JP2004226844A - Image forming apparatus, image forming method, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a stable output image even when the obtained density of an image is varied from an initial stage due to time change or replacement of consumables, etc., and difference in output density by positions within the paper occurs. <P>SOLUTION: A density adjusting sheet, on which a plurality of patches of reference density set beforehand in positions set beforehand on the paper, is outputted, the patch on the outputted density adjusting sheet is read, and the density converting characteristic when forming an image is varied on the basis of the read batch density. At this time, the density adjusting sheet has the patches regularly distributed within the paper dispersed from the lower density so that highlight, middle and shadow parts are not concentrated. The density conversion characteristic is varied with the average density of each patch as the measured value of the reference density. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

ただし＾はｘの４乗というように累乗を示す（以下、同様）。図７における多項式は近似式（１）に対応する。
【００５０】
一方、出力および読み取りの際に、何らかの不確定要素により計測したデータが不正な場合がある。これらの不正値を取り除くことにより、より正確な現状の濃度データを得ることができる。そこで、上記近似式（１）のｘに出力濃度を入れて、得られた結果を近似値ｚとする。この近似値ｚから測定値の差を変数として、標準偏差σを求める。上記例では、
σ＝０．９９７
となる。ここで、変数が±２σ以外の値を不正値として扱う。この標準偏差σに乗算する±２の値は画像形成装置および画像読み取り装置それぞれの安定性により変動させる。図６の中では３つの濃度で±２σを超える値となり、これらを不正値として扱う。図８で黒丸で示した値が不正値である。これらの不正値を除去すると、図９に示すグラフとなる。
【００５１】
また、不正値の除去を行った測定値に基づいて再度最小二乗法を用いて近似式を導き出すこともできる。上記例では、

となる。
【００５２】
このようにして不正値を除去した計測データから導き出した多項近似式を現状の濃度データとして扱う。すでに、初期状態のガンマ曲線、すなわち画像形成装置に合わせたガンマ曲線を画像形成装置に保持させておき、現状の濃度データで初期状態のガンマ曲線に合わせる。図１０は上記例での初期値（ガンマ曲線）と不正値を除去した計測データの近似曲線（現状の濃度データ）を示す。図１１に図１０の一部を拡大して示す。
【００５３】
図１０から分かるように現状の濃度では、濃度５０％のときに４８．３％の出力が得られるが、初期値では、５２．４％の出力を期待している。入力が５０％の時には、入力５３．３％での出力を得るように調整する。同様に、すべての階調において調整を行う。このように調整をすることにより、初期状態と同じ出力結果を得ることができる。
【００５４】
従って、画像調整シートの出力と、画像調整シートの読み取りを定期的に行って前記調整を行えば、常に初期状態での濃度で画像出力が可能となる。
【００５５】
【発明の効果】
以上のように本発明によれば、他のコンピュータや濃度計等を使用しなくてもその機器のみで濃度を調整し、経時変化や消耗品の交換による濃度の変化を吸収して、常に初期状態の機器に合わせて調整されたガンマ曲線に合わせることができる。
【図面の簡単な説明】
【図１】本発明の実施形態に係る画像形成装置の概略構成を示す図である。
【図２】図１に示した画像形成装置の制御回路の概略構成を示すブロック図である。
【図３】図１の画像形成装置から出力される画像調整シートを示す図である。
【図４】図３の画像調整シートの１つの基準濃度の描画領域を読み取った状態を示す図である。
【図５】図４の読み取り結果をヒストグラムとして示す図である。
【図６】読み取った画像から得られる出力濃度と測定値との関係を表形式で示す図である。
【図７】図６の関係をグラフとして示す図である。
【図８】何らかの不確定要素が入った不正値を示す図である。
【図９】図８から不正値を除去した状態を示す図である。
【図１０】初期状態のガンマ曲線と不正値を除去した計測データの近似曲線を示す図である、
【図１１】図１０の一部を拡大して示す図である。
【符号の説明】
２０ メインコントローラ
３０ 操作部
４９ 画像処理ユニット
５０ 画像読み取りユニット
８０ メモリ[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a printer, a copying machine, a facsimile, etc. having an image reading device, an image forming method used in the image forming apparatus, and a computer program for executing the image forming method.
[0002]
[Prior art]
As this kind of invention, for example, the invention described in JP-A-2001-268381 is known. An object of the present invention is to suppress fluctuations in color tone and density and to easily and accurately perform adjustment for a user, and to provide reference patch means having patches serving as references for four colors of cyan, magenta, yellow, and black; Patch output means for outputting patches of at least one of cyan, magenta, and yellow and black; comparison means for comparing a patch output by the patch output means with a reference patch of the reference patch means; Density adjusting means for adjusting the density of a color image to be output based on the result of comparison by the comparing means; and gray for adjusting the density by adjusting the gray balance for two colors other than the colors output by the patch output means. Balance adjustment means, and a gray patch in black after density adjustment by the density adjustment means Checking means for printing gray patches and gradations made of three colors of cyan, magenta, and yellow and outputting a check chart, wherein the checking means adjusts the density by the density adjusting means by the gray balance adjusting means. If there is a gray balance or a part which is confirmed to be inaccurate in the density part in the comparison by the comparing means, the density adjusting means performs the density adjustment again for the density of the part where the density adjustment is not accurate. is there.
[0003]
In addition, the invention described in JP-A-2002-232730 is also known. An object of the present invention is to provide a calibration method for a color image output device that does not cause unevenness in adjustment according to the change even when an adjuster changes during adjustment. When correcting the density fluctuation of the color image output device that forms the color image, a color patch is printed on a test print chart prepared in advance, and a comparison result between the reference single color density and the CMYK single color patch and selection of a patch having a gray balance are selected. In a calibration method of a color image output device that determines a density adjustment value based on a result, a reliability measurement chart in which correct values of selection of a reference single-color density and a selection of a CMYK single-color patch are provided is provided. Register the deviation of the selected patch on the reliability measurement chart from the correct answer value for the patch considered to be the correct answer in the registration means. Then, as a second step, a test print completion chart is created by printing on the test print chart using the color image output device, and as a third step, an adjuster sends the test print completion chart to the registration means. The patch considered as the correct answer is selected and registered, and as a fourth step, the tendency of the adjuster's deviation from the correct value and the result selected on the test printing completion chart is obtained, and according to the tendency of the deviation, The density adjustment value is determined.
[0004]
Furthermore, the invention described in JP-A-2002-237960 is also known. An object of the present invention is to provide an image output apparatus for performing high-precision density adjustment and a calibration method thereof. The image output apparatus has four colors of C (cyan), M (magenta), Y (yellow), and K (black). Density fluctuation of an image output device that forms a color image using a color material is determined by an image output device that prints a patch on a reference chart prepared in advance and determines a density adjustment value based on a comparison result between a reference density and a single-color patch. Then, after selecting a patch having the same density as the reference density, a gamma curve creating means for creating a plurality of types of gamma curves based on the selection result, and a CMYK single color gradation chart using the created gamma curve. Output means for outputting, and a gradation chart which is optimal for each of CMYK in the outputted gradation chart. It is obtained by a registration means for registering a selected result.
[0005]
[Patent Document 1]
JP 2001-268381 A
[Patent Document 2]
JP-A-2002-232730
[Patent Document 3]
JP 2002-237960 A
[Problems to be solved by the invention]
As described above, a patch for density adjustment is printed and the density is adjusted based on the print result, but in each of the above-described known examples, the variation due to the position on the printing surface at the same density is considered. No change due to position. However, in the image forming apparatus, the density of an image obtained due to a change over time or replacement of consumables fluctuates from an initial stage. Also, a difference in output density occurs depending on the location in the paper. Therefore, in order to measure the actual density of each output density, it is necessary to print on the entire surface of the paper with the output density corresponding to the number of gradations that can be output by the image forming apparatus, and to measure the density at every place.
[0009]
Further, in the image reading apparatus, the reading performance such as resolution and gradation differs depending on the apparatus, and a uniform result cannot be obtained even when reading a portion drawn with each reference density in the density adjustment sheet. Furthermore, in output and reading, it is impossible to obtain a stable output result or read data, and there may be unevenness even in a portion drawn at a uniform density.
[0010]
Therefore, the present invention is to obtain a stable output image even if the density of an image obtained due to aging or replacement of consumables fluctuates from an initial stage, or a difference in output density depending on a location in paper occurs. And an image forming method.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, a first means forms a plurality of patches of a preset reference density at a preset position on a sheet of paper in an image forming apparatus provided with an image reading means and an image output means. Output means for outputting a density adjustment sheet; reading means for reading a patch on the density adjustment sheet output from the output means; and density for forming an image from the density of the patch read by the reading means. Control means for changing the conversion characteristic.
[0012]
The second means is that, in the first means, the patches are dispersed from a lower density and are regularly arranged in a sheet so that highlights, middles, and shadows are not concentrated. I do.
[0013]
The third means is the first means, wherein the outputted density adjustment sheet is read by an image reading means, and the control means calculates an average value of the read density of the reference density patches as a measured value of the reference density. It is characterized by the following.
[0014]
A fourth means is the first means, wherein the control means derives a polynomial approximation equation using the least squares method from the acquired reference densities and the measured values of the densities of the patches corresponding to the reference densities. And
[0015]
Fifth means is the fourth means, wherein the control means uses a difference between the derived polynomial approximation formula and each measured value as a variable, and sets a measured value apart from the polynomial approximation formula as an incorrect value. , And the polynomial approximation formula is obtained again with the remaining measured values.
[0016]
A sixth means is the fifth means, wherein the control means changes a density conversion characteristic from the obtained polynomial approximation formula to a gamma curve adapted to the density of the image output means.
[0017]
The seventh means outputs a density adjustment sheet in which a plurality of patches of a predetermined reference density are formed at predetermined positions in the paper, and outputs the patches on the density adjustment sheet output from the output means. The average of the read and read densities of the patches of the reference density is defined as the measured value of the reference density, and the polynomial approximation is performed using the least squares method from the obtained reference densities and the measured values of the densities of the patches corresponding to the reference densities. Deriving the formula, using the difference between the derived polynomial approximation formula and each measured value as a variable, removing the measured value away from the polynomial approximation formula from the measured value as an incorrect value, and re-calculating the polynomial approximation formula with the remaining measured values An image is formed by changing the density conversion characteristic from the obtained polynomial approximation formula to a gamma curve corresponding to the density of the image output means.
[0018]
Eighth means includes: a first procedure for outputting a density adjustment sheet having a plurality of patches of a preset reference density formed at preset locations in a sheet; and the density adjustment sheet output in the first procedure. A second procedure of reading the patches on the adjustment sheet, and using the average of the densities of the patches of the reference density read in the second procedure as the measured values of the reference densities; A third procedure of deriving a polynomial approximation equation from the measured values of the corresponding patch densities using the least squares method, and using the difference between the polynomial approximation equation derived in the third procedure and each measurement value as a variable, A fourth step of removing the measured value deviating from the polynomial approximation formula from the measured value as an incorrect value, and obtaining the polynomial approximation formula again with the remaining measured values; and outputting the image from the polynomial approximation formula obtained again in the fourth procedure. Gamma according to the concentration of the means A fifth step is characterized in that it is executable programmed in a computer which changes the density conversion characteristic line to form an image.
[0019]
According to the first means, an image reading device attached to the image forming apparatus is used to measure the density at that point in time, and the output density is changed to the output density at the initial stage, whereby a stable output image is always obtained. It becomes possible.
[0020]
According to the second means, in one density adjustment sheet for measuring the density, the patches are dispersed from the lower density, so that highlights, middles, and shadows are not concentrated in the paper. With such an arrangement, it is possible to obtain a polynomial approximation that also absorbs differences in concentration depending on the location when obtaining the polynomial approximation of the measured value.
[0021]
According to the third means, in accordance with the reading performance such as resolution and gradation of the apparatus, an average of data obtained by reading a portion drawn at each reference density in the density adjustment sheet is obtained, and the measured value of the reference density is obtained. It can be.
[0022]
According to the fourth means, instead of using the obtained data itself, a polynomial approximation is obtained from the obtained data, thereby absorbing the difference in output and the difference in reading due to the uncertain element, and With the density adjustment sheets, it is possible to derive the density of all gradations that can be output by the image forming apparatus. This gradation is obtained from the average density of each patch on the density adjustment sheet.
[0023]
According to the fifth means, the difference between the value at each gradation of the polynomial approximation equation and the actual measurement data is used as a variable, a value far from the approximation equation is treated as an incorrect measurement value, and the polynomial approximation is again performed from the remaining measurement values. By obtaining the expression, the accuracy of the approximate expression can be improved. Thereby, stable output results and read data can be obtained.
[0024]
According to the sixth means, by using the polynomial approximation formula obtained by the fifth means to change the density of each gradation of the image output means to the initial stage density, it is possible to obtain a stable density output result. At this time, by performing the density change operation periodically, even if the density of the image obtained by aging or replacement of consumables fluctuates from the initial stage, it is possible to always set the density at the initial stage. Become.
[0025]
According to the seventh means, an image reading device attached to the image forming apparatus is used to measure the density at that point in time, and the output density is changed to the output density at the initial stage, whereby a stable output image is always obtained. It becomes possible.
[0026]
According to the eighth means, the output density is measured in the initial stage by downloading to the control device of the image forming apparatus and measuring the density at that time by using the image reading device attached to the image forming apparatus. , It is possible to always obtain a stable output image.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0028]
FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus of an image forming apparatus according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a schematic configuration of a control circuit of the image forming apparatus shown in FIG.
[0029]
Hereinafter, the image forming apparatus according to the present embodiment will be described.
When a start key on the operation unit 30 is pressed, a document bundle placed on a document table 2 in an automatic document feeder (hereinafter ADF) 1 is fed from the bottom document. The sheet is fed to a predetermined position on the contact glass 6 by the feed roller 3 and the feed belt 4. After reading the image data of the document on the contact glass 6 by the image reading unit 50, the document that has been read is discharged by the feed belt 4 and the discharge roller 5. Further, when the document set detection sensor 7 detects that the next document is present on the document table 2, the document is fed onto the contact glass 6 in the same manner as the previous document. The feed roller 3, the feed belt 4, and the discharge roller 5 are driven by a transport motor 26.
[0030]
The transfer sheets stacked on the first tray 8, the second tray 9, and the third tray 10 are fed by the first sheet feeding device 11, the second sheet feeding device 12, and the third sheet feeding device 13, respectively, and are vertically conveyed. The sheet is transported by the unit 14 to a position where it contacts the photoconductor 15. The image data read by the image reading unit 50 is written on the photoconductor 15 by the laser from the writing unit 57, and passes through the developing unit 27 to form a toner image. Then, the toner image on the photoconductor 15 is transferred while the transfer paper is conveyed by the conveyance belt 16 at the same speed as the rotation of the photoconductor 15. Thereafter, the image is fixed by the fixing unit 17, and the image is discharged to the finisher 60 of the post-processing device by the sheet discharging unit 18.
[0031]
The finisher 60 of the post-processing device can guide the transfer paper conveyed by the paper discharge roller 19 of the main body toward the normal paper discharge roller 62 and the staple processing unit. When the switching plate 61 is switched upward, the sheet is discharged to the normal paper output tray 64 via the transport roller 63, and when the switching plate 61 is switched downward, the staple table 68 is transported via the transport rollers 65 and 67. Can be transported.
[0032]
The transfer paper stacked on the staple table 68 is aligned by a paper alignment jogger 69 every time one sheet is discharged, and is stapled by the stapler 66 when a part of the copy is completed. The transfer paper group bound by the stapler 66 is stored in the stapling completion paper discharge tray 70 by its own weight.
[0033]
On the other hand, the normal paper discharge tray 64 is a paper discharge tray that can move back and forth. The paper discharge tray section 64 that can be moved back and forth has a function of moving back and forth for each document or each copy section sorted by the image memory, and sorting the copy paper that is simply discharged.
[0034]
When images are formed on both sides of the transfer paper, the transfer paper fed and imaged from each of the paper feed trays 8 to 10 is not guided to the paper output tray 64 side, and the branch claw 41 for path switching is used. By setting it on the upper side, it is once stocked in the duplex paper supply unit 111. Thereafter, the transfer paper stocked in the duplex paper supply unit 111 is re-fed from the duplex paper supply unit 111 in order to transfer the toner image formed on the photoconductor 15 again, and the branch pawl 41 for switching the path is used. Is set on the lower side, and guided to the discharge tray 64. As described above, the double-sided paper feeding unit 111 is used when forming images on both sides of the transfer paper.
[0035]
The photoconductor 15, the transport belt 16, the fixing unit 17, the paper discharging unit 18, and the developing unit 27 are driven by a main motor 25, and the respective paper feeding devices 11 to 13 drive the main motor 25 by paper feeding clutches 22 to 24, respectively. Driven by transmission. The vertical transport unit 14 is driven to transmit the drive of the main motor 25 by the intermediate clutch 21.
[0036]
FIG. 2 illustrates the control device with the main controller at the center. The main controller 20 controls the entire image forming apparatus. The main controller 20 is connected with a main motor 25 and various clutches 21 to 24 necessary for paper conveyance and the like. An operation unit 30 for displaying to an operator, inputting function settings from the operator, controlling a scanner, controlling to write a document image in an image memory, controlling to form an image from an image memory, and the like. 49, a distributed control device such as an automatic document feeder (ADF) 1 is connected. The display is performed via the liquid crystal display 31, and the function setting input from the operator is performed by the key input device 32. Each decentralized control device and the main controller 20 exchange machine status and operation commands as needed. A control program executed by each distributed control device is stored in a ROM inside each distributed control device. A memory 80 is connected to the main controller 20, and the memory 80 stores data necessary for control, including pattern data.
[0037]
The operation from image reading to image writing in the image forming apparatus will be described with reference to FIG. 1 again.
[0038]
The image reading unit 50 includes a contact glass 6 on which a document is placed and an optical scanning system. The optical scanning system includes an exposure lamp 51, mirrors 52, 55, 56, a lens 53, a CCD image sensor 54, and the like. It is configured. The exposure lamp 51 and the first mirror 52 are fixed on a first carriage (not shown), and the second mirror 55 and the third mirror 56 are fixed on a second carriage (not shown). When reading a document image, the first carriage and the second carriage are mechanically scanned at a relative speed of 2: 1 so that the optical path length does not change.
[0039]
This optical scanning system is driven by a scanner drive motor (not shown). The document image is read by the CCD image sensor 54, converted into an electric signal, and processed. By moving the lens 53 and the CCD image sensor 54 in the left-right direction in FIG. 1, the image magnification changes. That is, the positions of the lens 53 and the CCD image sensor 54 in the left-right direction are set in accordance with the designated magnification.
[0040]
The writing unit 57 includes a laser output unit 58, an imaging lens 59, and a mirror 48. Inside the laser output unit 58, a rotating polygon mirror (polygon mirror) that rotates at a high speed at a constant speed by a laser diode as a laser light source and a motor. ) Is provided.
[0041]
The laser light emitted from the laser output unit 58 is deflected by a polygon mirror rotating at a constant speed, passes through an imaging lens 59, is turned back by the mirror 48, and is condensed and imaged on the surface of the photoreceptor 15.
[0042]
The deflected laser beam 57 is exposed and scanned in a direction (main scanning direction) orthogonal to the direction in which the photoconductor 15 rotates, and performs recording in units of lines of an image signal output from a selector of an image processing unit described later. An image (electrostatic latent image) is formed on the photoconductor surface by repeating main scanning at a predetermined cycle corresponding to the rotation speed of the photoconductor 15 and the recording density.
[0043]
As described above, the laser light output from the writing unit 57 is applied to the photoconductor 15 of the image forming system. Although not shown, a beam sensor that generates a main scanning synchronization signal is disposed at a position near one end of the photoconductor 15 where the laser beam is irradiated.
[0044]
In such an image forming apparatus, the image adjustment sheet 100 shown in FIG. 3 is output from the image forming apparatus. The pattern of the image adjustment sheet 100 is stored in the memory 80 in advance, and is output when a pattern output instruction is given by a key input from the key input device 32. The keys are composed of soft keys such as a touch panel superimposed on the liquid crystal display 31, and input elements and input positions change according to instructions on the liquid crystal display surface. Since the image adjustment sheet 100 has a difference in density depending on the location in the sheet, instead of drawing in order from the lower density from the end of the sheet, the image adjustment sheet 100 is dispersed from the lower density as shown in FIG. Each reference density is arranged so that the middle and shadow parts do not concentrate.
[0045]
FIG. 4 shows a drawing of a drawing area (patch) 101 of one reference density in the image adjustment sheet 100 of FIG. FIG. 5 shows a histogram when this portion is read by an image reading device of 600 dpi and 256 gradations, that is, in the case of this embodiment, by the image reading unit 50. The average of this histogram is
133.73 (256 gradations) = 52.4%
It becomes. The information from the image reading unit 50 is obtained by summing the values of the read data at 256 gradations of each pixel and dividing the sum by the total number of pixels. The average value of each density is extracted for all patches. Thus, the gradation of each patch is obtained from the average density. This process is executed by the main controller 20.
[0046]
The analysis of the measurement data is performed as follows.
[0047]
FIG. 6 is a diagram showing the relationship between the measured output density and the measured value in a table format, and FIG. 7 is a diagram showing the relationship in the form of a graph. x is an output density when a patch is output from the image forming apparatus, and y is a measured value obtained by reading the output patch. Here, an approximate expression is derived from the output density x and the geodetic value y using the least squares method.
[0048]
The approximate expression in the example of FIG. 6 is as follows. The order is set to the order of the gamma curve in the initial state to be adjusted, and the y intercept is set to 0.
[0049]

Where ＾ indicates a power such as x to the fourth power (the same applies hereinafter). The polynomial in FIG. 7 corresponds to the approximate expression (1).
[0050]
On the other hand, at the time of output and reading, data measured by some uncertain factor may be incorrect. By removing these incorrect values, more accurate current density data can be obtained. Therefore, the output density is put in x of the above approximate expression (1), and the obtained result is set as an approximate value z. The standard deviation σ is obtained from the approximate value z using the difference between the measured values as a variable. In the above example,
σ = 0.997
It becomes. Here, values whose variables are other than ± 2σ are treated as incorrect values. The value of ± 2 multiplied by the standard deviation σ varies depending on the stability of each of the image forming apparatus and the image reading apparatus. In FIG. 6, values exceeding ± 2σ are obtained for the three densities, and these are treated as incorrect values. The value indicated by a black circle in FIG. 8 is an incorrect value. When these incorrect values are removed, a graph shown in FIG. 9 is obtained.
[0051]
Also, an approximate expression can be derived again by using the least squares method based on the measured value from which the incorrect value has been removed. In the above example,

It becomes.
[0052]
The polynomial approximation derived from the measurement data from which the incorrect value has been removed in this way is treated as the current concentration data. The gamma curve in the initial state, that is, the gamma curve matched to the image forming apparatus is already held in the image forming apparatus, and the gamma curve in the initial state is matched with the current density data. FIG. 10 shows an approximate curve (current density data) of the measurement data from which the initial value (gamma curve) and the incorrect value have been removed in the above example. FIG. 11 shows an enlarged part of FIG.
[0053]
As can be seen from FIG. 10, at the current density, an output of 48.3% is obtained when the density is 50%, but an output of 52.4% is expected at the initial value. When the input is 50%, adjustment is made so as to obtain an output at the input of 53.3%. Similarly, adjustment is performed for all gradations. By performing such adjustment, the same output result as in the initial state can be obtained.
[0054]
Therefore, if the output of the image adjustment sheet and the reading of the image adjustment sheet are periodically performed to perform the adjustment, it is possible to always output the image with the density in the initial state.
[0055]
【The invention's effect】
As described above, according to the present invention, the concentration is adjusted only by the device without using another computer or a densitometer, and the change in the concentration due to the aging or the replacement of the consumables is absorbed, and the initial change is always performed. It can be adjusted to the gamma curve adjusted to the device in the state.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a schematic configuration of a control circuit of the image forming apparatus illustrated in FIG.
FIG. 3 is a diagram illustrating an image adjustment sheet output from the image forming apparatus of FIG. 1;
FIG. 4 is a diagram illustrating a state where a drawing area of one reference density of the image adjustment sheet of FIG. 3 is read;
FIG. 5 is a diagram showing a reading result of FIG. 4 as a histogram.
FIG. 6 is a diagram showing, in a table format, a relationship between an output density obtained from a read image and a measured value.
FIG. 7 is a diagram showing the relationship of FIG. 6 as a graph.
FIG. 8 is a diagram showing an incorrect value including some uncertain element.
FIG. 9 is a diagram showing a state in which an incorrect value has been removed from FIG. 8;
FIG. 10 is a diagram showing a gamma curve in an initial state and an approximate curve of measurement data from which incorrect values have been removed;
FIG. 11 is an enlarged view showing a part of FIG. 10;
[Explanation of symbols]
Reference Signs List 20 main controller 30 operation unit 49 image processing unit 50 image reading unit 80 memory

Claims (8)

In an image forming apparatus including an image reading unit and an image output unit,
Output means for outputting a density adjustment sheet in which a plurality of patches of a preset reference density are formed at preset positions in the paper,
Reading means for reading a patch on the density adjustment sheet output from the output means,
Control means for changing the density conversion characteristic when forming an image from the density of the patch read by the reading means,
An image forming apparatus comprising: 2. The image forming apparatus according to claim 1, wherein the patches are dispersed from a lower density and are regularly arranged in a sheet so that highlights, middles, and shadows are not concentrated. 2. The image forming apparatus according to claim 1, wherein the output density adjustment sheet is read by an image reading unit, and the control unit sets an average value of the read density of the reference density patches as a measured value of the reference density. Image forming device. The image forming apparatus according to claim 1, wherein the control unit derives a polynomial approximation from each of the acquired reference densities and a measured value of the density of the patch corresponding to the reference densities using a least squares method. The control means uses the difference between the derived polynomial approximation formula and each measured value as a variable, removes a measurement value distant from the polynomial approximation formula as an incorrect value from the measurement value, and again uses the remaining measurement values as a polynomial approximation formula. The image forming apparatus according to claim 4, wherein: 6. The image forming apparatus according to claim 5, wherein the control unit changes a density conversion characteristic from the obtained polynomial approximation formula to a gamma curve corresponding to a density of the image output unit. Outputting a density adjustment sheet in which a plurality of patches of a preset reference density are formed at preset positions in the paper,
Reading the patch on the density adjustment sheet output from the output means,
The average of the read densities of the patches of the reference density is defined as the measured value of the reference density, and a polynomial approximation formula is obtained using the least squares method from the acquired measured values of the reference densities and the densities of the patches corresponding to the reference densities. Derive,
With the difference between the derived polynomial approximation and each measured value as a variable, remove the measured value away from the polynomial approximation from the measured value as an incorrect value, and obtain the polynomial approximation again with the remaining measured values,
An image forming method, wherein an image is formed by changing a density conversion characteristic from the re-calculated polynomial approximation formula to a gamma curve corresponding to the density of the image output means. A first procedure for outputting a density adjustment sheet in which a plurality of patches of a preset reference density are formed at preset positions in a sheet;
A second procedure for reading patches on the density adjustment sheet output in the first procedure;
Using the average of the densities of the patches of the reference density read in the second procedure as the measured values of the reference densities, using the least square method from the acquired reference densities and the measured values of the densities of the patches corresponding to the reference densities A third procedure for deriving a polynomial approximation formula by
Using the difference between the polynomial approximation formula derived in the third procedure and each measured value as a variable, a measurement value distant from the polynomial approximation formula is excluded from the measurement value as an incorrect value, and the polynomial approximation formula is again calculated with the remaining measurement values. A fourth step to seek;
A fifth procedure of forming an image by changing a density conversion characteristic from a polynomial approximation formula obtained again in a fourth procedure to a gamma curve corresponding to the density of the image output means,
A computer program characterized by being configured to be executable on a computer.

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