JP2016178372A - Image processing apparatus, image forming apparatus, and image processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately correct variation in image density due to a halo effect.SOLUTION: An image processing apparatus which generates information to be used to execute an image forming output by an image forming apparatus of an electronic photograph system comprises: a correction value storage part 403 which stores correction value information in which correction values of image density designated in accordance with halo effects are set in accordance with the types of sheets; and a density adjustment part 402 which corrects the image density of an edge portion of an image in generated drawing information with a correction value corresponding to a sheet, on the basis of the correction value information.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image processing apparatus, an image forming apparatus, and an image processing method.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, electrophotographic image forming apparatuses are widely used in image forming apparatuses used for outputting digitized documents. In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing a photosensitive member, and the electrostatic latent image is developed using a developer such as toner to form a toner image. Then, paper output is performed by transferring the toner image onto paper.

  In such an electrophotographic image forming apparatus, when an electrostatic latent image is formed on a photoreceptor, an influence on the image density due to the halo effect occurs at an edge portion where the density of the image changes sharply. There is a case. The effect on the image density due to the halo effect is that the charge in the low charge portion is attracted to the high charge portion, and as a result, the charge in the region adjacent to the high charge portion is more than the intended state. It becomes lower and the density of the image changes.

  In order to solve such a problem, the image density is corrected based on the difference in the image density at the edge and the density of the original image at the edge portion of the image, thereby affecting the image density due to the halo effect. Has been proposed (see, for example, Patent Document 1).

  According to the technique disclosed in Patent Document 1, the correction value for correcting the image density in advance is determined based on the density difference of the image at the edge and the density of the target pixel. However, the amount of change in density caused by the halo effect varies depending on the recording medium to be transferred, such as paper, and individual differences among image forming apparatuses. Therefore, in the method disclosed in Patent Document 1, the accuracy of correction of density fluctuation due to the halo effect is low.

  The present invention has been made in view of the above circumstances, and an object thereof is to highly accurately correct fluctuations in image density due to the halo effect.

  In order to solve the above-described problem, an aspect of the present invention is an image processing apparatus that generates information used by an electrophotographic image forming apparatus to execute an image forming output. A command receiving unit for receiving a command; a drawing information generating unit for generating drawing information in which an image to be imaged and output is expressed for each pixel constituting the image based on the execution command; and electrophotographic image formation A recording medium on which an image density correction value designated in accordance with the movement of electric charges at a position corresponding to an edge portion of an image on a photoreceptor on which an electrostatic latent image is to be formed is transferred in an image forming output. Is generated by a correction value storage unit that stores correction value information set according to the type of the recording medium, and a correction value according to the recording medium used in the image forming output based on the correction value information. Characterized in that it comprises an image correction unit for correcting the image density of the edge portion of the image in the drawing information.

  According to the present invention, it is possible to accurately correct fluctuations in image density due to the halo effect.

It is a figure which shows the hardware constitutions of the image processing apparatus which concerns on embodiment of this invention. It is a figure which shows the function structure of the image processing apparatus which concerns on embodiment of this invention. It is a block diagram which shows the function structure of the image process part which concerns on embodiment of this invention. It is a block diagram which shows the function structure of the image correction part which concerns on embodiment of this invention. It is a figure which shows the example of the information memorize | stored in the correction value memory | storage part which concerns on embodiment of this invention. It is a flowchart which shows the correction value production | generation operation | movement which concerns on embodiment of this invention. It is a figure which shows the example of the halo correction chart of the main scanning direction which concerns on embodiment of this invention. It is a figure which shows the example of the halo correction chart of the subscanning direction which concerns on embodiment of this invention. It is a figure which shows the example of the halo correction chart of the main scanning direction which concerns on embodiment of this invention, and a subscanning direction mixing. It is a figure which shows the example of the patch contained in the halo correction chart which concerns on embodiment of this invention. It is a figure which shows the influence of the halo effect when not performing halo correction. It is a figure which shows the reduction aspect of the halo effect at the time of performing halo correction. It is a figure which shows the reading result of the halo correction chart which concerns on embodiment of this invention. It is the figure which graphed the reading result of the halo correction chart which concerns on embodiment of this invention. It is the figure which graphed the reading result of the halo correction chart which concerns on embodiment of this invention. It is the figure which graphed the reading result of the halo correction chart which concerns on embodiment of this invention. It is a figure which shows the parameter extracted from the reading result of the halo correction chart which concerns on embodiment of this invention. It is a flowchart which shows the halo correction | amendment operation | movement which concerns on embodiment of this invention. It is a figure which shows the example of the edge determination tag which concerns on embodiment of this invention. It is a figure which shows the example of the image density according to the pixel position before the halo correction which concerns on embodiment of this invention. It is a figure which shows the example of the image density according to the pixel position after the halo correction which concerns on embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, in an electrophotographic image forming apparatus, by correcting in advance the density of the lower-density area of the edge portion of the image to be output, image density fluctuation due to the halo effect is suppressed. This will be described as a feature.

  FIG. 1 is a block diagram illustrating a hardware configuration of the image processing apparatus 1 according to the present embodiment. As shown in FIG. 1, the image processing apparatus 1 according to the present embodiment includes an engine that executes image formation in addition to a configuration similar to an information processing terminal such as a general server or a PC (Personal Computer). That is, the image processing apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 11, a ROM (Read Only Memory) 12, an engine 13, an HDD (Hard Disk Drive) 14, and an I / O. F15 is connected via the bus 18. Further, an LCD (Liquid Crystal Display) 16 and an operation unit 17 are connected to the I / F 15.

  The CPU 10 is a calculation unit and controls the operation of the entire image processing apparatus 1. The RAM 11 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The engine 13 is a mechanism that actually executes image formation in the image processing apparatus 1.

  The HDD 14 is a nonvolatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The I / F 15 connects and controls the bus 18 and various hardware and networks. The LCD 16 is a visual user interface that displays various types of information and allows the user to check the state of the image processing apparatus 1. The operation unit 17 is a user interface such as a keyboard and a mouse for the user to input information to the image processing apparatus 1.

  In such a hardware configuration, the software control unit is configured by the CPU 10 performing calculations in accordance with a program stored in the ROM 12 or a program read to the RAM 11 from a recording medium such as the HDD 14 or an optical disk (not shown). . A functional block that realizes the functions of the image processing apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, a functional configuration of the image processing apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a functional configuration of the image processing apparatus 1 according to the present embodiment. As shown in FIG. 2, the image processing apparatus 1 according to the present embodiment includes a controller 20, an ADF (Auto Document Feeder) 21, a scanner unit 22, a paper discharge tray 23, a display panel 24, and a paper feed table. 25, a print engine 26, a paper discharge tray 27, and a network I / F 28.

  The controller 20 includes a main control unit 30, an engine control unit 31, an input / output control unit 32, an image processing unit 33, and an operation display control unit 34. As shown in FIG. 2, the image processing apparatus 1 according to the present embodiment is configured as a multifunction machine having a scanner unit 22 and a print engine 26. In FIG. 2, the electrical connection is indicated by solid arrows, and the flow of paper is indicated by broken arrows.

  The display panel 24 is an output interface that visually displays the state of the image processing apparatus 1 and is an input when the user directly operates the image processing apparatus 1 or inputs information to the image processing apparatus 1 as a touch panel. It is also an interface (operation unit). The network I / F 28 is an interface for the image processing apparatus 1 to communicate with other devices via the network, and uses an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface.

  The controller 20 is configured by a combination of software and hardware. Specifically, as described above, the controller 20 is configured by the software control unit configured by the calculation of the CPU 10 and hardware such as an integrated circuit. The controller 20 functions as a control unit that controls the entire image processing apparatus 1.

  The main control unit 30 plays a role of controlling each unit included in the controller 20 and gives a command to each unit of the controller 20. The engine control unit 31 serves as a drive unit that controls or drives the print engine 26, the scanner unit 22, and the like. The input / output control unit 32 inputs a signal or a command input via the network I / F 28 to the main control unit 30. The main control unit 30 controls the input / output control unit 32 and accesses other devices via the network I / F 28.

  Under the control of the main control unit 30, the image processing unit 33 generates drawing information based on print information included in a print job that is an execution instruction for image formation output. The drawing information is information for drawing an image to be formed in the image forming operation by the print engine 26 as an image forming unit, that is, an image to be output. The print information included in the print job is image information converted into a format that can be recognized by the image processing apparatus 1 by a printer driver installed in an information processing apparatus such as a PC.

  Further, the image processing unit 33 according to the present embodiment includes a function of generating drawing information in which image density variation due to the halo effect is corrected in advance when drawing information is generated as a characteristic function of the present embodiment. Details of the functions included in the image processing unit 33 will be described later. The operation display control unit 34 displays information on the display panel 24 or notifies the main control unit 30 of information input via the display panel 24.

  When the image processing apparatus 1 operates as a printer, first, the input / output control unit 32 receives a print job via the network I / F 28. The input / output control unit 32 transfers the received print job to the main control unit 30. When receiving the print job, the main control unit 30 controls the image processing unit 33 to generate drawing information based on the print information included in the print job.

  When drawing information is generated by the image processing unit 33, the engine control unit 31 controls the print engine 26 based on the generated drawing information, and executes image formation on the paper conveyed from the paper supply table 25. To do. That is, the print engine 26 functions as an image forming unit.

  The print engine 26 according to the present embodiment is an electrophotographic image forming mechanism. Accordingly, an electrostatic latent image is formed on the photoconductor in accordance with the above-described drawing information, and the electrostatic latent image is developed with a developer such as toner to form an image. One of the gist according to the present embodiment is to reduce the halo effect in the edge portion of the image density included in the electrostatic latent image formed on the photoreceptor, that is, in the portion where the charge changes sharply. A document on which an image has been formed by the print engine 26 is discharged to a discharge tray 27.

  When the image processing apparatus 1 operates as a scanner, the operation display control unit 34 or the input / output unit is operated according to a user's operation of the display panel 24 or a scan execution instruction input from an external PC or the like via the network I / F 28. The control unit 32 transfers a scan execution signal to the main control unit 30. The main control unit 30 controls the engine control unit 31 based on the received scan execution signal.

  The engine control unit 31 drives the ADF 21 and conveys the document to be imaged set on the ADF 21 to the scanner unit 22. Further, the engine control unit 31 drives the scanner unit 22 and images a document conveyed from the ADF 21. If no original is set on the ADF 21 and the original is directly set on the scanner unit 22, the scanner unit 22 takes an image of the set original under the control of the engine control unit 31. That is, the scanner unit 22 operates as an imaging unit.

  In the imaging operation, an imaging element such as a CCD included in the scanner unit 22 optically scans the document, and imaging information generated based on the optical information is generated. The engine control unit 31 transfers the imaging information generated by the scanner unit 22 to the image processing unit 33. The image processing unit 33 generates image information based on the imaging information received from the engine control unit 31 according to the control of the main control unit 30. Image information generated by the image processing unit 33 is stored in a storage medium attached to the image processing apparatus 1 such as the HDD 14. That is, the scanner unit 22, the engine control unit 31, and the image processing unit 33 work together to function as a document reading unit.

  The image information generated by the image processing unit 33 is stored in the HDD 14 or the like as it is according to a user instruction or transmitted to an external device via the input / output control unit 32 and the network I / F 28. That is, the ADF 21 and the engine control unit 31 function as an image input unit.

  When the image processing apparatus 1 operates as a copying machine, the image processing unit 33 generates drawing information based on the imaging information received by the engine control unit 31 from the scanner unit 22 or the image information generated by the image processing unit 33. To do. Based on the drawing information, the engine control unit 31 drives the print engine 26 as in the case of the printer operation.

  Next, functions included in the image processing unit 33 according to the present embodiment will be described with reference to FIG. As illustrated in FIG. 3, the image processing unit 33 according to the present embodiment includes a rendering unit 330, a color conversion unit 331, a total amount regulation unit 332, a gamma conversion unit 333, an image correction unit 334, and a gradation processing unit 335. The rendering unit 330 performs rendering processing on the image data included in the print job, and generates drawing information that is bitmap format image data. Bitmap format image data is information in which an image to be imaged and output is represented for each pixel constituting the image. That is, the rendering unit 330 functions as a drawing information generation unit. The color conversion unit 331 converts the color format of the image data into CMYK.

  The total amount restriction unit 332 thins out the colored pixels in order to restrict the number of colored pixels among the pixels constituting the output target image to the restriction value of the number of colored pixels determined in the print engine 26. The gamma conversion unit 333 performs color conversion according to the color development characteristics of the print engine 26.

  The image correction unit 334 has a characteristic configuration according to the present embodiment, and corrects the image density of the edge portion as described above. The gradation processing unit 335 performs screen processing for reproducing halftone image density in a low-value pixel format in which one pixel is 1 to 4 bits by pseudo intermediate processing.

  Next, the configuration of the image correction unit 334, which is a characteristic configuration according to the present embodiment, will be described with reference to FIG. As shown in FIG. 4, the image correction unit 334 includes an edge extraction unit 401, a density adjustment unit 402, and a correction value storage unit 403. The edge extraction unit 401 performs filtering processing on the image data to be output, and extracts pixels corresponding to edge portions in which the image density changes sharply in the output target image.

  The edge extraction unit 401 performs edge extraction using a filter having a size of vertical and horizontal N pixels. The filter size N is determined according to the hardware that executes the filter process. Various known filters can be used as the edge extraction filter. Based on the correction value information stored in the correction value storage unit 403, the density adjustment unit 402 corrects the image density variation due to the halo effect in advance by correcting the density of pixels around the pixel determined to be an edge. To do. That is, the density adjustment unit 402 in the image correction unit 334 plays an important function as an image correction unit.

  The correction value storage unit 403 stores information that is referred to when the density adjustment unit 402 performs correction on pixels around the pixel determined to be an edge. The information stored in the correction value storage unit 403 will be described with reference to FIG. As shown in FIG. 5, the correction value information according to the present embodiment is information associated with information on “sheet type”, “density difference”, “correction range”, and “correction amount”. This is information in which “correction range” and “correction amount” corresponding to “density difference” are designated for each type.

  “Sheet type” is information indicating the type of paper, such as “plain paper”, “coated paper”, “quality paper”, and the like. The variation amount of the image density caused by the halo effect varies depending on the sheet type in addition to the image density at the edge portion. Therefore, as shown in FIG. 5, by using “density difference”, “correction range”, and “correction amount” that are different for each “sheet type”, the halo effect can be corrected with high accuracy.

  “Density difference” is a value indicating a difference in image density of a portion determined to be an edge in an output target image. The “correction range” is a value that specifies how many pixels from the image determined to be an edge are to be corrected. The “correction amount” is a value indicating a correction amount when correcting the image density, that is, an image density adjustment amount.

  In the image processing apparatus 1 according to the present embodiment, correction value information as shown in FIG. 5 is generated by forming and outputting a halo correction chart using a target type of paper. The correction value information generation operation according to the present embodiment will be described with reference to FIG. As shown in FIG. 6, first, the image processing apparatus 1 executes image formation output of a halo correction chart (S601).

  Here, the halo correction chart according to the present embodiment will be described. FIG. 7 is a diagram illustrating a halo correction chart including patches configured with different densities in the main scanning direction. FIG. 8 is a diagram illustrating a halo correction chart including patches configured with different densities in the sub-scanning direction. In FIGS. 7 and 8, the density of the halftone image is indicated by the density of hatching lines. 7 and 8, the alternate long and short dash line indicates cyan, the broken line indicates magenta, the dotted line indicates yellow, and the solid line indicates black.

  As shown in FIGS. 7 and 8, the halo correction chart according to the present embodiment is a pattern image in which patches having different densities are arranged in the main scanning direction and the sub-scanning direction. This patch is a plurality of marks constituting the halo correction char. Since the occurrence of the halo effect differs between the main scanning direction and the sub scanning direction, a chart in which patches are arranged in the main scanning direction and the sub scanning direction as shown in FIGS. 7 and 8 is required. However, when the print engine 26 supports only one color such as monochrome, as shown in FIG. 9, a chart in which patches are arranged in both the main scanning direction and the sub-scanning direction is used. Also good. Further, the charts shown in FIGS. 7 and 8 may be formed on one sheet.

  FIG. 10 is a diagram showing a patch 500 included in the halo correction chart. As shown in FIG. 10, a solid area 501 having a high density such as a black solid exists at the center of each patch, and a halftone area 502 is drawn around the area. That is, the solid area 501 and the halftone area 502 are arranged adjacent to each other to form an edge portion. In other words, the solid area 501 is a high density area having a relatively high density, and the density in each patch is common. FIG. 11 is a diagram illustrating how the image density varies due to the halo effect. As shown in FIG. 11, a halo effect is generated on the halftone area 502 side at the edge portion between the solid area 501 and the halftone area 502, and the density is reduced.

  The density variation caused by the halo effect as shown in FIG. 11 is read, and the image density of the portion corresponding to the edge portion of the halftone area 502 in the image data to be output is increased in advance according to the read result. Is the halo effect correction process. FIG. 12 is a diagram showing an aspect of such processing.

  As shown in FIG. 12, if the density on the halftone area 502 side at the edge portion between the solid area 501 and the halftone area 502 is increased in advance, in the image transferred to the paper, the correction target is corrected by the halo effect. The image density in the range is the intended density. In the image processing apparatus 1 according to the present embodiment, the image formation output results of the halo correction charts as shown in FIGS. 7 to 9 are read to analyze the image density fluctuation mode due to the halo effect, and based on the analysis results. Correction value information as shown in FIG. 5 is generated. As a result, it is possible to generate a highly accurate correction value according to the type of paper and the density difference.

  In step S601, the image processing unit 33 outputs an image for forming a halo correction chart as shown in FIGS. 7 to 9 under the control of the main control unit 30, and the engine control unit 31 controls the print engine 26. Execute image formation output. That is, the image processing unit 33 functions as an adjustment image output unit that outputs an image of a halo correction chart that is an adjustment image for adjusting the halo effect.

  When the halo correction chart is output in the process of S601, the scanner and the colorimeter read each patch displayed on the output paper (S602), and generate read information. Thereafter, the read information is processed by an apparatus having the information processing configuration as described in FIG. In the reading process of S602, the main scanning direction corresponds to the pixel position in the main scanning direction shown in FIG. 7, and the sub scanning direction corresponds to the sub scanning direction in the sub scanning direction shown in FIG. Read the image density. As a result, read information as shown in FIG. 13 is generated.

  14, 15 and 16 are graphs of the read information generated as shown in FIG. As shown in FIG. 14, when the read information is graphed, in addition to the high density portion 501 ′ that is the read result of the solid region 501 and the halftone portion 502 ′ that is the read result of the halftone region 502, A density reduction portion 503 ′ where the density decreases appears.

  FIG. 15 is a diagram showing a graph when the range of the halo effect portion is wider than that in FIG. FIG. 16 is a diagram illustrating a graph in the case where the range of the density decrease portion 503 ′ is different before and after the solid region 501 in the reading direction. The range of the halo effect portion 503 ′ corresponds to the “correction range” shown in FIG.

  As illustrated in FIGS. 14 to 16, the read information generated by reading the halo correction chart includes high-frequency noise with respect to the reading position. Therefore, the information processing apparatus that processes the read information performs a moving average process on the read information shown in FIG. 13 (S603) to remove noise. The information processing apparatus from which noise has been removed by moving average processing calculates a correction range and a correction amount based on the read information from which noise has been removed (S604). By such processing, correction value information shown in FIG. 5 is generated.

  FIG. 17 is a diagram showing a concept of correction range and correction amount calculation processing according to the present embodiment. As shown in FIG. 17, the width L of the high density portion 501 ′ is grasped based on the size of the solid area 501 in the original image information for image formation output of the halo correction chart. The information processing apparatus calculates the correction range based on the distance from the end portion of the width L to the halftone portion 502 ′, that is, the width k of the density reduction portion 503 ′ described with reference to FIGS.

  Various existing methods such as differential processing can be used for extracting the end of the halftone portion 502 ′. Here, as described with reference to FIGS. 7 to 9, the halo correction chart includes a plurality of patches having different densities in the halftone area 502. The information processing apparatus extracts a width k as shown in FIG. 17 for each density difference between the solid area 501 and the halftone area 502. As a result, as shown in FIG. 5, a “correction range” corresponding to the “density difference” is obtained.

  Further, as described with reference to FIGS. 7 to 9, as the reading information of the halo correction chart, reading information in each of the main scanning direction and the sub-scanning direction is generated. Further, as described with reference to FIG. 16, even with one piece of reading information, the width of the density-decreasing portion 503 ′ may be different depending on the front and back of the solid region 501 in the reading direction.

  The information processing apparatus acquires the width k of the density reduction portion 503 ′ in each of the main scanning direction and the sub-scanning direction for each density difference. Also, the width k of the density-decreasing portion 503 ′ before and after the solid region 501 in the reading direction is acquired. Then, the information processing apparatus calculates the “correction range” by averaging the acquired width k for each density difference.

  In addition, a mode using the acquired maximum value or minimum value of k is also possible. By using the maximum value, correction omission can be prevented. Moreover, redundant correction can be prevented by using the minimum value.

  As shown in FIG. 17, the information processing apparatus obtains a difference a between the density of the halftone portion 502 ′ and the lowest value, that is, the minimum value in the density reduction portion 503 ′, when calculating the “correction amount”. To do. As the density of the halftone portion 502 ′, various existing methods such as using the average value of the density of the area determined as the halftone area 502 can be used.

  Then, the information processing apparatus, for each density difference between the solid area 501 and the halftone area 502, for the density reduction portion 503 ′ before and after the solid area 501 in the reading direction of each of the main scanning and the sub scanning, similarly to the width k. The “correction amount” is calculated by obtaining the difference a and calculating the average value. An aspect using the calculated maximum value or minimum value of a is also possible.

  As a result, as described with reference to FIG. 5, “correction range” and “correction amount” corresponding to each “density difference” are calculated. Such processing. By executing for each type of paper such as “plain paper” and “coated paper”, the “sheet type”, “density difference”, “correction range”, and “correction amount” are set as shown in FIG. Associated correction value information is generated.

  Next, the halo effect correcting operation by the image correcting unit 334 will be described with reference to FIG. As shown in FIG. 18, first, the edge extraction unit 401 selects one pixel from the output target image (S1801), and calculates an edge amount by performing filter processing (S1802). The calculated edge amount is input from the edge extraction unit 401 to the density adjustment unit 402.

  The density adjustment unit 402 selects a density difference threshold value for comparison with the calculated edge amount (S1803). The density difference threshold selected in S1803 is a value corresponding to the “density difference” described in FIG. The density adjustment unit 402 selects the “density difference” associated with the target “sheet type” in order from the largest value.

  The density adjustment unit 402 that has selected the density difference threshold compares the input edge amount with the selected density difference threshold, and determines whether or not the input edge amount is greater than the selected density difference threshold. It is determined whether or not it is within the processing range based on the density difference threshold value in the middle (S1804). As a result of the determination in S1804, when the input edge amount is smaller than the selected density difference threshold (S1804 / NO), the density adjustment unit 402 performs S1803 until all of the “density differences” shown in FIG. 5 are selected. The processes from are repeated (S1805 / NO).

  As a result of the determination in S1804, if the input edge amount is larger than the selected density difference threshold (S1804 / YES), the density adjustment unit 402 updates the edge determination tags of the pixels around the selected pixel ( S1806). FIG. 19 is a diagram illustrating the content of information included in the edge determination tag. As shown in FIG. 19, the edge determination tag includes information on “applied density difference threshold” and “edge distance”.

  The “applied density difference threshold” is the density difference threshold that was selected when YES in S1804, and is information that specifies the “density difference” in FIG. The “edge distance” is information indicating how many pixels are away from the pixel selected when YES in S1804. As described with reference to FIGS. 14 to 16, the amount of change in density due to the halo effect becomes more prominent as it approaches the edge. Therefore, the “edge distance” is an important parameter when density correction is performed.

  In S1806, the range of pixels for which the edge determination tag is to be generated is determined according to the density-decreasing portion 503 ′ as described with reference to FIGS. First, even for pixels around an edge determined to be an edge, a pixel with a higher density is not a generation target, and a pixel with a lower density is a generation target. A range wider than the range of the density reduction portion 503 ′ that can be generated is determined empirically as to the number of pixels from the currently selected pixel.

  The density adjustment unit 402 repeats the processing from S801 until the selection is completed for all the pixels constituting the output target image (S1807 / YES). In this repetition, an edge determination tag may be generated again depending on the result of edge determination of another pixel for a pixel for which an edge determination tag has already been generated.

  In such a case, a short “edge distance” is given priority. That is, the density adjustment unit 402 newly generates an “edge distance” included in an already generated edge determination tag when a pixel for which an edge determination tag has already been generated becomes a generation target of an edge determination tag again. The “edge distance” of the edge determination tag is compared. Then, the edge determination tag is stored by adopting the one having the shorter “edge distance”.

  When the processing from S1801 is completed for all the pixels (S1807 / YES), the density adjustment unit 402 sequentially selects the pixels for which the edge determination tag is generated (S1808), and the content and correction value of the edge determination tag. Based on the information, the density of the target pixel is corrected (S1809).

  In step S1809, the density adjustment unit 402 selects a record corresponding to a combination of “sheet type” used for output and “density difference” corresponding to “applied density difference threshold” included in the edge determination tag, and selects “correction range”. "And" correction amount "are extracted. If the “edge distance” included in the edge determination tag is within the “correction range”, the “correction amount” is multiplied by a ratio corresponding to the “edge distance” and added to the pixel value of the currently selected pixel. To do. In other words, the density adjustment unit 402 corrects the density of each pixel by correcting the value of “correction amount” shown in FIG. 5 based on the “edge distance” included in the edge determination tag.

  FIG. 20 is a graph showing pixel values according to pixel positions before density adjustment, and FIG. 21 is a graph showing pixel values according to pixel positions before density adjustment. As shown in FIG. 21, the density adjustment unit 402 performs “correction amount” at a rate corresponding to the “edge distance” that is the distance from the edge portion with respect to the pixels in the range of “correction range” k ′ from the edge portion. Add a '.

  As a result, as described with reference to FIGS. 14 to 16, it is possible to cope with fluctuations in image density due to the halo effect that appears more prominently closer to the edge portion with high accuracy. The ratio of the “correction amount” a ′ corresponding to the distance from the edge portion can be variously reduced, as shown in FIG. 21, such as inverse proportion, quadratic function, cubic function, etc. .

  The density adjustment unit 402 repeats the process until the process from S1808 is completed for all the pixels for which the edge determination tag is generated (S1810 / NO), and when the process is completed for all the pixels (S1810 / NO), the density adjustment is performed. Complete the operation.

1 Image forming apparatus 10 CPU
11 RAM
12 ROM
13 Engine 14 HDD
15 I / F
16 LCD
17 Operation unit 18 Bus 20 Controller 21 ADF
22 Scanner unit
23 Paper Tray 24 Display Panel 25 Paper Feed Table 26 Print Engine 27 Paper Tray 28 Network I / F
DESCRIPTION OF SYMBOLS 30 Main control part 31 Engine control part 32 Input / output control part 33 Image processing part 34 Operation display control part 330 Rendering part 331 Color conversion part 332 Total amount control part 333 Gamma conversion part 334 Image correction part 335 Tone processing part 401 Edge extraction part 402 Density adjustment unit 403 Correction value storage unit

JP 2010-50708 A

Claims (7)

An image processing apparatus for generating information used by an electrophotographic image forming apparatus to execute image forming output,
Based on the execution instruction of the image formation output, a drawing information generation unit that generates drawing information in which an image of the image formation output target is expressed for each pixel constituting the image;
In the electrophotographic image forming apparatus, the correction value of the image density specified in accordance with the movement of the charge at the position corresponding to the edge portion of the image on the photosensitive member on which the electrostatic latent image is formed is A correction value storage unit that stores correction value information set according to the type of recording medium to which the image is transferred,
And an image correction unit that corrects the image density of the edge portion of the image in the generated drawing information based on the correction value information based on a correction value corresponding to a recording medium used for image formation output. Image processing device. The image correction unit
Set information indicating the distance from the pixel corresponding to the edge portion with respect to the pixels around the pixel corresponding to the edge portion extracted from the drawing information,
The image processing according to claim 1, wherein each pixel constituting the drawing information is corrected by correcting a correction amount set in the correction value information based on the set information indicating the distance. apparatus. The correction value information is information in which a correction amount of the image density is associated with a difference in image density at an edge portion of the image,
The image correction unit
Information indicating a difference in image density in the edge portion extracted from the drawing information is set in a pixel corresponding to the extracted edge portion;
3. The correction value information according to claim 1, wherein each pixel constituting the drawing information is corrected by a correction amount associated with information indicating the set density difference of the image. Image processing device. An image forming apparatus including the image processing apparatus according to claim 3,
A plurality of marks including an edge portion where two regions having different image densities are adjacent are displayed as an image forming output target image, and an image of a halftone region that is a region having a lower image density of the two regions An adjustment image output unit that outputs an adjustment image in which the image density of the high-density region that is different in density in each of the plurality of marks and in which the image density is higher is common,
The correction value information includes correction amount information obtained based on reading results of the marks having different densities in the halftone area, among the read information generated by reading the adjustment image. By associating with the difference between the image density of the halftone area and the image density of the high density area, it is generated as information in which the correction amount of the image density is associated with the difference of the image density at the edge portion of the image. An image forming apparatus.   The adjustment image output unit includes the adjustment image in which a plurality of marks having different densities in the halftone area are arranged in the main scanning direction on the photosensitive member and the adjustment image in which the marks are arranged in the sub scanning direction. The image forming apparatus according to claim 4, wherein the image forming apparatus outputs the image.   The adjustment image output unit outputs the adjustment image in which a plurality of marks having different densities in the halftone area are arranged for each color of a developer for developing the electrostatic latent image formed on the photosensitive member. The image forming apparatus according to claim 4, wherein the image forming apparatus outputs the image. An image processing method for generating information used by an electrophotographic image forming apparatus to execute image forming output,
Receiving an execution instruction of the image forming output;
Based on the execution command, the image forming output target image generates drawing information expressed for each pixel constituting the image,
In the electrophotographic image forming apparatus, the correction value of the image density specified in accordance with the movement of the charge at the position corresponding to the edge portion of the image on the photosensitive member on which the electrostatic latent image is formed is The correction value information is acquired from the correction value storage unit storing the correction value information set according to the type of the recording medium to which the image is transferred,
An image processing method comprising: correcting an image density of an edge portion of an image in the generated drawing information based on the correction value information, using a correction value corresponding to a recording medium used in image formation output.