JP6743590B2 - Image forming apparatus and image processing method - Google Patents

Description

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

In image forming apparatuses of recent years, the gray level of image information transmitted from an information processing apparatus such as a personal computer may be greater in the gray level that can be processed by the image forming apparatus that receives the image information. I'm doing it. As an example, the shading of the image information transmitted to the image forming apparatus is 8 [bit]=2 ⁸ =256 [steps], while the shading that can be processed by the image forming apparatus is 10 [bit]=2 ¹⁰ =1024 [stages] in some cases. Although different from the image forming apparatus, the techniques described in Patent Documents 1 and 2 below regarding the technique of performing image processing when the gradation level of the displayed image is higher than the gradation level of the input image. It has been known.
Japanese Unexamined Patent Publication No. 2009-157656 as Patent Document 1 discloses an image processing apparatus 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 it is a gradation region. With respect to the generated pixels, a technique is described in which the input image signal is smoothed and the image signal is expanded to N+k bits.
Further, as a technique for performing correction for expanding the number of gradations of an input image signal, when a difference value between adjacent pixels is less than or equal to a predetermined value, it is determined to be a region indicating gradation and smoothing is performed, Japanese Patent Laid-Open No. 2007-213460, which is JP-A-2007-213460, describes a technique for expanding the number of gradations without performing smoothing by determining an area indicating an edge when the value exceeds a predetermined value.

JP, 2009-157656, A ("0049"-"0058") JP, 2007-213460, A

An object of the present invention is 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.

In order to solve the technical problem, the image processing method of the invention according to claim 1 is
In an image having a plurality of pixels, when the number of adjacent pixels having a common density reaches a preset threshold value, gradation processing for continuously changing the density of the image is performed, and the threshold value is set to the pixel value. It is characterized by changing according to the concentration of .

The invention described in claim 2 is the image processing method according to claim 1,
When the density of the pixel reaches a preset value, the gradation process is not performed .

The invention described in claim 3 is the image processing method according to claim 1 or 2, wherein
The threshold value is increased as the density of the pixel increases.

In order to solve the technical problem, the image forming apparatus of the invention according to claim 4 is
In an image having a plurality of pixels, when the number of adjacent pixels having a common density reaches a threshold value set in advance according to the density of the pixel, gradation processing for continuously changing the density of the image is performed. Gradation processing means,
Means for changing the threshold value according to the density of the pixel;
Characterized by comprising a.

According to a fifth aspect of the invention, in the image forming apparatus according to the fourth aspect ,
When the density of the pixel reaches a preset value, the gradation process is not performed .

The invention described in 請 Motomeko 6, in the image forming apparatus according to claim 4 or 5,
The threshold value is increased as the density of the pixel increases .

According to the first and fourth aspects of the invention, the processing speed can be improved while suppressing the deterioration of the image quality, as compared with the case where the gradation processing is always executed .
According to the invention described in claims 2 and 5 , the processing speed can be improved as compared with the case where the gradation processing is performed when the density of the pixel reaches a preset value.
According to the invention described in claims 3 and 6 , the processing speed can be improved as compared with the case where the threshold value is not increased as the density of the pixel increases.

First Embodiment FIG. 1 is an overall explanatory diagram of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a block diagram showing the functions of the control unit of the image forming apparatus according to the first embodiment. FIG. 3 is an explanatory diagram showing an outline of the 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. FIG. 4C is an explanatory diagram of a case where the calibration process is performed, and FIG. 4C is an explanatory diagram of a case where the calibration process is performed on the data after the color conversion process of FIG. 4B. FIG. 5 is an explanation regarding division of an image area in the image processing of the first embodiment. FIG. 6 is an explanatory diagram of a list showing the density difference, the threshold value, and the presence/absence of the opening process in the first embodiment. FIG. 7 is an explanatory diagram of the change rate 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 diagrams of conventional image processing, FIG. 9A is an explanatory diagram of an example of the density of pixels of an original image, and FIG. 9B is an explanatory diagram 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. FIG. 10 is an explanatory diagram of the 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 of FIG. 10A, and FIG. 10C is of (iii). 10D is an explanatory diagram of the end portion of the gradation image before the gradation processing, and FIG. 10D is an explanatory diagram of the end portion of the gradation image after the gradation processing of FIG. 10C. 11A and 11B are explanatory diagrams of the image processing method. FIG. 11A is an explanatory diagram of an example of the gradation image in the case of (vii), FIG. 11B is an explanatory diagram of an example of the gradation image in the case of (iv), and FIG. 11C. FIG. 8 is an explanatory diagram of an example of a gradation image in the case of (v). 12A and 12B are explanatory diagrams of the 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. 12D is an explanatory diagram of an example of the gradation image in the case of (ii), and FIG. 12D is an explanatory diagram of an example of the gradation image in the case of (vi). FIG. 13 is an explanatory diagram of image processing of the boundary portion of the divided areas according to the first embodiment.

Next, examples as specific examples 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.
To facilitate understanding of the following description, 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 arrows X, -X, Y, -Y, The directions indicated by Z and -Z are indicated as front, rear, right, left, upper, lower, or front, rear, right, left, upper, lower.
Also, in the figure, the one marked with "." in "○" means an arrow pointing from the back of the paper to the front, and the one marked "x" in "○" is the front of the paper. Shall mean the arrow from the back to the back.
In the following description using the drawings, illustrations other than the members necessary for the description are appropriately omitted for easy understanding.

First Embodiment FIG. 1 is an overall explanatory diagram of an image forming apparatus according to a first embodiment of the present invention.
In FIG. 1, the image forming apparatus U includes an operation unit UI, a scanner apparatus U1 as an example of an image reading apparatus, a sheet feeding apparatus U2, an image forming apparatus body U3 as an example of an image recording apparatus, and a sheet discharge section U4. doing.

The operation unit UI includes a power button as an example of an input unit, a copy start key, a copy number setting key, a ten-key pad, a display unit, and the like.
The scanner device U1 reads a document (not shown), converts it into image information, and inputs it to the image forming device body U3.
The paper feeding device U2 has a plurality of paper feeding trays TR1 to TR4 as an example of a paper feeding unit. A recording sheet S, which is an example of a 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 each of 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 includes a control unit C, a power supply circuit E that is controlled by the control unit C to supply power to each member of the image forming apparatus main body U3, and the like. The control unit C receives image information of a document read by the scanner device U1 and image information transmitted from a personal computer as an example of an information transmitting device (not shown) connected to the image forming device U.
The control unit C processes the received image information into printing information of Y: yellow, M: magenta, C: cyan, and K: black, and a laser as an example of a drive circuit of a latent image writing device. Output to the 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.

Below the latent image forming devices ROSy to ROSk, Y, M, C, and K image carrier units Uy, Um, Uc, and Uk are arranged.
In FIG. 1, a K: black image carrier unit Uk includes a photoconductor drum Pk as an example of an image carrier, a corotron CCk as an example of a charger, and a photoconductor as an example of a cleaner for the image carrier. It has a body cleaner CLk. The image carrier units Uy, Um, and Uc of the other colors Y, M, and C also include the photoconductor drums Py, Pm, Pc, the charging corotrons CCy, CCm, CCc, and the photoconductor cleaners CLy, CLm, CLc.
In the first embodiment, the K-color photosensitive drum Pk, which is frequently used and whose surface is often worn, is configured to have a larger diameter than the photosensitive drums Py, Pm, and Pc of other colors. It has a long life.

The photoconductor drums Py, Pm, Pc and Pk are uniformly charged by the charging corotrons CCy, CCm, CCc and CCk, respectively, and then written by the latent image forming devices ROSy, ROSm, ROSc and ROSk. An electrostatic latent image is formed on the surfaces of the photoconductor drums Py to Pk by the laser beams Ly, Lm, Lc, and Lk as an example of light. The electrostatic latent images on the surfaces of the photoconductor drums Py, Pm, Pc, Pk are Y: yellow, M: by a developing roll R0 as an example of a developing member provided in the developing devices Gy, Gm, Gc, Gk. A toner image as an example of a visible image is developed with developers of magenta, C: cyan, and K: black.

The toner images on the surfaces of the photoconductor drums Py, Pm, Pc, and Pk are formed by the primary transfer rolls T1y, T1m, T1c, and T1k as an example of the primary transfer device in the primary transfer area Q3 as an example of an intermediate transfer member. Therefore, the images are sequentially transferred onto the intermediate transfer belt B, which is an example of the image carrier, so that a multicolor image, that is, a color image is formed on the intermediate transfer belt B. The color image formed on the intermediate transfer belt B is conveyed to the secondary transfer area Q4.
In the case of only black image data, only K: black photosensitive 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.
A toner image forming member Uy+Gy, Um+Gm, Uc+Gc as an example of a visible image forming unit is formed by each of the image carrier units Uy, Um, Uc, Uk and developing devices Gy, Gm, Gc, Gk as an example of a developing device. , Uk+Gk are configured.

A toner dispenser U3a, which is an example of a replenishing device, is arranged above the image forming apparatus main body U3. It is detachably attached. When the toner is consumed in the developing devices Gy to Gk due to the image formation, the toner is supplied from the toner cartridges Ky to Kk to the developing devices Gy to Gk.

The intermediate transfer belt B disposed below the photoconductor drums Py to Pk is an example of an intermediate drive roll Rd that is an example of a drive member for the intermediate transfer body, and an example of a tension applying member that applies tension to the intermediate transfer belt B. Intermediate tension roll Rt, an intermediate steering roll Rw as an example of a first offset correction member that corrects deviation and meandering of the intermediate transfer belt B, and a plurality of intermediate idlers as an example of driven members of the intermediate transfer member. The roll Rf and a backup roll T2a as an example of a facing member in the secondary transfer area are stretched. The intermediate transfer belt B is rotatably supported in the arrow Ya direction by the driving of 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 a support member for the intermediate transfer member of the first embodiment. 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 an intermediate transfer device. The belt module BM according to the first exemplary embodiment includes a unit that can be attached to and detached from the image forming apparatus body U3 and can be replaced.

The intermediate steering roll Rw according to the first exemplary embodiment includes a rotating body having a rotating shaft, and the rotating shaft is inclined in a direction in which the offset is corrected according to the offset in the width direction of the intermediate transfer belt B. The deviation and meandering of the intermediate transfer belt B are prevented. As described above, a method of correcting the deviation by inclining the rotating shaft according to the detection result of the member that detects the deviation of the belt such as the optical sensor and the member that contacts the end of the belt, that is, the so-called active steering method is used. The steering roll Rw is conventionally known and, for example, various conventionally known configurations described in JP 2009-86463 A, JP 2010-231112 A, and the like can be adopted, and thus detailed description thereof is omitted. To do.

Below the backup roll T2a, a secondary transfer unit Ut as an example of a transfer/transport device is arranged. The secondary transfer unit Ut has a secondary transfer roll T2b as an example of a transfer member. The secondary transfer roll T2b is arranged to face the backup roll T2a. The area where the secondary transfer roll T2b faces the intermediate transfer belt B constitutes a secondary transfer area Q4. A contact roll T2c, which is an example of a contact member for voltage application, is in contact with the backup roll T2a. Each of the rolls T2a to T2c constitutes a secondary transfer device T2.
A secondary transfer voltage having the same polarity as the charging polarity of the toner is applied to the contact roll T2c from a power supply circuit E controlled by the controller C at a preset time.

Below the belt module BM, a paper transport path SH2 is arranged. The recording sheet S fed from the sheet feeding path SH1 of the sheet feeding device U2 is conveyed to the sheet conveying path SH2 by a conveying roll Ra as an example of a conveying member. The recording paper S on the paper transport path SH2 is sent by a registration roll Rr, which is an example of a sending member, at the time when the toner image is carried to the secondary transfer area Q4, and a paper guide SG1 that is an example of a medium guiding member. Guided by SG2, it is conveyed to the secondary transfer area Q4.
The toner image on the intermediate transfer belt B is transferred to the recording sheet S by the secondary transfer device T2 when passing through the secondary transfer area Q4. In the case of a color image, the toner images that have been primarily transferred and superposed on the surface of the intermediate transfer belt B 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 which is an example of a cleaning device for the intermediate transfer body. The secondary transfer roll T2b is supported so as to be separated from and in contact with the intermediate transfer belt B.
By the primary transfer rolls T1y, T1m, T1c, T1k, the intermediate transfer belt B, the secondary transfer device T2, and the belt cleaner CLB, a transfer device T1+B+T2+CLB for transferring the image on the surface of the photosensitive drums Py to Pk to the recording paper S is provided. It is configured.

The recording sheet S to which the toner image is secondarily transferred is sent to a medium carrying belt BH as an example of a carrying member. The medium conveyance belt BH conveys the recording sheet S to the fixing device F. The fixing device F includes a heating member Fh as an example of a heat fixing member and a pressure member Fp as an example of a pressure fixing member, and fixing is performed by a region where the heating member Fh and the pressure member Fp are in contact with each other. A region Q5 is formed.
The toner image on the recording paper S is heated and fixed by the fixing device F when passing through the fixing area Q5. The recording paper S on which the toner image has been fixed by the fixing device F is discharged to a discharge tray TRh which is an example of a discharge unit.
A sheet transport path SH is constituted by the symbols SH1, SH2 and the like. Further, the sheet conveying device SU is constituted by the symbols SH, Ra, Rr, SG1, SG2, BH and the like.

(Explanation of the control unit of the first embodiment)
FIG. 2 is a block diagram showing the functions of the control unit of the image forming apparatus according to the first embodiment.
In FIG. 2, the control unit C of the image forming apparatus U has an input/output interface I/O for inputting/outputting signals to/from the outside. The control unit C also has a ROM: read only memory in which programs and information for performing necessary processing are stored. Further, the control unit C has a random access memory (RAM) for temporarily storing necessary data. Further, the control unit C has a CPU: 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 configured by a small information processing device, a so-called microcomputer. Therefore, the control unit C can realize various functions by executing the programs 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 input buttons UIa such as a power button, a copy start key, a copy number setting key, and a ten-key pad as an example of an input member. In addition, the operation unit UI includes a display unit UIb as an example of a display member.

(Controlled element connected to control unit C)
The control unit C is connected to the drive circuit D1 of the main drive source, the power supply circuit E, and other control elements (not shown). The control section C outputs those control signals to the circuits D1, E and the like.
D1: Drive circuit of main drive source The drive circuit D1 of the main drive source is an example of the drive source of the image carrier, and the photosensitive drums Py to Pk and the main body 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 has 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 for development Ea applies a developing voltage to the developing 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 the charging corotrons CCy to CCk, respectively.

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 Forming Control Unit The image forming control unit C1 controls the driving of each member of the image forming apparatus main body U3 and the application timing of each voltage according to the image information input from the scanner device U1 or the personal computer. Then, execution, termination, and interruption of the job that is the image forming operation are controlled.
C2: Power Supply Circuit Control Unit The power supply circuit control unit C2 controls the power supply circuits Ea to Ed to control the voltage applied to each member and the power supplied to each member.

FIG. 3 is an explanatory diagram showing an outline of the processing flow in the control unit of the image forming apparatus of the first embodiment.
C3: Information Receiving Unit The information receiving unit C3 receives the image information transmitted from the scanner device U1 or the personal computer.
C4: Image Processing Unit In FIG. 2, the image processing unit 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 unit C4 of the first embodiment, for example, the image forming apparatus main body U3 can perform printing 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, the image processing for increasing the gradation step difference to 10 bits by 2 bits=4 steps is executed. 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. FIG. 4C is an explanatory diagram of a case where the calibration process is performed, and FIG. 4C is an explanatory diagram of a case where the calibration process is performed on the data after the color conversion process of FIG. 4B.
C401: Profile Data Storage Means Profile data storage means C401 stores color profile data as an example of conversion information. In FIG. 4, as an example, when the 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. In the first embodiment, the 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 or overseas or manually by the user can be used. The color profile data set in can be used.
C402: Color Converting Unit The color converting unit C402, which is an example of the converting unit, performs the color converting process on the received image information based on the color profile data stored in the profile data storing unit C401.

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

The calibration LUT is created in the image forming apparatus U when the operation of creating the calibration LUT is executed separately from the image forming operation. Specifically, a preset calibration image is printed, the printed calibration image is read by the scanner device U1, and the preset density of the calibration image and the actually set calibration image are read. A calibration LUT is created from the difference between the printed density and the actual density of the calibration image. Since the process of creating such a calibration LUT has been publicly 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 image forming apparatus U. Therefore, the color profile data is subjected to image processing according to the specifications and settings of each model, and the calibration LUT performs image processing according to individual differences.

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

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

C406: Density Acquisition Unit The density acquisition unit C406 acquires the density C0 of each pixel in the image 101 to be printed.
C407: Pixel Group Extraction Unit The pixel group extraction unit 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, for each divided area A2, a run, which is a pixel group in which pixels having a common density are adjacent to the pixels arranged adjacent in the sub-scanning direction, is extracted.
C408: Run Length Acquisition Unit The run length acquisition unit C408, which is an example of a pixel group length acquisition unit, has the length of the run extracted by the pixel group extraction unit C407, that is, the number of pixels of the pixel group (run length). Get N1. The run length acquisition unit C408 of the first embodiment acquires the run length N1 for each run.

C409: Run Length Threshold Storage Means A run length threshold storage means C409, which is an example of a pixel group threshold storage means, is based on the density C0 of each run, and is an interpolation target run that is an example of a run length threshold. Remember long Na. In the first embodiment, the setting information in which the interpolation target run length Na increases as the density 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)] ] Setting information is stored. It should be noted that the interpolation target run length Na is a gradation process for increasing the gradation step in the run to continuously change the density when the run length N1 reaches the interpolation target run length Na (interpolation processing of the gradation step). ) Is performed, and when the run length N1 does not reach the interpolation target run length Na, it is a threshold value for determining not to perform gradation processing. In the first embodiment, when the density C0 is higher than 30%, the interpolation target run length Na is set to ∞, and no gradation process is 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 illustrated numerical value, and can be arbitrarily changed by design, specifications, manual setting by the user, or the like.

C410: Interpolation Threshold Setting Unit An interpolation threshold setting unit C410, which is an example of a density difference threshold setting unit, sets an interpolation threshold (interpolation target reference Gap value) Ca, which is an example of a density difference threshold. The interpolation threshold setting unit C410 according to the first embodiment sets an interpolation threshold Ca for determining whether or not to perform gradation processing (gradation step interpolation processing) 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 complementary process on the original image is 1, the interpolation threshold value Ca is set based on the following formula (1).
Ca=Max [CalibLUT(Profile(C0))-CalibLUT(Profile(C0-1))] Equation (1)
In Expression (1), Profile(x) is a function for calculating the density after performing the color conversion process on the density x with the color profile data, and CalibLUT(y) is a function for calculating the density y in the calibration LUT. This is a function for calculating the density after the correction processing is performed using the function. Therefore, when C0=100, Profile(100)=100, CalibLUT(Profile(100))=100, 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 densities (1 to 100) of C0, and the maximum value (Max) is calculated as the interpolation threshold. Set to Ca.
Note that when the threshold value for determining whether or not to perform interpolation processing on the original image is m, the term of CalibLUT (Profile(C0-1)) in Expression (1) is set to CalibLUT(Profile(C0-m)). It is possible.

C411: Run Length Determining Means The run length determining means C411 determines whether or not the run length N1 of each run reaches the interpolation target run length Na. When the run length N1 reaches the interpolation target run length Na, the run length determining unit C411 according to the first embodiment determines to execute the gradation process. As the run length Na to be interpolated, one corresponding to the density C0 of each run stored in the storage unit C409 of the run length threshold value is used.
C412: Edge Discriminating Means The edge discriminating means C412 discriminates for each run whether or not a pixel at the edge of the divided area A2 is included, that is, whether or not the run extends from the edge of the divided area A2. ..

C413: Density Difference Discrimination Means The density difference discrimination means C413 discriminates 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 value Ca. The density difference determination unit C413 according to the first exemplary embodiment uses, for each run, the density C0a of the pixel adjacent to the downstream side in the sub-scanning direction (medium carrying direction) of the run and the density C0b of the pixel adjacent to the upstream side. On the other hand, it is determined whether or not each density difference C0a-C0, C0b-C0 is larger than the interpolation threshold value Ca or the preset edge threshold value Cb. The edge threshold Cb is a threshold for determining the edge of the gradation image portion 102, and is used when the gradation image portion 102 is adjacent to a background portion (blank paper portion), a solid image, a natural image, or the like. It is stored in advance in order to determine the edge of the gradation image portion 102 based on the density difference between the adjacent image and the edge of the gradation image portion 102. In the first embodiment, Ca<Cb is set.

Further, when the run extends from the end of the divided area A2, the density difference determination unit C413 according to the first exemplary embodiment uses the density difference C0a-C0 or C0b with respect to the densities C0a and C0b of the pixel on the side opposite to the end. It is determined whether -C0 is larger than the interpolation threshold Ca.
In the following description, for ease of understanding, the pixel on the downstream side is the “right” side and the pixel on the upstream side is the “left” side. Further, the “density difference” may be expressed as a “step”.

FIG. 6 is an explanatory diagram of a list showing the density difference, the threshold value, and the presence/absence of the opening process in the first embodiment.
In the first embodiment, the presence/absence of the gradation processing is determined as shown in FIG. 6 in the run in which the gradation processing is determined to be executed by the determination of the run length. Specifically, it is determined to execute the gradation process in the following cases.
(I) When C0a-C0>0 (the right step is +) and C0b-C0>0 (the 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 densities of the pixels on both the left and right sides, and if interpolation processing of a gradation step in which the density increases from the left end to the right end (upward to the right) Determine. That is, it is determined that the process is performed such that the density increases from the density C0 of the determination target run toward the density C0a of the pixel on the right side.
(Ii) If 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 densities of the pixels on both the left and right sides, and if interpolation processing of gradation step where the density decreases from the left end to the right end of the run (downward to the right) Determine. That is, it is determined that the run is one in which processing is performed such that the density decreases from the density C0b of the pixel on the left side to the density C0 of the run to be determined.

(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. Determine. Therefore, it is determined that the run is one in which the process is performed such that the density increases from the density C0 of the determination target run to the right according to a change rate described later. Therefore, unlike (i) and (ii), the density at the right end is predicted and estimated from the density C0 at the left end at the rate of change, and thus the predictive interpolation process is performed.
(Iv) When C0a-C0<0 (the right step is −) and C0b-C0<0 (the 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 densities of the pixels on both the left and right sides. Determine. That is, it is determined that the prediction interpolation process is performed so that the density increases from the density C0 of the determination target run on the right side to the left side according to the change rate.

(V) In the case of C0a-C0>0 (the right step is +) and C0b-C0<0 (the left step is −), and |C0a-C0|<Ca, the pixel on the left of the run is inserted. It is determined that the density is increasing toward the pixel on the right side, and the run to be determined is subjected to the interpolation process of the gradation step where the density increases from the left to the right of the run (upward to the right). To determine. That is, it is determined that the process is performed so that the density increases from the density C0 of the determination target run toward the density C0a of the pixel on the right.
(Vi) If C0a-C0>0 (the right step is +) and C0b-C0<0 (the left step is −) and |C0a-C0|>Ca and |C0b-C0|<Ca, it is determined. It is determined that the target run is the right end of the gradation image portion 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 determined is subjected to the predictive interpolation process of the gradation step in which the density increases from the left to the right of the run (upward to the right). That is, it is determined that the process is performed so that the concentration increases from the concentration C0 of the determination target run to the right side according to the change rate.

(Vii) If C0a-C0<0 (right step is −) and C0b-C0>0 (left step is +), and |C0b-C0|<Ca, the pixel on the left of the run is inserted. It is determined that the density decreases toward the pixel on the right. Therefore, it is determined that the run to be determined is subjected to the interpolation process of the gradation step where the density decreases from the left to the right of the run (downward to the right). That is, it is determined that the run is one in which processing is performed such that the density decreases from the density C0b of the adjacent pixel on the left to the density C0 of the determination target run.
(Viii) When C0a-C0<0 (the right step is −) and C0b-C0>0 (the left step is +) and |C0a-C0|<Ca and |C0b-C0|>Ca, it is determined. It is determined that the target run is the left end of the gradation image portion 102 with the high density image such as a solid image adjacent to the left side. Therefore, it is determined that the run to be determined is subjected to the predictive interpolation process of the gradation step where the density decreases from the left to the right of the run (downward to the right). That is, it is determined that the process is performed such that the concentration increases from the concentration C0 of the determination target run to the left side according to the change rate.

(Ix) When the left end is the end of the divided area A2 and |C0a−C0|<Ca, it is determined that the left end is the end of the divided area A2 and the prediction interpolation process of the gradation step is performed. When C0a-C0>0 (the right step is +), it is determined that the density increases from the left to the right of the run (up to the right), and the density C0a and the change rate of the pixel on the right side are determined. Therefore, it is determined that the prediction interpolation processing is performed so that the density decreases toward the left side. When 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 the density C0b and the rate of change of the pixel on the left side are determined. Then, it is determined that the prediction interpolation processing is performed so that the density decreases toward the right side.
(X) When the right edge is the edge of the divided area A2 and |C0b−C0|<Ca, it is determined as the edge of the divided area A2 and the run for performing the gradation step predictive interpolation processing. When C0b-C0>0 (the left step is +), it is determined that the density decreases from the left to the right of the run (falls to the right), and the density C0b of the pixel adjacent to the left and the change rate are determined. Then, it is determined that the prediction interpolation processing is performed so that the density decreases toward the right side. When C0b−C0<0 (the left step is −), it is determined that the density of the run increases from the left to the right (up to the right), and the density C0 of the run to be determined and the rate of change are determined. It is determined that the run is one in which the predictive interpolation process is performed so that the density increases toward the right side.

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

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

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

(Explanation of the flow chart 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 flow chart.

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

In ST1 of FIG. 8, color conversion processing using the color profile is executed. Then, it proceeds to ST2.
In ST2, a calibration correction process using the calibration LUT is executed. Then, it proceeds to ST3.
In ST3, the image area A1 is divided into band-shaped divided areas A2. Then, it proceeds to ST4.
In ST4, the density C0 of each pixel is acquired in each divided area A2. Then, it proceeds to ST5.

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

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

(Operation 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, interpolation processing of gradation steps (gradation of gradation steps for expanding the number of gradation steps of image information) Process). Therefore, the gradation process is executed, the change in gradation becomes fine, and the image quality is improved as compared with the case where the gradation process is not executed.

9A and 9B are explanatory diagrams of conventional image processing, FIG. 9A is an explanatory diagram of an example of pixel densities of an original image, and FIG. 9B is an explanatory diagram 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 related art, when performing gradation processing on an image after color conversion and calibration correction, a fixed value is used as the interpolation threshold Ca. Therefore, as shown in FIG. 9A, when the density difference 02 exceeds the interpolation threshold Ca after the color conversion and the calibration correction are applied to the gradation image portion 01 in which the density changes by one step, the gradation is originally changed. In some cases, the gradation process 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 process is performed 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, when the interpolation threshold value Ca is set to a large value, there is also a problem in that a gradation process is executed on a portion where the gradation process is originally unnecessary in a natural image or the like with a large change in color.

On the other hand, in the first embodiment, the interpolation threshold Ca is calculated according to the color profile data and the calibration LUT. Therefore, the interpolation threshold Ca is updated according to the change of the color profile and the update of the calibration LUT. Therefore, it is possible to reduce the situation in which the gradation process is not executed in the run in which the gradation process is originally supposed to be performed, or the unnecessary gradation process is executed. 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 gradation processing is fixed.

FIG. 10 is an explanatory diagram of the 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 of FIG. 10A, and FIG. 10C is of (iii). 10D is an explanatory diagram of the end portion of the gradation image before the gradation processing, and FIG. 10D is an explanatory diagram of the end portion of the gradation image after the gradation processing of FIG. 10C.
11A and 11B are explanatory diagrams of the image processing method. FIG. 11A is an explanatory diagram of an example of the gradation image in the case of (vii), FIG. 11B is an explanatory diagram of an example of the gradation image in the case of (iv), and FIG. 11C. FIG. 8 is an explanatory diagram of an example of a gradation image in the case of (v).
12A and 12B are explanatory diagrams of the 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. 12D is an explanatory diagram of an example of the gradation image in the case of (ii), and FIG. 12D is an explanatory diagram of an example of the gradation image in the case of (vi).

In FIG. 10A and FIG. 10B, inside the gradation image unit 102, this corresponds to the case of (v) in the judgment of the density difference judging means C 413, and the gradation step difference is generated so that the density of each run continuously changes. Interpolation processing is executed. Here, even in the conventional technique, such a gradation step interpolation process is executed, but as shown in FIG. 10C, the edge portion 102a of the gradation image portion 102 has a low density such as a white paper (background portion). In the case of being adjacent to the high density image such as the image portion or the solid image, that is, in the case of (iii), it was determined that the density difference was large and the image was a natural image, so the gradation process was not executed. Therefore, the gradation process as shown by the solid line in FIG. 10D has been executed on the portion of the end portion 102a where the gradation process should be originally performed as shown by the chain 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 portion 102 and the image 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 FIG. 10D and FIG. 11A to FIG. Gradation processing is executed as indicated by the alternate long and short dash line at the end portions of the adjacent gradation image portions 102 and the end portions of the gradation image portions 102 adjacent to the high density portion such as a solid image as shown in FIG. .. Therefore, when there is a density difference between the end portion of the gradation image portion 102 and the area outside the gradation image portion 102, it is possible to reduce deterioration in image quality as compared with the case where no gradation processing is performed.
In the cases of (iii), (iv), (vi), and (viii), unlike the cases of (i), (ii), (v), and (vii), on the side where the run at the end is rising. The density does not change continuously, but changes so-called discontinuously on the side of white paper or solid. Therefore, instead of the gradation processing similar to (i), (ii), (v), and (vii), the side of the gradation image unit 102 that is continuously changing is used using a preset change rate. The gradation process (predictive interpolation process) is executed in a form of extrapolating (predicting) the density change from. The rate of change is configured such that it can be set by the user, and can be changed according to the user's purpose or preference.

FIG. 13 is an explanatory diagram of image processing of the boundary portion of the divided areas according to the first embodiment.
In FIG. 13, when the image area A1 is divided into the divided areas A2 for processing as in the case of the first embodiment, if the gradation image portion 102 extends over the boundary 104 between the divided areas A2, the run across the boundary 104 is , Are divided into respective divided areas A2 and processed respectively. Since one end of the divided run is the end of the divided area A2, the divided previous portion is processed in an indefinite state during the processing of the divided area 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 portion 102, or a natural image. Therefore, conventionally, for a run that crosses the boundary 104, the gradation process is not performed on the part that should originally be subjected to the gradation process as shown by the broken line in FIG. Therefore, there is a problem that the gradation becomes uneven at the boundary of the divided area A2 and the image quality is deteriorated.

On the other hand, in the first embodiment, in the case of (ix) and (x), when the run length N1 is equal to or larger 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 a plurality of divided areas A2 and processed.

Further, in the first embodiment, when determining whether or not to execute gradation processing, the interpolation target run length Na is changed to a larger value as the run density C0 is higher. In the gradation process, the darker the run density C0, the less noticeable the difference becomes, and the difference becomes difficult to understand whether or not the gradation process is performed. Therefore, in the first embodiment, as the density C0 increases, the interpolation target run length Na increases, and the gradation process becomes difficult to execute. In particular, when the density C0 reaches 30%, gradation processing is not executed. Therefore, in the first embodiment, gradation processing is not executed for runs for which gradation processing is less necessary. Therefore, as compared with the case where the gradation process is always executed, it is possible to suppress the deterioration of the image quality and improve the processing speed.

(Example of change)
Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications are made within the scope of the gist of the present invention described in the claims. It is possible. Modifications (H01) to (H04) of the present invention are exemplified below.
(H01) In the above-described embodiment, the multifunction machine is illustrated as an example of the image forming apparatus, but the invention is not limited to this, and the image forming apparatus may be configured by, for example, a copying machine, a FAX, or a printer.

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

C0... pixel density,
C415... Gradation processing means,
N1... The number of adjacent pixels having a common density,
Na... a preset threshold value,
U... Image forming apparatus.

Claims (6)

In an image having a plurality of pixels, when the number of adjacent pixels having a common density reaches a preset threshold value, gradation processing for continuously changing the density of the image is performed, and the threshold value is set to the pixel value. An image processing method characterized in that the image density is changed according to the density of the image. The image processing method according to claim 1 , wherein the gradation process is not performed when the density of the pixel reaches a preset value. The image processing method according to claim 1 or 2, characterized in that to increase the threshold to bring the concentration of the pixels is increased. In an image having a plurality of pixels, when the number of adjacent pixels having a common density reaches a threshold value set in advance according to the density of the pixel, gradation processing for continuously changing the density of the image is performed. Gradation processing means ,
Means for changing the threshold value according to the density of the pixel;
An image forming apparatus comprising: The image forming apparatus according to claim 4, wherein when the density of the pixel reaches a preset value, the gradation process is not performed. The image forming apparatus according to claim 4, wherein the threshold value is increased as the density of the pixel increases.