JP6798197B2 - Image forming device, image processing method and image processing program - Google Patents

Description

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

In recent image forming apparatus, the shading stage that can be processed by the image forming apparatus that has received the image information is larger than the shading stage of the image information transmitted from the information processing device such as a personal computer. I'm doing it. As an example, while the shading of the image information transmitted is ^{8 [bit] = 2 8 =} 256 [ stage] in the image forming apparatus, the image forming apparatus can process shades ¹⁰ [bit] ^{= 2} 10 = 1024 [stage] may be. Although different from the image forming apparatus, the techniques described in Patent Documents 1 and 2 below relate to a technique for performing image processing when the step of shading of an image to be displayed is higher than the step of shading of an input image. It has been known.
Japanese Patent Application Laid-Open No. 2009-157656 as Patent Document 1 describes an image processing device having a gradation number expansion unit that converts an N-bit input image signal into an N + k-bit output image signal, and determines that the image processing device is a gradation region. For the pixels, a technique for smoothing the input image signal and expanding the image signal to N + k bits is described.
Further, as a technique for performing correction to expand the number of gradations of the input image signal, when the difference value between adjacent pixels is equal to or less than a predetermined value, it is determined as an area showing gradation and smoothed. Japanese Patent Application Laid-Open No. 2007-21460 as Patent Document 2 describes a technique for determining a region indicating an edge when the value exceeds a predetermined value and expanding the number of gradations without smoothing.

Japanese Unexamined Patent Publication No. 2009-157656 ("0049" to "0058") Japanese Unexamined Patent Publication No. 2007-21460

An object of the present invention is to improve the image quality as compared with the case where the value for determining whether or not to perform the gradation processing is fixed.

In order to solve the technical problem, the image forming apparatus of the invention according to claim 1 is used.
A conversion means for converting image information to be printed into a print image in an image forming apparatus based on preset conversion information, and
A correction means for correcting the print information converted by the conversion means based on the correction information of the density set in advance in the image forming apparatus, and a correction means for correcting the print information converted by the conversion means.
A threshold value setting means for setting a threshold value of the density difference based on the conversion information and the correction information of the density, and
Based on the density difference in the threshold and before Symbol print images of the set density difference setting means of the threshold value, density difference in the print image does not reach the threshold value of the density difference, and, a plurality of adjacent pixels For runs with a common density, the positive / negative of the difference between the density of one outer pixel of the run and the density of the run and the positive / negative of the difference between the density of the other outer pixel of the run and the density of the run are opposite or A gradation processing means that performs gradation processing that continuously changes the density when the outer pixel of either one does not exist , and
It is characterized by being equipped with.

The invention according to claim 2 is the image forming apparatus according to claim 1.
The conversion information preset for each model of the image forming apparatus and
The correction information of the density set for each individual of the image forming apparatus and
It is characterized by being equipped with.

The invention according to claim 3 is the image forming apparatus according to claim 1 or 2.
An image recording device that prints a preset image for density correction, and
An image reading device that reads an image printed by the image recording device,
Correction information setting means for setting correction information of the density based on the density of the scanned image read by the image reader and the density of the image for density correction, and
It is characterized by being equipped with.

The invention according to claim 4 is the image forming apparatus according to any one of claims 1 to 3.
The density difference after applying the conversion information and the correction information of the density to the density difference in one step is calculated for all the concentrations, and the maximum value of the density difference after application is the threshold value of the density difference. The threshold setting means, which is set as
It is characterized by being equipped with.

In order to solve the technical problem, the image processing method of the invention according to claim 5 is
A conversion step of converting image information to be printed into a printed image in an image forming apparatus based on preset conversion information, and
A correction step of correcting the print information converted in the conversion step based on the correction information of the density set in advance in the image forming apparatus, and a correction step of correcting the print information converted in the conversion step.
Based on the density difference in the threshold and before Symbol print images of the set density difference based on the correction information of the said conversion information density, density difference in the print image does not reach the threshold value of the density difference, and For a run with a common density of multiple adjacent pixels, the positive and negative of the difference between the density of one outer pixel of the run and the density of the run, and the density of the other outer pixel of the run and the density of the run A gradation processing step that performs gradation processing that continuously changes the density when there is no outer pixel that is opposite to the positive or negative of the difference or one of them .
It is characterized by being equipped with.

In order to solve the technical problem, the image processing program of the invention according to claim 6 is used.
Computer,
A conversion means for converting image information to be printed into a printed image in an image forming apparatus based on preset conversion information.
A correction means that corrects the print information converted by the conversion means based on the correction information of the density set in advance in the image forming apparatus.
A threshold value setting means for setting a threshold value of a density difference based on the conversion information and the correction information of the density.
Based on the density difference in the threshold and before Symbol print images of the set density difference setting means of the threshold value, density difference in the print image does not reach the threshold value of the density difference, and, a plurality of adjacent pixels For runs with a common density, the positive / negative of the difference between the density of one outer pixel of the run and the density of the run and the positive / negative of the difference between the density of the other outer pixel of the run and the density of the run are opposite or A gradation processing means that performs gradation processing that continuously changes the density when the outer pixel of either one does not exist .
It is characterized by functioning as.

According to the inventions of claims 1, 5 and 6, the image quality can be improved as compared with the case where the value for determining whether or not to perform the gradation processing is fixed.
According to the second aspect of the invention, the threshold value of the concentration difference can be set based on the conversion information for each model and the concentration correction information for each individual.
According to the third aspect of the present invention, the density correction information can be updated based on the image read by the image reading device.
According to the invention of claim 4, the gradation processing can be performed even when the change in density difference is maximum when the conversion information and the density correction information are applied.

FIG. 1 is an overall explanatory view of the image forming apparatus of the first embodiment of the present invention. FIG. 2 is a block diagram showing each function provided by the control unit of the image forming apparatus of the first embodiment. FIG. 3 is an explanatory diagram showing an outline of a processing flow in the control unit of the image forming apparatus of the first embodiment. FIG. 4 is an explanatory diagram of an example of image processing of the first embodiment, FIG. 4A is an explanatory diagram of an example of a gradation image, and FIG. 4B is a color conversion process using an example of color profile data for the image data of FIG. 4A. An explanatory diagram of the case where the data is performed, FIG. 4C is an explanatory diagram of the data after the color conversion process of FIG. 4B when the calibration process is performed. FIG. 5 is a description of division of an image area in the image processing of the first embodiment. FIG. 6 is an explanatory diagram of a list showing the concentration difference and the threshold value of Example 1 and the presence or absence of the opening treatment. FIG. 7 is an explanatory diagram of the rate of change of the first embodiment. FIG. 8 is an explanatory diagram of a flowchart of image processing according to the first embodiment. 9A and 9B are explanatory views of conventional image processing, FIG. 9A is an explanatory view of an example of pixel density of the original image, and FIG. 9B is an explanatory view after applying color profile data and a calibration LUT to the image of FIG. 9A. 9C is an explanatory diagram when gradation processing is performed on the image of FIG. 9B. 10A is an explanatory diagram of an image processing method, FIG. 10A is a gradation image before gradation processing in the case of (v), FIG. 10B is a gradation image after gradation processing in FIG. 10A, and FIG. 10C is (iii). 10D is an explanatory diagram of an end portion of the gradation image after the gradation processing of FIG. 10C. 11A and 11B are explanatory views of an image processing method, FIG. 11A is an explanatory diagram of an example of a gradation image in the case of (vii), FIG. 11B is an explanatory diagram of an example of a gradation image in the case of (iv), and FIG. 11C. Is an explanatory diagram of an example of a gradation image in the case of (v). FIG. 12 is an explanatory diagram of an image processing method, FIG. 12A is an explanatory diagram of an example of a gradation image in the case of (viii), FIG. 12B is an explanatory diagram of an example of a gradation image in the case of (i), and FIG. 12C. Is an explanatory diagram of an example of a gradation image in the case of (ii), and FIG. 12D is an explanatory diagram of an example of a gradation image in the case of (vi). FIG. 13 is an explanatory diagram of image processing of the boundary portion of the divided region of the first embodiment.

Next, an embodiment as a specific example of the embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited to the following examples.
In order to facilitate the understanding of the following explanations, in the drawings, the front-back direction is the X-axis direction, the left-right direction is the Y-axis direction, and the up-down direction is the Z-axis direction, and the arrows X, -X, Y, -Y,. The directions indicated by Z and −Z or the indicated sides are defined as front, rear, right, left, upward, downward, or front, rear, right, left, upper, and lower, respectively.
In addition, in the figure, the one with "・" in "○" means the arrow from the back to the front of the paper, and the one with "×" in "○" is the front of the paper. It shall mean an arrow pointing from to the back.
In addition, in the explanation using the following drawings, the illustrations other than the members necessary for the explanation are omitted as appropriate for the sake of easy understanding.

FIG. 1 is an overall explanatory view of the image forming apparatus of the first embodiment of the present invention.
In FIG. 1, the image forming apparatus U includes an operation unit UI, a scanner device U1 as an example of an image reading device, a paper feeding device U2, an image forming apparatus main body U3 as an example of an image recording device, and a paper ejection unit U4. doing.

The operation unit UI has a power button, a copy start key, a copy number setting key, a numeric keypad, etc., a display unit, and the like as an example of an input unit.
The scanner device U1 reads a document (not shown), converts it into image information, and inputs it to the image forming device main body U3.
The paper feed device U2 has a plurality of paper feed trays TR1 to TR4 as an example of the paper feed unit. Recording paper S as an example of the medium is housed in each of the paper feed trays TR1 to TR4. A paper feed path SH1 as an example of a medium transport path extends from the paper feed trays TR1 to TR4 toward the image forming apparatus main body U3.

In FIG. 1, the image forming apparatus main body U3 has a control unit C, a power supply circuit E which is controlled by the control unit C and supplies power to each member of the image forming apparatus main body U3, and the like. The control unit C receives the image information of the document read by the scanner device U1 and the image information transmitted from a personal computer as an example of an information transmission device (not shown) connected to the image forming device U.
The control unit C processes the received image information into Y: yellow, M: magenta, C: cyan, and K: black printing information, and a laser as an example of a drive circuit of a latent image writing device. Output to drive circuit D. The laser drive circuit D outputs the laser drive signal input from the control unit C to the latent image forming devices ROSy, ROSm, ROSc, and ROSk of each color at a preset time.

Image holder units Uy, Um, Uc, and Uk of Y, M, C, and K are arranged below each latent image forming device ROSy to ROSk.
In FIG. 1, the K: black image holder unit Uk includes a photoconductor drum Pk as an example of an image holder, a corotron CCk as an example of a charger, and a photosensitizer as an example of a cleaner for an image holder. It has a body cleaner CLk. The image holder units Uy, Um, and Uc of the other colors Y, M, and C also have the photoconductor drums Py, Pm, Pc, the charged corotron CCy, CCm, CCc, and the photoconductor cleaners CLy, CLm, and CLc.
In Example 1, the K-color photoconductor drum Pk, which is frequently used and has a large surface wear, is configured to have a larger diameter than the photoconductor drums Py, Pm, and Pc of other colors, and is compatible with high-speed rotation. It has a long life.

The photoconductor drums Py, Pm, Pc, and Pk are uniformly charged by the charged corotrons CCy, CCm, CCc, and CCk, respectively, and then the latent image writing device ROSy, ROSm, ROSc, and ROSk output the latent image. A laser beam Ly, Lm, Lc, Lk as an example of light forms an electrostatic latent image on the surface of the photoconductor drums Py to Pk. The electrostatic latent image on the surface of the photoconductor drums Py, Pm, Pc, Pk is produced by a developing roll R0 as an example of a developing member provided in the developing apparatus Gy, Gm, Gc, Gk. It is developed into a toner image as an example of a visible image with a developer of each color of magenta, C: cyan, and K: black.

The toner image on the surface of the photoconductor drums Py, Pm, Pc, Pk is an example of an intermediate transfer body in the primary transfer region Q3 by the primary transfer rolls T1y, T1m, T1c, T1k as an example of the primary transfer device. Therefore, the images are sequentially superimposed and transferred on the intermediate transfer belt B as an example of the image holder, and a multicolor image, a so-called color image, is formed on the intermediate transfer belt B. The color image formed on the intermediate transfer belt B is transferred to the secondary transfer region Q4.
In the case of only black image data, only K: black photoconductor drum Pk and developing device Gk are used, and only a black toner image is formed.
After the primary transfer, the residual toner remaining on the surface of the photoconductor drums Py, Pm, Pc, Pk is cleaned by the photoconductor cleaners CLy, CLm, CLc, CLk.
The toner image forming member Uy + Gy, Um + Gm, Uc + Gc as an example of the visible image forming unit by the image holder units Uy, Um, Uc, Uk and the developing device Gy, Gm, Gc, Gk as an example of the developing device , Uk + Gk are configured.

A toner dispenser U3a as an example of a replenishment device is arranged on the upper part of the image forming apparatus main body U3, and a toner cartridge Ky, Km, Kc, Kk as an example of a developing agent storage container is arranged in the toner dispenser U3a. It is attached detachably. When the toner is consumed in the developing devices Gy to Gk with the image formation, the toner is supplied from the toner cartridges Ky to Kk to the developing devices Gy to Gk.

The intermediate transfer belts B arranged below the photoconductor drums Py to Pk are an intermediate drive roll Rd as an example of a driving member of the intermediate transfer body and an example of a tension applying member for applying tension to the intermediate transfer belt B. Intermediate tension roll Rt, intermediate steering roll Rw as an example of a first offset correction member for correcting offset and meandering of the intermediate transfer belt B, and a plurality of intermediate idlers as an example of a driven member of an intermediate transfer body. It is stretched by a roll Rf and a backup roll T2a as an example of a member facing the secondary transfer region. The intermediate transfer belt B is supported so as to be rotatable in the direction of arrow Ya by being driven by the intermediate drive roll Rd.
The intermediate drive roll Rd, the intermediate tension roll Rt, the intermediate steering roll Rw, the intermediate idler roll Rf, and the backup roll T2a constitute a belt support roll Rd + Rt + Rw + Rf + T2a as an example of the support member of the intermediate transfer body of the first embodiment. Further, the intermediate transfer belt B and the belt support rolls Rd + Rt + Rw + Rf + T2a and the primary transfer rolls T1y to T1k constitute a belt module BM as an example of the intermediate transfer device. The belt module BM of the first embodiment is composed of a unit that can be attached to and detached from the image forming apparatus main body U3.

The intermediate steering roll Rw of the first embodiment is composed of a rotating body having a rotating shaft, and the rotating shaft is inclined in a direction for correcting the bias in the width direction of the intermediate transfer belt B. Prevents the intermediate transfer belt B from shifting or meandering. In this way, the so-called active steering method is a method in which the rotation axis is tilted according to the detection result of a member that detects the deviation of the belt, such as an optical sensor or a member that contacts the end of the belt, to correct the deviation. Since the steering roll Rw is conventionally known and can adopt various conventionally known configurations described in, for example, JP-A-2009-86463 and JP-A-2010-231112, detailed description thereof will be omitted. To do.

Below the backup roll T2a, a secondary transfer unit Ut as an example of the transfer transfer device is arranged. The secondary transfer unit Ut has a secondary transfer roll T2b as an example of the transfer member. The secondary transfer roll T2b is arranged so as to face the backup roll T2a. The secondary transfer region Q4 is formed by the region where the secondary transfer roll T2b faces the intermediate transfer belt B. Further, the backup roll T2a is in contact with the contact roll T2c as an example of the contact member for applying a voltage. The secondary transfer device T2 is composed of the rolls T2a to T2c.
A secondary transfer voltage having the same polarity as the charging polarity of the toner is applied to the contact roll T2c at a preset time from the power supply circuit E controlled by the control unit C.

A paper transport path SH2 is arranged below the belt module BM. The recording paper S fed from the paper feed path SH1 of the paper feed device U2 is conveyed to the paper transfer path SH2 by the transfer roll Ra as an example of the transfer member. The recording paper S of the paper transport path SH2 is fed by the register roll Rr as an example of the delivery member at the timing when the toner image is conveyed to the secondary transfer region Q4, and the paper guide SG1 as an example of the medium guide member. Guided by SG2, it is transported to the secondary transfer region Q4.
The toner image on the intermediate transfer belt B is transferred to the recording paper S by the secondary transfer device T2 when passing through the secondary transfer region Q4. In the case of a color image, the toner images that are overlaid on the surface of the intermediate transfer belt B and are primarily transferred are collectively secondarily transferred to the recording paper S.

The intermediate transfer belt B after the secondary transfer is cleaned, that is, cleaned by a belt cleaner CLB as an example of a cleaner for the intermediate transfer body. The secondary transfer roll T2b is supported so as to be separated and contactable with the intermediate transfer belt B.
The transfer device T1 + B + T2 + CLB that transfers the image of the surface of the photoconductor drums Py to Pk to the recording paper S by the primary transfer rolls T1y, T1m, T1c, T1k, the intermediate transfer belt B, the secondary transfer device T2, the belt cleaner CLB, etc. It is configured.

The recording paper S on which the toner image is secondarily transferred is sent to the medium transport belt BH as an example of the transport member. The medium transport belt BH transports the recording paper S to the fixing device F. The fixing device F has a heating member Fh as an example of a heating fixing member and a pressure member Fp as an example of a pressure fixing member, and is fixed by a region where the heating member Fh and the pressure member Fp come into contact with each other. Region Q5 is formed.
The toner image on the recording paper S is heat-fixed by the fixing device F when passing through the fixing region Q5. The recording paper S on which the toner image is fixed by the fixing device F is discharged to the discharge tray TRh as an example of the discharge unit.
The paper transport path SH is configured by the reference numerals SH1, SH2 and the like. Further, the paper transport device SU is composed of the symbols SH, Ra, Rr, SG1, SG2, BH and the like.

(Explanation of Control Unit of Example 1)
FIG. 2 is a block diagram showing each function provided by the control unit of the image forming apparatus of the first embodiment.
In FIG. 2, the control unit C of the image forming apparatus U has an input / output interface I / O that inputs / outputs signals to / from the outside. Further, the control unit C has a ROM: read-only memory in which a program, information, and the like for performing necessary processing are stored. Further, the control unit C has a RAM: random access memory for temporarily storing necessary data. Further, the control unit C has a CPU: a central processing unit that performs processing according to a program stored in a ROM or the like. Therefore, the control unit C of the first embodiment is composed of a small information processing device, a so-called microcomputer. Therefore, the control unit C can realize various functions by executing the program stored in the ROM or the like.

(Signal output element connected to control unit C)
The control unit C receives an output signal from a signal output element such as the operation unit UI or the scanner device U1.
The operation unit UI has an input button UIa such as a power button, a copy start key, a copy number setting key, and a numeric keypad as an example of an input member. Further, the operation unit UI includes a display unit UIb or the like as an example of the display member.

(Controlled element connected to control unit C)
The control unit C is connected to a drive circuit D1 of the main drive source, a power supply circuit E, and other control elements (not shown). The control unit C outputs the control signals to the circuits D1, E and the like.
D1: Drive circuit of the main drive source The drive circuit D1 of the main drive source is an example of the drive source of the image holder, and the photoconductor drums Py to Pk and the like via the main motor M1 as an example of the main drive source. The intermediate transfer belt B and the like are rotationally driven.
E: Power supply circuit The power supply circuit E includes a power supply circuit Ea for development, a power supply circuit Eb for charging, a power supply circuit Ec for transfer, a power supply circuit Ed for fixing, and the like.
Ea: Power supply circuit for development The power supply circuit Ea for development applies a development voltage to the development rolls of the developing devices Gy to Gk.
Eb: Power supply circuit for charging The power supply circuit Eb for charging applies a charging voltage for charging the surfaces of the photoconductor drums Py to Pk to each of the charging corotrons CCy to CCk.

Ec: Power supply circuit for transfer The power supply circuit Ec for transfer applies a transfer voltage to the primary transfer rolls T1y to T1k and the backup roll T2a.
Ed: Power supply circuit for fixing The power supply circuit Ed for fixing supplies electric power to the built-in heater of the heating roll Fh of the fixing device F.

(Function of control unit C)
The control unit C has a function of executing processing according to an input signal from the signal output element and outputting a control signal to each of the control elements. That is, the control unit C has the following functions.
C1: Image formation control means The image formation control means C1 controls the drive of each member of the image formation device main body U3, the application timing of each voltage, and the like according to the image information input from the scanner device U1 and the personal computer. Then, the execution, end, and interruption of the job, which is an image forming operation, are controlled.
C2: Power supply circuit control means The power supply circuit control means C2 controls the power supply circuits Ea to Ed to control the voltage applied to each member and the electric power supplied to each member.

FIG. 3 is an explanatory diagram showing an outline of a processing flow in the control unit of the image forming apparatus of the first embodiment.
C3: Information receiving means The information receiving means C3 receives the image information transmitted from the scanner device U1 or the personal computer.
C4: Image processing means In FIG. 2, the image processing means C4 as an example of the image processing program processes the received image information into print information for printing by the image forming apparatus main body U3. In the image processing means C4 of the first embodiment, as an example, the image forming apparatus main body U3 can print with a gradation step of 10 bits (1024 gradations), and the gradation step of the received image information is 8 bits, that is, In the case of 256 gradations, image processing is performed in which the gradation step is increased by 2 bits = 4 steps to 10 bits. The image processing means C4 of the first embodiment has the following means C401 to C415.

FIG. 4 is an explanatory diagram of an example of image processing of the first embodiment, FIG. 4A is an explanatory diagram of an example of a gradation image, and FIG. 4B is a color conversion process using an example of color profile data for the image data of FIG. 4A. An explanatory diagram of the case where the data is performed, FIG. 4C is an explanatory diagram of the data after the color conversion process of FIG. 4B when the calibration process is performed.
C401: Profile data storage means The profile data storage means C401 stores color profile data as an example of conversion information. In FIG. 4, as an example, when color profile data is applied to an image whose density changes in the order of 100%, 99%, 98%, 97%, ... As shown in FIG. 4A, 100% is 100%. , 99% is 98%, 98% is 97%, 97% is 96%, and so on, and color profile data whose density is converted is stored. In the first embodiment, CMYK profile JC2011 is used as an example of the color profile data, but the color profile data is not limited to this, and any color profile data conventionally used in Japan and overseas or a user manually performs the color profile data. The color profile data set in is available.
C402: Color conversion means The color conversion means C402 as an example of the conversion means performs color conversion processing of the received image information based on the color profile data stored in the profile data storage means C401.

C403: Calibration data storage means Calibration data storage means as an example of correction information storage means C403 stores a calibration LUT (Look Up Table) as an example of density correction information. In FIG. 4, as an example, when color profile data is applied to an image whose density changes in the order of 100%, 99%, 98%, 97%, ..., 100% is 100%, 99% is 99%. , 98% is 95%, 97% is 94%, 96% is 93%, and so on, and the calibration LUT in which the concentration is converted is stored.

The calibration LUT is created by executing the operation of creating the calibration LUT in the image forming apparatus U separately from the image forming operation. Specifically, a preset image for calibration is printed, the printed image for calibration is read by the scanner device U1, and the preset density of the image for calibration and the actual density of the image for calibration are actually set. A calibration LUT is created from the difference from the actual density of the printed image for calibration. Since the process of creating such a calibration LUT is conventionally known, detailed description thereof will be omitted.
In the first embodiment, the color profile data is set for the model of the image forming apparatus U, and the calibration LUT is set for each individual of the image forming apparatus U. Therefore, the color profile data is image-processed according to the specifications and settings of each model, and the calibration LUT is image-processed according to individual differences.

C404: Calibration correction means The calibration correction means C404 as an example of the correction means corrects the print information converted by the color conversion means C402 based on the calibration LUT. Therefore, in the example shown in FIG. 4, the calibration LUT is applied to the image whose density changes in the order of 100%, 99%, 98%, 97%, ... As shown in FIG. 4A after the color profile data is applied. When applied, 100% pixels are 100% → 100% → 100%, 99% pixels are 99% → 98% → 95%, 98% pixels are 98% → 97% → 94%, 97% pixels. Will be converted as 97% → 96% → 93%, and so on.

FIG. 5 is a description of division of an image area in the image processing of the first embodiment.
C405: Image dividing means The image dividing means C405 as an example of the dividing means divides the image area for printing correspondence into a plurality of areas along a preset direction. In FIG. 5, the image dividing means C405 of the first embodiment divides the image region A1 of the image 101 to be printed into a plurality of regions A2 along a sub-scanning direction as an example of a preset direction. .. In the first embodiment, the image processing is speeded up by dividing the image area A1 into a plurality of divided areas A2 and performing the processing in parallel, but the parallel processing is difficult due to the processing capacity of the processor and the like. In such cases, or when the overall processing speed decreases when parallel processing is performed, it is possible to perform image processing without dividing. Further, the dividing direction is the sub-scanning direction, but the sub-scanning direction is not limited to this, and any division method such as dividing in the main scanning direction or dividing in a grid pattern in the sub-scanning direction and the main scanning direction can be used. It is possible. Further, in the first embodiment, a configuration in which the image region A1 is divided after the color conversion process and the calibration correction process is illustrated, but the present invention is not limited to this. For example, it is also possible to perform the color conversion process or the like for each division area A2 before the color conversion process or the calibration correction process.

C406: Density acquisition means The density acquisition means C406 acquires the density C0 of each pixel in the image 101 to be printed.
C407: Pixel group extraction means The pixel group extraction means C407 extracts a run as an example of a pixel group in which a plurality of pixels having a common density C0 are adjacent to each other. In the first embodiment, a run, which is a pixel group in which pixels having a common density are adjacent to pixels arranged adjacent to each other in the sub-scanning direction, is extracted for each division region A2.
C408: Run length acquisition means The run length acquisition means C408 as an example of the pixel group length acquisition means is the run length extracted by the pixel group extraction means C407, that is, the number of pixels (run length) of the pixel group. Acquire N1. The run length acquisition means C408 of the first embodiment acquires the run length N1 for each run.

C409: Run length threshold storage means The run length threshold storage means C409 as an example of the pixel group threshold storage means is an interpolation target run as an example of the run length threshold based on the density C0 of each run. Memorize long Na. In the first embodiment, the setting information in which the run length Na to be interpolated increases as the concentration C0 increases is stored. As an example, when the density C0 is 0 to 10%, the interpolation target run length Na = 40 [pixels], and when the density C0 is 10 to 20%, the interpolation target run length Na = 80 [pixel]. When the density C0 is 20 to 30%, the interpolation target run length Na = 120 [pixel (pixel)], and when the density C0 is higher than 30%, the interpolation target run length Na = ∞ [pixel (pixel)]. ] The setting information to be set is stored. The interpolation target run length Na is a gradation process (interpolation process of the gradation step) in which the gradation step is increased in the run to continuously change the density when the run length N1 reaches the interpolation target run length Na. ), And it is a threshold value for determining that the gradation processing is not performed when the run length N1 does not reach the interpolation target run length Na. Further, in the first embodiment, when the density C0 is higher than 30%, the run length Na to be interpolated is set to ∞, and the gradation processing is not executed no matter how long the run length N1 is. The specific numerical value of the run length Na to be interpolated is not limited to the exemplified numerical value, and can be arbitrarily changed by the design, specifications, manual setting of the user, and the like.

C410: Interpolation threshold value setting means The interpolation threshold value setting means C410 as an example of the density difference threshold value setting means sets the interpolation threshold value (interpolation target reference Gap value) Ca as an example of the density difference threshold value. The interpolation threshold value setting means C410 of the first embodiment sets the interpolation threshold value Ca for determining whether or not to perform the gradation processing (interpolation processing of the gradation step) based on the color profile data and the calibration LUT. To do. In the first embodiment, when the threshold value for determining whether or not to perform the complement processing in the original image is set to 1, the interpolation threshold value Ca is set based on the following equation (1).
Ca = Max [CalibLUT (Profile (C0))-CalibLUT (Profile (C0-1))] ... Equation (1)
In the equation (1), Profile (x) is a function for calculating the density after the density x is color-converted with the color profile data, and CalibLUT (y) is the calibration LUT for the density y. It is a function that calculates the density after performing correction processing using it. Therefore, when C0 = 100, Profile (100) = 100, CalibLUT (Profile (100)) = 100, and CalibLUT (Profile (C1-1)) = CalibLUT (Profile (99)) = CalibLUT (98) = It becomes 95. Then, CalibLUT (Profile (C0))-CalibLUT (Profile (C0-1)) is calculated for all the concentrations (1 to 100) of C0, and the maximum value (Max) is set as the interpolation threshold value. Set to Ca.
When the threshold value for determining whether or not to perform interpolation processing in the original image is m, the term of CalibLUT (Profile (C0-1)) in the equation (1) is set to CalibLUT (Profile (C0-m)). It is possible.

C411: Run length determination means The run length determination means C411 determines whether or not the run length N1 of each run reaches the interpolation target run length Na. The run length determination means C411 of the first embodiment determines that the gradation processing is executed when the run length N1 reaches the interpolation target run length Na. As the run length Na to be interpolated, one corresponding to the concentration C0 of each run stored in the run length threshold storage means C409 is used.
C412: Edge discriminating means The edge discriminating means C412 determines for each run whether or not the pixel at the end of the divided region A2 is included, that is, whether or not the run extends from the end of the divided region A2. ..

C413: Concentration difference discriminating means The density difference discriminating means C413 determines whether or not the density difference between the density of the pixel adjacent to the run and the density C0 of the run reaches the interpolation threshold Ca. The density difference determination means C413 of the first embodiment has, for each run, the density C0a of the pixels adjacent to the downstream side in the sub-scanning direction (media transport direction) of the run and the density C0b of the pixels adjacent to the upstream side. On the other hand, it is determined whether or not the respective density differences C0a-C0 and C0b-C0 are larger than the interpolation threshold value Ca and the preset edge threshold value Cb. The edge threshold Cb is a threshold for determining the edge of the gradation image unit 102, and is when a background portion (blank paper portion), a solid image, a natural image, or the like is adjacent to the gradation image unit 102. , It is stored in advance in order to discriminate the edge of the gradation image unit 102 based on the density difference between the adjacent image and the edge of the gradation image unit 102. In Example 1, Ca <Cb is set.

Further, when the run extends from the end of the divided region A2, the density difference discriminating means C413 of the first embodiment has a density difference C0a-C0 or C0b with respect to the densities C0a, C0b of the pixels on the opposite side of the end. It is determined whether or not −C0 is larger than the interpolation threshold value Ca.
In the following description, for the sake of clarity of explanation, the pixels on the downstream side will be referred to as the "right" side, and the pixels on the upstream side will be referred to as the "left" side. In addition, the "concentration difference" may be expressed as a "step".

FIG. 6 is an explanatory diagram of a list showing the concentration difference and the threshold value of Example 1 and the presence or absence of the opening treatment.
In the first embodiment, in the run where it is determined that the gradation processing is executed by the determination of the run length, the presence or absence of the gradation processing is determined as shown in FIG. Specifically, it is determined that the gradation processing is executed in the following cases.
(I) When C0a-C0> 0 (right step is +) and C0b-C0> 0 (left step is +) and | C0a-C0 | <Ca and | C0b-C0 |> Cb, The run to be discriminated is the "bottom" of the density with respect to the density of the pixels on both the left and right sides, and when the interpolation processing of the gradation step (upward to the right) where the density increases from the left end to the right end of the run is performed. Determine. That is, it is determined that the run is processed so that the density increases from the density C0 of the discrimination target run toward the density C0a of the pixel on the right side.
(Ii) When C0a-C0> 0 (right step is +) and C0b-C0> 0 (left step is +), and | C0a-C0 |> Cb and | C0b-C0 | <Ca, The run to be discriminated is the "bottom" of the density with respect to the density of the pixels on both the left and right sides, and when the interpolation processing of the gradation step (downward to the right) where the density decreases from the left end to the right end of the run is performed. Determine. That is, it is determined that the run is processed so that the density decreases from the density C0b of the pixel on the left side toward the density C0 of the run to be discriminated.

(Iii) When C0a-C0 <0 (right step is −) and C0b-C0 <0 (left step is −), and | C0a-C0 |> Cb and | C0b-C0 | <Ca, The run to be discriminated is the "vertex" of the density with respect to the density of the pixels on both the left and right sides, and when the interpolation process of the gradation step (upward to the right) in which the density increases from the left end to the right end of the run is performed. Determine. Therefore, it is determined that the run is processed so that the concentration of the run to be discriminated increases from the concentration C0 toward the right side according to the rate of change described later. Therefore, unlike (i) and (ii), the concentration at the right end is predicted and estimated from the concentration C0 at the left end by the rate of change, so that the prediction interpolation processing is performed.
(Iv) When C0a-C0 <0 (right step is-) and C0b-C0 <0 (left step is-) and | C0a-C0 | <Ca and | C0b-C0 |> Cb, The run to be discriminated is the "vertex" of the density with respect to the density of the pixels on both the left and right sides, and when the interpolation processing of the gradation step (downward to the right) in which the density decreases from the left end to the right end of the run is performed. Determine. That is, it is determined that the run is subjected to the prediction interpolation processing so that the concentration increases from the concentration C0 of the discrimination target run on the right side toward the left side according to the rate of change.

(V) When C0a-C0> 0 (right step is +) and C0b-C0 <0 (left step is-) and | C0a-C0 | <Ca, from the pixel on the left side of the run. Judging that the density is increasing toward the pixel on the right side, the run to be discriminated performs interpolation processing of the gradation step whose density increases from the left to the right of the run (upward to the right). To determine. That is, it is determined that the run is processed so that the density increases from the density C0 of the discrimination target run toward the density C0a of the pixel on the right side.
(Vi) When C0a-C0> 0 (right step is +) and C0b-C0 <0 (left step is-), and | C0a-C0 |> Ca and | C0b-C0 | <Ca, the determination is made. It is determined that the target run is the right end of the gradation image unit 102 adjacent to the high density image such as a solid image on the right side. Therefore, it is determined that the run to be discriminated performs the predictive interpolation processing of the gradation step whose density increases (upward to the right) from the left to the right of the run. That is, it is determined that the run is processed so that the concentration increases from the concentration C0 of the discrimination target run toward the right side according to the rate of change.

(Vii) When C0a-C0 <0 (right step is-) and C0b-C0> 0 (left step is +) and | C0b-C0 | <Ca, from the pixel on the left side of the run. It is judged that the density is decreasing toward the pixel on the right. Therefore, it is determined that the run to be discriminated is subjected to the interpolation processing of the gradation step whose density decreases (decreasing to the right) from the left to the right of the run. That is, it is determined that the run is processed so that the density decreases from the density C0b of the pixel on the left side toward the density C0 of the run to be discriminated.
(Viii) When C0a-C0 <0 (right step is-) and C0b-C0> 0 (left step is +) and | C0a-C0 | <Ca and | C0b-C0 |> Ca, the determination is made. It is determined that the target run is the left end of the gradation image unit 102 adjacent to the high density image such as a solid image on the left side. Therefore, it is determined that the run to be discriminated performs the predictive interpolation processing of the gradation step whose density decreases (decreasing to the right) from the left to the right of the run. That is, it is determined that the run is processed so that the concentration increases from the concentration C0 of the discrimination target run toward the left side according to the rate of change.

(Ix) When the left end is the end of the divided region A2 and | C0a-C0 | <Ca, it is determined that the left end is the end of the divided region A2 and the run is to perform the prediction interpolation processing of the gradation step. When C0a-C0> 0 (the right step is +), it is determined that the density increases from the left to the right of the run (rising to the right), and it corresponds to the density C0a of the pixel on the right and the rate of change. It is determined that the run is subjected to predictive interpolation processing so that the density decreases toward the left side. If C0a-C0 <0 (the right step is-), it is determined that the density decreases from the left to the right of the run (downward to the right), and it depends on the density C0b of the pixel on the left and the rate of change. It is determined that the run is subjected to predictive interpolation processing so that the density decreases toward the right side.
(X) When the right end is the end of the divided region A2 and | C0b-C0 | <Ca, it is determined that the right end is the end of the divided region A2 and the run is to perform the prediction interpolation processing of the gradation step. Then, when C0b-C0> 0 (the left step is +), it is determined that the density decreases from the left to the right of the run (downward to the right), and it corresponds to the density C0b of the pixel on the left and the rate of change. It is determined that the run is subjected to predictive interpolation processing so that the density decreases toward the right side. When C0b-C0 <0 (the left step is-), it is determined that the concentration increases from the left to the right of the run (upward to the right), and the concentration is determined according to the concentration C0 of the run to be discriminated and the rate of change. It is determined to be a run that performs predictive interpolation processing so that the density increases toward the right side.

FIG. 7 is an explanatory diagram of the rate of change of the first embodiment.
C414: Change rate selection means The change rate selection means C414 selects a density change in gradation processing from a plurality of preset change rates. In the first embodiment, three types of change rates, strong change, medium change, and weak change, are set in advance. In the first embodiment, the rate of change is used when gradation processing is performed on a run at the end of the gradation image unit 102 or a run extending from the end of the divided region A2. In FIG. 7, in the first embodiment, in the case of strong change, (the number of changing gradation steps) × (density difference from the pixels inside the adjacent gradation image unit 102: Gap value) is the density at the end of the run. The rate of change is set. Further, in the medium change, a change rate is set in which (number of changing gradation steps) × (Gap value) × 1/2 is the density at the end of the run. Further, in the medium change, a rate of change is set in which (number of changing gradation steps) × (Gap value) × 1/4 is the density at the end of the run. In the first embodiment, the initial value of the change rate is set to a weak change, and the user can select and set the change rate according to the input from the operation unit UI. The specific calculated value of the rate of change is not limited to the illustrated configuration, and can be arbitrarily changed according to the design, specifications, and the like. Further, although it is desirable that the rate of change is selectable, it is also possible to fix the rate of change to a specific rate.

C415: Gradation processing means The gradation processing means C415 performs gradation processing (gradation processing, interpolation processing of gradation steps) for continuously changing the density of the gradation image unit 102 of the image 101 to be printed. Execute. The gradation processing means C415 of the first embodiment determines the density in the run when the number of gradation steps (gradation step) increases based on the discrimination results of the run length discriminating means C411 and the density difference discriminating means C413. Executes the interpolation processing (gradation processing) of the gradation step that makes the change continuous. Therefore, in the first embodiment, the gradation processing is executed based on the interpolation threshold value Ca and the edge threshold value Cb and the respective density differences C0-C0a and C0-C0b. The gradation processing means C415 of the first embodiment executes interpolation processing or predictive interpolation processing according to the discrimination results (i) to (x) of the density difference discriminating means C413. For example, in the case of (i), it is possible to set the density to increase by (C0a-C0) / (gradation step) as the {N1 / (gradation step)} pixel advances. ..

In the first embodiment, when the run length N1 reaches the interpolation target run length Na, the gradation processing is performed and the interpolation target run length Na is changed according to the pixel density C0. Then, in the first embodiment, when the pixel density C0 reaches 30%, which is a preset density, the gradation processing is not performed. Further, when the run length N1 reaches the run length Na to be interpolated and the pixel density C0 does not reach 30%, the gradation processing is executed.

(Explanation of Flow Diagram of Example 1)
Next, the flow of control in the image forming apparatus U of the first embodiment will be described using a flow chart, a so-called flowchart.

(Explanation of image processing flowchart)
FIG. 8 is an explanatory diagram of a flowchart of image processing according to the first embodiment.
The processing of each step ST in the flowchart of FIG. 8 is performed according to the program stored in the control unit C of the image forming apparatus U. Further, this process is executed in parallel with various other processes of the image forming apparatus U.
The flowchart shown in FIG. 8 is started by the image forming apparatus U receiving image information, that is, receiving the image information from the personal computer PC and the read image information from the scanner apparatus U1.

In ST1 of FIG. 8, the color conversion process using the color profile is executed. Then, proceed to ST2.
In ST2, the calibration correction process using the calibration LUT is executed. Then, proceed to ST3.
In ST3, the image region A1 is divided into band-shaped division regions A2. Then, proceed to ST4.
In ST4, the density C0 of each pixel is acquired in each division region A2. Then, proceed to ST5.

In ST5, a pixel group: run having a common density C0 is extracted from pixels adjacent to each other in the sub-scanning direction. Then, proceed to ST6.
In ST6, the length N1 of each run is acquired. Then, proceed to ST7.
In ST7, the interpolation target run length Na corresponding to the concentration C0 of the discrimination target run is read out. Then, proceed to ST8.
In ST8, the interpolation threshold Ca is calculated from the color profile data and the calibration LUT. Then, proceed to ST9.
In ST9, it is determined whether or not the run length N1 is equal to or greater than the interpolation target run length Na. If yes (Y), proceed to ST10, and if no (N), proceed to ST13.

In ST10, it is determined whether or not (i) to (x) are applicable based on the density C0 of the discrimination target run, the densities C0a and C0b of the adjacent pixels, and the respective threshold values Ca and Cb. Then, the process proceeds to ST11.
In ST11, it is determined whether or not the determination target run is the target run for which the interpolation processing is executed, that is, whether or not it corresponds to any of (i) to (x). If yes (Y), proceed to ST12, and if no (N), proceed to ST13.
In ST12, the interpolation process of the gradation step is executed in the run to be discriminated. Then, the process proceeds to ST14.
In ST13, the interpolation process of the gradation step is not executed in the run to be discriminated. Then, the process proceeds to ST14.
In ST14, it is determined whether or not the processing of all runs is completed. If yes (Y), proceed to ST15, and if no (N), return to ST7.
In ST15, it is determined whether or not the processing of all the divided regions A2 being processed in parallel is completed. If no (N), ST15 is repeated, and if yes (Y), the processed print information is output to the image forming apparatus main body U3, and the processing of FIG. 8 is completed.

(Action of Example 1)
In the image forming apparatus U of the first embodiment having the above configuration, when the image information transmitted from the external personal computer PC or the image information read by the scanner apparatus U1 is received, the color conversion process and the calibration LUT are used. Calibration correction processing is performed. Then, when the number of gradation steps of the received image information is lower than the number of gradation steps that can be processed by the image forming apparatus main body U3, the gradation step interpolation processing (gradation) that expands the number of gradation steps of the image information. Process) is executed. Therefore, when the gradation processing is executed, the change in gradation becomes precise, and the image quality is improved as compared with the case where the gradation processing is not executed.

9A and 9B are explanatory views of conventional image processing, FIG. 9A is an explanatory view of an example of pixel density of the original image, and FIG. 9B is an explanatory view after applying color profile data and a calibration LUT to the image of FIG. 9A. 9C is an explanatory diagram when gradation processing is performed on the image of FIG. 9B.
Here, in the prior art, a fixed value is used for the interpolation threshold value Ca when performing the gradation processing on the image after the color conversion and the calibration correction. Therefore, as shown in FIG. 9A, when the density difference 02 exceeds the interpolation threshold Ca after applying the color conversion and the calibration correction to the gradation image unit 01 whose density changes step by step, the gradation is originally generated. In some cases, the gradation processing was not executed for the run 03 to be processed. As described above, depending on the color profile and the calibration LUT, if the gradation processing is executed or not performed, the image quality is not stable and an image quality defect such as unevenness occurs in the gradation image portion. There is. On the other hand, if the interpolation threshold value Ca is set to a large value, there is a problem that the gradation processing is executed in the portion where the gradation processing is originally unnecessary in a natural image or the like in which the color change is large.

On the other hand, in the first embodiment, the interpolation threshold value Ca is calculated according to the color profile data and the calibration LUT. Therefore, the interpolation threshold value Ca is updated according to the change of the color profile and the update of the calibration LUT. Therefore, the situation where the gradation processing is not executed for the run to which the gradation processing should be originally performed or the unnecessary gradation processing is executed is reduced. Therefore, it is possible to improve the image quality as compared with the conventional case in which the interpolation threshold value Ca for determining whether or not to perform the gradation processing is fixed.

10A is an explanatory diagram of an image processing method, FIG. 10A is a gradation image before gradation processing in the case of (v), FIG. 10B is a gradation image after gradation processing in FIG. 10A, and FIG. 10C is (iii). 10D is an explanatory diagram of an end portion of the gradation image after the gradation processing of FIG. 10C.
11A and 11B are explanatory views of an image processing method, FIG. 11A is an explanatory diagram of an example of a gradation image in the case of (vii), FIG. 11B is an explanatory diagram of an example of a gradation image in the case of (iv), and FIG. 11C. Is an explanatory diagram of an example of a gradation image in the case of (v).
FIG. 12 is an explanatory diagram of an image processing method, FIG. 12A is an explanatory diagram of an example of a gradation image in the case of (viii), FIG. 12B is an explanatory diagram of an example of a gradation image in the case of (i), and FIG. 12C. Is an explanatory diagram of an example of a gradation image in the case of (ii), and FIG. 12D is an explanatory diagram of an example of a gradation image in the case of (vi).

In FIGS. 10A and 10B, inside the gradation image unit 102, the case of (v) in the determination of the density difference determination means C413 corresponds to the case of the gradation step so that the density of each run changes continuously. Interpolation processing is executed. Here, even in the conventional technique, such an interpolation process of the gradation step is executed, but as shown in FIG. 10C, the end portion 102a of the gradation image portion 102 has a low density such as a blank sheet (background portion). When the image portion or a high-density image such as a solid image is adjacent to the image, that is, in the case of (iii), the density difference is large and it is determined that the image is a natural image, so that the gradation processing is not executed. Therefore, the portion of the end 102a to be subjected to the gradation processing as shown by the alternate long and short dash line in FIG. 10D is subjected to the gradation processing as shown by the solid line in FIG. 10D. Therefore, in the conventional gradation processing, there is a problem that the gradation is conspicuous at the end of the gradation image unit 102 and looks like an image quality defect.

On the other hand, in Example 1, in the cases of (iii), (iv), (v), and (vii), that is, as shown in FIGS. 10D and 11A to 11C, in a low density portion such as a blank sheet. Gradation processing is also executed at the end of the adjacent gradation image unit 102 and the end of the gradation image unit 102 adjacent to the high density part such as a solid image as shown in FIG. 12 as shown by the alternate long and short dash line. .. Therefore, it is possible to reduce the deterioration of the image quality as compared with the case where the gradation processing is not performed when there is a density difference between the end portion of the gradation image unit 102 and the region outside the gradation image unit 102.
In the case of (iii), (iv), (vi), (viii), unlike the case of (i), (ii), (v), (vii), the end run is on the rising side. The density does not change continuously, but changes discontinuously on the side of blank paper or solid. Therefore, instead of the same gradation processing as in (i), (ii), (v), and (vii), the continuously changing side of the gradation image unit 102 is used by using a preset rate of change. Gradation processing (predictive interpolation processing) is executed in the form of extrapolating (predicting) the change in density from. The rate of change is configured to be set by the user, and can be changed according to the user's purpose and preference.

FIG. 13 is an explanatory diagram of image processing of the boundary portion of the divided region of the first embodiment.
In FIG. 13, when the image area A1 is divided into the divided areas A2 and processed as in the first embodiment, if the gradation image unit 102 straddles the boundary 104 between the divided areas A2, the run straddling the boundary 104 is generated. , It will be divided into each division area A2 and processed respectively. Since one end of the divided run is the end of the divided region A2, the divided run is processed in an indefinite state during the processing of the divided region A2. Therefore, it is uncertain how long the indefinite portion has a run length, whether the adjacent pixel is a continuation of the gradation image unit 102, a natural image, and the like. Therefore, conventionally, for the run straddling the boundary 104, the gradation processing is not performed even in the portion where the gradation processing should be originally performed as shown by the broken line in FIG. Therefore, there is a problem that the gradation becomes uneven at the boundary portion of the divided region A2 and the image quality deteriorates.

On the other hand, in Example 1, in the case of (ix) and (x), when the run length N1 is equal to or greater than the threshold value (interpolation target run length) Na, gradation processing is performed as shown by the alternate long and short dash line in FIG. Execute. Therefore, it is possible to reduce the deterioration of the image quality at the boundary portion as compared with the conventional case in which the gradation processing is not performed at the boundary portion when the image information is divided into the plurality of division regions A2 and processed.

Further, in the first embodiment, when determining whether or not to execute the gradation processing, the interpolation target run length Na is changed to a larger value as the run concentration C0 becomes higher. The higher the concentration C0 of the run, the less noticeable the gradation processing becomes, and the more difficult it is to understand the difference with or without the gradation processing. Therefore, in the first embodiment, the higher the concentration C0, the larger the run length Na to be interpolated, and the more difficult it is to execute the gradation process. In particular, when the density C0 reaches 30%, the gradation processing is not executed. Therefore, in the first embodiment, the gradation processing is not executed for the run for which the necessity of the gradation processing is low. Therefore, it is possible to improve the processing speed while suppressing the deterioration of the image quality as compared with the case where the gradation processing is always executed.

(Change example)
Although the examples of the present invention have been described in detail above, the present invention is not limited to the above examples, and various modifications are made within the scope of the gist of the present invention described in the claims. It is possible. Examples of modifications (H01) to (H04) of the present invention are illustrated below.
(H01) In the above embodiment, a multifunction device as an example of an image forming apparatus has been illustrated, but the present invention is not limited to this, and for example, a copying machine, a fax machine, and a printer may be used.

(H02) In the above embodiment, a configuration in which a four-color developer is used as the image forming apparatus U has been illustrated, but the present invention is not limited to this, and for example, a monochromatic image forming apparatus, three colors or less, or five colors. It can also be applied to the above multicolor image forming apparatus.
(H03) In the above embodiment, the image processing in the image forming apparatus has been illustrated, but the present invention is not limited to this, and a configuration in which a gradation step exists between the input image and the output image, for example, the input image data has a lower rank. It can also be applied to an image processing unit that interpolates gradation steps when the output display is high resolution in a toned image.
(H04) In the above embodiment, the image processing for storing the gradation step when the number of bits, that is, the number of steps (gradation number) of the density increases, has been described, but the present invention is not limited to this. For example, it can be applied to gradation processing for correcting a gradation image whose density changes stepwise so that the density change becomes continuous even if the number of gradations does not increase.

C4 ... Image processing program,
C402 ... Conversion means,
C403 ... Means of storing correction information,
C404 ... Correction means,
C410 ... Threshold setting means,
C415 ... Gradation processing means,
Ca ... Threshold of concentration difference,
U ... Image forming device,
U1 ... Image reader,
U3 ... Image recording device,
C0-C0a, C0-C0b ... Concentration difference.

Claims (6)

A conversion means for converting image information to be printed into a print image in an image forming apparatus based on preset conversion information, and
A correction means for correcting the print information converted by the conversion means based on the correction information of the density set in advance in the image forming apparatus, and a correction means for correcting the print information converted by the conversion means.
A threshold value setting means for setting a threshold value of the density difference based on the conversion information and the correction information of the density, and
Based on the density difference in the threshold and before Symbol print images of the set density difference setting means of the threshold value, density difference in the print image does not reach the threshold value of the density difference, and, a plurality of adjacent pixels For runs with a common density, the positive / negative of the difference between the density of one outer pixel of the run and the density of the run and the positive / negative of the difference between the density of the other outer pixel of the run and the density of the run are opposite or A gradation processing means that performs gradation processing that continuously changes the density when the outer pixel of either one does not exist , and
An image forming apparatus characterized by being provided with. The conversion information preset for each model of the image forming apparatus and
The correction information of the density set for each individual of the image forming apparatus and
The image forming apparatus according to claim 1, wherein the image forming apparatus is provided. An image recording device that prints a preset image for density correction, and
An image reading device that reads an image printed by the image recording device,
A correction information storage means for storing correction information of the density set based on the density of the scanned image read by the image reader and the density of the image for density correction.
The image forming apparatus according to claim 1 or 2, wherein the image forming apparatus is provided. The density difference after applying the conversion information and the correction information of the density to the density difference in one step is calculated for all the concentrations, and the maximum value of the density difference after application is the threshold value of the density difference. The threshold setting means, which is set as
The image forming apparatus according to any one of claims 1 to 3, wherein the image forming apparatus is provided. A conversion step of converting image information to be printed into a printed image in an image forming apparatus based on preset conversion information, and
A correction step of correcting the print information converted in the conversion step based on the correction information of the density set in advance in the image forming apparatus, and a correction step of correcting the print information converted in the conversion step.
Based on the density difference in the threshold and before Symbol print images of the set density difference based on the correction information of the said conversion information density, density difference in the print image does not reach the threshold value of the density difference, and For a run with a common density of multiple adjacent pixels, the positive and negative of the difference between the density of one outer pixel of the run and the density of the run, and the density of the other outer pixel of the run and the density of the run A gradation processing step that performs gradation processing that continuously changes the density when there is no outer pixel that is opposite to the positive or negative of the difference or one of them .
An image processing method characterized by being provided with. Computer,
A conversion means for converting image information to be printed into a printed image in an image forming apparatus based on preset conversion information.
A correction means that corrects the print information converted by the conversion means based on the correction information of the density set in advance in the image forming apparatus.
A threshold value setting means for setting a threshold value of a density difference based on the conversion information and the correction information of the density.
Based on the density difference in the threshold and before Symbol print images of the set density difference setting means of the threshold value, density difference in the print image does not reach the threshold value of the density difference, and, a plurality of adjacent pixels For runs with a common density, the positive / negative of the difference between the density of one outer pixel of the run and the density of the run and the positive / negative of the difference between the density of the other outer pixel of the run and the density of the run are opposite or A gradation processing means that performs gradation processing that continuously changes the density when the outer pixel of either one does not exist .
An image processing program characterized by functioning as.