JP2005210432A - Apparatus, method, and program for correcting color unevenness - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus, a method, and a program for easily correcting color unevenness in a printed image surface by an image forming apparatus. <P>SOLUTION: The color unevenness correcting apparatus 10 corrects the color unevenness of a printed image to be formed on a sheet of paper by an image forming apparatus 20 on the basis of original image data. The apparatus 10 has a storage unit 120 for storing data for correction; a means for acquiring original image data; and a control unit 100 for automatically selecting a reference color used for color unevenness correction on the basis of the original image data, selecting data for correcting a color same as or most approximating to the automatically selected reference color from a storage unit 120, and changing the image forming conditions of the apparatus 20 on the basis of the selected data for correction. In the apparatus 10, the data for correction are calculated on the basis of color information of a printing image for correction and formed on a sheet of paper by the apparatus 20 on the basis of the original data for correction, and formed into a database. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color unevenness correction device, a color unevenness correction method, and a color unevenness correction program for a printing result image formed on a sheet by an image forming apparatus.

  In general, the quality of a printed image formed on a sheet by an image forming apparatus such as a printing machine, a printer, or a copier is determined by visual inspection by a human. In particular, in the case of color printing, visual inspection is performed for colors determined by superimposing primary colors such as yellow (Y), cyan (C), and magenta (M) by comparison with reference products. By this visual inspection, color unevenness in the printed surface is determined, and the color is adjusted by adjusting the image forming conditions in the image forming apparatus.

On the other hand, a method of automatically inspecting color unevenness is also known. For example, an image of a print result is read by a CCD sensor or the like, and red (R), green (G), and blue (B) image signals are obtained as color signals for each pixel. It is converted to a color space in the CIEL ^* a ^* b ^* system recommended by the International Lighting Commission). Then, using the color difference value ΔE ^* ab in the CIE L ^* a ^* b ^* color space, color deviation from the reference product, in-plane color unevenness, etc. are evaluated, and the evaluation results are fed back to the image inspection apparatus. Adjust the color.

  However, in actual color inspections, there are parts that humans easily perceive color deviation according to the pattern of the printed material, that is, parts that are important, and parts that humans hardly perceive color deviation, that is, parts that are not important. To do. However, in the conventional color determination method, the difference in the importance of the region is not taken into consideration, and the color determination suitable for human sense cannot be performed.

  For example, Japanese Patent Laid-Open No. 6-160298 (Patent Document 1) emphasizes a stepwise difference in color quantitatively in automatic color determination and is important in an inspection for each local region of a printing surface. For the purpose of making a determination close to human visual determination, a multi-stage comprehensive evaluation determination result by a visual inspector is input, and color difference values are measured for a plurality of color regions in the printing surface, A weight for each color region is calculated, and a quantitative value for each multistage evaluation is calculated. At the time of inspection, the evaluation value of the color as the inspection target printed matter is calculated by using the information on the important place and the degree of importance. It is disclosed that the quality of a printed matter is determined by comparing the result with a threshold value determined according to a quantitative value for multistage evaluation.

JP-A-6-160298

  However, in the method described in Patent Document 1, it is determined whether each area is regarded as important for each of a large number of local areas included in the printing surface, or is not considered important. It is necessary to set. This setting value has to be changed for each color, which makes the setting operation very complicated and problematic.

  The present invention provides a color unevenness correction apparatus, a color unevenness correction method, and a color unevenness correction program that can easily correct color unevenness of a print result image formed on a sheet by an image forming apparatus.

  The present invention relates to a color unevenness correction device that corrects color unevenness of a printed image formed on a sheet based on original image data by an image forming apparatus, the storage unit storing correction data, and the original image data. And a reference color used for color unevenness correction based on the original image data is automatically selected, and correction data of a color that is the same as or closest to the automatically selected reference color is obtained. Control means for selecting from the storage means and changing image forming conditions of the image forming apparatus based on the selected correction data, and the correction data is based on the correction original data. A calculation is made based on the color information of the correction print image formed on the sheet by the image forming apparatus, and the database is created.

  In the color unevenness correction apparatus, it is preferable that the correction document data includes a plurality of color patterns.

  In the color unevenness correction apparatus, it is preferable that the color pattern includes at least one color selected from yellow, magenta, cyan, and black.

  In the color unevenness correction apparatus, it is preferable that the color pattern is a color obtained by superposing at least two colors selected from yellow, magenta, cyan, and black.

  In the color unevenness correction apparatus, it is preferable that the color pattern includes a belt-like pattern having a uniform color in the main scanning direction of the image forming apparatus.

  Further, in the color unevenness correction apparatus, the control means sets a size and a shape in advance, detects a region in which the region of the set size and shape is a uniform color in the inspection image data, and the same It is preferable to select a color having the largest number of regions having colors as the reference color.

  Further, in the color unevenness correction apparatus, the control means detects a region having the largest area of a single region having a uniform color included in the inspection image data, and selects the color of the region as the reference color It is preferable to do.

  In the color unevenness correction apparatus, it is preferable that the control unit detects a total area of regions having the same color included in the inspection image data and selects the color of the region as the reference color. .

  According to another aspect of the present invention, there is provided a color unevenness correction device that corrects color unevenness of a print image formed on a sheet based on original image data by an image forming apparatus, the storage means storing correction data, and the original Means for acquiring image data; means for acquiring inspection image data read from a reference print image formed on a sheet by the image forming apparatus based on the original image data; and the original image data and the inspection image data. Based on this, a reference color to be used for color unevenness correction is automatically selected, correction data for a color that is the same as or closest to the automatically selected reference color is selected from the storage means, and the selected color is selected. Control means for changing the image forming conditions of the image forming apparatus based on the correction data, and the correction data is formed based on the correction original data. Formed on the sheet by location, is calculated based on the color information of the correction print image, are database.

Further, in the color unevenness correction apparatus, the control unit sets a certain region in the inspection image data as a region of interest, and calculates an L ^* a ^* b ^* color space of a region corresponding to the region of interest in the document image data. It is preferable to select a color having the largest color difference as the reference color. .

  In the color unevenness correction apparatus, the image forming apparatus is preferably an electrophotographic image forming apparatus.

  According to another aspect of the present invention, there is provided a color unevenness correction method for correcting color unevenness of a printed image formed on a sheet based on original image data by an image forming apparatus, the step of acquiring the original image data, and a control unit A reference color selection step for automatically selecting a reference color to be used for color unevenness correction based on the document image data, and a controller for correcting a color that is the same as or closest to the selected reference color A correction data selecting step for selecting data from the storage unit, and a control unit changing the image forming conditions of the image forming apparatus based on the selected correction data, wherein the correction data is Based on the color data of the correction print image formed on the paper by the image forming apparatus based on the correction original data, the calculation is made into a database.

  According to another aspect of the present invention, there is provided a color unevenness correction method for correcting color unevenness of a print image formed on a sheet based on original image data by an image forming apparatus, wherein the control unit acquires the original image data. A control unit acquiring inspection image data read from a reference print image formed on a sheet by the image forming apparatus based on the original image data; and a control unit acquiring the original image data and the inspection A reference color selection step for automatically selecting a reference color to be used for color unevenness correction based on image data, and a controller stores correction data for a color that is the same as or closest to the selected reference color A correction data selection step selected from the image forming unit, and a control unit changing the image forming conditions of the image forming apparatus based on the selected correction data. Seen, the correction data is formed on the paper by the image forming apparatus on the basis of the correction document data, is calculated based on the color information of the correction print image, it is database.

  According to another aspect of the present invention, there is provided a color unevenness correction program for correcting color unevenness of a print image formed on a sheet based on original image data by an image forming apparatus, wherein the computer includes storage means for storing correction data. A means for obtaining the original image data, and a reference color to be used for color unevenness correction based on the original image data, and a color that is the same as or closest to the automatically selected reference color Control data for selecting the correction data of the image forming apparatus based on the selected correction data, and the correction data is a correction document. Based on the data, it is calculated based on the color information of the correction print image formed on the sheet by the image forming apparatus, and functions as a color unevenness correction apparatus stored in a database.

  Furthermore, the present invention is a color unevenness correction program for correcting color unevenness of a print image formed on a sheet based on original image data by an image forming apparatus, and a computer storing a correction data. Means for acquiring the original image data; means for acquiring inspection image data read from a reference print image formed on a sheet by the image forming apparatus based on the original image data; and the original image data and the inspection Based on the image data, a reference color to be used for color unevenness correction is automatically selected, and correction data of a color that is the same as or closest to the automatically selected reference color is selected from the storage unit, Control means for changing the image forming conditions of the image forming apparatus based on the selected correction data, and the correction data is the correction document data. Formed on the sheet by the image forming apparatus based on, it is calculated based on the color information of the correction print image, to function as a color unevenness correction apparatus which is a database.

  According to the present invention, it is possible to easily correct color unevenness of a print result image formed on a sheet by an image forming apparatus. In addition, since color unevenness can be corrected based on original document data of each user instead of a dedicated chart, color unevenness can be corrected according to the color usage of the user original.

  As shown in FIG. 1, the color unevenness correction system according to an embodiment of the present invention includes a color unevenness correction apparatus 10 and an image forming apparatus 20. In some embodiments, the image reading device 30 may be included. The image forming apparatus 20 receives image data to be printed from the outside and forms an image on a sheet based on the image data. The image forming apparatus 20 is, for example, various printers such as an electrophotographic system, an inkjet system, a thermal system, and a plotter system, a copying machine, a multifunction machine, or a printing machine. The image reading device 30 reads an image printed by the image forming device 20 and acquires it as inspection image data. The acquired inspection image data is transmitted to the color unevenness correction apparatus 10. The image reading device 30 is, for example, a scanner including an optical sensor and a data interface. Here, the paper means not only paper but also general printing objects such as OHP sheets.

  As illustrated in FIG. 1, the color unevenness correction apparatus 10 includes a control unit 100, a storage unit 120, a display unit 140, an input unit 160, and a data interface 180. Note that it is not necessary for all of these configurations to be included in one apparatus. For example, the control unit 100, the storage unit 120, the display unit 140, the input unit 160, and the data interface 180 may be configured as independent devices and combined as appropriate. The control unit 100 includes a control element such as a CPU, and has a function of controlling the color unevenness correction apparatus 10 in an integrated manner. The storage unit 120 includes a semiconductor memory, a hard disk, and the like, and stores and holds various data and programs used when correcting color unevenness. The display unit 140 includes a monitor and a touch panel, and is used to present information used for processing to the user. The input unit 160 includes a keyboard, a touch panel, and the like, and is used to acquire various types of information used for processing from the user. The color unevenness correction apparatus 10 uses the data interface 180 to exchange data with the image forming apparatus 20 and the image reading apparatus 30 via a network or the like.

  The color unevenness correction apparatus 10 executes a color unevenness correction program stored in the storage unit 120 to correct color misregistration and unevenness of a printed material on which an image is formed in the image forming apparatus 20. One embodiment of the uneven color correction method of the present invention is realized by executing each step of the flowchart shown in FIG. A more specific procedure of the color unevenness correction method of this embodiment is shown in the flowchart of FIG.

  As a previous step, correction data used to adjust image forming conditions in the image forming apparatus 20 is obtained based on the correction original data, and the data is stored in a database. First, document data for correction is prepared. The correction document data is preferably a pattern including a plurality of colors, for example, primary colors (colors formed by any one of yellow, magenta, cyan, and black), secondary colors (yellow, magenta, cyan, According to an image pattern including a plurality of colors selected from three colors selected from among three colors (yellow, magenta, cyan, black). Preferably, it is configured. The correction document data may have a pattern of a quaternary color (a color formed by superposing four colors of yellow, magenta, cyan, and black). Further, it is preferable that the correction document data has a plurality of patterns with different gradations for the same color.

FIG. 4 shows an example of a primary color bar chart used for database creation. FIG. 5 shows an example of a bar chart of multiple colors (secondary colors and tertiary colors). In this manner, a pattern having a uniform color in a strip shape in the main scanning direction and the density and mixing ratio of the basic color (primary color) being changed in the sub scanning direction is formed. Here, a plurality of patterns (here, 20% and 60%) with different densities are formed for each color included in the bar chart. 4 and 5, Y represents yellow, M represents magenta, C represents cyan, K represents black, and W represents white. Here, “uniform” means that the color difference value ΔE ^* ab in the CIEL ^* a ^* b ^* color space is within 3.0 within the region.

  By transmitting the correction document data to the image forming apparatus 20 to be corrected, a correction print image is formed on the sheet based on the correction document data. The image reading device 30 reads the correction print image using an optical sensor or the like, and acquires correction print image data. In the correction print image data, the distribution of color information (for example, color density, chromaticity, etc.) is measured for each primary color, secondary color, and tertiary color. Based on the measured distribution information, correction data such as correction parameters for image forming conditions for making the distribution uniform is calculated.

  Further, the correction document data is not limited to the image data read by the image reading device 30 from the paper on which the color pattern is formed, but the image data including the color pattern transmitted from the host computer or the like, or the host It may be image data obtained by converting PDL data transmitted from a computer or the like by a print server or the like.

  When the image forming apparatus 20 is an electrophotographic image forming apparatus, uneven exposure is likely to occur in the main scanning direction of a light beam such as a laser that exposes the photosensitive member. The pattern is preferably a bar chart including a band-like region having a uniform color in the main scanning direction. Here, the main scanning direction is a direction orthogonal to the paper transport direction during printing, and the sub-scanning direction is a direction parallel to the paper transport direction.

  Here, how to obtain correction data such as correction parameters will be described by taking an electrophotographic image forming apparatus as an example. In an electrophotographic image forming apparatus, a test pattern print image is output by the image forming apparatus, and the density of the image (RGB signal value of the output of the scanner or the like) is measured from the print image by a scanner or the like. Correction is performed by adjusting the exposure amount so as to be flat. However, the density distribution does not always have the same slope for all gradations. For example, one color image is printed on the entire surface of the paper with a gradation of 60% (Cin 60%), and the exposure amount is adjusted so that the density distribution in the main scanning direction of this image is uniform. Next, when the same image is printed at a gradation of 20% (Cin 20%) with the adjusted exposure amount, and the density distribution in the main scanning direction is measured, it is not uniform. Therefore, in order to prevent color unevenness from occurring in the main scanning direction even when exposure is performed with the same exposure amount for each of a plurality of gradations, it is preferable to correct as follows.

First, the relationship between the monochrome YMC density in the multiple color image and the L ^* a ^* b ^* color space of the multiple color corresponding to the density is obtained in advance. This relationship is obtained as follows. For a plurality of gradations (for example, Cin 20% and Cin 60%), a light beam is scanned based on image data of Y, C, M single-color patches and YC, YM, CM, YCM multi-color patches. The photosensitive member is exposed, and a printed image is output using the exposed photosensitive member. The RGB density is measured by a scanner or the like at several points in each patch of the image formed in this way, and converted to YMC density. On the other hand, the L ^* a ^* b ^* color space at the same point is measured with a colorimeter or the like. From the YMC density of the single color in the multiple colors thus measured and the L ^* a ^* b ^* color space of the multiple colors corresponding to the density, A and B matrices satisfying the conversion equation (1) are obtained by a regression method.

  Next, the density distribution of the print image based on the correction document data formed by the image forming apparatus 20 is measured. For example, a bar chart including a band-like single color and multiple color patterns having a uniform color region in the main scanning direction of a plurality of gradations (20% and 60%) as shown in FIGS. 4 and 5 is used as the correction original data. The photosensitive member is exposed by scanning the light beam, and a printed image is output using the exposed photosensitive member. The RGB density of each image thus formed is measured by a scanner or the like. Specifically, the RGB density at each point in the main scanning direction of the chart (for example, each point from the one end position (0 mm) to the other end position (300 mm) of the exposure surface of the photoreceptor) is sub-scanned in the same pattern. Measure several points in the direction. The average density of each point measured in the sub-scanning direction is obtained. When this RGB density is converted to YMC density, a YMC density distribution as shown in FIG. 6 is obtained for each color Y, M, and C. In the example of FIG. 6, the horizontal axis indicates the position in the main scanning direction, and the vertical axis indicates the measured density of yellow (Y).

Next, after conversion into L ^* a ^* b ^* color space distribution information using the conversion formula (1) obtained from the YMC density distribution, the distribution of the color difference ΔE ^* ab for the point with the lowest density is obtained. . FIG. 7 shows the relationship between the position in the main scanning direction and the color difference ΔE ^* ab obtained in this way. In FIG. 7, the horizontal axis indicates the position in the main scanning direction, and the vertical axis is obtained by averaging changes in color difference.

Next, with reference to the exposure amount R ₀ when the density distribution of FIG. 6 is obtained, the exposure amount at each point from the one end to the other end along the main scanning direction of the photoreceptor is uniformly reduced to −9%. Then, a print image is output again based on the same document data. Similar to the above, the maximum in the main scanning direction density information of the print image L ^* a ^* b ^* after conversion to the color space information, obtains the color difference Delta] E ^* ab for the low point of lowest density, the color difference Delta] E ^* ab The difference between the value and the minimum value (here, 1.6) is taken (FIG. 8). The above processing is performed stepwise from −9% to + 6% of the exposure amount, and a graph showing the relationship between the exposure amount and the difference between the maximum value and the minimum value of the color difference ΔE ^* ab is obtained for each gradation of each color pattern ( FIG. 9).

Here, as shown in FIG. 9, the exposure value and the maximum value of the color difference ΔE ^* ab obtained for a plurality of gradations, for example, a gradation of 60% (Cin 60%) and a gradation of 20% (Cin 20%). As for the relationship between the difference between the maximum value and the minimum value, a value having a larger difference between the maximum value and the minimum value of the color difference ΔE ^* ab among the values for any gradation for each exposure amount is selected and set as a total value. . The exposure amount R0 = −2.5% at which the difference between the maximum value and the minimum value of the color difference ΔE ^* ab is minimum can be obtained as the optimum exposure value. At this time, instead of selecting a value having a larger difference between the maximum value and the minimum value of the color difference ΔE ^* ab, values for a plurality of gradations at each exposure amount may be simply added to obtain a total value. Moreover, the average value may be taken. Further, a total value may be obtained by weighting and calculating for each gradation, and an optimum exposure amount may be determined based on the total value. That is, for the side on which the value of the difference between the maximum value and the minimum value of the color difference ΔE ^* ab corresponding to the exposure distribution control value obtained for each of the 60% gradation and 20% gradation shown in FIG. The weight may be increased. In this example, the optimum exposure amount is obtained for 60% and 20% gradations, but may be obtained in the same manner for more other gradations.

  The above processing is performed for each color of single color and multiple colors, and the optimum exposure amount condition is obtained. As for the mixing ratio of each single color in the multiple colors, for example, an optimum exposure amount condition is determined in a ratio of Y: M = 100: 0 to 0: 100, preferably in increments of 5%, more preferably in increments of 1%. It is preferable.

  In the case of a full-color output device that superimposes colors, the density distribution in the main scanning direction may differ between when printing a single color image and when printing a multi-color image where two or more colors are superimposed. For example, when a G image is formed, a C image is superimposed on a Y image, but a phenomenon occurs in which an already existing Y color material interferes with the overlap of the C color material. In this case, even if the single color is corrected accurately, the single color density distribution is not flat in the multiple colors. Therefore, it is preferable to correct as follows.

  First, a relationship between the RGB density of each of a plurality of multiple color images and the YMC density of a single color image corresponding to the density is obtained in advance. This relationship is obtained as follows. For example, for a plurality of gradations (20% and 60%), a photoconductor is exposed by scanning a light beam on the basis of image data of multi-color patches of YC, YM, CM, and YCM. The printed image is output using the body. At the same time, print images of primary colors of Y, C, and M are also output. After measuring the RGB density of each image of a plurality of gradations formed in this way with a scanner or the like, it is converted into a YMC density, and the density of each YMC single color in multiple colors is obtained.

  Next, the RGB density distribution of the print image based on the correction document data formed by the image forming apparatus 20 is measured. For example, a bar chart including a strip-like single color and a multiple color pattern having a uniform color region in the main scanning direction of a plurality of gradations (20% and 60%) as shown in FIGS. 4 and 5 is used as document data. The photosensitive member is exposed by scanning the light beam, and a printed image is output using the exposed photosensitive member. The RGB density of each image thus formed is measured by a scanner or the like. Specifically, the RGB density at each point in the main scanning direction of the chart (for example, each point from the one end position (0 mm) to the other end position (300 mm) of the exposure surface of the photoconductor) is subtracted within the same pattern. Measure several points along the scanning direction. An average of the density of each point measured in the sub-scanning direction is obtained to obtain an RGB density distribution.

  From the combination of the density distribution, the various densities of the secondary color and the tertiary color obtained above, and the image density of the primary colors of Y, C, and M at that time, as shown in FIG. It is possible to estimate how much and where the monochromatic YMC density in the multiple colors changes. Then, a corrected exposure amount for flattening the YMC density distribution of each single color in the multiple colors can be calculated from the relationship between the light amount correction amount and the YMC density obtained in advance shown in FIG. The above processing is performed for each of the multiple colors, and the optimum exposure conditions are obtained. As for the mixing ratio of each single color in the multiple colors, for example, it is preferable to obtain the optimum exposure condition at a ratio of Y: M = 100: 0 to 0: 100, preferably in increments of 5%, more preferably in increments of 1%. .

  The correction data such as the optimum exposure conditions for each single color of YMCK calculated as described above and each of the multiple colors in which the combination ratio of each single color is changed is stored in the storage unit 120 as a database.

  In step S <b> 500, the control unit 100 acquires the user's original image data from the host computer or the like using the data interface 180.

  The document image data is not limited to image data transmitted from a host computer or the like, but may be image data obtained by converting PDL data or the like transmitted from a host computer or the like by a print server or the like. The document image data may be read from a document such as paper by a document image data acquisition unit including a scanner or the like included in the image forming apparatus 20 and transmitted to the color unevenness correction apparatus 10 via a network or the like. Good.

In step S520, the color irregularity correction apparatus 10 automatically selects a reference color as a reference for color irregularity correction. The control unit 100 selects a reference color as a reference for correcting color unevenness in the image plane based on the document image data. Here, as a selection method thereof, for example, original image data is uniformly primary color, secondary color, and tertiary color within a predetermined size and shape area, for example, a 5 mm × 5 mm square area. When there is only one uniform color area in the original image data, the color of that area is set as the reference color. Further, when there are a plurality of such areas, it is preferable that the color having the largest number of areas having the same color in the document image data is used as the reference color. The size and shape of the area can be arbitrarily set according to the document. Here, “same color” means that the color difference value ΔE ^* ab in the CIEL ^* a ^* b ^* color space is within 3.0. Further, the range of ΔE ^* ab regarded as the same color may be arbitrarily set.

  As a reference color selection method, it is also preferable to detect a region having the largest area among single regions having a uniform color included in the document image data, and to set the color of the region as the reference color. In addition, it is also preferable that the reference color is the color having the largest total area of the areas having the same color. Furthermore, it is also preferable to set the selection methods so that they can be switched easily.

  In step S540, the control unit 100 selects the same color (for example, M20% Y50%) from the database stored in the storage unit 120 based on the reference color, and forms an image for making the reference color uniform. Data for correction including correction parameters for conditions is acquired. When the same color is not in the database, it is preferable to select the color closest to the reference color and acquire the correction data.

  In step S560, color unevenness is corrected based on the correction data. The control unit 100 transmits the correction data to the image forming apparatus 20. The image forming apparatus 20 receives the correction data, and changes the image forming conditions based on the correction data. When the image forming apparatus 20 is an electrophotographic system, the image forming conditions are changed, for example, by adjusting the exposure amount of the photosensitive member by a light beam such as a laser as described above. In addition, the ejection amount of each color ink is adjusted in the case of the ink jet method, the heat generation amount of the thermal head is adjusted in the case of the thermal method, and the ink amount is adjusted in the case of printing with a plate.

  FIG. 12 shows a flowchart of another embodiment of the color unevenness correction method of the present invention.

  First, in step S600, as in step S500, the control unit 100 acquires user document image data from the host computer or the like using the data interface 180. The document image data is not limited to image data transmitted from a host computer or the like, but may be image data obtained by converting PDL data or the like transmitted from a host computer or the like by a print server or the like. The document image data may be read from a document such as paper by a document image data acquisition unit including a scanner or the like included in the image forming apparatus 20 and transmitted to the color unevenness correction apparatus 10 via a network or the like. Good.

  In step S <b> 620, the image forming apparatus 20 outputs one reference printed material on which an image is formed on paper based on the document image data, and the image reading device 30 reads the image of the printed material. This reading is preferably performed automatically. For example, the inspection image data is automatically acquired by irradiating the image surface of the printed material conveyed in the image forming apparatus 20 with an irradiation lamp and detecting the reflected light with an imaging device such as a CCD. Can do. The inspection image data read by the image reading device 30 is sent to the color unevenness correction device 10.

  In step S640, the color irregularity correction apparatus 10 automatically selects a reference color as a reference for color irregularity correction. The control unit 100 receives the document image data and the inspection image data, compares them, and selects a reference color as a reference for correcting color unevenness in the image plane based on the comparison data. Here, examples of the selection method include the following methods.

A certain region in the inspection image data, for example, a region having a predetermined size and shape is set as a target region, and the L ^* a ^* b ^* color space of the region corresponding to the target region in the document image data is compared. It is preferable that a color region having the largest color difference ΔE ^* ab be a reference color.

  In step S660, the control unit 100 selects the same color (for example, M20% Y50%) from the database stored in the storage unit 120 based on the reference color, and forms an image for making the reference color uniform. Data for correction including correction parameters for conditions is acquired. If the same color is not in the database, it is preferable to select the closest color and obtain the correction data.

  In step S680, color unevenness is corrected based on the correction data. The control unit 100 transmits the correction data to the image forming apparatus 20. The image forming apparatus 20 receives the correction data, and changes the image forming conditions based on the correction data.

  In this way, color unevenness can be corrected based on the reference printed matter by the user original, that is, the original data of each user, instead of the dedicated chart, so that it is possible to perform color unevenness correction that matches the color usage of the user original. It is.

  The color unevenness correction method, color unevenness correction apparatus, and color unevenness correction program of the present invention include an electrophotographic system such as a copying machine, a laser printer, a facsimile, and a composite machine thereof; an ink jet system; a direct thermal type; Printed images formed on paper by image forming devices such as heat transfer methods such as mold thermal transfer; flat printing such as offset flat printing, intaglio printing such as gravure printing, relief printing, stencil printing such as screen printing, etc. However, the color of the printed image by the electrophotographic image forming apparatus in which it is difficult to print uniformly within the printing surface with the same color and local color unevenness is likely to occur. It can be suitably applied to unevenness correction.

  In accordance with the present invention, an electrophotographic system such as a copying machine, a laser printer, a facsimile machine, and a composite machine thereof; an ink jet system; a thermal system; a plotter system; and a printed image formed on a sheet by an image forming apparatus for general printing. Can be easily corrected. In addition, since color unevenness can be corrected based on original document data of each user instead of a dedicated chart, color unevenness can be corrected according to the color usage of the user original.

It is a block diagram which shows one Embodiment of the color nonuniformity correction apparatus of this invention. It is a chart figure which shows one Embodiment of the uneven color correction method of this invention. It is a chart figure which shows the specific example of one Embodiment of the uneven color correction method of this invention. It is a figure which shows an example of the monochrome bar chart used in one Embodiment of this invention. It is a figure which shows an example of the multicolor bar chart used in one Embodiment of this invention. It is a graph which shows YMC density distribution of the main scanning direction in one Embodiment of this invention. It is a graph which shows the color difference distribution of the main scanning direction in one Embodiment of this invention. It is a graph which shows the color difference distribution of the main scanning direction in one Embodiment of this invention. It is a graph which shows the relationship between the exposure distribution control value and color difference in one Embodiment of this invention. It is a graph which shows the distribution of the main scanning direction of the monochrome YMC density | concentration in the multiple color in one Embodiment of this invention. It is a graph showing the relationship between the exposure amount and monochrome YMC density in one embodiment of the present invention. It is a chart figure which shows another embodiment of the uneven color correction method of this invention.

Explanation of symbols

  10 color unevenness correction device, 20 image forming device, 30 image reading device, 100 control unit, 120 storage unit, 140 display unit, 160 input unit, 180 data interface.

Claims (15)

An uneven color correction device that corrects uneven color of a printed image formed on a sheet based on original image data by an image forming apparatus,
Storage means for storing correction data;
Means for obtaining the document image data;
A reference color to be used for color unevenness correction is automatically selected based on the original image data, and correction data for a color that is the same as or closest to the automatically selected reference color is selected from the storage means. Control means for changing image forming conditions of the image forming apparatus based on the selected correction data;
Have
The correction data is
A color unevenness correction apparatus, which is calculated based on color information of a correction print image formed on a sheet by the image forming apparatus based on correction original data and is made into a database. The uneven color correction device according to claim 1,
The color unevenness correction apparatus, wherein the correction document data includes a plurality of color patterns. The uneven color correction device according to claim 2,
The color unevenness correction apparatus, wherein the color pattern includes at least one color selected from yellow, magenta, cyan, and black. The uneven color correction device according to claim 2,
The color unevenness correction apparatus, wherein the color pattern is a color obtained by superposing at least two colors selected from yellow, magenta, cyan, and black. The uneven color correction device according to any one of claims 2 to 4,
The color unevenness correction apparatus, wherein the color pattern includes a belt-like pattern having a uniform color in a main scanning direction of the image forming apparatus. The color unevenness correction apparatus according to any one of claims 1 to 5,
The control means includes
A size and a shape are set in advance, a region having a uniform color in the region of the set size and shape is detected in the inspection image data, and a color having the largest number of regions having the same color is selected as the reference color An uneven color correction device characterized by being selected as: The color unevenness correction apparatus according to any one of claims 1 to 5,
The control means includes
A color unevenness correction apparatus, wherein a region having the largest area of a single region having a uniform color included in the inspection image data is detected and a color of the region is selected as the reference color. The color unevenness correction apparatus according to any one of claims 1 to 5,
The control means includes
An uneven color correction apparatus, comprising: detecting a total area of regions having the same color included in the inspection image data; and selecting a color of the region as the reference color. An uneven color correction device that corrects uneven color of a printed image formed on a sheet based on original image data by an image forming apparatus,
Storage means for storing correction data;
Means for obtaining the document image data;
Means for acquiring inspection image data read from a reference print image formed on a sheet by the image forming apparatus based on the document image data;
Based on the original image data and the inspection image data, a reference color to be used for color unevenness correction is automatically selected, and correction data having a color that is the same as or closest to the automatically selected reference color is selected. Control means for selecting from the storage means and changing the image forming conditions of the image forming apparatus based on the selected correction data;
Have
The correction data is
A color unevenness correction apparatus, which is calculated based on color information of a correction print image formed on a sheet by the image forming apparatus based on correction original data and is made into a database. The uneven color correction device according to claim 9,
The control means includes
A region in the inspection image data is set as a target region, and a color having the largest color difference is selected as the reference color by comparing the L ^* a ^* b ^* color spaces of the region corresponding to the target region in the document image data. An uneven color correction device characterized in that: The uneven color correction device according to any one of claims 1 to 10,
The color unevenness correcting apparatus, wherein the image forming apparatus is an electrophotographic image forming apparatus. An uneven color correction method for correcting uneven color of a printed image formed on a sheet based on original image data by an image forming apparatus,
Obtaining the document image data;
A reference color selection step in which the control unit automatically selects a reference color to be used for color unevenness correction based on the document image data;
A correction data selection step in which the control unit selects correction data for the same or most similar color as the selected reference color from the storage unit;
A control unit changing an image forming condition of the image forming apparatus based on the selected correction data;
Including
The correction data is
A method for correcting color unevenness, characterized in that a database is calculated based on color information of a correction print image formed on a sheet by the image forming apparatus based on correction original data and is stored in a database. An uneven color correction method for correcting uneven color of a printed image formed on a sheet based on original image data by an image forming apparatus,
A control unit acquiring the document image data;
A step of acquiring inspection image data read from a reference print image formed on a sheet by the image forming apparatus based on the document image data;
A reference color selection step in which a control unit automatically selects a reference color to be used for color unevenness correction based on the document image data and the inspection image data;
A correction data selection step in which the control unit selects correction data for the same or most similar color as the selected reference color from the storage unit;
A control unit changing an image forming condition of the image forming apparatus based on the selected correction data;
Including
The correction data is
A method for correcting color unevenness, characterized in that a database is calculated based on color information of a correction print image formed on a sheet by the image forming apparatus based on correction original data and is stored in a database. An uneven color correction program for correcting uneven color of a printed image formed on paper based on original image data by an image forming apparatus,
Computer
Storage means for storing correction data;
Means for obtaining the document image data;
A reference color to be used for color unevenness correction is automatically selected based on the original image data, and correction data for a color that is the same as or closest to the automatically selected reference color is selected from the storage means. Control means for changing image forming conditions of the image forming apparatus based on the selected correction data;
Have
The correction data is
A color that functions as a color unevenness correction device that is calculated based on color information of a correction print image formed on a sheet by the image forming apparatus based on correction original data and is stored in a database. Unevenness correction program. An uneven color correction program for correcting uneven color of a printed image formed on paper based on original image data by an image forming apparatus,
Computer
Storage means for storing correction data;
Means for obtaining the document image data;
Means for acquiring inspection image data read from a reference print image formed on a sheet by the image forming apparatus based on the document image data;
Based on the original image data and the inspection image data, a reference color to be used for color unevenness correction is automatically selected, and correction data having a color that is the same as or closest to the automatically selected reference color is selected. Control means for selecting from the storage means and changing the image forming conditions of the image forming apparatus based on the selected correction data;
Have
The correction data is
A color that functions as a color unevenness correction device that is calculated based on color information of a correction print image formed on a sheet by the image forming apparatus based on correction original data and is stored in a database. Unevenness correction program.

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