JPH089154A - Image processing unit - Google Patents

Abstract

PURPOSE:To prevent occurrence of pseudo contour or void due to a change in UCR amount. CONSTITUTION:A color conversion - UCR processing circuit 406 conducts undercolor removal by replacing each color separation signal with a black level signal depending on an undercolor removal quantity and a gamma conversion section 410 has a printer gamma correction table having a prescribed gamma conversion characteristic generated in advance for a monochromatic mode or in which the undercolor removal quantity rate is 100%. A CPU 415 revises the gamma conversion characteristic of the printer gamma correction table 410 so as to avoid the occurrence of pseudo contour or void when undercolor removal quantity rate is <100%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus such as a digital type copying machine, printer or facsimile.
In particular, it relates to a correction gradation curve (γ conversion characteristic of the printer γ correction table) for converting the gradation of image data.

[0002]

2. Description of the Related Art When creating a γ correction table, RO
In order to effectively use the limited capacity of M, the LUT (Look Up Table) that constitutes the γ correction table is Y (yellow), M (magenta), C (cyan), K (black).
The colors are used in common as much as possible without being divided according to the color or the image quality mode such as a single color, a photograph, or a character.

[0003]

However, if the γ correction table is used in common regardless of the color or the image quality mode, the following first problem may occur especially for K (black). Problems in image processing In full color mode, the relationship between the range of input values and the original density and output density of the γ correction table used for black is UCR (Under Color Removal).
It may vary depending on the quantity. Explaining with reference to FIG. 21, when the UCR amount is 100%, FIG.
As shown in, the three YMC colors have the smallest amount α ・ min
(Y, M, C) colors (C, UCR amount is 100 in the figure)
In the case of [%], the same amount as α = 1) is replaced with black, and this black and other colors removed by this amount (Y,
An image is formed by M). Also, the UCR amount is 50%
In the case of C, as shown in FIG.
Of 50% (α = 0.5) is removed from each YMC and this amount of black is added.

In this case, the black printer γ correction table is used as an output in the range of 0 to 255 (in the case of 8-bit processing) according to the read image density. The lower limit of the density range that can be output is determined by the whiteness of the transfer body and the transfer paper used, and the upper limit is determined by the color of the toner used.

Incidentally, it is not always desirable that the original density and the output image density are reproduced at exactly the same density. For example, in a double-sided original, the image on the back side may be seen through the surface (front side) from which the actual copy image is obtained. In this case, if the original is faithfully reproduced, the unnecessary image on the back side is also formed together with the image on the front side. It In order to prevent this, an image processing parameter (printer γ correction table, scanner γ correction table, or color conversion coefficient, etc.) is set to, for example, an image having a Macbeth densitometer value of about 0.20 or less so as not to reproduce the image on the back side. Is set so as not to be reproduced.

The sensitometry graph shown in FIG. 22 will be described. The horizontal axis of the first quadrant in FIG. 22 represents the original density OD of an arbitrary scale, and the vertical axis represents the density (IDBk) of the black component of the copy image. The OD-IDBk characteristic represents the density of the black component formed as a copy image on the read document. Characteristic a shows the case where the UCR amount is 100%, and the background is removed so that it does not appear in the copy image in the low density area b of the original density OD. Further, the characteristic c shows the case where the UCR amount is 50 [%], and is a characteristic obtained by shifting the characteristic a as it is in the direction of the horizontal axis (original density OD) by 50 [%].

The vertical axis of the fourth quadrant is the input value of the printer γ correction table, and this characteristic represents the relationship between the read document density OD and the input value of the printer γ correction table.
Refers to UCR / color conversion characteristics. The horizontal axis of the third quadrant represents, for example, an 8-bit write signal of an LD (laser diode), and this characteristic represents a printer γ correction table. The second quadrant shows the relationship between the LD write signal (horizontal axis) and the image density (vertical axis) actually formed, and represents the developing characteristics of the printer section.

OD-IDBk when UCR amount is 100%
Characteristic a, UCR / color conversion characteristic a, and printer γ correction table a are shown in the first, fourth, and third quadrants, respectively. It should be noted that such a setting is made not only for the printer γ correction table for black whose UCR amount is 100%, but also for the printer γ correction table for YMC in full color and in single color.

Here, as shown in, for example, Japanese Patent Application Laid-Open No. 4-369970, it is called skeleton black, and UC
A method of changing the R amount according to the document density is used for an image that requires smoothness such as a photographic image. In this method, in an area where the original density is low (thin), the UCR amount is reduced in order to prevent the occurrence of graininess and the loss of vividness due to the inclusion of black, and to improve the blackness of dark areas. Set a higher UCR amount.

The relationship in this case will be described with reference to FIG. 22. O in the case where the UCR amount is 100% in the first quadrant.
In contrast to the D-IDBk characteristic a, the low density area b represents a density area where a latent image is not formed in order to prevent the show-through and the background stain. Also, when the UCR amount is 50%, OD-IDBk
Characteristic c is the density with the original density OD on the horizontal axis (0.
From 5), black is put in, and it indicates that an image is formed with three colors of YMC in a region lower than the density and a region between the characteristics a and c.

When the UCR amount is 100%, the printer γ correction table a does not reproduce the highlight portion having the input value f or less to prevent the background stain and the show-through as shown by the low density area e in the third quadrant. Is set. Looking at the region g in the first quadrant when the UCR / color conversion characteristic of the skeleton black (c in the fourth quadrant) is used by using the printer γ correction table a at this time, the characteristic c is a desirable characteristic c ′. And a difference d is generated. As a result, since the black becomes lighter by the density difference d, it looks like a blank area, and on the other hand, in the original density area of the area g or higher, the black looks like abruptly entering. For example, as shown in FIG. It may look like a contour.

Further, the following second problem is caused as a problem due to the temporal change of the printer and the environmental change.
The development characteristics shown in the second quadrant fluctuate due to changes in the printer over time and environmental changes, and the density in the area g described above changes, so that this portion is reproduced darkly and appears as a pseudo contour, or conversely, is reproduced thinly. It is reproduced like a blank area.

In view of the above-mentioned first problem, the present invention is a UCR.
It is an object of the present invention to provide an image processing apparatus capable of preventing a pseudo contour or a blank area from occurring due to a change in amount.

In view of the above-mentioned second problem, the present invention has an object to provide an image processing apparatus capable of preventing the occurrence of false contours and blank areas regardless of the temporal change and environmental change of the printer. To do.

[0015]

In order to achieve the above object, a first means is an undercolor removing means for removing an undercolor by replacing each color separation signal with a black signal in accordance with an undercolor removal amount, A printer γ correction table having a predetermined γ conversion characteristic which is generated in advance for the monochrome mode with an undercolor removal amount of 100%, and the printer γ when the undercolor removal amount is less than 100%.
And a γ conversion characteristic changing means for changing the γ conversion characteristic of the correction table.

The second means is the above-mentioned γ in the first means.
The conversion characteristic changing means changes the γ conversion characteristic of a certain density area in the printer γ correction table when the undercolor removal amount is less than 100%.

A third means is characterized in that, in the first or second means, the γ conversion characteristic changing means changes the γ conversion characteristic of the printer γ correction table according to an image quality mode.

The fourth means is characterized in that, in the first to third means, the changed value of the γ conversion characteristic can be adjusted from the operating portion or from the outside.

The fifth means is characterized in that the density region in which the γ conversion characteristic is changed in the fourth means can be adjusted from the operating section or the outside.

The sixth means further comprises developing characteristic detecting means for detecting the developing characteristics in the first to fifth means,
The γ conversion characteristic changing unit changes the γ conversion characteristic of the printer γ correction table according to the developing characteristic detected by the developing characteristic detecting unit.

According to a seventh means, in the sixth means, the developing characteristic detecting means forms an electrostatic latent image of a gradation density pattern on the image bearing member, develops the electrostatic latent image, and visualizes it. An image is formed, and the developing characteristic is detected by detecting the density of the visible image of this gradation density pattern.

An eighth means is the center of the density region in which the γ conversion characteristic changing means in the sixth or eighth means changes the γ conversion characteristic in accordance with the developing characteristics detected by the developing characteristic detecting means. The γ conversion characteristic of the printer γ correction table is changed based on the value.

The ninth means further comprises transfer characteristic detecting means for detecting the transfer characteristic of the transfer material onto which the visible image is transferred by the first to eighth means, and the γ conversion characteristic changing means is the transfer characteristic detecting means. The γ conversion characteristic of the printer γ correction table is changed according to the developing characteristic detected by the characteristic detecting means.

According to a tenth means, in the ninth means, the transfer characteristic detecting means forms an electrostatic latent image of a gradation density pattern on the image carrier, develops the electrostatic latent image, and visualizes it. An image is formed, the visible image is transferred to the transfer material, and the transfer characteristic is detected by detecting the density of the visible image of the gradation density pattern.

The eleventh means is the center of the density region in which the γ conversion characteristic changing means in the ninth or tenth means changes the γ conversion characteristics in accordance with the transfer characteristics detected by the transfer characteristic detecting means. Based on the value, the printer γ
The γ conversion characteristic of the correction table is changed.

[0026]

According to the first means, the printer γ correction table having the undercolor removal amount of 100% or the predetermined γ conversion characteristic generated in advance for the single color mode is changed when the undercolor removal amount is less than 100%. , It is possible to prevent the occurrence of false contours and blank areas due to changes in the UCR amount.

According to the second means, when the amount of undercolor removal is less than 100%, γ of a density area in the printer γ correction table is
Since the conversion characteristic is changed, it is possible to prevent the pseudo contour and the blank area from occurring due to the change in the UCR amount.

In the third means, since the γ conversion characteristic of the printer γ correction table is changed according to the image quality mode, it is possible to prevent a defective image from being generated due to the circuit configuration in the photographic mode or the automatic image separation mode. You can

In the fourth means, since the changed value of the γ conversion characteristic can be adjusted from the operation unit or from the outside, pseudo contours and white spots are generated by the adjustment by the service person or the user when there are variations due to the machine. Can be prevented.

In the fifth means, since the density region where the γ conversion characteristic is changed can be adjusted from the operation unit or the outside,
It is possible to prevent the occurrence of false contours and blank areas due to adjustment by a service person or a user when there are variations due to machines.

In the sixth means, since the γ conversion characteristic of the printer γ correction table is changed according to the developing characteristic, it is possible to prevent the occurrence of false contours and blank areas due to the variation of the developing characteristic of the printer.

In the seventh means, since the variation of the developing characteristic is automatically detected, it is possible to automatically prevent the pseudo contour and the white spot from occurring due to the variation of the developing characteristic of the printer.

In the eighth means, since the central value of the density region in which the γ conversion characteristic is changed according to the developing characteristic is changed as a reference, there are variations in the developing characteristic of the printer, which varies depending on the machine. Can be automatically prevented.

In the ninth means, since the γ conversion characteristic of the printer γ correction table is changed according to the transfer characteristic, it is possible to prevent the pseudo contour and the blank area from occurring due to the change of the transfer characteristic.

Since the tenth means automatically detects the change in the transfer characteristic, it is possible to automatically prevent the pseudo contour and the blank area from occurring due to the change in the transfer characteristic of the printer.

In the eleventh means, since the central value of the density region in which the γ conversion characteristic is changed according to the transfer characteristic is changed as a reference, there are variations in the transfer characteristic of the printer which varies depending on the machine. Can be automatically prevented.

[0037]

Embodiments of the present invention will be described below with reference to the drawings. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention, FIG. 2 is a block diagram showing an electrophotographic copying machine to which the image processing apparatus of this embodiment is applied, and FIG. 3 is an electrophotographic apparatus shown in FIG. 4 is an explanatory view showing a control system of the copying machine, FIG. 4 is a block diagram showing a laser modulation circuit of the image processing apparatus of FIG. 1, FIG. 5 is an explanatory view showing an image formed by the laser modulation circuit of FIG. 4, and FIG. FIG. 5 is an explanatory diagram showing the relationship between adjacent pixels, and FIG. 7 is an explanatory diagram showing an example of the processing of the γ conversion unit in FIG. 1.

First, a copying machine to which the image processing apparatus of this embodiment is applied will be described with reference to FIG. An organic photoconductor (OPC) drum 102 having a diameter of 120 mm is arranged as an image bearing member at substantially the center of the copying machine main body 101. Around this drum 102, a charger 103 for uniformly charging the surface of the drum 102, and Charger 103
A laser optical system 104 for forming an electrostatic latent image by irradiating the surface of the drum 102 charged by the semiconductor laser beam.
A black developing device 105 and color developing devices 106 to 108 that develop the electrostatic latent image on the drum 102 with toners of black, Y, M, and C colors, respectively, and an intermediate transfer belt to which the toner image on the drum 102 is transferred. 109 and a bias roller 110 that applies a transfer voltage to the intermediate transfer belt 109,
A cleaning device 111 that removes the residual toner on the drum 102 after the transfer and a charge eliminator 112 that removes the residual charge on the drum 102 after the transfer are sequentially arranged.

Around the intermediate transfer belt 109, a transfer bias roller 113 for applying a voltage for transferring the toner image on the intermediate transfer belt 109, and a belt cleaning device for removing the residual toner on the belt 109 after the transfer. 114 are sequentially arranged. A fixing device 116 and a discharge tray 117 that heat and pressurize and fix the toner image on the transfer material are provided downstream of the conveyor belt 115 that conveys the transfer material separated from the intermediate transfer belt 109.

A contact glass 118 on which a document is placed is provided above the copying machine main body 101, and the document on the contact glass 118 is irradiated with scanning light by an exposure lamp 119 to reflect light from the document. Is guided to the imaging lens 122 by the reflection mirror 121, and photoelectrically converted by the CCD image sensor array 123 which is a photoelectric conversion element. The image signal converted into an electric signal by the image sensor array 123 is output to the laser optical system 104 via the image processing device shown in FIG. 1, and the laser oscillation of the internal semiconductor laser is controlled.

Next, referring to FIG. 3, the copying machine main body 10 is described.
The control system of No. 1 will be described. Main control unit (CPU)
A ROM 131 for a program and a RAM 132 for a work are connected to 130, and a laser optical system control unit 134 via an interface (I / O) 133,
The power supply circuit 135, the optical sensors 136 and 308, the toner concentration sensor 137, the environment sensor 138, the photoconductor surface potential sensor 139, the toner supply circuit 140, and the intermediate transfer belt drive unit 141 are connected.

Under the control of the CPU 130, the laser optical system controller 134 adjusts the laser output of the laser optical system 104, the power supply circuit 135 gives a predetermined charging discharge voltage to the charging charger 113, and the developing device 105.
To 108, and a predetermined transfer voltage to the bias roller 110 and the transfer bias roller 113.

The optical sensor 136 is composed of a light emitting element such as a light emitting diode and a light receiving element such as a photo sensor which are arranged in close proximity to each other in the area of the drum 102 after development, and adheres toner in a predetermined pattern formed on the drum 102. The amount of toner and the amount of toner adhered to the background portion are detected for each color, and the so-called residual potential after static elimination is detected. CPU
Reference numeral 130 obtains the ratio of the toner adhesion amount of the predetermined pattern and the toner adhesion amount on the background portion, and compares the ratio with a reference value to detect a change in image density. Optical sensor 308
Detects the toner density on the intermediate transfer belt 109 in the same manner.

The toner density sensor 137 is the developing device 105.
To 108, the toner density is detected based on the magnetic permeability of the developer including each toner, and the CPU 130 compares the detected toner density with the reference value, and the toner density is below the reference value, and the toner is in a shortage state. In that case, a toner replenishment signal having a magnitude corresponding to the shortage is applied to the toner replenishment circuit 140. The potential sensor 139 detects the surface potential on the drum 102, and the intermediate transfer belt drive unit 141 controls the drive of the intermediate transfer belt 109. Reference numeral 30 is a current detection circuit that detects a current flowing through the developing sleeve 201.

For example, the black developing device 105 contains a developer containing black toner and a carrier. The developer is agitated by the rotation of the agitating member 202, and the amount of the developer pumped up onto the developing sleeve 201 is the agitating member. Adjusted by 202. The developer thus supplied is magnetically carried on the developing sleeve 201 and rotates as a magnetic brush in the rotating direction of the developing sleeve 201.

Next, the image processing apparatus of this embodiment will be described with reference to FIG. The original is color-separated by a color scanner 401 into R, G, and B signals and read.
/ D converted. In the shading correction circuit 402, C
The unevenness of each pixel of the CD image sensor array 123, the exposure lamp 119, the reflection mirror 121, and the imaging lens 12
Illumination unevenness of 2 is corrected, and R via I / F 413
It is applied to the GBγ correction circuit 403.

The RGBγ correction circuit 403 converts each RGB data from the reflectance data into the lightness data, and the image separation unit 404 determines the character portion and the photograph portion and the chromatic color or achromatic color. The MTF correction circuit 405 corrects the deterioration of the MTF characteristics of the input system, especially in the high frequency region. The color conversion-UCR processing circuit 406 corrects the difference between the color separation characteristic of the input system and the spectral characteristic of the color material of the output system, and calculates the amount of each material of YMC necessary to reproduce a faithful color. It has a processing unit and a UCR processing unit that removes undercolor by replacing each color separation signal of YMC with a black signal (Bk) according to the amount of undercolor removal (UCR). The color correction processing is realized by the matrix calculation as shown in the following equation.

[0048]

[Equation 1]

Here, (/ R), (/ G), (/ B)
(“/” Is used for the inversion symbol.), R, G, B respectively.
The matrix coefficient a _ij is determined by the spectral characteristics of the input system and the output system (color material). Although the first-order masking equation is taken as an example here, (/ B) ² ,
By using a quadratic term such as (/ B) / (/ G) or a higher order term, color correction can be performed with higher accuracy. Further, the calculation formula may be changed depending on the hue, or the Neugebauer equation may be used. In any method, Y, M, and C are (/ B), (/ G), (/
R) (or B, G, R may be used).

On the other hand, the UCR process can be performed by calculating using the following equation.

Y '= Y-.alpha.min (Y, M, C) M' = M-.alpha.min (Y, M, C) C '= C-.alpha.min (Y, M, C) Bk = α · min (Y, M, C) In the above equation, α is a coefficient indicating the UCR amount, and α = 1
In the case of, it becomes 100% UCR. The coefficient α may be a constant value, and for example, by making the coefficient α close to “1” in the high density portion and close to “0” in the highlight portion, the image in the highlight portion can be smoothed.

In FIG. 1, a scaling unit 407 scales vertically and horizontally, and an image processing (create) unit 408 performs repeat processing and the like. The MTF filter 409 changes the frequency characteristic of the image signal by edge enhancement or smoothing according to the user's preference such as a sharp image or a soft image. In the γ conversion circuit 410, the printer 412
The image signal is corrected according to the characteristics of, and the background is also skipped at the same time. The gradation processing circuit 411 performs dither processing and pattern processing, and outputs the result to the printer 412 via the I / F 414.

The I / Fs 413 and 414 are provided for processing the image data read by the scanner 401 by an external image processing device and outputting the image data from the external image processing device to the printer 412. CPU 415, ROM 4 for controlling the above image processing circuit
16, a RAM 417 is connected via a bus 418, and a CPU 415 is connected to a system controller 419 via a serial I / F to input commands from an operation unit (not shown). A command from the host computer 420 is also input to the CPU 415.

Next, the laser modulation circuit will be described with reference to FIG. The writing frequency is 18.6 MHz, and the scanning time for one pixel is 53.8 nsec. The 8-bit image data is converted into γ by the lookup table (LUT) 451.
The pulse width is converted, and then converted into a quaternary pulse width by the pulse width modulation (PWM) circuit 452 based on the upper 2 bits of the 8-bit image signal. The LUT 451 is composed of a plurality of γ conversion tables, and this table is selected by a table selection signal.

Next, the power modulation circuit (PW) 453 performs 64-value power based on the lower 6 bits,
A laser diode (LD) 454 emits light based on this power modulation signal. Further, the emission intensity is monitored by the photo detector (PD) 455 and is corrected for each dot. The maximum value of the intensity of the laser light can be changed in 8 bits (256 steps) independently of the image signal.

The emission start timing of the laser light of the image signal subjected to the dither processing is controlled so that the exposure distributions (N ₁ + N ₂ ) of two pixels are close to each other, as shown in FIGS. . At the light emission timings shown in FIGS.
As shown in FIGS. 5 (c) and 5 (d), a line pattern continuous in the sub-scanning direction is formed, and the width of this line pattern can form a latent image substantially proportional to the emission pulse width (N ₁ + N ₂ ). it can.

This control has an advantage that the detection output of the optical sensor 136 has good linearity of the detection output with respect to the image signal as shown in FIG. This also depends on the beam diameter, and the beam diameter in the main scanning direction for one pixel size (this is the maximum beam intensity at rest,
It is defined as the width when decaying to 1 / e ² . ) Is 9
It is 0% or less, preferably 80%. In addition, 400DP
I, when 1 pixel is 63.5 μm, the desirable beam diameter is 50
μm.

Next, the case of setting the UCR amount will be described with reference to FIG. The first to fourth quadrants shown in FIG. 7 are the same as those shown in FIG. 22, and are indicated by the thick line O in the first quadrant.
The D-IDBk characteristic a shows the black component density IDBk of the copy image with respect to the document density OD when the UCR is 100%. With this characteristic a, the black component density IDBk is not reproduced in the low density region b of the document density OD. Also, the characteristic c shown by the thin line is U
The conventional OD-IDBk characteristic in the case of CR50% is shown, and the characteristic a is slid in the horizontal axis direction by OD = 0.5.

The development characteristic of the second quadrant shows the actual image density with respect to the 8-bit LD write signal. When the LD write signal is at a low level, an image is not formed. It is formed.

The printer correction table in the third quadrant shows the gradation conversion processing by the γ conversion processing unit 410 shown in FIG. In the setting of the UCR amount in the present embodiment, a density value for inserting black (UCR start density) and a black UCR amount (reference UCR amount) at a certain reference density (1.0 as the original density value OD of an arbitrary scale in the figure) Set the two values of. The UCR start concentration and the reference UCR amount may be set to arbitrary values by the operation unit or an external controller, or a set of preset numerical values may be selectable.

Explaining this in the fourth quadrant, the start position is set by the value of the intersection (X intercept) with the horizontal axis. The positive and negative values can be set for the UCR start concentration,
When a negative value is set, more black can be put in a portion where the original density is low (bright). On the other hand, the standard UC
The amount of R can set the numerical value in the range of 0-510. Note that when a numerical value larger than "255" is set, the copy image density is reproduced darker (blacker) than the original density.

In the case of processing with 100% UCR, FIG.
In the fourth quadrant, the UCR / color conversion characteristic indicated by the symbol a is selected, and in the third quadrant, the OD-IDBk characteristic indicated by the symbol a is selected by the printer γ conversion table indicated by the symbol a. Therefore, in the low density area b of the original density value OD, the background stain and the show-through can be prevented by the characteristic a.

On the other hand, when the UCR / color conversion characteristic as indicated by the symbol c in the fourth quadrant is selected as the set value of the UCR, if the γ conversion is performed by the printer γ conversion table a in the third quadrant. In the first quadrant, an image having the OD-IDBk characteristic as shown by the code c is reproduced,
There is a difference d between the desired characteristic c '. as a result,
Since the black becomes lighter by the density difference d, it looks like a blank area, and on the other hand, in the area where the original density is larger than the area g, the black looks like abruptly entered, so that, for example, as shown in FIG. It may look like.

Therefore, in the present embodiment, when the UCR / color conversion characteristic c is set, the highlight portion e of the printer γ conversion table a in the third quadrant is proportionally converted like the characteristic c ′. It should be noted that although the table c ′ intersects at the intersection of the horizontal axes (circle in the figure), it indicates that the input value of the vertical axis is “0” and the output value of the vertical axis is “0”. .
By setting in this way, the code c'in the first quadrant
It is possible to obtain the OD-IDBk characteristic indicated by, and thus it is possible to prevent white spots and false contours. In addition,
An example c ′ in the third quadrant of FIG. 7 shows that a tangent line passing through the output value with respect to the input value f of the table a is extrapolated to the input value “0”.

From the UCR 100% setting, the UCR
When lowering the reference value and changing the UCR start position to the high density side, set the black printer γ correction table to UCR10.
When 0% is set, the appearance may be improved by setting the image density to be slightly higher even if it is appropriate. In this case, depending on the set value of UCR, the first and the third
In the quadrant, for example, characteristics having different slopes are selected as indicated by a symbol h.

By the way, in FIG. 7, the development characteristics in the second quadrant and the UCR / color conversion table in the fourth quadrant are shown by straight lines for simplification, but in reality, they are S-shaped and slightly curved downwardly, respectively. And other complex characteristics. In particular, the development characteristics differ depending on the image forming conditions such as the charging potential of the photoconductor, the developing bias at the time of development, the exposure energy of the LD, and also the number of times the developer is used and the surrounding environmental conditions. Therefore,
The characteristics of the printer γ correction table are complicatedly set according to the developing characteristics and UCR / color conversion characteristics.

Next, the influence of fluctuations in the developing characteristics especially when the toner adhesion amount is low will be described. In the third quadrant shown in FIG. 8, there is an initial characteristic a, that is, an image is not formed when the LD write signal is at a low level, and a density proportional to the write signal is formed when the LD write signal is above a certain value. A characteristic b with a decreased value and a characteristic c with an increased value are shown.

In the developing characteristic b, the low density area is easily developed, and the density is likely to appear. Therefore, if the printer γ correction table a is used for correction in this state, the OD-IDBk characteristic at UCR 50% in the first quadrant is from a to b. , The density at the time of entering the black component becomes high, and it seems that black has abruptly entered, so that a pseudo contour occurs. On the other hand, in the developing characteristic c, it is difficult to develop the low density area. Therefore, if the printer γ correction table a is used for correction in this state, the UCR50 in the first quadrant is used.
The OD-IDBk characteristic at the time of% changes from a to c and becomes lower than the desired density by the area e indicated by diagonal lines, resulting in a blank image.

Therefore, by changing the printer γ correction table a to the characteristics b and c having different inclinations for the developing characteristics b and c, it is possible to prevent the pseudo contour and the blank image. The printer γ correction table can be changed by the user or a service person. The output value for the input range f of the printer γ correction table in the low-density area indicated by the frame d in the figure is made variable, and when a pseudo contour or a blank image occurs, the user or the service person corrects the printer γ correction via the operation unit. Select tables b and c.

In this case, the pseudo contour and the blank image are UCR.
It does not occur at 100% and occurs when the UCR amount becomes low. Therefore, for example, when the UCR start concentration is equal to or higher than a predetermined threshold value, the setting of the operation unit is validated. In addition, several kinds of characteristics having different inclinations are prepared in advance with reference to an output value h for a certain input value g (this differs depending on a set printer γ correction table), and the obtained image is visually evaluated. select.

As another method, as shown in the third quadrant of FIG. 9, printer γ correction table characteristics a, b, and c having different inclinations over the entire range may be selected. In addition,
When the printer γ correction table characteristics a, b and c are used, the OD-IDBk characteristics in the first quadrant are a, b and
As shown in c, a pseudo contour and a blank image are not generated.

Further, when the output value for the input range f is made variable as shown in FIG. 8, the threshold value g of the input range f may be settable. This is set by the "UCR movable range" of the operation unit, and when the operator wants to expand the input range f to the UCR 100% side, the "wide" key is selected, and U
If you want to narrow to the CR0% side, select the "narrow" key.

This is particularly effective in the following cases. For example, in the fourth quadrant of FIG. 10, UCR / color conversion characteristics a to d
When one of a plurality of types of characteristics in which the combination of the UCR start density and the UCR reference density is different as shown in (3), the printer γ correction table characteristic is determined to be variable or not. Here, the case where the above correction is performed from the UCR / color conversion characteristics a and b is the case where the “UCR movable range” is widened, and conversely, when the correction is not performed up to the threshold value of the UCR / color conversion characteristic d. Is when the "UCR movable range" is narrowed.

In the example shown in FIG. 10, it is appropriate to set the UCR / color conversion characteristics c and d so that the correction is performed, but if a finer UCR can be set, this By thus varying the threshold value to be corrected, it is possible to prevent the occurrence of false contours and blank images due to variations between machines.

Next, description will be made on the case where white spots are prevented by the control of the printer section. As shown in FIG. 11, this is p density gradation patterns n _i on the photosensitive drum 102.
This is performed by forming (i = 1 to p). First, each surface potential V _Si on the drum 102 on which the density gradation pattern _ni is to be formed is read via the surface potential sensor 132, and then the density gradation pattern n _i (= LD output value).
And the toner concentration V _Pi of each pattern n _i is detected by the optical sensor 136. Therefore, (n ₁ , V _P1 ), (n ₂ , V _P2 ) to (n _P , V _Pp ) are obtained by this method.

The vertical axis of the first quadrant in FIG. 12 is the optical sensor 13
6 shows the output value V _Pi and the horizontal axis shows the LD output value n _i (p = 10). To explain FIG. 12 in the clockwise direction, the vertical axis of the fourth quadrant represents the output value V _Si of the surface potential sensor 132, which represents the light attenuation characteristic of the photoconductor with respect to the LD output value n _i .

The horizontal axis of the third quadrant represents the toner adhesion amount on the photoconductor 102, and represents the developing characteristic with respect to the output value V _Si (or developing potential ΔV) of the surface potential sensor 132. The second quadrant represents the output characteristic V _P of the optical sensor 136 with respect to the toner adhesion amount on the photoconductor 102. This characteristic varies depending on the type of the optical sensor 136, the mounting angle, the distance from the photoconductor, etc. Be present.

Explaining the method of calculating the correction amount, first, in the first quadrant, the output target value V of the optical sensor 136 is calculated.
_The LD output value n _t that matches _Pt is obtained. The output target value V _Pt is selected so as to satisfy the following criteria.

The value is not likely to be affected by the unevenness (rotational unevenness or coating unevenness) on the photosensitive member 102 side when toner is not attached to the photosensitive member 102, and the uneven output on the optical sensor 136 side due to irregular reflection.

The amount of adhesion is such that the toner is developed on the photosensitive member 102 and adheres to the transfer paper. That is, since the reversely charged toner (toner charged to the opposite polarity to the desired charge) is not normally transferred to the transfer paper, the amount of adhesion should be such that it is not affected.

Based on the above, as the toner adhesion amount on the photoconductor 102, the output target value V _Pt of the optical sensor 136 for the adhesion amount of about 0.05 to 0.1 mg / cm ² is selected, and the LD output value n _t is selected. Ask for. As the simplest method for obtaining the approximate value of the LD output value n _t, the set (n _t1 , V _P1 ) which is the closest and larger than the output target value V _Pt from the output values n _i by the 10 detection patterns, and the output target value It can be obtained by interpolating from the closest pair (n _t2 , V _P2 ) smaller than V _Pt .

Then, the above set (n _t1 , V _P1 ) and (n
It is determined by extrapolating n ₀ from which V _P = V _PMAX from _t2 , V _P2 ). However, as the value of n _i is smaller, the detection accuracy of n _t and n ₀ is improved. On the contrary, when the interval is narrow, n _t and n ₀ cannot be detected when the developing characteristics are changed. In the case of 8 bits, it is desirable to form gradation patterns at intervals of about 8 to 16 values. The thus obtained n ₀ is the output value when the input value of the printer γ correction table is “1” as shown in FIG. 13, and n _t is the output value when the input value of the printer γ correction table is a predetermined value. And

By the way, the automatic γ correction amount and the operation portion and the whiteout adjustment amount have the following relationship.

When the automatic UCR correction is off, FIG.
As shown in 4, constant γ correction is always performed according to the whiteout adjustment value. In this γ correction, the output value at a certain input value in the printer γ correction table is used, and the output value is extrapolated to the input value in the printer γ correction table with a constant inclination (inclination at that value or constant inclination).

When the automatic UCR correction is turned on, FIG.
As shown in FIG. 5, the adjustment amount that is the center value of the UCR γ correction is the correction for the automatic correction amount.

Next, switching between image quality modes will be described. As described above, by performing the UCR γ correction in the photo mode, it is possible to prevent the occurrence of white spots and false contours. However, in the automatic image separation mode for automatically separating the text area and the photo area,
As shown in (c), when the automatic UCR correction is turned on, an image (dots) that is not in the original document may be formed along the contour of the character due to a circuit reason for separating the image area.

This is an automatic UC as shown in FIG. 16 (b).
It is not seen when R correction is off and is unique in the automatic image separation mode. Further, this phenomenon is formed not only in black but also in all colors of YMC. Regarding YMC, if the background is set to be slightly thin, this phenomenon will not be seen, but in the case of black, it cannot be solved unless the above-mentioned whiteout correction is reversed from normal and the automatic UCR correction is turned off. . Therefore, the above problem can be solved by automatically turning on or off the UCR γ correction depending on the set image quality mode such as the photo mode and the automatic image separation mode.

Next, a case where the UCR is set through the operation unit will be described with reference to FIG. FIG. 17 shows a liquid crystal screen of the operation unit. In the UCR setting screen of this embodiment, a UCR start density 501 and a UCR reference density 502 are displayed.
And UCR γ adjustment 503 and automatic UCR γ correction 504
, Image separation mode 505, and UCR correction range 506
And the UCR adjustment 507 is settable.

The UCR starting concentration 501 is -0.5 to 1.0.
The UCR reference density 502 can be set in the range of 0 to 512 by the ten-key 508 on the right side of the figure in the range of 0.1 to 0.1. The UCR γ adjustment 503 can be set by moving the arrow “↓” with the soft keys indicated by “dark” and “light” with the default value as the center value, and the automatic UCR γ correction 504 and the image separation mode 505 are turned on. , It can be set by the soft key of OFF. U
When the CR correction range 506 is set to the “wide” side, the correction is performed from the setting of the UCR amount having a large black portion, and when the “narrow” side is set, the correction is performed from the setting of the UCR amount having a small black portion. Can be set.

Next, the operation of the above embodiment will be described with reference to FIGS. First, when the full color mode is selected, the processing shown in FIG. 18 is executed (step S1). When the automatic image separation mode is not selected in the full color mode (step S2), the automatic image separation mode is selected. Even when the correction is set by the operation unit or the external controller (step S3), the UCR γ correction routine shown in FIG. 19 is executed.

In FIG. 19, the UCR set value selected by the operation unit or the external controller (step S1
1) and the UCR correction range data (step S12), and then it is determined whether or not the correction needs to be performed based on the UCR set value and the UCR correction range data (step S13). If correction is required, the correction setting value selected by the operation unit or the external controller is referred to (step S14), and then it is determined whether or not the automatic correction mode is on (step S15).

When the automatic correction mode is ON, the automatic correction amount calculation routine shown in FIG. 20 is executed (step S1).
6) On the other hand, when it is off, the automatic correction amount is set to "0" (step S17). Next, the printer γ correction table is calculated from the correction setting value and the automatic correction value (step S1).
8). In the automatic correction amount calculation routine shown in FIG. 20, a density gradation pattern is created on the photoconductor 102 (step S2).
1), the detection pattern on the photoconductor 102 is set to the optical sensor 13
6 and the potential sensor 139 (step S2
2) The detected data is compared with the reference data stored in the ROM, and the automatic correction amount is obtained based on the data stored in the ROM (step S23).

Finally, the transfer characteristics will be described. Also in this case, similarly to the case of the developing characteristic, the photosensitive drum 102
This can be performed by forming p density gradation patterns n _i (i = 1 to p) on top and transferring them to the intermediate transfer belt 109. First, each surface potential V _Si i on the drum 102 on which the density gradation pattern n _i is to be formed is read via the surface potential sensor 132, and then the density gradation pattern n _i (= LD output value) is read on the drum 102. It is formed on the surface and developed, and this toner image is transferred to the intermediate transfer belt 109,
The optical sensor 308 detects the toner density V _Pi of each pattern n _i . Then, the γ conversion characteristic of the printer γ correction table is changed based on this detection result.

[0094]

As described above, according to the first aspect of the invention, the undercolor removal amount is 100% or the printer γ correction table of the predetermined γ conversion characteristic generated in advance for the single color mode is used as the undercolor removal amount. Since it will be changed if it is less than 100%, UC
It is possible to prevent the occurrence of false contours and blank areas due to changes in the R amount.

According to the second aspect of the invention, the undercolor removal amount is 10
When it is less than 0%, the γ conversion characteristic of a certain density area of the printer γ correction table is changed, so that it is possible to prevent the occurrence of pseudo contours and blank areas due to changes in the UCR amount.

According to the third aspect of the present invention, since the γ conversion characteristic of the printer γ correction table is changed according to the image quality mode, it is possible to prevent a defective image from being generated due to the circuit configuration in the photographic mode or the automatic image separation mode. can do.

According to the fourth aspect of the present invention, since the changed value of the γ conversion characteristic can be adjusted from the operation unit or from the outside, the pseudo contour and the blank area can be adjusted by the service person or the user when the variation is caused by the machine. Can be prevented.

According to the fifth aspect of the present invention, since the density region in which the γ conversion characteristic is changed can be adjusted from the operation unit or from the outside, the pseudo contour can be adjusted by a service person or a user when there are variations due to machines. It is possible to prevent the occurrence of white spots.

According to the sixth aspect of the invention, since the γ conversion characteristic of the printer γ correction table is changed according to the developing characteristic,
It is possible to prevent the occurrence of false contours and blank areas due to variations in the developing characteristics of the printer.

According to the seventh aspect of the invention, since the variation of the developing characteristic is automatically detected, it is possible to automatically prevent the pseudo contour and the blank area from occurring due to the variation of the developing characteristic of the printer.

According to the eighth aspect of the present invention, since the central value of the density region in which the γ conversion characteristic is changed according to the developing characteristic is changed as a reference, the pseudo contour and It is possible to automatically prevent the occurrence of blank areas.

According to the ninth aspect of the invention, since the γ conversion characteristic of the printer γ correction table is changed according to the transfer characteristic,
It is possible to prevent the occurrence of false contours and blank areas due to variations in the transfer characteristics of the printer.

According to the tenth aspect of the invention, since the variation of the transfer characteristic is automatically detected, it is possible to automatically prevent the pseudo contour and the white spot from occurring due to the variation of the transfer characteristic of the printer.

According to the eleventh aspect of the present invention, since the central value of the density region in which the γ conversion characteristic is changed according to the transfer characteristic is changed as a reference, the pseudo contour or the contour due to the variation of the transfer characteristic of the printer which varies depending on the machine. It is possible to automatically prevent the occurrence of blank areas.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an image processing apparatus according to the present invention.

FIG. 2 is a configuration diagram showing an electrophotographic copying machine to which the image processing apparatus of this embodiment is applied.

FIG. 3 is an explanatory diagram showing a control system of the electrophotographic copying machine of FIG.

4 is a block diagram showing a laser modulation circuit of the image processing apparatus of FIG.

5 is an explanatory diagram showing an image formed by the laser modulation circuit in FIG.

FIG. 6 is an explanatory diagram showing a relationship between adjacent pixels in FIG.

FIG. 7 is an explanatory diagram illustrating an example of processing of a γ conversion unit in FIG. 1.

FIG. 8 is an explanatory diagram showing a process of a γ conversion unit when a developing characteristic changes.

FIG. 9 is an explanatory diagram showing another process of the γ conversion unit when the developing characteristic is changed.

FIG. 10 is an explanatory diagram showing UCR / color conversion characteristics when the γ conversion characteristics are changed.

FIG. 11 is an explanatory diagram showing a gradation density pattern on a photoconductor.

FIG. 12 is an explanatory diagram showing a process of detecting development characteristics using the tone density pattern of FIG.

FIG. 13 is an explanatory diagram showing a process of changing the γ conversion characteristic using the development characteristic of FIG.

FIG. 14 is an explanatory diagram showing γ conversion characteristics when the automatic UCR γ correction is off.

FIG. 15 is an explanatory diagram showing a γ conversion characteristic when the automatic UCR γ correction is on.

FIG. 16 is an explanatory diagram showing a copy image in the automatic image separation mode.

FIG. 17 is an explanatory diagram showing an operation screen for adjusting the γ conversion characteristic.

FIG. 18 is a flowchart for explaining an operation in full color mode.

FIG. 19 is a flowchart for explaining the UCR γ correction routine of FIG. 18 in detail.

FIG. 20 is a flow chart for explaining the automatic correction amount calculation routine of FIG. 19 in detail.

FIG. 21 is an explanatory diagram showing UCR processing.

FIG. 22 is an explanatory diagram showing a conventional printer γ correction table when the UCR amount is 100% and 50%.

FIG. 23 is an explanatory diagram showing blank areas and pseudo contours.

[Explanation of symbols]

 102 Photoconductor drum 109 Intermediate transfer belt 105-108 Developing device 136,308 Optical sensor 406 Color conversion-UCR processing circuit 410 γ conversion unit (printer γ correction table) 415 CPU

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H04N 1/46 Z

Claims (11)

[Claims] 1. An undercolor removing unit for removing an undercolor by replacing each color separation signal with a black signal in accordance with an undercolor removal amount, and an undercolor removal amount of 100% or a predetermined value generated in advance for a single color mode. An image comprising: Processing equipment. 2. The γ conversion characteristic changing means changes the γ conversion characteristic of a density area in the printer γ correction table when the undercolor removal amount is less than 100%. Image processing device. 3. The image processing apparatus according to claim 1, wherein the γ conversion characteristic changing unit changes the γ conversion characteristic of the printer γ correction table according to an image quality mode. 4. The change value of the γ conversion characteristic can be adjusted from the operation unit or from the outside.
The image processing device according to any one of 1. 5. The image processing apparatus according to claim 4, wherein the density region in which the γ conversion characteristic is changed can be adjusted from the operation unit or the outside. 6. A development characteristic detecting unit for detecting a development characteristic is further provided, and the γ conversion characteristic changing unit determines the γ conversion characteristic of the printer γ correction table according to the development characteristic detected by the development characteristic detecting unit. The image processing apparatus according to claim 1, wherein the image processing apparatus is changed. 7. The developing characteristic detecting means forms an electrostatic latent image of a gradation density pattern on an image carrier, develops the electrostatic latent image to form a visible image, and 7. The image processing apparatus according to claim 6, wherein the developing characteristic is detected by detecting the density of the visible image of the pattern. 8. The gamma conversion characteristic changing means uses the center value of a density area in which the gamma conversion characteristic is changed according to the development characteristic detected by the development characteristic detecting means as a reference, and the gamma conversion of the printer gamma correction table is performed. The image processing apparatus according to claim 6, wherein the characteristics are changed. 9. A transfer characteristic detecting means for detecting a transfer characteristic of a transfer material onto which a visible image is transferred, wherein the γ conversion characteristic changing means is responsive to the developing characteristic detected by the transfer characteristic detecting means. 9. The image processing apparatus according to claim 1, wherein the gamma conversion characteristic of the printer gamma correction table is changed. 10. The transfer characteristic detecting means forms an electrostatic latent image of a gradation density pattern on an image carrier, develops the electrostatic latent image to form a visible image, and the visible image is formed. 10. The image processing apparatus according to claim 9, wherein the transfer characteristic is transferred to the transfer material, and the transfer characteristic is detected by detecting the density of the visible image of the gradation density pattern. 11. The γ conversion characteristic changing means uses the center value of a density area where the γ conversion characteristic is changed according to the transfer characteristic detected by the transfer characteristic detecting means as a reference, and the γ conversion of the printer γ correction table is performed. The image processing apparatus according to claim 9 or 10, wherein the characteristics are changed.