JP2009230138A - Image forming apparatus and image processing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus can switch correction processing control for a half tone value according to circumstances of hardware resource in a page memory part, and an image processing method therefor. <P>SOLUTION: When the image forming apparatus 1 is started by depressing a power supply, or after predetermined number of sheets (for example, 1,000 sheets) of paper are printed, correction processing of a maximum tone value is performed. After correction operation of the maximum tone value is finished, a control part 10 confirms the hardware resource of the page memory part 13. The control part 20 performs processing fitting to a mode according to whether it is a time priority mode or an image quality priority mode. When a user sets the image quality priority mode, the control part 10 waits for printing or processing for transmission/reception of FAX until the hardware resource of the page memory part 13 is secured. When the user sets the time priority mode, the control part 10 does not wait for printing or processing for transmission/reception of FAX. Therefore, tone correction is performed only for the maximum tone value but correction processing for a half tone value is not performed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that estimates gradation characteristics and an image processing method thereof.

  In an image forming apparatus incorporated in a digital color multifunction peripheral, a color printer, or the like, the density of a printed image may change due to changes in the surrounding environment such as temperature or the passage of usage time.

  Therefore, in a conventional image forming apparatus, a predetermined density test pattern is formed on an image carrier such as a photoreceptor or a transfer belt, and density adjustment is performed so that the density of the density test pattern falls within a predetermined reference range. There are many things to do. Normally, the density test pattern used for density adjustment is a so-called solid or a solid-equivalent pattern, and the gradation value of the maximum or near maximum is set as the gradation value of the density test pattern. For example, the density of the density test pattern formed on the image carrier is detected by a density sensor or the like, and the charged potential, development potential, exposure amount, etc. of the photoconductor are set so that the detected density approaches the reference density (maximum gradation value). Make adjustments. Therefore, in the density adjustment, the maximum gradation value of the image data is adjusted to an appropriate print density.

  In some image forming apparatuses, a gradation correction table is created using a gradation patch pattern stored in advance by the apparatus, and gradation correction is performed using the gradation correction table. A gradation patch pattern is a pattern in which a plurality of vertical lines and dots are printed within a predetermined frame so that the density changes from a low density to a high density (the thickness and spacing of vertical lines, or the size and spacing of dots are changed). The pattern is arranged at a predetermined density interval.

  While the density test pattern is used to correct the maximum gradation value, the gradation correction table created from the gradation patch pattern is a correction table from a low density to a high density. Used for.

  For example, a gradation patch pattern is once printed on a sheet and read by a reading unit. The gradation correction table is changed and updated so that the density of the read gradation patch pattern falls within a predetermined range of the reference gradation density held in advance.

  Alternatively, the density of the gradation patch pattern formed on the image carrier such as a transfer belt is detected by a density sensor, and the gradation is detected so that the density for each detected gradation falls within a predetermined range of the reference gradation density stored in advance. Change and update the adjustment table.

  By the way, the gradation patch pattern is created from the halftone screen. At this time, the gradation patch pattern is temporarily stored in the page memory unit. Therefore, it is necessary to secure hardware resources of the page memory unit when correcting the intermediate gradation value.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique for creating an image in which gradations are always appropriately expressed even if the usage state of the image forming apparatus changes with time by creating a plurality of gradation correction tables.

JP-A-8-286442

  The page memory unit also uses hardware resources in printing and FAX transmission / reception operations. The page memory section has a very small hardware resource capacity of about one to two sheets. Therefore, if an intermediate tone value correction process is performed during printing or FAX transmission / reception operation, the hardware resources of the page memory unit are occupied by image data, and thus the correction process cannot be performed simultaneously. .

  The present invention has been made in view of the above points, and provides an image forming apparatus and an image processing method thereof that can switch correction processing control of intermediate gradation values in accordance with the status of hardware resources in a page memory unit. The purpose is to provide.

  An image forming apparatus according to the present invention includes a density information acquisition unit that acquires density information of a test pattern, and density information of the test pattern acquired by the density information acquisition unit in an image forming apparatus that performs gradation correction of an image. A gradation correction processing unit that performs correction processing of at least one of maximum gradation value correction and intermediate gradation value correction processing so that a value falls within a predetermined range of the reference density, and temporarily stores image data in units of pages. A page memory unit that preferentially stores the image data in the hardware resource when printing the image data input from the outside at least, and the gradation correction processing unit includes When the hardware resources of the page memory unit are vacant, both the correction processing of the maximum gradation value and the correction processing of the intermediate gradation value are performed, and the page memory unit If there is no room to over de hardware resources, it corrects at least the maximum tone value, characterized in that.

  The image processing method according to the present invention is an image processing method for performing tone correction of an image, acquires density information of a test pattern, and the density information of the test pattern acquired by the density information acquisition unit is a predetermined reference density. The correction processing of the maximum gradation value and the correction processing of the intermediate gradation value are performed so as to be within the range, the image data is temporarily stored in units of pages, and at least input from the outside When printing image data, the image data is preferentially stored in the hardware resource, and if the hardware resource of the page memory unit is empty, the correction process of the maximum gradation value and the intermediate gradation value If the hardware resources of the page memory unit are not available, at least the maximum gradation value is corrected. And butterflies.

  According to the image forming apparatus and the image processing method thereof according to the present invention, it is possible to switch the correction processing control of the intermediate gradation value according to the state of the hardware resource in the page memory unit.

1 is a block diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a schematic cross-sectional view showing an example of an internal configuration of an image forming unit according to the embodiment. FIG. 2 is a block diagram showing a detailed configuration of a printer image processing unit according to the embodiment. The block diagram which shows the detailed structure at the time of the maximum gradation value correction | amendment of the printer type image process part which concerns on embodiment same as the above. 6 is a flowchart showing an operation at the time of maximum gradation value correction of the printer-type image processing unit according to the embodiment. FIG. 3 is a block diagram showing a detailed configuration of the printer-type image processing unit according to the embodiment when correcting an intermediate gradation value. FIG. 3 is a block diagram showing a detailed configuration at the time of halftone value correction when the hardware resources of the page memory unit cannot be secured in the printer image processing unit according to the embodiment. 6 is a flowchart showing an operation at the time of intermediate gradation value correction of the printer-type image processing unit according to the embodiment. (A) is a conceptual diagram of density adjustment in the above embodiment, and (B) is a conceptual diagram of gradation characteristic correction in the above embodiment. The figure which shows the gradation correction table of gradation characteristic correction in embodiment same as the above.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a diagram illustrating a system configuration example of an image forming apparatus 1 according to an embodiment of the present invention, for example, a digital MFP (Digital Multi-Function Peripheral). The image forming apparatus 1 functions as a digital color multifunction peripheral. For example, a copy function, a printer function, a scanner function, a FAX function, a storage function, and the like are realized.

  The image forming apparatus 1 includes a reading unit 11, a scanner system image processing unit 21, a printer system image processing unit 22, a page memory unit 13, and an image recording unit 14, and a copy function is realized by these configurations.

  The reading unit 11 optically reads a document with a three-line CCD sensor and converts it into red (R), green (G), and blue (B) color digital image signals.

  The scanner system image processing unit 21 performs various image processing such as shading correction for correcting non-uniformity of the signal level in the main scanning direction and spatial filtering processing. Further, when operating as a copy function, the page memory unit 13 converts the primary colors of R, G, and B into, for example, cyan (C), magenta (M), yellow (Y), and black (K) color signals. On the other hand, when it operates as a scanner function, it outputs to the page memory unit 13 as three primary colors of R, G, and B.

  The page memory unit 13 temporarily stores the image signal output by the scanner system image processing unit 21 in units of pages, for example, and outputs the image signal to the printer system image processing unit 22 again. Further, image data output from the printer controller unit 16 or the FAX controller unit 17 is temporarily stored in hardware resources.

  The printer image processing unit 22 performs gradation correction on the image signal output from the page memory unit 13, performs image processing for printing, and outputs the image signal to the image recording unit 14. Details will be described later.

  The image recording unit 14 is a component that prints an image on a recording sheet by, for example, an electrophotographic method, and includes an exposure device, a photosensitive drum, a developing device, and the like (all not shown).

  The image forming apparatus 1 includes a storage unit 15, a printer controller unit 16, a FAX controller unit 17, an electronic data creation unit 18, and an external I / F unit 19. These components are used when the image forming apparatus 1 is operated as a storage function, a printer function, a FAX function, a scanner function, and the like.

  The storage unit 15 is configured by, for example, an HDD (Hard Disk Drive), and stores an image signal read by the reading unit 11 and an image signal input from an external personal computer or the like. The image signal stored in the storage unit 15 can be read out as necessary, printed by the image recording unit 14, or output to the outside as scan data.

  When the image forming apparatus 1 operates as a scanner function, the electronic data creation unit 18 converts the image signal into a predetermined data format and generates scan data. The generated scan data is output to the outside via the external I / F unit 19.

  The FAX controller unit 17 operates the image forming apparatus 1 as a FAX function. The image signal read by the reading unit 11 is converted into a data format for FAX and output to an external telephone line via the external I / F unit 19. In addition, FAX data input from a telephone line can be converted into an image signal, and printing can be performed by the image recording unit 14.

  The printer controller unit 16 performs various controls and various processes necessary for the print function when the image forming apparatus 1 operates as a printer function. The control unit 10 performs control related to the entire image forming apparatus 1.

  FIG. 2 is a schematic cross-sectional view mainly showing an internal configuration example of the image forming unit 14. The image forming apparatus 1 according to the present embodiment has a configuration capable of color printing by a so-called tandem type electrophotographic system.

  The image forming unit 14 includes a transfer belt (image carrier) 500, a density sensor unit (density information acquisition unit) 520, a paper feed unit 530, a recording paper transfer unit 540, a fixing unit 550, and a paper discharge unit 560. ing.

  Further, four photosensitive drums (photosensitive members) 510 a to 510 d corresponding to four colors of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in parallel along the conveyance direction of the transfer belt 500. It is arranged. Around each photosensitive drum 510, charging units 511a to 511d, developing units 512a to 512d, transfer rollers 513a to 513d, cleaners 514a to 514d, and the like are sequentially arranged from upstream to downstream of rotation. Further, exposure units 515a to 515d for irradiating the photosensitive drums 510a to 510d with laser light are provided for each color. Here, the letters a, b, c, and d attached to the reference numbers of the components correspond to the printing colors Y, M, C, and K, respectively.

  The surfaces of the photosensitive drums 510a to 510d are charged to a predetermined potential by the charging units 511a to 511d, and electrostatic latent images are formed on the surfaces by the light emitted from the exposure units 515a to 515d, for example, laser light. The electrostatic latent images are developed with toner supplied from the developing units 512a to 512d, and developed images corresponding to the toner colors are formed on the surfaces of the photosensitive drums 510a to 510d.

  The developed images formed on the photoconductor drums 510a to 510d are transferred onto the transfer belt 500 in the order of Y, M, C, and K, and the four colors are combined when they pass the K photoconductor drum 510d. The full color toner image thus formed is formed on the transfer belt 500. However, in the operation of performing gradation correction using a gradation patch pattern, the gradation patch pattern is transferred in a single color of each of cyan (C), magenta (M), yellow (Y), and black (K). This is done a total of 4 times.

  A density sensor unit 520 for detecting the density of the toner image transferred onto the transfer belt 500 is disposed on the most downstream side of the transfer belt 500 (downstream side of the photosensitive drum 510d).

  The toner image on the transfer belt 500 is transferred to the recording paper supplied from the paper supply unit 530 in the recording paper transfer unit 540. The toner image transferred to the recording paper is fixed on the recording paper by the fixing unit 550 and discharged from the paper discharge unit 560 to the outside.

  In each of the photosensitive drums 510a to 510d after the transfer to the transfer belt 500, the toner remaining on the surface is removed by the cleaners 514a to 514d to prepare for the printing of the next sheet. By repeating the above processing, continuous full color printing can be performed.

  The density test pattern 600 is a so-called solid pattern corresponding to the maximum gradation value used for density adjustment. When density adjustment is performed, the density test pattern 600 is read and a toner image of the density test pattern is formed on the transfer belt 500. The density of these density test patterns is detected by the density sensor 520.

  Next, the detailed configuration of the printer image processing unit 22 will be described with reference to FIG.

  The density adjustment unit 231 compares and determines the density detected by the density sensor 520 in the image forming unit 14 and the reference density, so that the detected density approaches the reference density (reference maximum gradation value). Correction is performed by adjusting the exposure amount.

  The gradation correction table creation unit 221 creates a gradation correction table for correcting the gradation characteristics of the image signal and stores the gradation correction table in the gradation correction table storage unit 222.

  The gradation adjustment unit 232 has a reference gradation density obtained and stored in advance for each gradation in the gradation patch pattern read by the density sensor 520 in the image forming unit 14 or the reading unit 11. The gradation characteristics of the image are changed and updated using the gradation correction table stored in the gradation correction table storage unit 222 so as to be within the predetermined range.

  The density adjustment unit 231 and the gradation adjustment unit 232 are combined to form a gradation correction processing unit 226. Here, density adjustment and gradation adjustment will be described with reference to FIG.

  The density adjustment at the maximum gradation is performed for the output density so that the density corresponding to the maximum gradation matches the reference density as shown in FIG. In the example of FIG. 9A, the horizontal axis is a gradation in the range of 0 to 255 when the gradation is expressed by 8 bits so that the density corresponding to the maximum 255 gradations matches 1. It is adjusted to.

  FIG. 9B is a conceptual diagram of gradation characteristic correction. If the set tone value (tone value of the input image signal) and the tone value (density) of the printed image have a one-to-one linear relationship, it is not necessary to correct the tone of the image signal. It is non-linear as indicated by the broken line 9. Therefore, as shown by the straight line in FIG. 9, the gradation (density) of the print image with respect to the set gradation value is corrected to be one-to-one or close. For example, the set gradation value is corrected using the gradation correction table shown in FIG.

  A curve indicated by a bold line below FIG. 10 is a diagram illustrating a gradation correction table. The shape of the characteristic of the gradation correction table is line symmetric with the characteristic indicating the relationship between the set gradation value and the density (before correction) of the printed image signal. By using the gradation correction table having such a shape, the relationship between the set gradation value and the print density can be corrected to be linear.

  The dither processing unit 227 selects a halftone screen stored in the halftone screen storage unit 240 corresponding to the gradation characteristics corrected by the gradation adjustment unit 232, and performs image processing.

  The test pattern 230 indicates pixel level values (numerical values) for each density that are stored in the printer image processing unit 22 in advance.

<Correction of maximum gradation value>
Next, correction processing for the maximum gradation value in the above configuration will be described with reference to FIGS.

  The start timing of the correction of the maximum gradation value is, for example, when the image forming apparatus 1 is started by pressing the power supply (step S101) or after printing a predetermined number of sheets (for example, 1000 sheets) (step S103). To be done. The density sensor 520 in the image forming unit 14 detects the density of the density test pattern 600 (step S105). This density test pattern 600 is a solid pattern. Next, the density sensor 520 sends the detected density to the density adjustment unit 231 (step S107). The density adjustment unit 231 compares and determines the density sent in step S107 and the reference density (reference maximum gradation value) that is previously held, and adjusts the charging potential, the development potential, the exposure amount, and the like to obtain the density. Is corrected (step S109).

  Since the page memory unit 13 is not used for correcting the maximum gradation value, the maximum gradation value can be corrected even when the page memory unit 13 is occupied by image data in printing or FAX transmission / reception.

<Control of intermediate tone value correction processing>
Next, the operation of the correction processing control of the intermediate gradation value in the above configuration will be described with reference to FIGS.

  After the maximum gradation value correction operation is completed, the control unit 10 checks the hardware resources of the page memory unit 13. When the hardware resource of the page memory unit 13 is not occupied by the image data in the printing or FAX transmission / reception operation and the hardware resource can be secured (“Yes” in step S201 in FIG. 8), the control unit 10 Intermediate tone value correction processing is performed (FIG. 6).

  The control unit 10 reads the test pattern 230 in the printer image processing unit 22 and applies the corresponding halftone screen stored in the halftone screen storage unit 240 by the dither processing unit 227 to apply the gradation patch pattern X. Is formed (step S203). At this time, it is temporarily stored in the hardware resource of the page memory unit 13 (shown as “tone patch pattern” in FIG. 6). The image forming unit 14 transfers the gradation patch pattern X to the transfer belt 500. The density sensor 520 acquires density data of the gradation patch pattern X (step S205).

  The image forming unit 14 transmits the acquired density data of the gradation patch pattern X to the gradation correction table creating unit 221 of the same image forming apparatus 1. The tone correction table creation unit 221 creates a tone correction table for correcting tone characteristics based on the density of the tone patch pattern X, and stores the tone correction table in the tone correction table storage unit 222 (step S207).

  Next, the gradation adjusting unit 232 adjusts the gradation patch pattern X so that the density for each gradation of the gradation patch pattern X falls within a predetermined range of the reference gradation density acquired and stored in advance. The tone characteristics are changed and updated using the tone correction table stored in the tone correction table storage unit 222 in step S207 (step S209).

<When hardware resources cannot be secured>
In FIG. 7, the hardware resources of the page memory unit 13 are first occupied by image data in printing or FAX transmission / reception operations (indicated by “print image data” and “FAX transmission / reception image data” in FIG. 7). If the resource cannot be secured immediately (“No” in step S201 in FIG. 8), the control unit 10 determines whether the “time priority mode” is specified in advance by the user through the operation unit (not shown) of the image forming apparatus 1. Depending on whether the “image quality priority mode” is set (step S250), processing corresponding to the mode is performed.

  When the user has set the “image quality priority mode” (“image quality priority” in step S250), the control unit 10 waits for the end of printing or FAX transmission / reception processing until the hardware resources of the page memory unit 13 are secured. (Step S252). When the processing of printing or FAX transmission / reception is finished and the hardware resources of the page memory unit 13 can be secured (“Yes” in step S254), the process proceeds to step S203.

  When the user has set the “time priority mode” (“time priority” in step S250), since the process of printing or FAX transmission / reception is not waited, the gradation correction is performed only for the maximum gradation value, and the intermediate gradation value is changed. Correction processing is not performed. Therefore, the process ends.

  In other words, when the hardware resources of the page memory unit 13 cannot be secured, either halfway gray level correction processing is waited until printing or FAX transmission / reception processing ends, or middle gray level correction processing is not performed. Do something.

  As mentioned above, although embodiment of this invention was explained in full detail with reference to drawings, the specific structure is not restricted to this embodiment, The design change etc. of the range which does not deviate from the summary of this invention are included.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Control part, 11 ... Reading part, 13 ... Page memory part, 14 ... Image forming part, 15 ... Storage part, 16 ... Printer controller part, 17 ... FAX controller part, 18 ... Electronic data creation , 21: Printer system image processing unit, 22 ... Printer system image processing unit, 520 ... Density sensor, 221 ... Tone correction table creation unit, 222 ... Tone correction table storage unit, 240 ... Halftone screen storage unit, 226 ... tone correction processing unit, 227 ... dither processing unit, 230 ... test pattern, 231 ... density adjustment unit, 232 ... tone correction unit, 600 ... density test pattern.

Claims (5)

In an image forming apparatus that performs gradation correction of an image,
A density information acquisition unit that acquires density information of the test pattern;
A correction process of at least one of a maximum gradation value correction process and an intermediate gradation value correction process so that the density information of the test pattern acquired by the density information acquisition unit is within a predetermined range of a reference density. A gradation correction processing unit to be performed;
Temporarily storing image data in units of pages, and at least when printing the image data input from the outside, a page memory unit that preferentially stores the image data in its hardware resources;
Have
The gradation correction processing unit
When there is a vacancy in the hardware resource of the page memory unit, both the correction process of the maximum gradation value and the correction process of the intermediate gradation value are performed, and when there is no vacancy in the hardware resource of the page memory unit, Correcting at least the maximum gradation value;
An image forming apparatus. The test pattern is a gradation test pattern having a plurality of gradations,
The gradation correction processing unit
The gradation test pattern temporarily stored in the hardware resource of the page memory unit is printed on an image carrier, and the density of the gradation test pattern on the image carrier acquired by the density information acquisition unit is The image forming apparatus according to claim 1, wherein the intermediate gradation value is corrected so as to be within a predetermined range of the reference gradation density. When there is no free hardware resource in the page memory unit, the gradation correction processing unit waits for the correction process of the intermediate gradation value until the free hardware resource is secured.
The image forming apparatus according to claim 1. The test pattern is a density test pattern corresponding to the maximum density,
The correction of the maximum gradation value performed by the gradation correction processing unit uses the density test pattern,
The image forming apparatus according to claim 1, wherein the maximum gradation characteristic is corrected so that the density of the density test pattern acquired by the density information acquisition unit falls within a predetermined range of a reference density. In an image processing method for correcting gradation of an image,
Obtain the density information of the test pattern,
Correction processing of at least one of maximum gradation value correction processing and intermediate gradation value correction processing so that the density information of the test pattern acquired by the density information acquisition unit is within a predetermined range of a reference density. Done
Temporarily storing image data in page units, and at least when printing the image data input from the outside, preferentially store the image data in its hardware resources,
When there is a vacancy in the hardware resource of the page memory unit, both the correction process of the maximum gradation value and the correction process of the intermediate gradation value are performed, and when there is no vacancy in the hardware resource of the page memory unit, Correcting at least the maximum gradation value;
An image processing method.

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