JP4408075B2 - Printing device - Google Patents

Description

  The present invention uses a printing unit that prints an image according to image data input in a plurality of modes, and an input gradation correction formula according to the mode to correct the input gradation of the image data and correct the input level. The present invention relates to a printing apparatus including an adjustment unit that adjusts the output gradation of a print image by generating a tone and outputting the tone to a printing unit.

  The digital multi-function peripheral includes a scanner that reads a document image and generates image data, and a printing unit that prints image data obtained from the scanner and the outside. The printer operates in three modes: a copier (copy machine), a printer, and a FAX.

  By the way, normally, in such a digital multi-function peripheral, in order to obtain an appropriate image desired by the user, the gradation (input gradation) of input image data is corrected by a correction formula (or correction table) and corrected input. Gradation is generated and output to the print engine.

However, “what correction formula should be used” changes due to the influence of environmental fluctuations and fluctuations with time.
Therefore, conventionally, a technique for recreating (correcting) a correction formula based on an image patch (test patch) corresponding to built-in test data has been developed (see Patent Document 1).
In this technique, a predetermined test patch composed of CMYK colors is generated and read by a detector. Then, based on the read result, the current output tone characteristic in the printing unit is obtained, and a correction formula or correction table is generated using this.
JP 2002-335401 A (publication date; November 22, 2002)

By the way, normally, an appropriate correction formula or correction table differs depending on the print mode. This is because the quality of image data to be used differs depending on each mode (for example, the quality is low in FAX but high in printer).
For this reason, conventionally, the correction formula as described above is created for each printing mode, and toner consumption and waiting time (time required for correction) are burdens on the user.

  The present invention has been made in view of the conventional problems as described above. An object of the present invention is to provide a printing apparatus capable of reducing toner consumption and standby time related to the creation of a correction formula.

In order to achieve the above object, the printing apparatus of the present invention (the present printing apparatus)
A printing unit that prints an image according to image data input in a plurality of modes;
An adjustment unit that adjusts the output tone of the print image by generating the corrected input tone by correcting the input tone of the image data using the input tone correction formula corresponding to the mode, and outputting the corrected input tone to the printing unit. In a printing apparatus equipped with
The adjustment section above
A measurement unit for measuring the output gradation of the printed image;
A plurality of images corresponding to a plurality of different input gradations are printed on the printing unit, and the output gradations of these images are measured by the measurement unit.
An input / output relational expression that is a relational expression between the plurality of input gradations and the output gradation measurement value obtained by the measurement unit is obtained,
Based on this input / output relational expression, a corrected input gradation that obtains an ideal value of the output gradation corresponding to the plurality of input gradations is obtained, and the relationship between the input gradation and the corrected input gradation is expressed. And a control unit that creates an input tone correction formula.
When creating a modified input tone for the second mode after creating a modified input tone for the first mode using a predetermined number of input tones,
The above control unit
Find the ideal value of the output gradation in the second mode according to the input gradation used when creating the input gradation correction formula of the first mode,
Based on the above output relational expression, this is a configuration designed to obtain a corrected input gradation that can obtain this ideal value.

The printing apparatus can print image data input in a plurality of printing modes such as copying, FAX, and printer by a printing unit.
Here, the gradation (input gradation) of the image data for printing is corrected before it is output to the printing unit (print engine).

In other words, the gradation (output gradation) of the image data to be printed usually changes depending on the input mode of the image data and the characteristics of the printing unit. In order to cope with such conversion, the printing apparatus appropriately adjusts the input gradation by the adjustment unit to adjust the output gradation of the print image, thereby obtaining an image desired by the user.
Such correction is performed by an input tone correction formula set for each mode. This input gradation correction formula indicates the correspondence between the input gradation and the corrected input gradation (corrected input gradation).

It should be noted that the relationship between the input gradation and the appropriate corrected input gradation corresponding to the input gradation changes due to the influence of environmental fluctuations and temporal fluctuations.
Therefore, it is necessary to correct (recreate) the input tone correction formula as described above at an appropriate timing.

Therefore, in this printing apparatus, the adjustment unit includes a configuration (measurement unit, control unit) for creating such an input gradation correction formula.
That is, the adjustment unit includes a measurement unit that measures the output gradation of the printed image. This measuring unit measures the gradation (output gradation) of a test patch (print image used for the test) for creating an input gradation correction formula.
The control unit controls the printing unit and the measurement unit to create an input tone correction formula.

That is, the control unit controls the printing unit to print a plurality of images (test patches) according to a plurality of different input gradations (test input gradations). This input gradation may be selected in any way, but is preferably a preset value.
And a control part measures the output gradation of these images by a measurement part.

Thereafter, the control unit obtains these relational expressions (input / output relational expressions) from the test input gradation and the measured value of the output gradation obtained by the measurement unit.
For example, when the above input / output relational expression is a linear expression, when the test input gradation is In and the output gradation measurement value is Cout, the input / output relational expression is
Cout (In) = α · In (1)
(Α is a constant).

After that, the control unit sets a corrected input gradation so as to obtain an ideal value (value desired by the user; set value) of the output gradation corresponding to the test input gradation based on the input / output relational expression. Ask.
That is, in the above example, if the ideal value (setting value) is Cref, the corrected input gradation Cn is
Cref (In) = Cout (Cn)
Is obtained by calculating back.
Note that the ideal value of the output gradation as described above can be stored in a storage unit provided in the printing apparatus.

Next, the control unit creates an input tone correction formula that represents the relationship between the test input tone and the corrected input tone.
That is, the control unit obtains the following correction coefficient An representing the relationship with the corrected input gradation Cn for all test input gradations In.
An = Cn / In
After that, the control unit as an input tone correction formula,
Cn = An · In
Ask for. Thus, the input tone correction formula creation (correction) process for one mode is completed.

  In particular, in this printing apparatus, the control unit creates an input tone correction formula for a certain mode (first mode) using test patches corresponding to a predetermined number of test input tones, and then applies the test patches. Without using it, an input tone correction formula for another mode (second mode) is created.

  That is, when creating the input gradation correction formula for the second mode, the control unit outputs in the second mode according to the predetermined number of input gradations used when creating the input gradation correction formula for the first mode. An ideal gradation value (Pref) is obtained. Such ideal values can be stored in advance in the storage unit described above.

And a control part calculates | requires the correction input gradation that a correction output gradation becomes this ideal value using above-mentioned (1) Formula. That is, the control unit calculates (back-calculates) the corrected output gradation Pn that satisfies the following expression (2).
Pref (In) = Cout (Pn) (2)
Such Pn is
Pn = Pref (In) / α
Sought by.

Thereafter, as in the first mode, the control unit creates an input tone correction formula for the second mode that represents the relationship between the test input tone and the corrected input tone.
That is, the control unit obtains the following correction coefficient Anp for the test input gradation In and the modified input gradation Pn used in the first mode.
Anp = Pn / In
After that, the control unit as an input tone correction formula,
Pn = Anp · In
Ask for. This completes the input tone correction formula creation (correction) process for the second mode.

As described above, in the printing apparatus, when the input gradation correction formula for the second mode is created, the output gradation measurement value obtained when the input tone correction formula for the first mode is created is used. Yes. Therefore, it is possible to derive an input tone correction formula without actually printing a test patch.
Thereby, in this printing apparatus, it is possible to reduce the toner consumption and the standby time related to the creation of the input tone correction formula.

  In this printing apparatus, after creating an input tone correction formula for each mode, a correction table may be created based on this formula. This correction table includes all (or part of) input gradations and correction input gradations corresponding to each input gradation.

The printing apparatus is preferably designed to print an image in a copy mode for copying an original image and a printer mode for printing image data input from the outside.
In this case, the control unit preferably selects the copy mode as the first mode.

  Since the copy mode is a mode for creating a copy of a document image, it can be said that it is preferable to create a printed material as close to the document as possible. Therefore, it is preferable to preferentially generate the input tone correction formula in the copy mode by a method capable of obtaining an accurate input tone correction formula.

The printing apparatus preferably includes a frequency storage unit that calculates and stores the usage frequency of each mode.
Such a frequency storage unit is a device that counts the number of printed sheets for each print mode, calculates the use frequency from the count number and the total number of prints, and stores the calculation result. For example, a copy counter can be used as such a frequency storage unit.
In such a case, it is preferable that the control unit is designed to select a mode with the highest usage frequency as the first mode. This makes it possible to generate an input tone correction formula for a frequently used mode with high accuracy.

Further, when the frequency storage unit as described above is provided, the control unit may be designed to determine the frequency of the first mode in each print mode according to the usage frequency.
In this configuration, for example, when the printing mode of the printing apparatus is the copy mode and the printer mode and the ratio of the usage frequencies is 3: 1, the copy mode is set to the first mode only three times. The printer mode is set to the first mode only once.

It is also preferable that the printing apparatus includes an operation unit that can input a user instruction. In this case, it is preferable that the control unit is designed so that the print mode to be the first mode can be selected based on a user instruction input via the operation unit.
In this configuration, the user can create an input tone correction expression in a mode that is considered important (for example, frequently used) with high accuracy.

Note that the input tone correction formula as described above may be created at any timing.
For example, immediately before the printing apparatus is shipped from the factory (at the time of factory shipment), when the printing apparatus is turned on (when the power is turned on), when a predetermined number of sheets are printed, and development conditions are changed, the photosensitive drum By performing the timing at the time when the printer is replaced, it is possible to suppress the influence of environmental variation and temporal variation on the printed image.

As described above, the printing apparatus of the present invention (the present printing apparatus)
A printing unit that prints an image according to image data input in a plurality of modes;
An adjustment unit that adjusts the output tone of the print image by generating the corrected input tone by correcting the input tone of the image data using the input tone correction formula corresponding to the mode, and outputting the corrected input tone to the printing unit. In a printing apparatus equipped with
The adjustment section above
A measurement unit for measuring the output gradation of the printed image;
A plurality of images corresponding to a plurality of different input gradations are printed on the printing unit, and the output gradations of these images are measured by the measurement unit.
An input / output relational expression that is a relational expression between the plurality of input gradations and the output gradation measurement value obtained by the measurement unit is obtained,
Based on this input / output relational expression, a corrected input gradation that obtains an ideal value of the output gradation corresponding to the plurality of input gradations is obtained, and the relationship between the input gradation and the corrected input gradation is expressed. And a control unit that creates an input tone correction formula.
When creating a modified input tone for the second mode after creating a modified input tone for the first mode using a predetermined number of input tones,
The above control unit
Find the ideal value of the output gradation in the second mode according to the input gradation used when creating the input gradation correction formula of the first mode,
Based on the above output relational expression, this is a configuration designed to obtain a corrected input gradation that can obtain this ideal value.

  In this printing apparatus, the control unit creates an input tone correction formula for a certain mode (first mode) using test patches corresponding to a predetermined number of test input tones, and then uses the test patches without using the test patches. In this mode (second mode), an input tone correction formula is created.

That is, in this printing apparatus, when the input tone correction formula for the second mode is created, the output tone measurement value obtained when the input tone correction formula for the first mode is created is used. Therefore, it is possible to derive an input tone correction formula without actually printing a test patch.
Thereby, in this printing apparatus, it is possible to reduce the toner consumption and the standby time related to the creation of the input tone correction formula.

An embodiment of the present invention will be described.
FIG. 2 is an explanatory diagram showing the configuration of the digital color multifunction peripheral (the present multifunction peripheral) according to the present embodiment. This multifunction device has functions as a facsimile machine and a printer (FAX mode, printer mode) in addition to a function as a normal copying machine (copy mode).

First, the configuration of the multifunction peripheral will be described.
As shown in FIG. 2, the multifunction machine is configured to include a RADF 112, a scanner unit 110, an image forming unit 210, and a paper feed mechanism 211, and further includes an operation panel (not shown).

  The RADF 112 is a document feeder in the multifunction peripheral, and has a function as a double-sided automatic document feeder (RADF).

  That is, the RADF 112 conveys a document set at a predetermined position onto a document table 111 in the scanner unit 110. Then, after the document image is read by the scanner unit 110, it has a function of carrying it out to a predetermined take-out position.

  The RADF 112 also has a function of turning over the original after reading the original image by the scanner unit 110 and transporting the original to the original table 111 again. As a result, in the present multifunction machine, the scanner unit 110 can read the images on both sides of the document.

  Further, the RADF 112 can be opened and closed with respect to the document table 111. Therefore, when using the RADF 112, the user can place the document directly on the document table 111 by closing the RADF 112 and opening the RADF 112.

  The scanner unit 110 is for reading an image of a document conveyed by the RADF 112, and is an image input device in the multifunction machine. As shown in FIG. 2, the scanner unit 110 includes a first scanning unit 113, a second scanning unit 114, an optical lens 115, and a CCD 116 in addition to the document table 111 described above.

  The scanning units 113 and 114 are for reading an image of a document placed on the document table 111 by reciprocating in parallel with the document table 111. The first scanning unit 113 includes an exposure lamp that exposes a document image and a first mirror that deflects a reflected light image from the document in a predetermined direction. Then, it is set so as to reciprocate in parallel with the document table 111 at a predetermined scanning speed while maintaining a certain distance from the lower surface of the document table 111.

  The second scanning unit 114 includes second and third mirrors for deflecting the reflected light image deflected by the first mirror in the direction in which the optical lens 115 is positioned. The first scanning unit 113 reciprocates in parallel with the document table 111 while maintaining a constant speed relationship.

  The optical lens 115 reduces the reflected light image from the original deflected by the first to third mirrors and forms an image at a predetermined position on the CCD 116.

  The CCD 116 is a photoelectric coupled device (CCD) line sensor for photoelectrically converting the formed reflected light image to generate image information of an electrical signal and outputting it to the image forming unit 210.

  Further, the CCD 116 can read a color image. That is, the CCD 116 can generate image information of line data color-separated for each color component of R (red), G (green), and B (blue) from the color reflected light image.

  The image information generated by the CCD 116 is further transferred to an image processing unit (see FIG. 3) described later, subjected to predetermined image processing, and then output to the image forming unit 210.

  The image forming unit 210 is for printing an image on a sheet based on the image information output from the CCD 116. The image forming unit 210 includes a black image transfer unit 301, a yellow image transfer unit 302, a magenta image transfer unit 303, and a cyan image transfer unit 304, as shown in FIG.

  These transfer units 301 to 304 have substantially the same configuration, and are set to transfer a black image, a yellow image, a magenta image, and a cyan image to the sheet based on the image information. Yes.

  As shown in FIG. 2, the transfer units 301 to 304 have LSUs 227a to 227d and image forming stations Ga to Pd, respectively.

Pixel signals corresponding to a black component, a yellow component, a magenta component, and a cyan component in image information are input to LSUs (laser beam scanner units) 227a to 227d, respectively.
Each of the LSUs 227a to 227d is set so as to expose photosensitive drums 222a to 222d (described later) in the image forming stations Ga to Pd based on these image signals to generate an electrostatic latent image.

  Further, these LSUs 227a to 227d include a semiconductor laser diode (not shown) and a laser adjustment unit that controls the power of the semiconductor laser diode and the timing of light generation in order to generate a dot-shaped laser beam modulated according to image information. And have.

  Further, as shown in FIG. 2, the LSUs 227a to 227d include polygon mirrors 240a to 240d, f-θ lenses 241a to 241d, and mirrors 242a to 242d and 243a to 243d.

  The polygon mirrors 240a to 240d have a function of deflecting a laser beam emitted from the semiconductor laser element in the main scanning direction. The f-θ lenses and mirrors described above are for imaging the laser beams deflected by the polygon mirrors 240a to 240d on the surfaces of the photosensitive drums 222a to 222d.

The image forming stations Ga to Pd generate toner images corresponding to the respective colors based on the laser beams irradiated from the LSUs 227a to 227d, and sequentially transfer the toner images to the sheet.
As shown in FIG. 2, these image forming stations Ga to Pd include photosensitive drums 222a to 222d. Chargers 223a to 223d, developing devices 224a to 224d, transfer discharge devices 225a to 225d, and cleaning devices 226a to 226d are arranged around the photosensitive drums 222a to 222d along the direction of arrow F.

Each of the photosensitive drums (transfer drums) 222a to 222d is a drum-shaped transfer roller having a photosensitive material on its surface, and is set to be rotationally driven in the direction of arrow F.
The chargers 223a to 223d are scorotron type corona dischargers for uniformly charging the photosensitive drums 222a to 222d, respectively.

  The developing devices 224a to 224d contain black, yellow, magenta, and cyan toners, respectively. These toners have a function of developing the electrostatic latent images generated on the photosensitive drums 222a to 222d to generate toner images.

The transfer dischargers 225a to 225d are corona dischargers for transferring the toner images on the photosensitive drums 222a to 222d to a sheet. Note that the power (potential) of the transfer dischargers 225a to 225d is controlled by a power adjusting unit (not shown).
Further, the cleaning devices 226a to 226d shown in FIG. 2 have a function of removing toner remaining on the photosensitive drums 222a to 222d after transfer to the sheet.

  The sheet feeding mechanism 211 conveys the sheet to a predetermined position of the image forming unit 210 in order to transfer the color toner images generated by the image forming unit 210 to the sheet. Further, the paper feed mechanism 211 has a function of discharging the sheet to the outside after the toner image is transferred.

  As shown in FIG. 2, the sheet feeding mechanism 211 includes a sheet cassette 251, a take-out roller 253, a plurality of conveyance rollers 252 and 261, a registration roller 212, a transfer conveyance belt mechanism 213, a fixing device 217, a conveyance direction switching gate 218, a discharge roller. A paper roller 219 and a paper discharge tray 220 are provided.

The sheet cassette 251 is for accommodating a cut sheet-like sheet P used in the present multifunction machine.
The take-out roller 252 is a pickup roller for taking out the sheets P one by one from the sheet cassette 251.
Further, the conveyance rollers 252... Feed the sheet P outputted from the sheet cassette 251 to the main conveyance path L and convey it on the conveyance path L.

  The pre-registration detection switch is for detecting that the sheet P conveyed by the conveying rollers 252... Has passed a predetermined position on the main conveying path L and outputting a predetermined detection signal.

  The registration rollers 212 temporarily hold the sheet P that has been transported along the main transport path L. The toner image on the photosensitive drums 222a to 222d has a function of feeding it to the transfer / conveying belt mechanism 213 at the same timing as the image forming stations Ga to Pd so that the toner images can be satisfactorily transferred to the sheet P.

  That is, the registration roller 212 transfers the sheet P based on the detection signal output by the pre-registration detection switch so that the leading edge of the toner image on the photosensitive drums 222a to 222d is pressed against the leading edge of the printing range on the sheet P. The feed belt mechanism 213 is set to feed.

  As shown in FIG. 2, the transfer conveyance belt mechanism 213 includes a driving roller 214, a driven roller 215, a conveyance belt 216, an adsorption charger 228, a static eliminator 229, an auxiliary roller 231, and an optical sensor 232.

  The conveyor belt 216 is a belt that is placed between the driving roller 214 and the driven roller 215, and is frictionally driven in the direction of arrow Z by the rollers 214 and 215. The sheet P fed by the registration roller 212 is electrostatically adsorbed and transported to the image forming stations Ga to Pd and the fixing device 217.

  The suction charger 228 is a brush provided between the image forming station Ga and the registration roller 212 and charges the surface of the transport belt 216. That is, in this multifunction machine, the conveyance belt 216 is charged and the sheet P is electrostatically adsorbed to prevent the sheet from being displaced during conveyance.

  The static eliminator 229 is provided between the image forming station Gd and the fixing device 217, and is for neutralizing the surface of the transport belt 216 with an alternating current.

  That is, each color toner image is transferred and superimposed on the sheet P conveyed to the image forming stations Ga to Pd. When the transfer by the image forming station Gd is completed, the sheet P is set so as to be peeled from the conveying belt 216 sequentially from the leading end portion thereof by the static eliminator 229 and guided to the fixing device 217.

  The fixing device 217 thermally fixes the unfixed toner image transferred to the sheet P. Then, the heat-fixed sheet P is conveyed to the conveyance direction switching gate 218.

  The switching gate 218 selectively switches the conveyance path of the fixed sheet P between the discharge path toward the sheet discharge tray 220 and the sub-transport path S.

  This sub-conveying path S is a conveying path for turning the sheet P over and re-supplying it to the image forming unit 210. That is, the sheet P sent to the sub conveyance path S is turned over via the switchback conveyance path 221, and then conveyed on the sub conveyance path S by the conveyance rollers 261... And supplied again to the image forming unit 210. Is set to be.

The paper discharge roller 219 is a roller for discharging the sheet that has passed through the switching gate 218 toward the paper discharge tray 220.
The optical sensor 232 is a sensor used for correcting printing conditions of the image forming unit 210. The optical sensor 232 will be described later.

The MFP is connected to a network (intranet, Internet) together with a communication line such as a telephone line, an external device such as a mobile device, a digital camera, a digital video camera, and a personal computer (PC). It can also function as a digital printer or digital facsimile that receives image data from these devices and prints an image according to the image data.
In addition, the multifunction machine is provided with a control unit (not shown) that controls all operations of the multifunction machine.

Next, the image processing unit of the multifunction machine will be described.
FIG. 3 is an explanatory diagram showing the configuration of the image processing unit. As shown in this figure, the image processing unit of the multifunction peripheral includes an A / D conversion unit 11, a shading correction unit 12, a document type automatic discrimination unit 13, an input tone correction unit 14, a color correction unit 15, and an area separation process. 16, a black generation / undercolor removal unit 17, a spatial filter processing unit 18, an output tone correction unit 19, and a tone reproduction processing unit 20.

  The A / D (analog / digital) converter 11 converts analog RGB data output from the scanner unit 110 into a digital signal (digital RGB data).

The shading correction unit 12 performs processing for removing various distortions (distortion removal processing) caused by the illumination system, the imaging system, and the imaging system of the scanner unit 110 from the digital RGB data generated by the A / D conversion unit 11. And output to the document type automatic discrimination section 13.
The shading correction unit 12 also has a function of inputting image data input from an external device and outputting the image data to the document type automatic determination unit 13.

  The input tone correction unit 14 performs processing for adjusting color balance on the digital RGB data (RGB reflectance signal) that has been subjected to distortion removal processing by the shading correction unit 12.

Based on the digital RGB data from which distortion has been removed by the shading correction unit 12, the document type automatic discrimination unit 13 determines whether the input document image is a text document or a photographic document (printed photograph / photographic paper photograph). Or a mixed character / photo original.
Then, the document type automatic determination unit 13 outputs a document type determination signal as a determination result to the input gradation correction unit 14, the color correction unit 15, the black generation / under color removal unit 17, the spatial filter processing unit 18, and the gradation. It is designed to output to the reproduction processing unit 20.

  Further, the document type automatic discrimination unit 13 performs complementary color inversion on the digital RGB data to obtain CMY (C: cyan, M: magenta, Y: yellow) digital data (CMY data), which is used in the image processing unit. It also has a function of converting into a signal (density signal or the like) that is easy to handle for the image processing system.

  The color correction unit 15 performs processing for removing color turbidity (color turbidity removal processing) based on the spectral characteristics of toner from CMY data in order to faithfully reproduce colors. This color turbidity is caused by an unnecessary absorption component contained in the CMY toner.

  The region separation processing unit 16 determines whether each pixel in the image (original image) corresponding to the digital RGB data output from the input tone correction unit 14 belongs to a halftone dot region, a character region, or a photographic region. Region separation processing is performed.

  In addition, the region separation processing unit 16 generates a signal (region identification signal) indicating the region to which each pixel belongs based on the result of the region separation processing, a black generation / under color removal unit 17, a spatial filter processing unit 18, The data is output to the reproduction processing unit 20.

  The black generation / under color removal unit 17 generates black (K) data from CMY data. Further, the black generation / under color removal unit 17 generates new CMY data by subtracting the K data from the CMY data. Further, the new CMY data and the K data are used to generate four-color data (CMYK data ( CMYK data) is generated.

  The spatial filter processing unit 18 performs spatial filter processing using a digital filter on CMYK data based on the region identification signal. That is, the spatial filter processing unit 18 has a function of correcting the spatial frequency characteristics of the CMYK data and preventing blurring of the output image and deterioration of graininess.

The output tone correction unit 19 modifies the tone data (input tone data) of the CMYK data output from the spatial filter processing unit 18 in order to adjust the output tone characteristics of the image forming unit 210. .
This correction is performed using a correction table stored in a storage unit (not shown) of the multifunction machine. The correction table is different for each mode (copy mode, FAX mode, printer mode) of the multifunction machine.

  The gradation reproduction processing unit 20 performs gradation reproduction processing (halftone generation processing) for separating the CMYK data output from the output gradation correction unit 19 for each pixel and processing so as to reproduce the gradation of each pixel. It is something to execute. The processed CMYK data is designed to be output to the image forming unit 210.

Next, correction of printing conditions in the multifunction machine will be described.
In a printing apparatus such as this multifunction peripheral, due to the influences of fluctuations in the environment (temperature, humidity, etc.) and changes over time, the appropriate values of the development voltages (development bias and grid voltage) of the development apparatuses 224a to 224d and image formation The output gradation characteristic of the unit 210 changes.
Therefore, in this multifunction machine, the control unit is designed so as to correct the development voltage and the correction table used by the output tone correction unit 19 in order to cope with such a change.

First, correction (high density correction) of the development voltage (development bias and grid voltage) will be described.
In this correction, first, the control unit fixes the laser power of the LSUs 227a to 227d to 100%, and fixes the grid voltage Vg of the developing devices 224a to 224d to −600V.

  Then, the control unit switches the development bias Vb to three types of −275V, −325V, and −375V, and as shown in FIG. 4, three patches (image patterns) P1 to P3 corresponding to the respective voltages are provided. Is generated. The generation of the patches P1 to P3 is performed on the conveyance belt 216, not on the sheet.

Next, the control unit measures the density of these three patches P <b> 1 to P <b> 3 using the optical sensor 232.
This measurement is performed by the optical sensor 232 irradiating the patch with light and measuring the intensity of the reflected light. Therefore, the density is proportional to the intensity of the reflected light.

FIG. 5 is a graph showing the relationship between the developing bias Vb and the density regarding the patches P1 to P3. As shown in this graph, the control unit connects the densities of the three patches P1 to P3 with a straight line. Then, on this graph, the developing bias Vbo that obtains a predetermined reference density level Io is obtained. Then, the control unit sets the developing bias of the developing devices 224a to 224d at the time of printing to this Vbo.
The control unit
Grid voltage Vg (−600 V) −development bias Vbo> −150 V
In order to prevent image fogging, the grid voltage Vg is
Grid voltage Vg = development bias Vbo-150V
Change to

  Thereafter, the control unit removes the patches P1 to P3 on the conveyor belt 216 with a cleaner (not shown), and ends the correction of the development voltage (high density correction).

Next, correction of the correction table (halftone correction) used by the output tone correction unit 19 will be described.
This correction is processing for creating (recreating) a correction table.
In this process, the control unit first creates a correction table (copy correction table) used in the copy mode.

That is, as shown in FIG. 6, the control unit generates 16 patches D1 to D16 corresponding to the 16 types of input gradations in the copy mode on the transport belt 216 (S1).
Next, the control unit reads out an ideal output gradation (set value Cref) in the copy mode according to these 16 types of input gradations (S2). Note that these output gradations are stored in advance in a storage unit (not shown) stored in the image processing unit.

Thereafter, the control unit controls the optical sensor 232 to measure the gradation of the patches D1 to D16 on the conveyor belt 216 (S3).
FIG. 7 is a graph showing the relationship between the input gradation In, the set value Cref, and the measured value Cout. As shown in this graph, usually, the actual measurement value and the ideal value often do not match.

Next, the control unit obtains a state of change in the actual output value Cout of the output gradation with respect to the input gradation In by linear approximation (primary expression).
That is,
Cout (In) = α · In (1)
(Α is a constant).

After that, the control unit obtains the corrected input gradation Cn so that an output gradation similar to the output gradation setting value Cref corresponding to the 16 types of input gradations In described above can be obtained as an actual measurement value (S5). .
That is, the control unit calculates (back-calculates) Cn that satisfies the following expression (2) using the above expression (1) (S4).
Cref (In) = Cout (Cn) (2)
Such Cn is
Cn = Cref (In) / α
Sought by.

Next, the control unit obtains the following correction coefficient An for the 16 types of input gradations In and Cn (S6).
An = Cn / In
Thereafter, the control unit obtains correction coefficients An and corrected input gradations Cn corresponding to all input gradations In based on the 16 types of correction coefficients An. Then, a copy correction table including the corrected input gradation Cn (= An · In) corresponding to all the input gradations In is created, and the process is terminated.

  Thereby, the output tone correction unit 19 corrects the tone data (input tone In) of the CMYK data output from the spatial filter processing unit 18 to the corrected input tone Cn based on the copy correction table. It becomes possible.

  Table 1 shows the input gradation In, the output gradation setting value Cref, the actual output gradation value Cout, the corrected input gradation Cn, the correction coefficient An, and the copy obtained by the processing shown in S1 to S6 above. It shows an example of the corrected output gradation (corrected output) Ca obtained by the processing using the correction table.

In the example shown in this table, the value of α described above is 1.25.
FIG. 8 is a graph showing the relationship between the output gradation set value Cref, the output gradation measured value Cout, the correction coefficient An, the corrected output gradation Ca, and the input gradation In in Table 1. .

Next, the control unit creates a correction table (printer correction table) used in the printer mode.
In this process, the control unit reads out ideal output gradation values (setting values Pref) in the printer mode according to the 16 types of input gradations used for creating the copy correction table (S11). Note that these output gradations are stored in advance in a storage unit (not shown) stored in the image processing unit.

Next, the control unit uses Cout (In) = α · In (1) used for creating the copy correction table.
Is used to calculate (reverse calculation) Pn that satisfies the following expression (3) (S12).
Pref (In) = Cout (Pn) (3)
Such Pn is
Pn = Pref (In) / α
Sought by.

Next, the control unit obtains the following correction coefficient Anp for the 16 types of input gradations In and Pn (S13).
Anp = Pn / In
Thereafter, the control unit obtains correction coefficients Anp and corrected input gradations Pn corresponding to all input gradations In based on the 16 types of correction coefficients Anp. Then, a printer correction table including the corrected input gradation Pn corresponding to all the input gradations In is created, and the process ends.

  As a result, the output tone correction unit 19 converts the CMYK data tone data (input tone In) output from the spatial filter processing unit 18 into the corrected input tone Pn (= Anp) based on the printer correction table. It becomes possible to correct to In).

  Table 2 shows the input gradation In, the output gradation setting value Pref, the actual output gradation measurement value Cout, the corrected input gradation Pn, the correction coefficient Anp, and the printer obtained by the processing shown in S11 to S13. It shows an example of the corrected output gradation (corrected output) Pa obtained by the process using the correction table.

In the example shown in this table, the value of α described above is 1.25.
FIG. 9 is a graph showing the relationship between the output gradation set value Pref, the output gradation measured value Cout, the correction coefficient Anp, the corrected output gradation Pa, and the input gradation In in Table 2. .

  Next, the control unit creates a correction table (FAX correction table) used in the FAX-mode in the same manner as the printer correction table, and ends the process.

  As described above, in this printing apparatus, the control unit creates a correction table for the copy mode (first mode) using a test patch corresponding to a predetermined number of test input gradations, and then does not use the test patch. A correction table for the printer mode (second mode) is created.

That is, in this printing apparatus, when the correction table for the printer mode is created, the output gradation measurement value Cout obtained when the correction table for the copy mode is created is used. Therefore, it is possible to derive a correction table without actually printing a test patch.
Thereby, in this printing apparatus, it is possible to reduce the toner consumption and the waiting time relating to the creation of the correction table.

In the present embodiment, it is assumed that the patch is not printed when the correction table for printer is created.
However, the present invention is not limited to this, and fewer patches may be generated than those used for creating the copy mode correction table.
In this case, the control unit first generates three patches D21 to D23 corresponding to the three types of input gradations on the transport belt 216 in the printer mode, as shown in FIG. 10 (S21).

Next, the control unit reads an ideal output gradation value (set value Pref) in the printer mode corresponding to the 16 types of input gradations used for creating the copy correction table (S22). Note that these output gradations are stored in advance in a storage unit (not shown) stored in the image processing unit.
Thereafter, the control unit reads the gradation Cout of the patches D1 to D16 measured when the copy correction table is created (S23). This gradation is stored in the storage unit (not shown).

Next, the control unit controls the optical sensor 232 to measure the gradation Pout of the three patches D21 to D23 described above on the transport belt 216 (S24).
Then, the patch correction coefficient Da is calculated using the following equation (4) (S25).
Da = Pout / Cout (4)
Next, the control unit obtains a state of change of the output gradation actual value Pout with respect to the input gradation In by linear approximation (primary expression) (S26).
That is,
Pout (In) = β · In (5)
(Β is a constant). As a result, it is possible to compensate (interpolate) the missing part of the patch.

Next, the control unit obtains a corrected output gradation P′out as described below based on the actual measurement value Cout and the patch correction coefficient Da (S27).
P′out = Cout · Da (6)
Thereafter, the control unit obtains a state of change with respect to the input gradation In in the corrected output gradation P′out by quadratic curve approximation (S28).
That is,
P′out (In) = a · In ² + b · In + c (7)
(A, b, and c are constants).

Next, the control unit calculates (reverse calculation) Pn that satisfies the following expression (8) using the expression (7) (S29).
Pref (In) = P′out (Pn) (8)
Next, the control unit obtains the following correction coefficient Anp for the 16 types of input gradations In and Pn (S30).
Anp = Pn / In
Thereafter, the control unit obtains correction coefficients Anp and modified input gradations Pn (= Anp · In) corresponding to all input gradations In based on the 16 types of correction coefficients Anp. Then, a printer correction table including the corrected input gradation Pn corresponding to all the input gradations In is created, and the process ends.

  As a result, the output tone correction unit 19 converts the CMYK data tone data (input tone In) output from the spatial filter processing unit 18 into the corrected input tone Pn (= Anp) based on the printer correction table. It becomes possible to correct to In).

  Table 3 shows the input gradation In, the output gradation setting value Pref, the output gradation actual measurement values Cout and Pout, the patch correction coefficient Da, and the corrected output gradation P obtained by the processing shown in S21 to S30. 'out, corrected input gradation Pn, correction coefficient Anp, and corrected output gradation (corrected output) Pa obtained by processing using the correction table for printer are shown.

In the example shown in this table, a, b, and c shown in equation (7) are
a = 0.902
b = 0.6552
c = 0.04- (the square root of Pref)
It has become.
The input gradations corresponding to the patches D21 to D23 newly created in the printer mode are normalized values of 0.1, 0.4, and 0.8.

  Also, FIG. 1 shows the output gradation set value Pref, the output gradation measured values Cout and Pout, the patch correction coefficient Da, the corrected output gradation P′out, the correction coefficient Anp, and the corrected output Pa in Table 3. It is a graph which shows the relationship with the input gradation In.

  As described above, in this configuration, the control unit creates a correction table for a certain copy mode (first mode) using test patches corresponding to 16 types of test input gradations, and then the number is smaller than 16 types. A correction table for the printer mode (second mode) is created using various types of test patches.

That is, when the correction table for the printer mode is created, the output gradation measurement value Cout obtained in the copy mode is used. Therefore, it is possible to reduce the number of test patches actually printed.
Thereby, it is possible to reduce the toner consumption and the waiting time related to the creation of the correction table.

In addition, when the control unit obtains the correction table using the three types of patches in the printer mode, the input / output relational expression (formula (1) described above) obtained when the input tone correction machine in the copy mode is created. May be used.
In this case, the control unit calculates Pn satisfying the expression (8) using the above expression (1) and Da. Therefore, in this case, the correction table can be easily obtained.

Further, the control unit may be designed to select a halftone input gradation when printing patches corresponding to fewer than three types (three types) of input gradations in the printer mode. In this case, the accuracy of the correction table can be improved in the halftone area. Accordingly, it is possible to print a halftone output gradation particularly appropriately (accurately).
Here, the halftone region is, for example, a range of 64 to 192 with an output duty of 255 as a full scale.

Further, the control unit may be designed to select a low gradation input gradation when printing an image corresponding to fewer than three types (three kinds) of input gradations in the printer mode. In this case, the accuracy of the correction table can be improved in the low gradation region. Accordingly, it is possible to print a low gradation output gradation particularly appropriately (accurately).
Here, the low gradation region is, for example, a range of 0 to 64 with an output duty of 255 as a full scale.

  In the above description, 16 types of patches are used when obtaining the first mode correction table, and three types of patches are used when obtaining the second mode correction table. However, the present invention is not limited to this, and the number of patches may be any number. However, the number of patches of the latter is preferably smaller than the number of patches of the former.

In this embodiment, the copy mode is selected as a mode (first mode) for generating patches according to 16 types of input gradations.
However, the present invention is not limited to this, and the FAX mode or the printer mode may be selected as the first mode.

  Since the copy mode is a mode for creating a copy of a document image, it can be said that it is preferable to create a printed material as close to the document as possible. Therefore, it is preferable to preferentially generate the correction table in the copy mode by a method capable of obtaining an accurate correction table. Therefore, it can be said that the copy mode is preferably the first mode.

Further, the control unit may be designed so that the mode to be the first mode can be selected based on a user instruction input via the operation panel.
In this configuration, the user can create a correction table in a mode that is considered important (for example, frequently used) with high accuracy.

Further, it is preferable that the printing apparatus includes a frequency storage unit that stores the usage frequency of each mode. Such a frequency storage unit is a device that counts the number of printed sheets for each print mode, calculates the use frequency from the count number and the total number of prints, and stores the calculation result. For example, a copy counter can be used as such a frequency storage unit.
In such a case, it is preferable that the control unit is designed to select a mode with the highest usage frequency as the first mode. Thereby, the correction table of the mode with high use frequency can be generated with high accuracy.

Further, when the frequency storage unit as described above is provided, the control unit may be designed to determine the frequency of the first mode in each print mode according to the usage frequency.
In this configuration, for example, when the printing mode of the printing apparatus is the copy mode and the printer mode and the ratio of the usage frequencies is 3: 1, the copy mode is set to the first mode only three times. The printer mode is set to the first mode only once.

The above-described high density correction (development voltage correction) and correction table creation (tone correction) may be performed at any timing.
For example, for high density correction, when the printing apparatus is turned on, when the sleep mode is released, the temperature of the fixing device 217 is 45 degrees or less, and when the number of printed sheets after high density correction reaches 1000, the humidity changes. After the toner density correction is performed, it is preferably performed after the replacement of the photosensitive drums 222a to 222d, after the replacement of the toner, or the like.
As a result, it is possible to suppress the influence of environmental variation and temporal variation on the printed image.

In addition, regarding the creation of the correction table, immediately before the printing device is shipped from the factory (at the time of factory shipment), when the printing device is turned on (when the power is turned on), after printing a predetermined number of sheets, the development conditions are set. When changed, it is preferably performed after the replacement of the photosensitive drums 222a to 222d, when the developing bias is changed by 45 V or more by high density correction, and after the replacement of the toner.
As a result, it is possible to suppress the influence of environmental variation and temporal variation on the printed image.

  Further, in the present embodiment, at the time of gradation correction, the control unit reads an ideal output gradation from a storage unit (not shown) stored in the image processing unit. However, the present invention is not limited to this, and instead of reading from the storage unit, these values may be set (calculated) by calculation.

In the present embodiment, the control unit creates a copy correction table including the correction input gradation Cn corresponding to all the input gradations In.
However, the present invention is not limited to this, and the control unit may create a correction table for copying including the correction coefficient An corresponding to all the input gradations In. The modified input gradation Cn may be calculated based on the input gradation In of the input CMYK data and the correction coefficient An of the table.

In this printing apparatus, after an input tone correction formula for each mode is created, a correction table is created based on this formula. The output tone correction unit 19 does not need to perform correction using the correction table.
For example, the correction coefficients An and Anp corresponding to the input gradation In are stored, and Cn = An · In, which is an arithmetic expression (input gradation correction expression) for deriving the corrected input gradation
Pn = Anp · In
May be used to appropriately modify the input gradation to generate a modified input gradation. In this case, a correction table including the correction input gradation is not necessary.

  In the present embodiment, the above equation (1) is a primary equation, and the equation (7) is a quadratic equation. However, these equations may be approximate equations of any order.

  In this embodiment, the printing apparatus performs color printing. However, the present invention is not limited to this, and the printing apparatus may be configured as a monochrome printing apparatus. A mode other than the fax, copy, and printer modes may be employed as the print mode of the printing apparatus.

  In the above description, all processes in the printing apparatus are performed under the control of the control unit. However, the present invention is not limited to this, and an information processing apparatus (computer) capable of recording a program for performing these processes on a recording medium and reading the program may be used instead of the control unit.

  In this configuration, the arithmetic unit (CPU or MPU) of the information processing apparatus reads the program recorded on the recording medium and executes the process. Therefore, it can be said that this program itself realizes the processing.

  Here, as the information processing apparatus, in addition to a general computer (workstation or personal computer), a function expansion board or a function expansion unit mounted on the computer can be used.

  The above program is a program code (execution format program, intermediate code program, source program, etc.) of software that realizes processing. This program may be used alone or in combination with other programs (such as OS). The program may be read from the recording medium, temporarily stored in a memory (RAM or the like) in the apparatus, and then read and executed again.

  Further, the recording medium for recording the program may be easily separable from the information processing apparatus, or may be fixed (attached) to the apparatus. Further, it may be connected to the apparatus as an external storage device.

Such recording media include magnetic tapes such as video tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks and hard disks, and optical disks such as CD-ROM, MO, MD, DVD and CD-R (magneto-optical). Disc), memory cards such as IC cards and optical cards, semiconductor memories such as mask ROM, EPROM, EEPROM, and flash ROM can be applied.
Also, a recording medium connected to the information processing apparatus via a network (intranet / Internet) may be used. In this case, the information processing apparatus acquires the program by downloading via the network. That is, the above program may be acquired via a transmission medium (a medium that dynamically holds the program) such as a network (connected to a wired line or a wireless line). The program for downloading is preferably stored in advance in the apparatus (or in the transmission side apparatus / reception side apparatus).

  The present invention can also be expressed as the following first to eleventh image forming apparatuses. That is, the first image forming apparatus creates a test pattern of a plurality of gradations with toner on the photosensitive member, and the test pattern created in the first mode (copy mode) in the image forming apparatus that corrects the gradation characteristics. The detection result A of the second mode (printer mode) is obtained, the detection result B of the test pattern having a smaller number than the test pattern of the first mode created in the second mode (printer mode) is obtained, and the correction amount of the second mode is calculated from the detection result A. The conversion formula to be obtained or the conversion result C is corrected by the detection result B to obtain the correction amount of the second mode. As a result, the creation of the second test pattern can be greatly reduced without reducing the accuracy of halftone correction, and the toner consumption and adjustment time can be reduced.

The second image forming apparatus has a configuration in which the test patch of the second mode is created in an area having a large gradation change in the first image forming apparatus. Thereby, the accuracy of halftone correction can be maintained.
Further, the third image forming apparatus is configured to be frequently created in the highlight portion of the test patch in the second mode in the first image forming apparatus. Thereby, although the variation in patch density increases in the highlight portion, the accuracy of halftone correction can be maintained.
Further, the fourth image forming apparatus is configured such that the first mode is the copy mode in the first image forming apparatus. As a result, the image quality of the copy mode in which the original and the printed matter are compared can be given the highest priority.

Further, the fifth image forming apparatus is configured such that the first mode can be selected in the first image forming apparatus. As a result, it is possible to cope with users who give top priority to the image quality of the printer such as printing and design.
The sixth image forming apparatus is configured such that the first step is performed at a predetermined timing in the first image forming apparatus. Accordingly, high image quality can be maintained without change over time by performing the process at a predetermined timing such as when shipped from the factory, when the power is turned on, when a predetermined number of sheets are printed, when development conditions are changed, and when the drum is replaced.

The seventh image forming apparatus has a first mode and a second mode in an image forming apparatus that creates a plurality of gradation test patterns with toner on a photoreceptor and corrects gradation characteristics. The frequency of use is obtained, and the correction amount of the mode is obtained from the detection result A of the test pattern created in the frequently used mode (copy mode). This is a configuration for determining the mode (printer mode) correction amount. As a result, mode correction that is frequently used can be performed with high accuracy, and toner consumption and adjustment time can be reduced. In addition, the eighth image forming apparatus creates a plurality of gradation test patterns with toner on the photosensitive member, An image forming apparatus that corrects gradation characteristics has a first mode and a second mode, obtains the frequency of use of each, and obtains the correction amount of the mode from the detection result of the test pattern created in the mode, and others The correction for obtaining the correction amount by conversion from the detection result of the test pattern created in the mode is switched according to the use frequency in one mode. For example, when the ratio is 3 in the copy mode and the ratio in the printer mode is 1, the patch is created in the copy mode three times, and the patch is created in the printer mode the fourth time. The ninth image forming apparatus is the seventh or eighth. In the image forming apparatus, the first mode is a copy mode. Thereby, the image quality in the copy mode in which the original and the printed matter are compared can be given the highest priority.
Further, the tenth image forming apparatus is configured to correct and convert the correction amount obtained in the patch of its own mode when converting the detection result of the patch in the other mode in the seventh or eighth image forming apparatus. . In addition, the eleventh image forming apparatus is configured to create a patch in which the one obtained by conversion is thinned out in the seventh or eighth image forming apparatus. Thereby, accuracy can be improved.

  The present invention can be suitably used for a printing apparatus capable of printing in a plurality of printing modes.

Output gradation setting value (Pref), actual output gradation value (Cout, Pout), patch correction coefficient (Da), patch correction output gradation (P'out), correction coefficient (Anp) in printer mode , Is a graph showing the relationship between the corrected output (Pa) and the input gradation (In). It is explanatory drawing which shows the structure of the digital color multifunctional device concerning one Embodiment of this invention. FIG. 3 is an explanatory diagram illustrating a configuration of an image processing unit in the multifunction peripheral illustrated in FIG. It is explanatory drawing which shows the patch used for correction | amendment of developing voltage. 5 is a graph showing the relationship between development bias and density for the patch shown in FIG. 4. It is explanatory drawing which shows the patch used when creating the correction table for copying. It is a graph which shows the relationship between the input gradation In, the output gradation set value Cref, and the actual measurement value Cout in copy mode. In the copy mode, the output gradation setting value (Cref), the output gradation measurement value (Cout), the correction coefficient (An), the corrected output gradation (Ca), and the input gradation (In) It is a graph which shows a relationship. In the printer mode, the output gradation setting value (Pref), the actual output gradation value (Cout), the correction coefficient (Anp), the corrected output gradation (Pa), and the input gradation (In) It is a graph which shows a relationship. It is explanatory drawing which shows the patch used when creating the correction table for printers.

Explanation of symbols

11 A / D conversion unit 12 Shading correction unit 13 Automatic document type discrimination unit 14 Input tone correction unit 15 Color correction unit 16 Region separation processing unit 17 Black generation / under color removal unit 18 Spatial filter processing unit 19 Output tone correction unit 20 gradation reproduction processing unit 110 scanner unit 111 document table 112 RADF
210 Image forming unit 211 Paper feeding mechanism 216 Conveying belt 217 Fixing devices 222a to 222d Photosensitive drums 224a to 224d Developing devices 227a to 227d LSU
232 Optical sensor (measurement unit)
301 Black image transfer unit 302 Yellow image transfer unit 303 Magenta image transfer unit 304 Cyan image transfer unit An, Anp Correction coefficient Ca, Pa Output gradation Cn, Pn Correction input gradation Cout, Pout Output gradation measurement values Cref, Pref Output gradation setting value (ideal value)
Da patch correction coefficient In input gradation P'out corrected output gradation

Claims (3)

A printing unit that prints an image according to image data input in a plurality of modes;
An adjustment unit that adjusts the output tone of the print image by generating the corrected input tone by correcting the input tone of the image data using the input tone correction formula corresponding to the mode, and outputting the corrected input tone to the printing unit. In a printing apparatus equipped with
It has a frequency storage unit that calculates and stores the usage frequency of each mode,
The adjustment section above
A measurement unit for measuring the output gradation of the printed image;
A plurality of images corresponding to a plurality of different input gradations are printed on the printing unit, and the output gradations of these images are measured by the measurement unit.
An input / output relational expression that is a relational expression between the plurality of input gradations and the output gradation measurement value obtained by the measurement unit is obtained,
Based on this input / output relational expression, a corrected input gradation that obtains an ideal value of the output gradation corresponding to the plurality of input gradations is obtained, and the relationship between the input gradation and the corrected input gradation is expressed. And a control unit that creates an input tone correction formula.
The control unit is designed to select the most frequently used mode as the first mode,
When creating a modified input tone for the second mode after creating a modified input tone for the first mode using a predetermined number of input tones,
The above control unit
Find the ideal value of the output gradation in the second mode according to the input gradation used when creating the input gradation correction formula of the first mode,
Based on the above input and output relation, the printing apparatus characterized by being designed to determine the correction input gradation as obtained the ideal value.   The printing apparatus according to claim 1, wherein the control unit is designed to generate a correction table including an input gradation and a corrected input gradation based on an input gradation correction formula. 3. The plurality of modes includes at least a copy mode for copying an original image and a printer mode for printing an image corresponding to image data input from the outside. The printing apparatus as described.

Images