JP3551988B2 - Image forming device - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an electrophotographic or jet digital color image forming apparatus used for a digital color printer, a digital color copying machine, a color facsimile, and the like, and more particularly, to calibration of the image forming apparatus.
[0002]
[Prior art]
In the digital color image forming apparatus, the calibration of the image forming apparatus refers to correcting the image forming apparatus so as to obtain a color that is predicted in advance. Japanese Patent Application Laid-Open No. 4-77060 discloses a method in which a gradation pattern is formed by a forming apparatus, the gradation pattern is read by an image reading sensor, and the correction content of the γ correction is changed.
However, in the above technique, the density area readable by the sensor may be smaller than the density area output by the image forming apparatus, so that the high density area portion of the gradation pattern may not be read.
[0003]
[Problems to be solved by the invention]
When calibrating a printer such as a digital color copier, when outputting a gradation pattern from a printer and reading it from a scanner, as described above, the density area readable by the scanner is the density area output by the printer. Therefore, a portion of the high-density area of the gradation pattern may not be read.
[0004]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to eliminate the above-described drawbacks, estimate the density of a high-density region of a gradation pattern, and accurately determine the γ characteristic of an image forming apparatus. It is another object of the present invention to accurately perform calibration of an image forming apparatus.
[0005]
[Means for Solving the Problems]
To achieve the above objectives,According to the present inventionThe image forming apparatus includes: a gradation pattern forming unit that forms a gradation pattern; an image forming unit that records the gradation pattern formed by the gradation pattern forming unit; and the gradation pattern output from the image forming unit. From the sum (R + G + B) of the output signals (for example, R (red), G (green), and B (blue) values) for each color separation of the image reading means. Γ characteristic calculating means for estimating γ (gamma) characteristics of the meansing.
[0006]
Further, according to the present invention,The image forming apparatus includes: a gradation pattern forming unit that forms a gradation pattern; an image forming unit that records the gradation pattern formed by the gradation pattern forming unit; and the gradation pattern output from the image forming unit. Image reading means for separating the image by color separation, and first γ characteristic calculating means for estimating a first γ characteristic of the image forming means from the image reading means in a density range where the sensitivity of the image reading means is good. An image colorimetric unit for measuring the gradation pattern output from the image forming unit; and a second range of the image forming unit from the image colorimetric unit in a density range where the sensitivity of the image reading unit is reduced. second gamma characteristic calculating means for estimating the gamma characteristicing.
[0007]
Of the present inventionClaim1The image forming apparatus according to the present invention includes a gradation pattern image signal generation unit that generates a gradation pattern image signal; a latent image formation unit that forms an electrostatic latent image on an image carrier based on the image signal; Surface potential detection means for detecting the surface potential of the electrostatic latent image of the gradation pattern formed on the image carrier based on the image signal of the gradation pattern image signal generation means, and developing the electrostatic latent image Developing means for forming a visible image on the image carrier, and a visible image developed on the image carrier by the developing means.On recording paperRecordHaving meansImage forming handsStepAn image reading device that reads a tone pattern formed based on the tone pattern image signal generating device by performing color separation, and the image reading device in a density range where the sensitivity of the image reading device is good. A first gamma characteristic calculating unit for estimating a first gamma characteristic of the image forming unit from the reading unit; and a surface potential of the surface potential detecting unit and a surface potential of the surface potential detecting unit in a density range where the sensitivity of the image reading unit decreases. And a second γ characteristic calculating means for estimating a second γ characteristic of the image forming means from a relational expression of image density.
[0008]
Claim2The image forming apparatus described in the claims1The image forming apparatus according to the above, further comprising means for displaying a message on an operation panel when the high-density area is insufficient in density, and when the γ characteristic of the image forming means is outside a predetermined range, a message is displayed on the operation panel. It is characterized by displaying.
[0009]
Claim3The image forming apparatus described inThe image forming apparatus according to claim 1,A gamma correction unit for performing gamma correction of the image forming unit;Estimated by the first γ characteristic calculating means or the second γ characteristic calculating meansA gamma correction curve changing means for changing a gamma correction curve of the gamma correction means based on the gamma characteristic is provided.
[0010]
Claim4The image forming apparatus described in the claims1 or 3In the image forming apparatus described above, when the γ characteristic of the image forming unit is out of a predetermined range, themeansThe target input / output characteristics (target γ characteristics)meansΓ correction curve changing means for changing the γ correction curve of the γ correction means for correcting the γ characteristic.
[0011]
Claim5The image forming apparatus described in the claimsAny one of 1-4In the image forming apparatus described above, the range of the density at which the sensitivity of the image reading unit is good isR (red), G (green), B (blue)Output signal of color-separated image reading meansOutput value X (X = R or G or B value)Is in a range not less than a predetermined value.
[0012]
Claim6The image forming apparatus described in the claimsAny one of 1-4In the image forming apparatus described above, the range of the density at which the sensitivity of the image reading unit is good isR (red), G (green), B (blue)Output signal of color-separated image reading meansOutput valueTotal of (R, G, B values)The value S (S =R + G + B)PlaceIt is characterized in that the range is equal to or more than a predetermined value.
[0013]
Claim7The image forming apparatus described in the claimsAny one of 1-4In the image forming apparatus described above, the range of density at which the sensitivity of the image reading unit is good is defined as a change in the density (ID) of the gradation pattern (ID) of the gradation pattern input to the image reading unit.R (red), G (green), B (blue)Output signal after color separationOutput value X (X = R or G or B value)Amount of change(ΔX / ΔID)The absolute value of( | ΔX / ΔID | )Is in a range not less than a predetermined value.
[0014]
Claim8The image forming apparatus described in the claimsAny one of 1-4In the image forming apparatus described above, the range of density at which the sensitivity of the image reading unit is good is defined as a change in the density (ID) of the gradation pattern (ID) of the gradation pattern input to the image reading unit.R (red), G (green), B (blue)Output signal after color separationOutput valueTotal of (R, G, B values)Value SThe absolute value (| ΔS / ΔID |) of the amount of change (ΔS / ΔID) of (S = R + G + B) is set to a range equal to or greater than a predetermined value.
[0015]
Claim9The image forming apparatus described in the claimsAny one of 1-8In the image forming apparatus described above, the relationship between the surface potential (VS) and the density (ID) in the gradation pattern is as follows:
ID = a · VS + b (where a and b are constants)
Or, the DC component of the developing bias is VDC,
ID = a · (VS−VDC) + b (where a and b are constants)
Characterized by the relational expression
[0016]
[Action]
In the present invention, since the gradation pattern is formed by the image forming unit, the gradation pattern is read by the image reading unit, and the γ characteristic of the image forming unit is calculated from the image reading unit. It is possible to obtain a good value, and it is possible to accurately perform calibration of the image forming apparatus.
[0017]
【Example】
Hereinafter, a case where the image forming apparatus of the present invention is applied to a copying machine will be described as an example. FIG. 1 is a diagram showing a configuration example of a copying machine according to the present embodiment. The copying machine is roughly composed of a printer 101 serving as image forming means and a scanner 102 serving as image reading means.
[0018]
The printer 101 has a photosensitive drum (OPC) 103 serving as an image carrier disposed substantially at the center thereof, a charging charger 104 for uniformly charging the surface of the photosensitive drum 103, and a uniformly charged surface. A laser optical system 105 that irradiates a semiconductor laser beam onto the surface of the photosensitive drum 103 to form an electrostatic latent image, and a black developing device 106 that supplies toner of each color to the electrostatic latent image and performs toner development for each color. , A yellow developing device 107, a magenta developing device 108, a cyan developing device 109, an intermediate transfer belt 110 for sequentially transferring toner images of respective colors formed on the photosensitive drum 103, and a transfer voltage to the intermediate transfer belt 110. Bias roller 111, a cleaning device for removing toner remaining on the surface of the photosensitive drum 103 after transfer, and a table of the photosensitive drum 103 after transfer. , A transfer bias roller 114 for applying a voltage for transferring the toner image transferred to the intermediate transfer belt 110 onto recording paper, and a toner image remaining on the intermediate transfer belt 110. A belt cleaning device 115 for cleaning, a conveyance belt 116 for conveying the recording paper separated from the intermediate transfer belt 110, a fixing device 117 for fixing the toner image transferred to the recording paper by heating and pressing, and And a discharge tray 118 for discharging the recording paper.
[0019]
The scanner 102 is disposed above the printer 101 as shown in the figure, and includes a contact glass 119 serving as a document placing table, an exposure lamp 120 for irradiating the document on the contact glass 119 with scanning light, and a reflected light from the document. , And a CCD (Charge Coupled Device) that is a photoelectric conversion element that receives reflected light guided through the reflecting mirror 121 and the imaging lens 122 and converts the reflected light into an electric signal. ) 123. The image signal converted into the electric signal by the CCD 123 is emitted as laser light from a semiconductor laser in the laser optical system 105 through an image processing unit (not shown).
[0020]
FIG. 2 is a diagram showing an example of a control system built in the above copying machine. The control system includes a main control unit 201. The main control unit 201 controls each part of the copying machine and performs arithmetic processing described later. The main control unit 201 includes a CPU 202 which is a central processing unit including a microcomputer and the like, a ROM 203 storing various data used by the CPU 202 and a control program, and a RAM 204 temporarily storing various data as a work memory. , And an interface I / O 205 for performing input and output between the CPU 202 and each unit described later.
[0021]
Further, a laser optical system control unit 206, a power supply circuit 207, an optical sensor 208, a toner density sensor 209, an environment sensor 210, a photoconductor surface potential sensor 211, a toner supply circuit are provided to the main control unit 201 via the interface I / O 205. 212, an intermediate transfer belt driving unit 213, an image processing unit (not shown), and the like are connected to each other.
[0022]
Note that the laser optical system control unit 206 controls the laser output of the laser optical system 105. Also, the power supply circuit 207 applies a predetermined charging discharge voltage to the charging charger 104, and also applies a developing bias of a predetermined voltage to the developing sleeves (for example, 108a in the drawing) of the developing devices 106 to 109, Further, a predetermined transfer voltage is applied to the bias roller 111 and the transfer bias roller 114.
[0023]
The optical sensor 208 includes a light emitting element such as a light emitting diode and a light receiving element such as a photo sensor, and is a toner image of a latent image of a gradation density pattern formed on the photosensitive drum 103 (a visible image of the gradation density pattern). Is detected for each color. The detection output signal from the optical sensor 208 is input to the main control unit 201, and is used for detecting a toner adhesion amount and correcting an image signal, which will be described later. A detection output signal from the optical sensor 208 is applied to a photoelectric sensor control (not shown), and the photoelectric sensor control unit determines a ratio between a toner adhesion amount in the toner image of the gradation density pattern and a toner adhesion amount in the background portion. , And the ratio value is compared with a reference value to detect a change in image density, and the control value of the toner density sensor 209 is corrected.
[0024]
Further, the toner density sensor 209 detects the toner density based on a change in the magnetic permeability of the developer present in the developing devices 106 to 109, compares the toner density value with a reference value, and determines that the toner density value is constant. When the toner is in a shortage state, the toner supply signal having a magnitude corresponding to the shortage is output. The surface potential sensor 211 detects the surface potential of the photosensitive drum 103 serving as an image carrier, and the intermediate transfer belt driving unit 213 controls driving of the intermediate transfer belt 110. The toner supply circuit 212 controls the amount of toner supplied into the developing devices 106 to 109 according to a toner supply signal from the toner density sensor 209.
[0025]
Next, the image processing unit will be described with reference to FIG. The image processing unit inputs an image signal read by the scanner 102, performs various image processing described later on the image signal, and outputs the processed image signal to the printer 101 (specifically, the laser optical system control unit 206). As shown in the figure, the image processing unit includes a shading correction circuit 301 for correcting unevenness of the image sensor (CCD 123) and illumination unevenness of a light source, and RGB for converting a read signal (reflectance data) from the scanner 102 into brightness data. A γ correction circuit 302, an image separation circuit 303 for determining a character portion and a photograph portion, and chromatic / achromatic color determination, and an MTF correction circuit 304 for correcting MTF characteristic deterioration of an input system (particularly, a high-frequency region). The difference between the color separation characteristics of the input system and the spectral characteristics of the output color materials is corrected, and the amounts of the color materials Y (yellow), M (magenta), and C (cyan) necessary for faithful color reproduction are calculated. , Y, M, and C, a color conversion UCR processing circuit 305 for performing UCR processing for replacing a portion where three colors overlap with Bk (black), a scaling circuit 306 for performing vertical and horizontal scaling, a repeat processing, and the like. An image processing (create) circuit 307 to be performed, an MTF filter 308 for changing the frequency characteristics of the image signal such as edge enhancement and smoothing so as to obtain a sharp image or a soft image according to the user's preference, and a printer A gamma conversion circuit 309 that corrects an image signal according to the characteristics of the image signal 101, a gradation processing circuit 310 that performs dither processing or pattern processing, and an image signal read by the scanner 102 is processed by an external image processing device or the like. And I / Fs (interfaces) 311 and 312 for outputting image signals from an external image processing apparatus to the printer 101, a CPU 313 for controlling the above-described units, a ROM 314, and a RAM 315. Incidentally, reference numeral 316 denotes a bus. The CPU 313 is connected to the main control unit 201 via a serial I / F (not shown), and commands from an operation unit (not shown) and the like are transmitted via the main control unit 201.
[0026]
FIG. 4 is a block diagram of the laser modulation circuit 401 provided in the laser optical system 105. The laser modulation circuit 401 has a writing frequency of 18.6 MHz and a scanning time of one pixel is 53.8 nsec. An 8-bit image signal (image data) can be subjected to γ conversion by an LUT (look-up table) 402. The pulse width modulation circuit (PWM) 403 converts the 8-bit image signal into a 4-level pulse width based on the upper 2 bits of the 8-bit image signal, and the power modulation circuit (PM) 404 converts the lower 6 bits into a 64-level power. The modulation is performed, and the laser diode (LD) 405 emits light based on the modulated signal. The light emission intensity is monitored by a photodetector (PD) 406, and correction is performed for each dot. The maximum value of the intensity of the laser beam can be changed to 8 bits (256 steps) independently of the image signal.
[0027]
The configuration of the copying machine has been described above. Next, calibration of the copying machine having the above configuration will be described.
(1) γ characteristic calculation processinga,
(2) γ characteristic calculation processingb,
(3) γ characteristic calculation processingc,
(4) gamma correction processing,
Will be described in this order.
[0028]
(1) γ characteristic calculation processing a:
The γ characteristic calculation processing a will be described with reference to the flowchart shown in FIG. 11 and the graph shown in FIG. First, by controlling the laser optical system 105, an electrostatic latent image having np (12 in this embodiment) gradation patterns is formed on the photosensitive drum 103 as shown in FIG. The toner is supplied to the image to perform toner development, and a toner image is formed on the photoconductor. After transferring the toner image to the intermediate transfer belt 110, the toner image is transferred and fixed on a recording sheet. After fixing, the recording paper is discharged. Then, the recording paper on which the gradation pattern is recorded is read by the scanner 102, and output signals R, G, and B of the scanner are stored in the RAM 204 of the main control unit 201.
Here, the laser output, that is, the laser signal when forming the gradation pattern is, for example, 00, 10, 20, 30, 40, 50, 60, 70, 80, 90, B0, D0 as the value of the image signal. , FF (both in hexadecimal).
[0029]
As a gradation pattern to be used, a pattern subjected to dither processing in the same manner as in actual image formation is used. Specifically, the sum of the image signals of two pixels in the main scanning direction is allocated to two pixels according to the value as follows. That is, assuming that the image signal of the first pixel is N1, the image signal of the second pixel is N2, the image signal of the first pixel after processing is N11, and the image signal of the second pixel after processing is N22.
When N1 + N2 ≦ FF (H), N11 = N1 + N2, N22 = 0,
When N1 + N2> FF (H), N11 = FF (H), N22 = N1 + N2-FF (H),
((H) represents a hexadecimal number).
[0030]
When the CPU 202 of the main control unit 201 calculates the total value S (= R + G + B) of the output signals R, G, and B values of the scanner 102 stored in the RAM 204, the laser output of the graph (d) in FIG. The relationship between the total output values can be determined. Graph (c) in FIG. 7 shows the relationship between the density (ID) of the gradation pattern and the total value S (= R + G + B) of the scanner output values R, G, and B. The relationship between the density (ID) of the gradation pattern and the total value S of the scanner output values R, G, and B is the minimum from the previously measured density (ID) of the gradation pattern and the total value S of the scanner output values. The density may be calculated by the square method. This calculation may be performed once.
[0031]
The relationship between the laser output and the density of the gradation pattern (γ characteristic) is expressed by the relationship between the laser output and the total scanner output value in the graph (d) of FIG. 7 and the density (ID) of the gradation pattern in the graph (c) of FIG. ) And the total value S of the scanner output values R, G, and B.
If the above-described γ characteristic calculation processing a is performed for each of the yellow, magenta, cyan, and black color components of the printer, the γ characteristic for each color component can be calculated.
[0032]
(2) γ characteristic calculation processing b:
The above-mentioned γ-characteristic calculation processing a can calculate the γ-characteristic of the gradation pattern of the yellow, magenta, and cyan color components. Can not.
Therefore, the γ characteristic calculation processing b will be described with reference to the flowchart shown in FIG. 12 and FIG. First, by controlling the laser optical system 105, an electrostatic latent image having np (12 in this embodiment) gradation patterns is formed on the photosensitive drum 103 as shown in FIG. The toner is supplied to the image to perform toner development, and a toner image is formed on the photoconductor. After transferring the toner image to the intermediate transfer belt 110, the toner image is transferred and fixed on a recording sheet. After fixing, the recording paper is discharged. Then, the recording paper on which the gradation pattern is recorded is read by the scanner 102, and output signals R, G, and B of the scanner are stored in the RAM 204 of the main control unit 201. Further, the gradation pattern of the high-density portion is measured by a densitometer and is input from the operation panel. The input density value is stored in the RAM 204 via the main control unit 201 and the CPU 313. Note that the processing used in the γ characteristic calculation processing (a) can be used for forming the gradation pattern.
[0033]
Here, a method for determining a range in which the scanner sensitivity is good will be described.
FIG. 6A shows the relationship between the image density (ID) and the scanner output value X (R or G or B) with respect to the image density. When the image density is within 1.5, that is, when the scanner output value is equal to or more than X, it is assumed that the scanner sensitivity is within a favorable range. The image density can be calculated from the output value of the scanner in this range. Further, a range in which the scanner sensitivity is good can be estimated from the total value S (= R + G + B) of the scanner output values R, G, and B. FIG. 6B shows the relationship between the image density (ID) and the total value S of the scanner output values R, G, and B with respect to the image density. The image density (ID) is within 1.5, that is, the scanner output value is S. When the above is the case, it is assumed that the sensitivity of the scanner is in a favorable range. The image density can be calculated from the output value of the scanner in this range.
[0034]
Further, the sensitivity of the scanner is good even from the absolute value (| ΔX / ΔID |) of the change amount (ΔX / ΔID) of the scanner output value X (R, G, or B) with respect to the image density (ID) change amount (ΔID). Range can be estimated. FIG. 6C shows a change amount (ΔX / ΔID) of the scanner output value X (R or G or B) with respect to the image density (ID), the scanner output value X with respect to the image density, and the change amount (ΔID) of the image density (ID). )), And the image density is within 1.5, that is, | ΔX / ΔID | is | ΔX₀/ ΔID₀When | is greater than or equal to, it is assumed that the sensitivity of the scanner is in a favorable range. The image density can be calculated from the output value of the scanner in this range.
[0035]
Also, the absolute value (| ΔS / ΔID |) of the amount of change (ΔS / ΔID) of the total value S (= R + G + B) of the scanner output values R, G, and B with respect to the amount of change (ΔID) of the image density (ID). A range in which the scanner sensitivity is good can be estimated. FIG. 6D shows the relationship between the image density (ID) and the absolute value (| ΔS / ΔID |) of the amount of change (ΔS / ΔID) of the total value S of the scanner output values R, G, and B with respect to the image density. The image density is within 1.5, that is, | ΔS₀/ ΔID₀When | is greater than or equal to, it is considered that the sensitivity of the scanner is in a good range. The image density can be calculated from the output value of the scanner in this range.
With the above-described method, a range in which the sensitivity of the scanner is good can be determined.
[0036]
The gamma characteristic calculation processing is performed as follows by dividing the range into a range where the scanner sensitivity is good and a range outside the range.
In the range where the sensitivity of the scanner is good, the γ characteristic may be calculated as in the γ characteristic calculation processing a. When the scanner sensitivity is out of the good range, it can be calculated from the maximum density (IDsmax) that can be calculated within the good scanner sensitivity range and the density value (IDmax) of the gradation pattern of the high density part stored in the RAM 204. . For example, as shown in FIG. 8, the point B (point of IDsmax) and the point A (point of IDmax) may be linearly interpolated. Thus, even with linear interpolation, it is possible to calculate with a value close to the actual image density.
If the above-described γ characteristic calculation processing b is performed for each of the yellow, magenta, cyan, and black color components of the printer, the γ characteristic for each color component can be calculated.
[0037]
(3) γ characteristic calculation processing c:
The gamma characteristic calculation processing b can calculate the gamma characteristics of the grayscale patterns of the color components of yellow, magenta, cyan, and black, but the density of the grayscale pattern in the high density portion must be measured with a densitometer. In the γ characteristic calculation processing c, the calculation of the high density portion is performed by the surface electrometer, so that the densitometer is not required.
The γ characteristic calculation processing c will be described with reference to the flowchart of FIG. 13 and the graph of FIG. The graph (f) in FIG. 9 shows the optical attenuation characteristics of the photoconductor, and this graph controls the laser optical system 105 to obtain np (12 in this embodiment) static patterns as shown in FIG. An electrostatic latent image is formed on the photosensitive drum 103 and is obtained by measuring the surface potential of the electrostatic latent image with the potential sensor 211. The measured values are stored in the RAM 204 of the main control unit 201.
[0038]
Next, toner is supplied to the electrostatic latent image on the photoconductor by a developing device to perform toner development, and a toner image is formed on the photoconductor. After transferring the toner image to the intermediate transfer belt 110, the toner image is transferred and fixed on a recording sheet. After fixing, the recording paper is discharged. Then, the recording paper on which the gradation pattern is recorded is read by the scanner 102, and output signals R, G, and B of the scanner are stored in the RAM 204 of the main control unit 201.
[0039]
Graph (e) of FIG. 9 shows the relationship between the surface potential of the photoconductor and the image density of the gradation pattern fixed on the recording paper. The surface potential (V_S), The image density (ID) corresponding to
ID = a · V_S+ B (a and b are constants)
Alternatively, the DC component of the developing bias is V_DCAs
ID = a · (V_S-V_DC) + B (where a and b are constants)
The surface potential (V_S) Is determined.
The image density at point A (ID_a) And surface potential (V_Sa), Image density at point B (ID_b) And surface potential (V_SbA) and b are determined from the above.
[0040]
As described above, from the surface potential of the photoconductor, the graph (f) of FIG. 9 shows the light attenuation characteristics of the photoconductor, and the surface potential of the photoconductor and the gradation pattern fixed on the recording paper in the graph (e). The relationship between the laser output and the image density (γ characteristic) is obtained from the relationship between the image densities.
Note that the method used in the γ characteristic calculation processing b can be used to determine the range in which the scanner sensitivity is good.
[0041]
The γ characteristic is calculated as follows by dividing the range into a range where the scanner sensitivity is good and a range outside the range.
In the range where the sensitivity of the scanner is good, the γ characteristic may be calculated as in the γ characteristic calculation processing a. When the sensitivity of the scanner is out of the good range, the γ characteristic is calculated from the surface potential of the photoconductor as described above (the section between points A and B in FIG. 9).
If the above-described γ characteristic calculation processing (c) is performed for each of the yellow, magenta, cyan, and black color components of the printer, the γ characteristic for each color component can be calculated.
[0042]
(4) γ correction processing:
Next, a method of determining the γ correction curve in the graphs (a) of FIGS. 7, 8, and 9 will be described. Graphs (b) in FIGS. 7, 8, and 9 show target input / output characteristics (horizontal axis: image input signal, vertical axis: output image density) of the printer. The target input / output characteristics are determined in advance for each of the yellow, magenta, cyan, and black color components of the printer.
[0043]
7 and 8, the relationship between the laser output and the output image density for each of the yellow, magenta, cyan, and black color components calculated in the γ characteristic calculation processes a, b, and c, that is, the γ characteristic and the target input / output characteristics. , 9 are calculated and determined.
[0044]
The gamma correction is performed by setting the gamma correction curve in a look-up table (hereinafter, LUT). Further, in the case of selecting a γ correction curve from the LUT, a curve closest to the γ correction curve in the graph (a) may be selected.
However, if the γ characteristics for each of the yellow, magenta, cyan, and black color components calculated by the γ characteristic calculation processes a, b, and c are out of the predetermined range, the target input / output characteristics cannot be obtained. In the example of FIG. 9, the density of the point A is a predetermined value (ID_tThis is when: In such a case, the fact that the γ characteristic is abnormal is displayed on the operation panel to notify the user.
[0045]
If the printer and copier are used in this state, the color balance will be deviated. Therefore, the target input / output characteristics of the printer shown in graphs (b) of FIGS. For example, as shown in FIG. 10, the maximum density (ID) of the image output densities of the color components whose gamma characteristics are out of the predetermined range._a  The target input / output characteristic may be changed so that ()) is the highest density of the target input / output characteristic. The γ correction curve may be calculated and determined as described above based on the target input / output characteristics changed as described above and the γ characteristics calculated by the γ characteristic calculation processes a, b, and c.
[0046]
【The invention's effect】
As explained above,In the image forming apparatus according to the present invention,The gamma characteristic of the image forming unit is calculated from the sum of output signals (for example, R, G, and B values) for each color component of the image reading unit.ByThus, the γ characteristics of the image forming apparatus can be accurately calculated.
[0047]
Also,In the range of the density where the sensitivity of the image reading unit is good, the γ characteristic of the image forming unit is calculated from the image reading unit, and in the range of the density where the sensitivity of the image reading unit is reduced, the γ characteristic of the image forming unit is changed. Calculate characteristicsByThus, the γ characteristics of the image forming apparatus can be accurately calculated.
[0048]
AndClaim1According to the invention described above, the gamma characteristic of the image forming unit is calculated from the image reading unit in the range of the density where the sensitivity of the image reading unit is good, and the electrostatic latent is calculated in the range of the density where the sensitivity of the image reading unit is reduced. Since the γ characteristic of the image forming means is calculated from the surface potential of the image, the γ characteristic of the image forming apparatus can be calculated with high accuracy.
[0049]
Claim2According to the described invention, image formationmeansWhen the γ characteristic is outside the predetermined range, a message is displayed on the operation panel, so that it is determined that the color balance is abnormal.
[0050]
Claim3According to the described invention, image formationmeansΓ correction means for performing the γ correction described above can perform γ correction based on the γ characteristics obtained from the γ characteristic calculation processing unit.
[0051]
Claim4According to the described invention, image formationmeansWhen the γ characteristic of the image is outside the predetermined range,means, The deviation of the color balance can be reduced.
[0052]
Claim5According to the described invention,R, G, BOutput signal of color-separated image reading meansOutput value X (X = R or G or B value)Is set as a range of density where the sensitivity of the image reading means is good, so that the γ characteristic of the image forming apparatus can be calculated with high accuracy, and the γ correction of the image forming apparatus can be performed with high accuracy.
[0053]
Claim6According to the described invention,R, G, BOutput signal of color-separated image reading meansOutput valueTotal of (R, G, B values)The value S (S =R + G + B)PlaceSince the range of the density equal to or higher than the predetermined value is set as the range of the density where the sensitivity of the image reading unit is good, the γ characteristic of the image forming apparatus can be accurately calculated, and the γ correction of the image forming apparatus can be accurately performed.
[0054]
Claim7According to the invention described in the above, the image reading means responds to the change amount (ΔID) of the density (ID) of the gradation pattern input to the image reading means.R, G, BOutput signal after color separationOutput value X (X = R or G or B value)Amount of change(ΔX / ΔID)The absolute value of( | ΔX / ΔID | )Is defined as a range of density where the sensitivity of the image reading unit is good, so that the γ characteristic of the image forming apparatus can be calculated with high accuracy, and the γ correction of the image forming apparatus can be performed with high accuracy.
[0055]
Claim8According to the invention described in the above, the image reading means responds to the change amount (ΔID) of the density (ID) of the gradation pattern input to the image reading means.R, G, BOutput signal after color separationOutput valueTotal of (R, G, B values)Value SSince the range in which the absolute value (| ΔS / ΔID |) of the amount of change (ΔS / ΔID) of (S = R + G + B) is equal to or greater than a predetermined value is defined as the range of density where the sensitivity of the image reading unit is good, γ of the image forming apparatus The characteristics can be calculated with high accuracy, and the γ correction of the image forming apparatus can be performed with high accuracy.
[0056]
Claim9According to the invention, the relationship between the surface potential (VS) and the density (ID) in the gradation pattern is
ID = a · VS + b (where a and b are constants),
Or, the DC component of the developing bias is VDC,
ID = a · (VS−VDC) + b (where a and b are constants),
Therefore, the gamma characteristic of the image forming apparatus can be accurately calculated, and the gamma correction of the image forming apparatus can be accurately performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a copying machine showing one embodiment of the present invention.
FIG. 2 is an explanatory diagram of a control system of the copying machine shown in FIG.
FIG. 3 is a block diagram illustrating a configuration example of an image processing unit of the copying machine illustrated in FIG. 1;
FIG. 4 is a block diagram showing a configuration example of a laser modulation circuit installed in a laser optical system of the copying machine shown in FIG.
FIG. 5 is an explanatory diagram of an image signal of a gradation pattern formed on a photoconductor.
6A is a graph showing a relationship between an image density and a scanner output value, FIG. 6B is a graph showing a relationship between an image density and a total of scanner output values, FIG. A graph simultaneously showing the relationship between the image density and the amount of change in the scanner output value (ΔX / ΔID) with respect to the amount of change in the image density, and (d) shows the relationship between the image density and the sum of the scanner output values and the relationship between the image density and the amount of change in the image density. It is a graph which simultaneously shows the relationship of the amount of change (ΔS / ΔID) of the scanner output value total.
FIG. 7 is a graph for explaining the r characteristic calculation processing a, which simultaneously shows a γ correction curve, a target input / output characteristic, a relationship between an output image density and a total of scanner output values, and a relationship between a total of scanner output values and a laser output. It is the graph shown.
FIG. 8 is a graph for explaining the r characteristic calculation processing b, which is a γ correction curve, a target input / output characteristic, a relationship between an output image density and a total scanner output value, a relationship between a total scanner output value and a laser output, 5 is a graph showing the relationship between output and output image density at the same time.
FIG. 9 is a graph for explaining an r characteristic calculation process c, which is a γ correction curve, a target input / output characteristic, a relationship between an output image density and a scanner output value total, a relationship between a scanner output value total and a laser output value, 5 is a graph simultaneously showing a relationship between a body surface potential and an output image density, and a relationship between a photoconductor surface potential and a laser output.
FIG. 10 is a graph used for explaining the γ correction processing, and is a graph simultaneously showing a relation between a γ correction curve, a target input / output characteristic, an output image density, and a laser output.
FIG. 11 is a flowchart illustrating an example of a gradation pattern reading process.
FIG. 12 is a flowchart illustrating another example of a gradation pattern reading process.
FIG. 13 is a flowchart illustrating still another example of a gradation pattern reading process.
[Explanation of symbols]
101: Printer (image forming means)
102: Scanner (image reading means)
103: Photoconductor drum
104: Charger
105: Laser optical system
106: Black developing device
107: Yellow developing device
108: Magenta developing device
109: cyan developing device
110: Intermediate transfer belt
111: bias roller
112: Cleaning device
113: Static eliminator
114: transfer bias roller
115: Belt cleaning device
116: Conveyor belt
117: Fixing device
120: Exposure lamp
121: Reflection mirror
122: Imaging lens
123: CCD
201: Main control unit
202: CPU (Central Processing Unit)
203: ROM
204: RAM
206: laser optical system control unit
207: Power supply circuit
208: Optical sensor
209: Toner density sensor
211: Photoconductor surface potential sensor
212: toner supply circuit
213: intermediate transfer belt driving unit
301: Shading correction circuit
302: RGB / γ correction circuit
303: Image separation circuit
304: MTF correction circuit
305: Color conversion UCR processing circuit
306: Magnification circuit
307: Image processing circuit
308: MTF filter
309: γ conversion circuit
310: gradation processing circuit
313: CPU (Central Processing Unit)
314: ROM
315: RAM
401: laser modulation circuit

Claims (9)

Gradation pattern image signal generation means for generating a gradation pattern image signal, latent image formation means for forming an electrostatic latent image on an image carrier based on the image signal, and the gradation pattern image signal generation means Surface potential detecting means for detecting the surface potential of the electrostatic latent image of the gradation pattern formed on the image carrier based on the image signal of In an image forming apparatus including an image forming unit having a developing unit that forms a visual image and a unit that records a visible image developed on an image carrier by the developing unit on a recording sheet,
Image reading means for reading a tone pattern formed on the basis of the tone pattern image signal generating means by color separation, and from the image reading means to the image forming means in a density range where the sensitivity of the image reading means is good. A first γ characteristic calculating means for estimating the first γ characteristic, and a surface potential of the surface potential detecting means in a density range where the sensitivity of the image reading means is reduced, and a relational expression of the surface potential and the image density. An image forming apparatus comprising: a second γ characteristic calculating unit that estimates a second γ characteristic of the image forming unit. 2. The image forming apparatus according to claim 1, further comprising: means for displaying a message on an operation panel when the density of the high-density area is insufficient, when the γ characteristic of the image forming means is outside a predetermined range. An image forming apparatus , wherein a message is displayed on the image forming apparatus. 2. The image forming apparatus according to claim 1, further comprising: a γ correction unit configured to perform γ correction of the image forming unit, wherein the γ correction unit is configured based on the γ characteristic estimated by the first γ characteristic calculation unit or the second γ characteristic calculation unit. An image forming apparatus comprising: a γ correction curve changing unit for changing the γ correction curve . 4. The image forming apparatus according to claim 1, wherein when a γ characteristic of the image forming unit is out of a predetermined range, a target input / output characteristic (a target γ characteristic) of the image forming unit is changed to perform the image forming. images forming device you comprising the γ correction curve changing means for changing the γ correction curve γ correcting means for correcting the γ characteristic of the unit. 5. The image forming apparatus according to claim 1, wherein the range of the density at which the sensitivity of the image reading unit is good is that the color is separated into R (red), G (green), and B (blue). An image forming apparatus, wherein an output value X (X = R or G or B value) of an output signal of an image reading unit is in a range of a predetermined value or more . 5. The image forming apparatus according to claim 1, wherein the range of the density at which the sensitivity of the image reading unit is good is that the color is separated into R (red), G (green), and B (blue). output value of the output signal of the image reading means (R, G, B values) of the sum S (S = R + G + B) is images forming device you characterized in that the range of a predetermined value or more. 5. The image forming apparatus according to claim 1, wherein the range of the density at which the sensitivity of the image reading unit is satisfactory is a change amount of a density (ID) of a gradation pattern input to the image reading unit. The change amount (ΔX / ΔID) of the output value X (X = R or G or B value) of the output signal of the image reading unit color-separated into R (red), G (green), and B (blue) with respect to ΔID) the absolute value (| ΔX / ΔID |) is images forming device you characterized in that the range of a predetermined value or more. 5. The image forming apparatus according to claim 1, wherein the range of the density at which the sensitivity of the image reading unit is satisfactory is a change amount of a density (ID) of a gradation pattern input to the image reading unit. ΔID) and the change amount of the total value S (S = R + G + B) of the output values (R, G, B values) of the output signals separated into R (red), G (green), and B (blue) by the image reading means (ΔS / ΔID) of the absolute value (| ΔS / ΔID |) is images forming device you characterized in that the range of a predetermined value or more. 9. The image forming apparatus according to claim 1, wherein a surface potential (VS) in the gradation pattern is set. ) And concentration (ID)
ID = a · VS + b (where a and b are constants)
Or, the DC component of the developing bias is VDC,
ID = a · (VS−VDC) + b (where a and b are constants)
That consists of the relationship images forming device you characterized.

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