuring devices are arranged in the main scanning direction Y. The color measuring devices 42 are arranged in at least the number of color patches on the color chart 100. While the paper facing the color measurement device 42 is conveyed, each color measurement device 42 performs color measurement a plurality of times at a predetermined interval, and based on the coordinate information of each color patch of the color chart output from the management PC 41 described above. The color measurement results of all color patches on the color chart 100 are output. This is sent to the management PC 41.

The color chart 100 that has passed through the color measuring device 42 is separated by the paper discharge branch device 81 from the color chart and other printed matter, and only the color chart is conveyed to the upper paper discharge stacker 82 that is the second paper discharge stacker. Printed materials other than, are discharged to a paper discharge stacker 58. Here, the discharge branching device 81 and the upper discharge stacker 82 are not essential, and the operator may separate the color chart from the discharge stacker 58. Further, the paper discharge branching device 81 may be disposed between the image forming apparatus 50 and the color measurement device 42, and the function is achieved by finally measuring the color chart with the color measurement device 42.
When the management PC 41 (see PC in FIG. 4) receives the measurement result from the color measurement device 42, the management PC 41 calculates an average color of a plurality of same color / same color patches in various scanning regions, and sets a target color for each preset color patch. Compare with

Furthermore, it compares with the measured color of each color patch measured in the past and stored in advance. Then, the comparison result is presented to the operator.
Here, more preferably, for all the color patches compared, if the difference between the measured average color and the target color or the past measured color exceeds a preset range, the operator performs an adjustment process. Preferably. For the adjustment step, various methods generally known as color calibration can be used.

Here, the detection of the temporal density fluctuation of the image forming apparatus 50 using the color chart 100 described above is performed periodically during printing when the number of printed sheets is large, so that the temporal fluctuation during printing can be accurately evaluated. . If this exceeds a preset range, the operator may be notified of this. It is more preferable that the operator interrupts the printing process as necessary and performs the adjustment process to generate a large amount of printed matter having a color deviated from a predetermined color, so that these are not discarded.
According to the image forming apparatus 50 according to the fourth embodiment, it is possible to automatically detect a change in density over time based on the image evaluation method described in the third embodiment before and during the printing process. As a result, it is possible to cope with the adjustment process by interrupting printing as necessary, and it is possible to reduce the printing time as a whole and to reduce waste paper, which is industrially suitable.

Next, an image evaluation apparatus (second embodiment) which is a functional unit included in a network (system configuration) including the image forming apparatus 50 and the management PC 41 will be described with reference to FIGS.
The image evaluation apparatus includes a color chart 100 printed by the image forming apparatus 50, a chart generation unit 110 that distributes and forms color patches in a planar shape, a color measurement device 42 that performs color measurement of the color patches, and a color patch. A chart comparison unit 120 that presents a comparison result between the average value and the target color is provided.
Here, the color chart (first embodiment) 100 is printed in order to detect a change in density over time of the image forming apparatus 50.

The chart generation unit 110 is a functional unit of the management PC 41, and takes in a deviation amount δ (see FIG. 1) according to an instruction from the operator as image information of the color chart 100. Based on the shift amount δ, the patch rows arranged in the sub-scanning direction X are generated so as to be shifted in the sub-scanning direction X with respect to the patch rows adjacent in the main scanning direction Y.
A color measurement device 42 as color measurement means is connected to the management PC 41 and performs color measurement of a plurality of color patches on the color chart based on the image information of the color chart printed by the image forming apparatus 50.
The chart comparison unit 120 is a functional unit of the management PC 41 and presents an operator with a comparison result between an average value of a plurality of color patches and a target color.

Next, a specific flow of image processing in the image evaluation apparatus is shown in FIG.
The image processing process is roughly divided into bits that are an array of color gradation values (usually 8-bit integer values from 0 to 255) for four sides of C, M, Y, and K of the document data 11 by the user. A first image processing unit 46 that develops a map and a second image processing unit are included. Here, the second image processing unit includes a chart generation unit 110 that converts a bitmap of each surface of CMYK into a gradation expression format that can be expressed by the image forming apparatus 50.

In the first image processing unit 46, first, the document data 11 including content such as fonts, line drawings, and bitmaps is converted by the image development unit 12 into CMYK or RGB 8-bit colors of a specific resolution (for example, 1200 dpi). Expands to bitmap data.
With respect to this bitmap data, the color correction unit 13 includes color reproduction characteristic data 16 describing color reproduction characteristics as a device in which the chart generation unit 110 which is the second image processing unit in the subsequent stage and the image forming apparatus 50 are combined. Based on the target color characteristic data 27, the following calculation is performed. Here, target color characteristic data 27 describing color reproduction characteristics of a target color as an output target, such as sRGB (IEC 61966-2-1) or Japan Color according to ISO / TC 130, is used. In order to reproduce the RGB or CMYK data of the input value into an appropriate color through the chart generation unit 110 and the image forming apparatus 50 as the second image processing unit at the subsequent stage based on the target color characteristic data 27 as described above. To CMYK data.

  The target color characteristic data 27 and the color reproduction characteristic data 16 at this time are set to the data format of the ICC profile format by the International Color Consortium. Thereby, as the color correction part 13, the color management module according to the same standard can be used.

  In the chart generation unit 110 that is the subsequent second image processing unit, the colorimetric correction unit (chart correction unit) 14 uses the chart data c, m, y, and k of CMYK of 8 bits per pixel. Further, here, the density gradation characteristics of each color of CMYK of the color chart (image) output from the image forming apparatus 50 through the processing after the color measurement processing unit (chart processing unit) 15 in the subsequent stage are used. Thus, the colorimetric correction data 17 which is correction data of predetermined chart information (target color, gradation information corresponding to the past measurement color) is corrected.

  Next, the colorimetric processing unit 15 reproduces the pixel density of each color on the color chart on which the chart data c, m, y, and k, which are the CMYK gradation values corrected by the colorimetric correction unit 14, are formed. For conversion. For example, when the image forming apparatus has a gradation of 1200 dpi and 2 bits per pixel (4 levels including a white background), it is assumed that one halftone dot is formed by 6 × 6 pixels. Further, by making four halftone dots as a set and growing the halftone dots cyclically between them, the gradation is expressed by the area ratio of one color patch.

Next, the chart image information (CMYK signal) converted into a 2-bit signal for each pixel through the chart generation unit 110 serving as the second image processing unit is exposed to C, M, Y, and K in the image forming apparatus 50. It is sent to the control device 10 (see FIG. 2). Then, the image is reproduced as an image on the paper Sp through an image forming process described later.
Next, the flow of color measurement correction data (gradation correction data), which is the color measurement result indicated by the dashed arrow in FIG. 5, will be described.
Here, the color measurement device 42 detects the density measurement value from the color chart 100 (see FIG. 1) in which each CMYK single color gradation patch is arranged, and this color measurement correction data (tone correction data) is the color measurement correction. The data is input to a data generation unit (gradation correction data generation unit) 18.

The color measurement correction data generation unit 18 compares the measured color measurement correction data (tone correction data) with predetermined color measurement correction data.
Based on the comparison result, the color measurement correction data (gradation correction data) is set so that the gradation characteristics of the image forming apparatus 50 after the chart generation section 110 as the second image processing section become the predetermined gradation characteristics. 17 is generated.

Next, in the construction of the color reproduction characteristic data 16, first, the colorimetric correction data (tone correction data) 17 obtained by the colorimetric correction data generation unit 18 in the previous process is set. Then, the color correction unit 13 is bypassed, and the color reproduction estimation unit 37 is constructed from the measurement values of the color measurement device 42 for the color chart 100 described later.
The color reproduction data generation unit 19 uses this color reproduction estimation unit 37 to generate color reproduction characteristic data 16 as a characteristic of the image forming apparatus 50 after the chart generation unit 110 that is the second image processing unit. It will be.
According to the image evaluation apparatus of the second embodiment, the color corresponding to the period of the periodic density fluctuation due to the model of the image forming apparatus 50 and individual differences, and avoiding aliasing with the period of the periodic density fluctuation. A chart can be generated. Therefore, the above effect can be obtained without depending on the model and individual of the image forming apparatus 50.

Next, an image evaluation control routine shown in FIG. 6 is referred to as an image evaluation method (third embodiment), which is a flow of control procedures over time performed by the image evaluation apparatus in the network including the image forming apparatus 50 and the management PC 41. It explains together.
In this image evaluation method, an operator (not shown) designates the aforementioned shift amount δ to the management PC 41 via a display, a mouse, a keyboard, etc. (step s1). Based on the designated deviation amount δ, image information of the color chart 100 described in the first embodiment is generated (step s2), and this is sent to the image forming apparatus 50 which is a printer. When the chart image information is sent to the image forming apparatus 50 (printer), the image forming apparatus 50 actually prints the color chart 100 (step s4).

Next, the color chart 100 printed on the paper is sent to the color measuring device 42 and set in a predetermined place.
Further, the management PC 41 sends measurement position information including the coordinates of each color patch on the color chart to the color measurement device 42 (step s3). The color measurement device 42 measures the colors of all the color patches on the color chart based on the measurement position information, and sends the measurement results to the management PC 41 (step s5).
Then, the management PC 41 obtains measurement results of a plurality of color patches having the same color and density in various scanning regions (step s6). From this, the average color patch color of each main scanning region, each color and each density is calculated.

  Next, each color patch average color is compared with a preset target color of each color and density, and the result is presented to the operator (step s7). Alternatively, it may be compared with each main scanning region color patch average value, which is a measurement result when the same measurement is performed in the past, and the result may be presented to the operator. Furthermore, when these comparison results exceed a predetermined range set in advance, it is even better to present them.

As a result, the operator sets (updates) a deviation amount δ such that the color patch array pitch of the color chart 100 and the periodic density fluctuation of the printer do not cause aliasing corresponding to each printer. Is generated. Furthermore, since the color chart color is evaluated based on this, it is possible to perform appropriate evaluation for each printer. In response to this evaluation result, existing color calibration is performed if necessary.
Here, when there are a plurality of printers capable of printing, the aforementioned shift amount δ corresponding to each printer is set and stored in advance. Therefore, the printer may be converted into a corresponding shift amount in the management PC 41 by selecting a printer to be output by the operator, thereby generating color chart image information.

  According to the image evaluation method according to the third embodiment, as in the second embodiment, it corresponds to the period of the periodic density fluctuation due to the model of the image forming apparatus 50 and individual differences, and the period of the periodic density fluctuation. A color chart that avoids aliasing can be generated. Therefore, the above effect can be obtained without depending on the model and individual of the image forming apparatus 50.

The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.
For example, the color chart to which the present invention is applied is printed in an image forming apparatus as a color printer, but is not limited to the above-described type of image forming apparatus, and may be another type of image forming apparatus. In addition, the image forming apparatus to which the present invention is applied may be a copier, a facsimile machine, or a multi-function machine having a plurality of these mechanisms. In addition, the image forming apparatus to which the present invention is applied may be an image forming apparatus used for forming an electric circuit or an image forming apparatus used for forming a predetermined image in the biotechnology field. The effects described in the embodiments of the present invention only list the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention. Absent.

16 color reproduction characteristic data 17 Colorimetric correction data (tone correction data)
18 Colorimetric correction data generation unit (tone correction data generation unit)
19 Color reproduction data generation unit 42 Color measurement device 50 Image forming device 100 Color chart 110 Chart generation unit 120 Chart comparison means X Sub-scanning direction Y Main-scanning direction

JP 2010-283687 A JP 2011-87285 A JP 2012-186712 A

Claims (4)

This is a color chart for measuring a plurality of color patches on a color chart printed by an image forming apparatus and detecting a change in density over time of the image forming apparatus from a difference from a target color or a difference from a past measurement result. And
7 is a color chart in which patch rows arranged in the sub-scanning direction are shifted from a patch row adjacent in the main scanning direction by a preset shift amount in the sub-scanning direction. A color chart printed to detect density fluctuations of the image forming apparatus over time;
Based on the shift amount of the color chart image information according to an instruction from the operator, the patch row arranged in the sub-scanning direction is generated so as to be shifted in the sub-scanning direction with respect to the patch row adjacent in the main scanning direction. Chart generating means for
Based on the image information of the color chart, color measuring means for measuring colors of a plurality of color patches on the color chart;
An average value of a plurality of color patches having the same color and the same density is obtained from the color measurement result, the average value is compared with a preset target color or a past measurement result, and this is presented to the operator. An image evaluation apparatus provided with a chart comparison means. An image evaluation method for detecting a change in density over time of an image forming apparatus from a printed color chart,
A chart generation step for generating a color chart in which patch rows arranged in the sub-scanning direction are shifted in the sub-scanning direction with respect to patch rows adjacent in the main-scanning direction, based on a shift amount according to an instruction from an operator When,
A printing step of printing the color chart generated in the chart generation step with the image forming apparatus;
A colorimetry process for measuring a plurality of color patches on a printed color chart;
Chart comparison process that calculates the average of multiple color patches of the same color and density from the multiple measurement results measured in the color measurement process, and compares this with the preset target color or past measurement results An image evaluation method comprising: Based on the shift amount according to an instruction from the operator, color chart image information is generated in which patch rows arranged in the sub-scanning direction are shifted in the sub-scanning direction with respect to patch rows adjacent in the main scanning direction. Chart generating means;
An image forming unit that prints a color chart based on image information of the color chart; a colorimetric unit that performs colorimetry of a plurality of color patches on the color chart;
An average value of a plurality of color patches having the same color and the same density is obtained from the color measurement result, the average value is compared with a preset target color or a past measurement result, and this is presented to the operator. An image forming apparatus provided with a chart comparing means.

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