JP2006270771A - Image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor which corrects the striped density ununiformity at a high resolution, without causing a significant rise in cost with excessive increase in the memory size, and forms an image superior in uniformity of the in-plane density. <P>SOLUTION: The image processor 12 converts first color signals to second color signals that are the image forming signals of an image forming apparatus, based on the image forming position of the image forming apparatus. It comprises a plurality of conversion tables 71 for converting the first color signals to the second color signals are disposed, according to the density gradient at each image forming position previously detected by an image density detecting means, and a conversion table selecting means 72 for selecting any one of the conversion table to be used among the plurality of conversion table, based on each image forming position of the image forming apparatus. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image processing apparatus used in an image forming apparatus such as a copying machine, a printer, or a facsimile employing an electrophotographic method, and more particularly to an image processing apparatus capable of forming an image with excellent in-plane density uniformity. Is.

JP 2002-135610 A

  Conventionally, an image forming apparatus such as a copying machine, a printer, or a facsimile that employs this type of electrophotographic method uniformly charges the surface of the photosensitive drum to a predetermined potential, and then images the surface of the photosensitive drum. The image is exposed by scanning with a laser beam according to information to form an electrostatic latent image, and the electrostatic latent image is developed to transfer and fix the toner image on a recording sheet as a toner image. Thus, an image is formed.

  By the way, in an image forming apparatus adopting such an electrophotographic system, it corresponds to a difference in sensitivity on the surface of the photosensitive drum, a variation in charging potential for uniformly charging the surface of the photosensitive drum, or image information. For example, when an image having a uniform density is formed on the entire surface of a recording sheet due to various factors such as partial fluctuations in the amount of image exposure for performing image exposure by scanning with laser light. However, density variations partially occur, and the uniformity of in-plane density (color) is inherently inferior to a printed image by offset printing or the like.

  Therefore, in order to solve such a problem, the density difference of the image signal is calculated using position information such as the position X in the laser scanning direction (main scanning direction) and the position Y in the rotation direction of the photosensitive drum (paper feeding direction). A technique for improving in-plane non-uniformity by converting to another corrected signal has already been proposed by the present applicant, as disclosed in JP-A-2002-135610.

  The image processing apparatus according to Japanese Patent Application Laid-Open No. 2002-135610 is an image processing apparatus that converts a first color signal into a second color signal that is an image recording signal of the image forming apparatus. The first color signal is converted into the second color signal based on the relationship determined by the recording position coordinate signal indicating the position where the image is recorded on the image carrier in accordance with the second color signal and the first color signal. The calculation means is configured to have an n-dimensional lookup table as the calculation means.

  According to the image processing apparatus according to Japanese Unexamined Patent Publication No. 2002-135610, an in-plane density non-uniformity problem can be solved in an image forming apparatus employing an electrophotographic system.

  However, the conventional technique has the following problems. That is, the image processing apparatus according to Japanese Patent Application Laid-Open No. 2002-135610 discloses an image processing apparatus that converts a first color signal into a second color signal that is an image recording signal of the image forming apparatus. The first color signal is converted into the second color signal based on the relationship determined by the recording position coordinate signal indicating the position where the image is recorded on the image carrier and the first color signal in accordance with the second color signal. An arithmetic means for converting to a color signal is provided. An n-dimensional lookup table is used as the arithmetic means.

  Therefore, the image processing apparatus according to Japanese Patent Laid-Open No. 2002-135610 has a problem that a very large memory is required.

  More specifically, as shown in FIG. 12, stripe-shaped density irregularities 101 and 102 having a width of about 24 mm partially exist along the photosensitive drum axial direction. When 102 is corrected, it is necessary to correct at a resolution of about 6 mm obtained by dividing the density unevenness having a width of 24 mm into four at the position X along the axial direction of the photosensitive drum. Therefore, in order to correct density unevenness at a pitch of 6 mm, a single conversion table (LUT: Lookup Table) that does not need to correct density unevenness looks up the entire width of the paper (about 300 mm). When the table is arranged, there is a problem that 300 (mm) ÷ 6 (mm) = 50 is required and about 50 pieces are required, that is, the memory size is required 50 times. In FIG. 12, the portion represented by a small black square shows the arrangement of the lookup table.

  Furthermore, in order to correct the density unevenness along the recording paper conveyance direction Y (about 420 mm), approximately 70 pieces are required as 420 (mm) ÷ 6 (mm) = 70. A memory of about 3500 times (50 × 70) is required, and a very large memory is required, resulting in a significant cost increase.

  In order to avoid such a problem, it is conceivable to set a wide interval for arranging the look-up table. However, in such a configuration, density unevenness 101 and 102 generated in a stripe shape with a width of about 24 mm. Cannot be corrected with high accuracy, and the problem of uniformity of in-plane density (color), which is the original purpose, cannot be solved.

  Therefore, the present invention has been made to solve the above-mentioned problems of the prior art, and the object of the present invention is high resolution without excessive memory size and significant cost increase. An object of the present invention is to provide an image processing apparatus that can correct uneven density of stripes and can form an image having excellent in-plane density uniformity.

In order to solve the above problem, the invention described in claim 1 is based on the image forming position of the image forming apparatus, and the second color signal is an image forming signal of the image forming apparatus. In the image processing apparatus for converting to
A plurality of conversion tables which are arranged according to density gradients at the respective image forming positions of the image forming apparatus detected in advance by the image density detecting means, and which convert the first color signal into a second color signal;
An image processing apparatus comprising: a conversion table selecting unit that selects which conversion table to use from among the plurality of conversion tables based on each image forming position of the image forming apparatus. .

  According to a second aspect of the present invention, the conversion table is densely arranged in an area where the gradient of the in-plane density of the image of the image forming apparatus detected by the image density detecting unit is large, and the image formation is performed. The image processing apparatus according to claim 1, wherein the conversion table is sparsely arranged in an area where an in-plane density gradient of an image of the apparatus is small.

  Furthermore, the invention described in claim 3 is characterized by comprising linear interpolation means for linearly interpolating values of two adjacent conversion tables at an image forming position positioned between the plurality of conversion tables. The image processing apparatus according to claim 1 or 2.

According to a fourth aspect of the present invention, there is provided an image processing apparatus for converting a first color signal into a second color signal which is an image forming signal of the image forming apparatus based on an image forming position of the image forming apparatus. In
Image density detection means for detecting in-plane density non-uniformity of an image formed by the image forming apparatus;
A conversion table in which a plurality of conversion tables for converting the first color signal into the second color signal are arranged in accordance with the gradient of the image density at each image forming position of the image forming apparatus detected by the image density detecting means. And arranging means,
An image characterized in that the first color signal is converted into a second color signal based on an image forming position of the image forming apparatus using a plurality of conversion tables arranged by the conversion table arrangement unit. It is a processing device.

  According to the present invention, it is possible to correct the stripe-like density unevenness with high resolution without increasing the memory size and incurring a significant cost increase, and an image having excellent in-plane density uniformity. An image processing apparatus that can be formed can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1
FIG. 2 is a block diagram showing a color complex machine as an image forming apparatus to which the image processing apparatus according to Embodiment 1 of the present invention can be applied. This color multifunction machine also has a function as a copying machine, a printer, or a facsimile.

  As shown in FIG. 2, the color multifunction peripheral 1 includes a scanner 2 as an image reading device at the top thereof, and is connected to a personal computer (not shown) via a network (not shown).

  The color multifunction device functions as a fax machine that copies an image of a document read by a scanner, prints based on image data sent from a personal computer, and transmits / receives image data via a telephone line. It is like that.

  In FIG. 2, reference numeral 1 denotes a main body of a color multifunction peripheral. An automatic document feeder (ADF) that automatically conveys unshown originals one by one is provided on the upper portion of the color multifunction peripheral main body 1. 2) and a scanner 3 as an image density detecting means for reading an image of a document conveyed by the automatic document conveying device 2. The scanner 3 illuminates a document placed on the platen glass 4 with a light source 5 and reduces a reflected light image from the document by a full-rate mirror 6, half-rate mirrors 7 and 8, and an imaging lens 9. The image reading element 10 made of a CCD or the like is scanned and exposed through 11 and the image reading element 10 reads the color material reflected light image of the document at a predetermined dot density (for example, 16 dots / mm). ing.

  The reflected light image of the document read by the scanner 3 is, for example, reflected in the image processing device 12 (IPS) as reflectance data of three colors of red (R), green (G), and blue (B) (each 8 bits). In this image processing apparatus 12, the data of the three colors of red (R), green (G), and blue (B) (each of 8 bits) is represented by a color system such as L * a * b *, for example. Are converted into yellow (Y), magenta (M), cyan (C), and black (K) images, and, if necessary, shading correction, positional deviation correction, gamma correction, frame Predetermined image processing is performed as described later, including processing such as erasing, color / moving editing, and the like. The image processing apparatus 12 also performs predetermined image processing on image data sent from a personal computer (not shown) or the like.

  The image data that has been subjected to the predetermined image processing by the image processing apparatus 12 has gradations of four colors of yellow (Y), magenta (M), cyan (C), and black (K) (each 8 bits). As described below, the ROS (RaserOutputScanner) common to the image forming units 13Y, 13M, 13C, and 13K of each color of yellow (Y), magenta (M), cyan (C), and black (K) is described below. In the ROS 14 as the image exposure apparatus, image exposure with the laser beam LB is performed according to gradation data of a predetermined color. Of course, not only a color image but also a monochrome image may be formed.

  By the way, as shown in FIG. 2, an image forming unit A is disposed inside the color MFP main body 1. The image forming unit A includes yellow (Y), magenta (M), and cyan. Four image forming units 13Y, 13M, 13C, 13K of (C) and black (K) are arranged in parallel at a constant interval in the horizontal direction.

  These four image forming units 13Y, 13M, 13C, and 13K are all configured in the same manner, and roughly divided, a photosensitive drum 15 as an image carrier that is rotationally driven at a predetermined speed, and the photosensitive drum. A charging roll 16 for primary charging that uniformly charges the surface of 15, and an ROS 14 as an image exposure device that forms an electrostatic latent image by exposing an image corresponding to a predetermined color on the surface of the photosensitive drum 15. And a developing unit 17 for developing the electrostatic latent image formed on the photosensitive drum 15 with toner of a predetermined color, and a cleaning device 18 for cleaning the surface of the photosensitive drum 15. These photosensitive drums 15 and image forming members disposed in the periphery are integrally unitized, and are configured to be individually replaceable from the color multifunction peripheral body 1.

  As shown in FIG. 2, the ROS 14 is configured in common to the four image forming units 13Y, 13M, 13C, and 13K. The ROS 14 modulates four semiconductor lasers (not shown) according to the gradation data of each color, Laser light beams LB-Y, LB-M, LB-C, and LB-K are emitted from these semiconductor lasers according to gradation data. Of course, the ROS 14 may be individually configured for each of a plurality of image forming units. The laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the semiconductor laser are irradiated to the polygon mirror 19 through an f-θ lens (not shown), and are deflected and scanned by the polygon mirror 19. The The laser beams LB-Y, LB-M, LB-C, and LB-K deflected and scanned by the polygon mirror 19 are exposed to exposure points on the photosensitive drum 15 through an imaging lens and a plurality of mirrors (not shown). Then, scanning exposure is performed obliquely from below.

  As shown in FIG. 2, the ROS 14 scans and exposes an image on the photosensitive drum 15 from below. Therefore, the ROS 14 includes four image forming units 13Y, 13M, 13C, and 13K located above. There is a possibility that toner or the like may fall from the developing unit 17 and be contaminated. Therefore, the periphery of the ROS 14 is hermetically sealed by a rectangular parallelepiped frame 20, and four laser beams LB-Y, LB-M, LB-C, and LB-K are placed on the upper portion of the frame 20, Transparent glass windows 21Y, 21M, 21C, and 21K as shield members are provided for exposure on the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K.

  From the image data processing apparatus 12, the ROS 14 provided in common for the image forming units 13Y, 13M, 13C, and 13K for each color of yellow (Y), magenta (M), cyan (C), and black (K) is provided. The image data of each color is sequentially output, and the laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the ROS 14 according to the image data are scanned on the surface of the corresponding photosensitive drum 15. Exposure is performed to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drum 15 are respectively developed in yellow (Y), magenta (M), cyan (C), and black (K) colors by developing units 17Y, 17M, 17C, and 17K. Developed as a toner image.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K are as follows. On the intermediate transfer belt 25 of the transfer unit 22 arranged over the image forming units 13Y, 13M, 13C, and 13K, the images are transferred in multiple by the four primary transfer rolls 26Y, 26M, 26C, and 26K. These primary transfer rolls 26Y, 26M, 26C, and 26K are disposed on the back side of the intermediate transfer belt 25 corresponding to the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K. In this embodiment, the primary transfer rolls 26Y, 26M, 26C, and 26K have a volume resistance adjusted to 10 5 to 10 8 Ωcm. The primary transfer rolls 26Y, 26M, 26C, and 26K are connected to a transfer bias power source (not shown), and a transfer bias having a polarity opposite to a predetermined toner polarity (positive polarity in the present embodiment) is predetermined. It is applied at the timing.

  Further, as shown in FIG. 2, the intermediate transfer belt 25 is wound around the drive roll 27, the tension roll 24, and the backup roll 28 with a certain tension, and has excellent constant speed (not shown). The drive roll 27 is rotationally driven by a dedicated drive motor and is circulated at a predetermined speed in the direction of the arrow. The intermediate transfer belt 25 is made of, for example, a belt material (rubber or resin) that does not cause charge-up.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred in multiple onto the intermediate transfer belt 25 are pressed against the backup roll 28 as shown in FIG. The secondary transfer roll 29 is secondarily transferred onto the sheet 30 as a sheet material, and the sheet 30 on which the toner images of these colors are transferred is conveyed to a fixing device 40 positioned above. The secondary transfer roll 29 is in pressure contact with the side of the backup roll 28, and secondary-transfers each color toner image onto a sheet 30 conveyed from below to above.

  The paper 30 is a sheet of a predetermined size from any of the paper feed trays 31, 32, 33, 34 arranged in a plurality of stages at the lower part of the color MFP main body 1, and is fed by a feed roll 35, a retard roll 36, etc. In a state where they are separated one by one, the paper is fed through a paper conveyance path 38 provided with a conveyance roll 37. Then, the paper 30 fed from any of the paper feed trays 31, 32, 33, 34 is temporarily stopped by the registration roll 39, and synchronized with the image on the intermediate transfer belt 25 by the registration roll 29. The sheet is fed again to the secondary transfer position of the intermediate transfer belt 25.

  As shown in FIG. 2, the sheet 30 on which the toner images of the respective colors are transferred is subjected to a fixing process with heat and pressure by a fixing device 40, and then the image forming surface is faced down by a conveying roll 41. An upper portion of the apparatus main body 1 is discharged by a discharge roll 44 provided at an outlet of the first paper transport path 43 through a first paper transport path 43 for discharging to a face down tray 42 as a single discharge tray. It is discharged onto a face-down tray 42 provided in.

  Further, when the sheet 30 on which the image is formed as described above is discharged with the image forming surface facing upward, as shown in FIG. 2, the image forming surface is faced up and the face up as a second discharge tray. A discharge roller 47 provided at the outlet of the second paper transport path 46 through the second paper transport path 46 for discharging to the tray 45 causes a side portion (left side surface in the figure) of the apparatus main body 1. The paper is discharged onto a face-up tray 45 provided in

  In the above-described color multifunction peripheral, when full-color double-sided copying is performed, the sheet 30 with the image fixed on one side is directly discharged onto the face-down tray 42 by the discharge roll 44 as shown in FIG. Instead, the conveyance direction is switched by a switching gate (not shown), the discharge roll 44 is temporarily stopped and then reversely rotated, and the discharge roll 44 conveys the sheet to the double-sided sheet conveyance path 48. Then, the sheet 30 is conveyed again to the registration roll 39 in the state where the front and back of the sheet 30 are reversed by the conveyance roller 49 provided along the conveyance path 48. Then, after the image is transferred and fixed on the back surface of the paper 30, it is discharged to either the face-down tray 42 or the face-up tray 45 through the first paper transport path 43 or the second paper transport path 46. The

  In FIG. 2, 50Y, 50M, 50C, and 50K are toner cartridges that supply toner of a predetermined color to the developing device 17 of each color of yellow (Y), magenta (M), cyan (C), and black (K). , 51 denotes a cleaning device for cleaning the surface of the intermediate transfer belt 25, respectively.

  FIG. 3 shows each image forming unit of the color multifunction peripheral.

  The four image forming units 13Y, 13M, 13C, and 13K for yellow, magenta, cyan, and black are all configured in the same manner as shown in FIG. 3, and these four image forming units 13Y, 13Y, In 13M, 13C, and 13K, as described above, yellow, magenta, cyan, and black toner images are sequentially formed at a predetermined timing. As described above, the image forming units 13Y, 13M, 13C, and 13K for the respective colors are each provided with the photosensitive drum 15, and the surface of the photosensitive drum 15 is uniformly provided by the charging roll 16 for primary charging. Charged. Thereafter, the surface of the photosensitive drum 15 is scanned and exposed to an image forming laser beam LB emitted from the ROS 14 according to the image data, and an electrostatic latent image corresponding to each color is formed. The laser beam LB that is scanned and exposed on the photosensitive drum 15 is set so as to be exposed from an obliquely lower side slightly to the right of the photosensitive drum 15. The electrostatic latent image formed on the photosensitive drum 15 is in the colors of yellow, magenta, cyan, and black by the developing roll 17a of the developing unit 17 of each image forming unit 13Y, 13M, 13C, and 13K. The visible toner images are developed with toner, and these visible toner images are sequentially transferred in multiple onto the intermediate transfer belt 25 by the charging of the primary transfer roll 26.

  By the way, the image processing apparatus applied to the image forming apparatus configured as described above, based on the image forming position of the image forming apparatus, the first color signal is the second image forming signal of the image forming apparatus. In the image processing device for converting to a color signal, the image processing device is arranged in accordance with the density gradient at each image forming position of the image forming apparatus detected in advance by the image density detecting means, and the first color signal is used as the second color signal. A plurality of conversion tables to be converted, and conversion table selection means for selecting which one of the plurality of conversion tables to use based on each image forming position of the image forming apparatus. Has been.

  In this embodiment, the conversion table is densely arranged in an area where the gradient of the in-plane density of the image of the image forming apparatus detected by the image density detecting unit is large, and the image of the image forming apparatus is The conversion table is sparsely arranged in a region where the gradient of the in-plane density is small.

  Furthermore, in this embodiment, the image forming position located in the middle of the plurality of conversion tables is configured to include linear interpolation means for linearly interpolating values of two adjacent conversion tables.

  In this embodiment, the image processing apparatus converts the first color signal into the second color signal which is the image forming signal of the image forming apparatus based on the image forming position of the image forming apparatus. An image density detecting unit for detecting in-plane density non-uniformity of an image formed by the forming apparatus, and an image density gradient at each image forming position of the image forming apparatus detected by the image density detecting unit. Conversion table arrangement means for arranging a plurality of conversion tables for converting the first color signal into the second color signal, and using the plurality of conversion tables arranged by the conversion table arrangement means, the image Based on the image forming position of the forming apparatus, the first color signal is converted into a second color signal.

  That is, in the image processing apparatus 12 according to this embodiment, as shown in FIG. 4, the magenta, cyan, yellow, and gray ladder charts 60M, 60C, 60Y, and 60K are displayed in the main scanning direction. For example, a set of these four magenta, cyan, yellow, and gray ladder charts 60M, 60C, 60Y, and 60K is formed as a set, for example, with a density of 60% and 20%. A test image formed on the entire surface in the sub-scanning direction is output alternately with the density of.

  In the test image 61 formed as described above, the ladder charts 60M, 60C, 60Y, and 60K for each color are uniformly formed at a predetermined density, and the density 60M, 60C, and 60Y of the ladder chart for each color are originally formed. , 60K is read by the skier 3 as the image density detection means, as shown in FIG. 5, although there are differences in the colors of magenta, cyan, yellow, and gray, the density is 60% and 20%. % Concentration should be constant.

  However, in a color multi-function machine employing the above-described electrophotographic system, a difference in sensitivity on the surface of the photoconductive drum 15 of each image forming unit and a variation in charging potential for uniformly charging the surface of the photoconductive drum 15 are obtained. Alternatively, due to partial fluctuations in the amount of image exposure for performing image exposure by scanning laser light according to image information, as shown in FIG.

  Therefore, in this embodiment, a test image 61 as shown in FIG. 4 is output at the time of shipment or maintenance of the color multifunction peripheral, and the density of the test image 61 is determined by the scanner-3 as the image density detection means. Read.

  Next, in the image processing apparatus 12, as shown in FIG. 6, the density of the ladder chart of each color is detected along the main scanning direction (X direction) and the sub-scanning direction (Y direction) (FIG. 7). Step 101). Here, the density detection of the ladder chart 61 of each color along the main scanning direction will be described. However, it is formed along the sub-scanning direction, which is a direction orthogonal to the ladder chart 61, also along the sub-scanning direction. Similar processing is performed using the ladder chart.

  Thereafter, in the CPU (not shown) of the image processing device 12, as shown in FIG. 8, a color change dD that is a density gradient at each image forming position along the main scanning direction x of the color multifunction peripheral detected by the image input device. In addition to calculating / dx, the absolute value | dD / dx | of the color change dD / dx is calculated as shown in FIG. 7 in order to obtain the magnitude of the color change dD / dx (step 102).

  Next, as shown in FIG. 9, the CPU sequentially adds the absolute value | dD / dx | of the color change calculated as described above to determine how the color change is distributed at each image forming position. | DD / dx |, which indicates whether or not, is determined (step 102). That is, when the absolute value | dD / dx | of the color change is small, even if the absolute value | dD / dx | of the color change is added, the addition result becomes a small value, but the absolute value of the color change | dD When / dx | is large, the addition result increases rapidly when the absolute value | dD / dx | of the color change is added.

  Thereafter, in order to obtain the arrangement of the conversion table based on | dD / dx | which is the addition result of the absolute value | dD / dx | of the color change, | dD / dx | is the number of lookup tables (LUT). Divide to find the number of SUM (x) = | dD / dx | / LUT (step 103). At that time, as shown in FIG. 10, x when the remainder of the SUM (x) division result is substantially 0 is selected as the arrangement position of the lookup table (LUT).

  Then, a plurality (20 in the illustrated example) of lookup tables (LUT) are created so that the density at the arrangement position (x) of the obtained lookup table (LUT) is equal to a predetermined density. In the lookup table (LUT), the same signal is generated based on the gradation reproduction characteristics (Cin-D) at the respective positions (x1, x2,...) Obtained from the test image 61 as shown in FIG. Are stored such that the first signal, which is the input signal, is converted into the second signal so that the density at each position is equal to the first signal.

  FIG. 1 is a block diagram showing a main part of the image processing apparatus 12 configured as described above.

As shown in FIG. 1, the image processing apparatus 12 is arranged according to the density gradient at each image forming position X of the color multifunction peripheral previously detected by the scanner 3, and converts the first color signal to the second color signal. The plurality of conversion tables 71 ₁ , 71 ₂ ,... 71 _i , 71 _{i + 1} ,... 71 _n and the image forming positions X of the color multifunction peripheral. ₁ , 71 ₂ ,... 71 _i , 71 _{i + 1} ,... 71 _n are configured to include a comparator 72 as conversion table selection means for selecting which conversion table to use. ing.

  Further, in this embodiment, the conversion table 71 is densely arranged in an area where the gradient of the in-plane density of the image of the color multifunction peripheral is large, and the conversion is performed to an area where the gradient of the in-plane density of the image of the color multifunction peripheral is small. The table 71 is configured to be sparsely arranged.

Further, in this embodiment, a plurality of conversion tables _{71 1, 71 2, ··· 71} i, 71 i + 1, of the · · · 71 _n, 2 two conversion tables 71 _i, 71 _{i + 1} of the intermediate The image forming position X located at is configured to include a linear interpolation circuit 73 as linear interpolation means for linearly interpolating the values DATA1 and DATA2 of two adjacent conversion tables 71 _i and 71 _{i + 1} .

The comparator 72, as the image forming position X, as shown in FIG. 11, a plurality of conversion tables _{71 1, 71 2, ··· 71} i, 71 i + 1, image · · · 71 _n is located When the formation position X is selected, the value DATA of the conversion table 71 arranged at the selected position is outputted as output data DataOUT as it is, and arranged in the middle between the two conversion tables 71 _i and 71 _{i + 1.} When the selected image forming position X is selected, the two adjacent conversion tables 71 _i and 71 _{i + 1} are selected. The DATA1 and DATA2 output from the two adjacent conversion tables 71 _i and 71 _{i + 1} are linearly interpolated by the linear interpolation circuit 73 and output as output data DataOUT.

  With the configuration described above, the image processing apparatus according to this embodiment corrects stripe-like density unevenness with high resolution without excessively increasing the memory size and causing a significant cost increase as follows. Therefore, it is possible to form an image having excellent in-plane density uniformity.

  That is, in the image processing apparatus 12 according to this embodiment, as shown in FIG. 1, an image of a document (not shown) is read by the scanner 3 and image data DataIN is input, or image data DataIN is input from a personal computer (not shown). And a position signal X indicating the image forming position of the input image data DataIN is input to the comparator 72.

The comparator 72 converts the position signal X indicating each image forming position into a plurality of lookup tables (LUT) 71 ₁ , 71 ₂ ,... 71 _i , 71 _{i + 1} ,. A plurality of lookup tables (LUTs) 71 ₁ , 71 ₂ ,... 71 _i , 71 _{i + 1} , arranged as described above, compared to the arrangement positions (x1, x2...) Of 71 _n ... 71 _n of which lookup table (LUT) is used.

If the position signal X indicating the image forming position is “0”, it is equal to the arrangement position (x1 = 0) of the _first look-up table (LUT) 71 ₁ , so the first look-up table ( LUT) 71 ₁ is selected.

  Further, when the position signal x indicating the image forming position is located between the two look-up tables (LUT (i)) and the look-up table (LUT (i + 1)), that is, x (i) <x <x (x + 1). ), Two adjacent lookup tables (LUT (i)) and lookup table (LUT (i + 1)) are selected. When the outputs of the lookup table (LUT (i)) and the lookup table (LUT (i + 1)) are Data (i) and Data (i + 1), the value DataOUT at the image position x is The linear interpolation circuit outputs (Data (i + 1) −Data (i)) / (x (i + 1) −x) * (x (i) −x) + Data (i) after linear interpolation. ing.

As described above, in the above embodiment, the comparator 72 uses the plurality of conversion tables 71 ₁ , 71 ₂ ,... According to the density gradient at each image forming position x of the color multifunction peripheral detected by the scanner-3. A conversion table to be used is selected from 71 _i , 71 _{i + 1} ,... 71 _n , and the first conversion table is used based on the image forming position x of the color multifunction peripheral using the selected conversion table. since the input signal as a color signal is configured to convert the output signal DataOUT as a second color signal, the conversion table _{71 1, 71 2, ··· 71} i, 71 i + 1, ··· 71 n Therefore, the memory size becomes excessive and the cost is not significantly increased. In this embodiment, since a plurality of conversion tables are arranged according to the density gradient at each image forming position x of the color multifunction peripheral, the conversion tables are arranged densely where the density gradient is large. It is possible to correct stripe-like density unevenness with high resolution, and to form an image with excellent uniformity of density within the surface.

  In the above embodiment, in order to correct the density unevenness with a pitch of 6 mm in the related art, about 50 looks with 300 (mm) ÷ 6 (mm) = 50 with respect to the total width of the paper (about 300 mm). In contrast to the need for an up table, only 21 look-up tables are required, and the memory size can be reduced to 40% of the conventional one.

  In the above embodiment, for convenience of explanation, one color image data has been described, but it is needless to say that the same applies to image data of yellow, magenta, cyan, and black colors. .

  In the above-described embodiment, the case where the test image 61 is read and adjusted, for example, at the time of shipment in the image processing apparatus has been described. However, the present invention is not limited to this, and the image forming apparatus is used in the market. Of course, even in the state, the service engineer can read the test image 61 and perform the same adjustment.

FIG. 1 is a block diagram showing an image processing apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing an image forming apparatus to which the image processing apparatus according to Embodiment 1 of the present invention can be applied. FIG. 3 is a block diagram showing an image forming unit of the image forming apparatus to which the image processing apparatus according to Embodiment 1 of the present invention can be applied. FIG. 4 is an explanatory diagram showing a test image. FIG. 5 is a graph showing an ideal state when a test image is input. FIG. 6 is a graph showing an actual state when a test image is input. FIG. 7 is a flowchart showing processing of the image processing apparatus according to Embodiment 1 of the present invention. FIG. 8 is a graph showing an image processed by the image processing apparatus according to Embodiment 1 of the present invention. FIG. 9 is a graph showing an image processed by the image processing apparatus according to Embodiment 1 of the present invention. FIG. 10 is a graph showing an image processed by the image processing apparatus according to Embodiment 1 of the present invention. FIG. 11 is a graph showing the arrangement of conversion tables in the image processing apparatus according to Embodiment 1 of the present invention. FIG. 12 is a graph showing the arrangement of conversion tables in a conventional image processing apparatus.

Explanation of symbols

12: Image processing device, 71: Conversion table, 72: Comparator (conversion table selection means), 73: Linear interpolation circuit (linear interpolation means).

Claims (4)

In an image processing apparatus that converts a first color signal into a second color signal that is an image forming signal of the image forming apparatus based on an image forming position of the image forming apparatus.
A plurality of conversion tables which are arranged according to density gradients at the respective image forming positions of the image forming apparatus detected in advance by the image density detecting means, and which convert the first color signal into a second color signal;
An image processing apparatus comprising: a conversion table selecting unit that selects which conversion table to use from among the plurality of conversion tables based on each image forming position of the image forming apparatus. An area in which the conversion table is densely arranged in a region where the gradient of the in-plane density of the image of the image forming apparatus detected by the image density detection unit is large, and the gradient of the in-plane density of the image of the image forming apparatus is small The image processing apparatus according to claim 1, wherein the conversion tables are arranged sparsely. 3. The image processing apparatus according to claim 1, further comprising: a linear interpolation unit that linearly interpolates values of two adjacent conversion tables at an image forming position positioned between the plurality of conversion tables. . In an image processing apparatus that converts a first color signal into a second color signal that is an image forming signal of the image forming apparatus based on an image forming position of the image forming apparatus.
Image density detection means for detecting in-plane density non-uniformity of an image formed by the image forming apparatus;
A conversion table in which a plurality of conversion tables for converting the first color signal into the second color signal are arranged in accordance with the gradient of the image density at each image forming position of the image forming apparatus detected by the image density detecting means. And arranging means,
An image characterized in that the first color signal is converted into a second color signal based on an image forming position of the image forming apparatus using a plurality of conversion tables arranged by the conversion table arrangement unit. Processing equipment.

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