JPH0686071A - Digital picture forming device - Google Patents

Abstract

PURPOSE:To make the storage capacity of gradation characteristic data small by calculating light emitting correction data by calculating gradation correction curve from a target curve data and basic gradation data each time. CONSTITUTION:In data ROM 203, n original gradation curves before correction are stored by, for instance, 28 pieces by the respective colors of C, M. Y and BK in accordance with the detection level of an AIDC sensor 210 and 13-kinds of settable gradation curves are stored. Besides, as an original gradation curve, a gradation curve obtd. in the case of converting the value of an inputted picture signal to exposure in linear and printing it is stored in each level of the AIDC sensor 210. First of all, a user sets the gradation curve by an operation panel. The gradation vurve can also be set by a tablet editor 232. On the other hand, the original gradation curve corresponding to the detection levels 1 to 28 of the sensor 210 is called. Next, gradation correction data is calculated from the called original gradation curve and the set gradation curve.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to gradation control of a digital image forming apparatus such as a digital printer or a digital copying machine.

[0002]

2. Description of the Related Art In an electrophotographic process in a digital printer, a digital copying machine or the like, laser emission is modulated in accordance with the original reading density (multivalued digital value) to reproduce an image. In image reproduction, the density of the output image is preferably proportional to the original reading density (digital value). The gradation characteristic, which is the relationship between the output image density and the document reading density, is a factor that greatly affects the impression of a pictorial image. Therefore, the input document density is processed to correct the light emission characteristics so that the density of the formed image is proportional to the input document density. This is called gradation correction. In color image reproduction, it is basically required that the output image changes linearly with the density of the original, and therefore, stabilization of the image is required. The gradation characteristics slightly change due to changes in the photoconductor sensitivity, surface potential, developing bias potential, developing characteristics, etc. in the electrophotographic process. Therefore, the image reproduction is stabilized by automatic density control and gradation correction. In the digital image forming apparatus, the density of the read original is
Although it is converted into a multi-valued digital value, non-linear conversion of multi-valued data is easy by a look-up table process, etc., so various stabilization controls are possible in the digital image forming apparatus (for example, according to the applicant). JP-A-3-271
764).

[0003]

However, in reality, since the image stabilization is not perfect, the quality of the reproduced image by the stabilization control may be unsatisfactory for some professional users. Further, as a digital equalizer function, if the user can arbitrarily select the gradation characteristic, the user can realize a desired image tone. Therefore, it is considered that if the user is allowed to positively change the gradation characteristics, the user can be satisfied. In addition,
In order to allow the user to change the gradation characteristics, it is necessary to operate the gradation correction and the image stabilization system in conjunction with each other, and a process control system corresponding to each image generation process is required. Therefore, the present inventor has proposed a digital image forming apparatus in which the user can change the gradation characteristics.
However, such a device has a problem that the number of gradation data to be stored becomes very large as the number of gradations to be realized increases. Therefore, it is desirable to reduce the storage capacity of gradation data.

An object of the present invention is to provide a digital image forming apparatus which allows a user to arbitrarily change the gradation characteristic and to reduce the storage capacity of the gradation characteristic data.

[0005]

A digital image forming apparatus according to the present invention is a digital image forming apparatus for forming an image by irradiating a photoconductor with light whose exposure amount is controlled according to a value of an image signal, A storage unit that stores a basic gradation characteristic that indicates the relationship between the value of the image signal and the density of the formed image, which is obtained when the image signal is converted into the exposure amount with predetermined gradation data, and the target gradation. Based on the setting means for setting the characteristics and the basic gradation characteristics stored in the storage means, a gradation indicating the relationship between the value of the image signal and the exposure amount for realizing the set target gradation characteristics. It is characterized in that it is provided with a calculating means for calculating data and a means for forming an image by converting an image signal to be formed into an exposure amount based on the gradation data obtained by the calculating means.

[0006]

In the digital image forming apparatus according to the present invention,
Electrophotographic image reproduction conditions selected by the image density control system, for example, the photosensitive member surface potential (V _G), the developing bias potential (V _B), a condition related to the laser emission intensity. Further, conditions relating to device variations, device durability changes, environmental changes, and developer lots may be added. These conditions for digital image formation are set so as to stabilize the image, and the process gradation data (basic gradation characteristics) is selected by this image density control system. The process gradation data (basic gradation characteristics) before correction at the time of process control (changes in V _B and V _G ) selected by the image density control system is stored in the storage means. On the other hand, the target gradation curve stored in the second storage means can be set by the user. The present device has a gradation correction calculation function, and calculates gradation data from the set target gradation curve and process gradation data. As the process gradation data before correction, the gradation correction curve (the fourth quadrant of the sensitometry in FIG. 8) is the most preferable, but the output characteristic data (the first quadrant of the sensitometry in FIG. 8) and the attenuation characteristic of the surface potential are used. It may be a combination with development characteristics (second quadrant + third quadrant of sensitometry in FIG. 8). For example, the target gradation curve for calculating the gradation correction characteristic and the process gradation data can be stored by polygonal line approximation in order to reduce the storage capacity. At the time of calculation in the gradation correction means, the original data is restored from the data of the polygonal line approximation, and the value is used for the calculation.

[0007]

Embodiments of the present invention will be described below in the following order with reference to the drawings. (a) Configuration of digital color copying machine (b) Printer control unit and image signal processing (c) Image stabilization (d) Gradation control (e) Gradation selection (f) Other gradation selection (g) Gradation Calculation of correction data (h) Printer control flow (i) Polygonal line approximation of gradation data (j) Use of external storage device

(A) Configuration of Digital Color Copying Machine FIG. 1 is a sectional view showing the overall configuration of a digital color copying machine according to an embodiment of the present invention. The digital color copying machine is roughly divided into an image reader unit 100 that reads an original image and a printer unit 200 that reproduces the image read by the image reader unit. Image reader unit 100
The scanner 10 of FIG.
A rod lens array 13 that collects the reflected light from the original,
And a contact-type CCD that converts condensed light into an electric signal
The sensor 14 is provided. The scanner 10 is driven by the motor 11 at the time of reading an original, moves in the direction of the arrow (sub scanning direction), and scans the original placed on the platen 15. As shown in FIG. 3, the image reader unit 100
Are controlled by the image reader control unit 101. The image reader control unit 101 controls the exposure lamp 12 via the drive I / O 103 according to a position signal from the position detection switch 102 indicating the position of the document on the platen 15, and also drives I / O 103 and parallel I.
The scan motor driver 105 is controlled via the / O 104. The scan motor 11 is driven by the scan motor driver 105.

Returning to FIG. 1 and continuing the description, the image of the original surface illuminated by the exposure lamp 12 is photoelectrically converted by the CCD sensor 14. The red (R), green (G), and blue (B) multi-valued electrical signals obtained by the CCD sensor 14 are
By the read signal processing unit 20, yellow (Y), magenta
(M), cyan (C), and black (K) are converted into 8-bit gradation data and output to the printer control unit 201. As shown in FIG. 3, the image control unit 106 includes a CCD
The color image sensor 14 and the image signal processing unit 20 are connected to each other via a bus. The image signal from the CCD color image sensor 14 is input to the image signal processing unit 20 and processed. As shown in FIG. 2, in the image signal processing unit 20, the image signal photoelectrically converted by the CCD sensor 14 is converted into multi-valued digital image data of R, G, B by the A / D converter 21, To
Shading correction is performed in the shading correction circuit 22. Since the shading-corrected image data is the reflected light data of the document, the log conversion circuit 23 performs log conversion to convert it into actual image density data. Further, the undercolor removal / blackening circuit 24 removes an unnecessary black color and generates true black data K from R, G, B data. Then, the masking processing circuit 25 converts the data of the three colors of R, G and B into the data of the three colors of Y, M and C. After the density correction circuit 26 performs density correction processing for multiplying the Y, M, and C data thus converted by a predetermined coefficient, the spatial frequency correction processing is performed in the spatial frequency correction circuit 27, and then the image is displayed in the printer control unit 201. Output as a density signal.

Returning to FIG. 1, in the printer section 200, the print head section 31 performs gradation correction according to the gradation characteristics of the photoconductor on the input gradation data, and then The corrected image data is D / A converted to generate a laser diode drive signal, and the semiconductor laser 264 (FIG. 4) is caused to emit light by this drive signal. The laser beam generated from the print head unit 31 by modulating the emission intensity corresponding to the gradation data passes through the polygon mirror,
Photoreceptor drum 41 that is rotationally driven via reflecting mirror 37
To expose. The photoconductor drum 41 is irradiated with an eraser lamp 42 before being exposed for each copy, and is uniformly charged by a charging charger 43. When exposed in this state, an electrostatic latent image of the original is formed on the photosensitive drum 41. Only one of the cyan, magenta, yellow, and black toner developing devices 45a to 45d is selected to develop the electrostatic latent image on the photosensitive drum 41. On the other hand, the copy paper is fed from the paper cassette 50 and wound around the transfer drum 51. The developed toner image is transferred to copy paper by the transfer charger 46. The above printing process is repeated for four colors of yellow (Y), magenta (M), cyan (C), and black (K). At this time, the photosensitive drum 41 and the transfer drum 51
The scanner 10 repeats the scanning operation in synchronization with the above operation. After that, the copy paper is separated from the transfer drum 51 by operating the separation claw 47, is fixed through the fixing device 48, and is discharged to the paper discharge tray 49.

(B) Printer Control Unit and Image Signal Processing FIGS. 3 and 4 are block diagrams of the entire control system of the digital color copying machine. The printer unit 200 includes a printer control unit 201 that controls general print operations. A printer control unit 201 including a CPU includes a control ROM 202 storing a control program and a data ROM 20 storing various data (gradation correction data and the like).
3 and RAM 204 are connected. Printer control unit 2
Reference numeral 01 controls the printing operation according to the data in the ROM and RAM. The printer control unit 201 includes a V ₀ sensor 44, an AIDC sensor 210, and an ATDC sensor 21.
1, analog signals from the temperature sensor 212 and the humidity sensor 213, and signals from the fog input switch 214, the color balance switch 216, and the photoconductor lot switch 218 are input. Here, the V ₀ sensor 44 detects the potential on the surface of the photoconductor. In addition, the AIDC sensor 210 is
For each color, the toner amount of the reference toner image on the photoconductor developed under the standard image forming conditions (photoconductor surface potential V ₀ , development bias potential V _B , exposure amount) is detected, and V ₀ , V _B , and exposure are performed. Set amount to optimum. In addition, from a panel CPU 190 that receives a key input from the operation panel 221 described later,
Various data is input to the printer control unit 201. Similarly, input values in the tablet editor 232 (see FIG. 13), which will be described in detail later, are also input to the printer control unit 201 via the panel CPU 190.

The printer control unit 201 controls the copy control unit 231 according to the contents of the control ROM 202 by various input data, and further, the grid potential V _{G of the} charger 43 via the parallel I / O 241 and the drive I / O 242. High voltage unit 24 for generating V _G
3 and controls the V _B generated high-voltage unit 244 that generates a developing bias voltage V _B of the developing unit 45a to 45d. The printer control unit 201 also includes the image reader unit 100.
The image data processing unit 20 is connected to the image data processing unit 20 via an image data bus, and data in which a gradation correction table is stored, as will be described later, based on the image density signal input via the image data bus. The light emission level is determined by referring to the contents of the ROM 203, and the drive I / O 261 and parallel I
The semiconductor laser driver 263 is controlled via / O262. The semiconductor laser 264 is driven to emit light by the semiconductor laser driver 263. The gradation expression is
This is performed by modulating the emission intensity of the semiconductor laser 264.

FIG. 5 shows the appearance of the operation panel 221.
Here, the LCD display unit 301 displays the mode set by the operation, explains the operation procedure to the user, and displays the status such as the jam display and the copy operation display. The panel reset key 302 is a key for initializing all modes. A key 303 is a ten-key for setting the number of copies and a clear key for clearing. The start key 304 is a key for instructing the start of copying. Image quality menu key 305
When is pressed, a menu for image quality adjustment is displayed on the LCD display unit 301. The user can adjust the image quality by operating this. Create menu key 30
When 6 is pressed, the LCD display unit 301 displays a setting menu for various create functions. By operating this, the user can set various functions and modes. The enter key 307 is used as an enter key and a next screen key in the operation screens of the image quality menu and the create menu described above. River ski 30
Reference numeral 8 is used as a cancel key and a previous screen key.
A cursor key 309 is a key for selecting a cursor on a menu and setting a level on each operation screen. The multifunction key 310 is used for the LCD display unit 301.
This is a key whose meaning can be changed according to each selection menu displayed in. This panel has IC card insertion ports 311 and 312 so that up to two IC cards can be inserted at the same time. A program call / registration key 313 and an IC card ejection key 314 are provided corresponding to each insertion slot. The bar code reader pen 315
With, it is possible to scan a barcode and set various modes.

FIG. 6 is a block diagram of image data processing in the printer control unit 201. Here, the image data (8 bits) from the image signal processing unit 20 is input to the first-in / first-out memory (hereinafter referred to as a FIFO memory) 252 via the interface unit 251. The FIFO memory 252 is a line buffer memory capable of storing gradation data of an image for a predetermined number of rows in the main scanning direction, and absorbs a difference in operating clock frequency between the image reader unit 100 and the printer unit 200. It is provided to do. The data in the FIFO memory 252 is then input to the γ correction unit 253. Data ROM 2
The various γ correction data of 03 is sent to the γ correction unit 253 by the printer control CPU 250, and the γ correction unit 253 corrects the input data and sends the emission level to the D / A conversion unit 254. The data ROM 203 stores various gradation correction data. The analog voltage converted from the light emission level (digital value) by the D / A converter 254 is
In the gain switching unit 255, the switches SW1, SW2, ... (corresponding to different powers P1, P2, ...) Are switched and set by the gain switching signal generation circuit unit 256 in accordance with the gain setting value from the printer control unit 201. After being amplified by the gain, it is sent to the semiconductor laser driver 263 via the drive I / O 261, and the semiconductor laser 26
4 is made to emit light with the light intensity of that value. On the other hand, the printer control CPU 250 sends a signal to the clock switching circuit 257 to select the clock generating circuit 258 or 259, and to output the clock signal generated by the clock generating circuit in parallel I.
It is sent to the semiconductor laser driver 263 via / O262 and the image data is modulated by the clock. By selecting the clock generation circuit, the duty ratio (pattern) of the light emission signal is changed (for example, 100% and 80%), and the reproducibility of gradation can be selected. When the duty ratio is 100%, it corresponds to normal light emission, but when the duty ratio is 80%, light emission is performed during 80% of the normal light emission period.

(C) Image Stabilization Gradation characteristics are basically the sensitivity characteristics of the photoconductor, the development characteristics,
Also, it is determined by setting the charging potential V ₀ , the developing bias potential V _B , and the attenuation potential V _S of the electrostatic latent image. An image that is basically formed in color image reproduction (output image)
Is required to change linearly with the original density.
For this reason, stabilization of the image is required. Although the present invention allows the user to select the gradation characteristic, the gradation control system operates in conjunction with the image stabilization system to constantly supply the selected gradation characteristic in a stable manner. Must be one.

Before describing image stabilization, a brief overview of the electrophotographic process is provided. FIG. 7 schematically shows the arrangement of the charging charger 43 and the developing device 45r around the photosensitive drum 41. Here, a charging charger 43 having a discharge potential V _G is installed opposite to the photoconductor 41. The grid of the charger 43 includes a grid potential generation unit 24.
3, the negative grid potential V _G is applied. The relationship between the grid potential V _G and the surface potential V _O of the photosensitive drum is
Since it can be regarded that V _O = V _G , the potential V _{0 on the} surface of the photosensitive drum 41 can be controlled by the grid potential V _G. The surface potential V _O is detected by a V _O sensor 44 which is a surface potential meter. First, before laser exposure, a negative surface potential V _O is applied to the photosensitive drum 41 by the charging charger 43, and a low negative development bias potential V _O is applied to the roller of the developing device 45r by the developing bias generating unit 244. _B (| V _B | <| V _O |) is given. That is, the developing sleeve potential of the developing device 45r is V _B. Due to the laser exposure, the potential of the irradiation position on the photosensitive drum 41 is lowered and the surface potential V _{O is changed} to the attenuation potential V _S of the electrostatic latent image. When the decay potential V _S becomes lower than the developing bias potential V _B, the negatively charged toner carried to the sleeve surface of the developing device 45r adheres onto the photosensitive drum 41.

Here, if the difference between V _O and V _B is too large, carrier adhesion to the non-exposed portion occurs, and if it is too small, toner fog occurs, so it is neither too large nor too small. The toner adhesion amount increases as the development potential difference ΔV = | V _B −V _S | increases. On the other hand, the attenuation potential V _S changes as the surface potential V _O changes even with the same exposure amount. Therefore, if the surface potential V _O and the developing bias potential V _B are changed while maintaining the difference between V _O and V _B within a certain range, for example, keeping the difference constant, the difference between V _B and V _S changes. Therefore, the toner adhesion amount can be changed and the density can be controlled (see, for example, Japanese Patent Laid-Open No. 3-271764). Further, the gain of laser emission is determined by the V ₀ sensor 44.
It is switched according to the sensitivity information of the photoconductor obtained by.

Further, since the electrophotographic process handles static electricity, it is affected by the environment. Therefore, the development characteristics and the photoreceptor characteristics mainly change, and this compensation is necessary. Therefore, for each of the four colors, the amount of toner adhering to the reference toner image developed under the standard image forming condition is calculated as AI.
It is detected by the DC sensor 210. That is, a reference toner image, which is the basis of density control, is formed outside the image area on the photoconductor drum 41, and an AI provided near the photoconductor drum 41 is formed.
The DC sensor 210 detects the toner amount. In accordance with this detected value, the developing bias potential V _B and the grid potential V _G are changed, the developing potential difference (ΔV) is selected, and automatic density control for keeping the toner adhesion amount at the maximum density level constant is performed. You can It is also necessary to remove the background fog.

(D) Gradation Control Next, the standard gradation correction in which the value of the input image signal and the density of the actually printed image are linear will be described.
Particularly in color images, basically linear characteristics are required. FIG. 8 is a diagram of sensitometry in reversal development. The value of the image signal input from the image reader (image input level OD) is output linearly with respect to the original density. When the laser emission amount P (Lx) is linearly changed with respect to this image input level value Lx, gradation characteristics (image density actually printed (output image density ID)
To the image input level OD) becomes non-linear.
The surface potential V _S of the photosensitive member is attenuated in response to the laser emission. That is, the surface potential gradually and non-linearly attenuates as the laser emission amount increases. The developing bias potential V _B is set with respect to the photoconductor charging potential V ₀ so as to remove the background fog, and the developing potential difference (V _B −V
_The output image density ID (V _S ) is obtained corresponding to _S (Lx), but this developing characteristic also exhibits non-linearity. Therefore, instead of linearly changing the laser emission amount P, the nonlinearity of each of the photoconductor characteristic and the developing characteristic is corrected so that the output image density becomes linear with respect to the input level, which will be described later. Thus, the light emission characteristic is corrected non-linearly. This allows the output image density to be linear with the image input level.

FIG. 9 is a diagram showing how to obtain the gradation correction data of the standard gradation characteristic that makes the output image density ID linear with the image input level OD. When the image input data is directly converted without conversion and exposed by linearly converting it into the laser exposure amount as shown in the lower side, the gradation curve (the relationship between the image input level and the output image density) shown in the upper side is as shown by the broken line. It becomes non-linear. The emission characteristic for converting this to the target gradation curve shown by the solid line is the curve shown by the solid line in the lower part of the figure. That is, point A on the dotted line in the figure (image input level L
_To convert ₁ ) to point A'on the solid line, output the laser exposure amount P (L ₁ ) at point A "on the broken line having the same output image density as point A'corresponding to the input image data L _1. Similarly,
To convert point B on the dotted line to point B'on the target solid line,
The laser exposure amount P (L ₂ ) at the point B ″ on the broken line having the same output image density as the point B ′ may be output. In this way, the laser exposure amount with respect to the image input level, that is, the gradation correction data is obtained.

(E) Gradation Selection In the above, it has been explained that a standard gradation curve that outputs the image density linearly with respect to the input image data is realized in order to obtain an output that is faithful to the original image. In this embodiment, the user can select a different gradation curve in addition to the standard linear gradation curve. In the selection of the gradation curve, in the present embodiment, in order to facilitate the selection by the user, the shape of the gradation curve and the degree of change of the shape are designated by two levels of input.

FIG. 10 schematically shows the concept of the shape of the target gradation curve and the degree of shape change. The following four types (a) to (d) can be considered as combinations of selection of the gradation curve, based on the relative relationship with the standard gradation curve.
Also, an infinite gradation curve can be realized by changing the degree of change of each shape. In the low density enhancement type (a), the gradation curve is convex upward. Using this gradation curve,
You can get a solid feeling. In the high density enhancement type (b), the gradation curve is made to be convex downward. A pastel feeling can be obtained by using this gradation curve. In addition, it is possible to correct a totally dark image. In the halftone density portion emphasizing type (c), the gradation curve is largely convex on the high level side, but is small convex on the low level side. Using this gradation curve gives a feeling of “colorful” or “sharp”. In the halftone density portion non-emphasized type (d), the gradation curve is slightly convex on the low level side, but is largely convex on the high level side. Using this gradation curve gives a feeling of "moist" or "smooth". The point where the gradation curves of the halftone density area emphasis type (c) and the halftone density area non-emphasized type (d) intersect with a linear straight line may be the same as in the case of the standard gradation curve (FIG. 8), for example. .

Next, a specific method of selecting these gradation curves will be described. First, the operation panel 2 shown in FIG.
The selection of the gradation curve by 21 will be described. In the setting of the operation panel 221, selection is made by two-step input of selection of a gradation curve and degree of change of its shape. First, key 3
The gradation curve selection screen is displayed on the display unit 3 by the operation of 06.
Call 01. FIG. 11 is a diagram of a selection screen displayed on the display unit 301. In the selection screen, the standard gradation curve and each kind of gradation curve shown in FIG. 10 represent the characteristics of the gradation curve (“standard”, “smooth”, “colorful”, “bright”). , "Heavy").
To select a desired gradation curve from the displayed five gradation curves, a key 310 provided below the display unit 301 is used.
Selected by. When one of the gradation curves is selected by the key 310, next, as shown in FIG. 12, the words (“weak”, “standard”, “strong”) indicating the degree of change of the gradation curve are displayed. It is displayed on 301. The user sets the degree of change by selecting one with the key 310 as in the previous case. That is,
Three levels of change can be selected, and "strong"
Is selected, the gradation curve shape of the type selected in FIG. 11 is selected, and the gradation curve farthest from the standard gradation curve shown in FIG. 10 is selected. The closest gradation curve is selected, and when "Standard" is selected, the intermediate gradation curve is selected.

In the above selection, after the desired gradation curve type is selected, a display prompting the input of the gradation curve level is output. When the level is not input, the level "0" is set as the standard target. The curve is selected. The gradation curve can also be selected using the tablet editor 232 shown in FIG. FIG. 13 shows the appearance of the tablet editor 232. In the coordinate input section 320, by pointing with the coordinate input pen 321, the position on the original can be specified. As a result, partial editing can be designated among various editing functions. Also, this coordinate input unit 3
The group 20 has mode setting key groups 322 and 323. That is, the mode setting keys 322 and 323, the gradation curve setting unit 324 and the color palette 325 are printed on the coordinate input unit 320, and the setting function causes
It can be used as a mode setting part or level setting part. The mode setting keys 322 and 323 are keys for setting various modes, respectively, and can be set by pressing the coordinate input pen 321. Therefore, it is possible to select the type and degree of the gradation curve using the key groups 322 and 323.

(F) Other gradation selection In the above, a method of selecting a standard gradation curve and another gradation curve by designating the shape and the degree of change of the curve has been described. However, setting the gradation curve is not always easy for the user. Therefore, it is necessary to facilitate the setting by the user. Various other gradation curve setting methods will be described below. Figure 1
In the example shown in FIG. 4, the shape of the gradation curve can be switched between the high density side (H) and the low density side (L) of the input image density (OD). That is, the gradation characteristics can be easily selected by adjusting the low density level and the high density level that the user can easily imagine. FIG. 14 is an external view of a tablet editor 140 that can be used instead of the tablet editor 232 of FIG. 13 described above. As shown in FIG. 14, in the tablet editor 140, dials 144 and 1 are provided on the lower side of the liquid crystal panel 142 displaying the gradation curve, corresponding to high density (H) and low density (L), respectively.
46 is provided. Set the dials 144 and 146 to + (H),
The gradation curve is selected by setting one of the three levels of 0 and-(L). 15 to 15 show gradation curves selected by this dial setting (see Table 1).

[Table 1] Similarly, as shown in FIG. 16, on the liquid crystal panel 142 ′,
Lever 144 ', 1 instead of dials 144, 146
46 'may be provided. Move the lever-144 'and 146' up and down to move the gradation curve at high and low density levels (+,
0,-) can be set.

FIG. 17 shows another tablet editor 1
In the gradation curve setting method shown in FIG. 17, the tablet editor 150 is provided with keys 152, 154, and 156 for setting the center, low density, and high density. The center key 152 is a key for moving the density (center point) P intersecting the broken line showing the linear relationship of the gradation curve to the left and right. The low density key 154 is a key for moving up and down the curve on the low density side from the center point. The high density key 156 is a key for moving up and down the curve on the high density side from the center point. here,
For low concentration and high concentration, ± N steps can be set around 0.

FIG. 18 shows another tablet editor 1
In the gradation curve setting method shown in FIG. 18 and shown in FIG. 18, the gradation curve can be freely set on the liquid crystal panel 160 using a point pen (not shown). That is, it is possible to set arbitrary break point coordinates 162 between the maximum value of the document density and 0, and in the example of the figure, it is set at four points. Here, the break point means a contact point connecting the break lines, and the break points (including both ends) are approximated by a break line.

(G) Calculation of gradation correction data In this embodiment, the toner adhesion amount detected by the AIDC sensor 210 is hierarchically divided into 28 levels, and the developing bias potential V _B and the photosensitivity are classified according to this level. Body surface potential V _O
(Grit potential V _G of charging charger 43) is set. Therefore, since the image forming condition is changed according to the level of the AIDC sensor 210, gradation correction data under the image forming condition corresponding to each level is required. When a plurality of gradation curves can be selected, for example, 4 × shown in FIG.
A total of 13 types of gradation correction curves and standard gradation correction curves
When it is possible to select different types of gradation correction curves, it is necessary to store the gradation correction data corresponding to the levels of Y, M, C, K, and 28 of the print color for each gradation correction curve. That is, it is necessary to store 13 × 28 × 4 = 1456 sets of gradation correction data. However, in order to store all such a large number of gradation correction data, a large storage capacity is required even if the polygonal line approximation is used as described later. Therefore, in the present embodiment, only a small number of basic gradation curves (original gradation curves) are stored, and gradation correction data is calculated each time in accordance with the shape of the selected gradation curve. As a result, it is not necessary to store all the gradation correction data, and the memory capacity can be reduced. If these data are stored by the polygonal line approximation, the storage capacity can be further reduced.

FIG. 19 is a diagram showing the concept of gradation control of this embodiment. In the data ROM 203, 28 original gradation curves before correction are stored for each color of C, M, Y, and BK corresponding to the detection level of the AIDC sensor 210, and 4 × 3 + 1 = shown in FIG. 13 kinds of settable gradation curves are also stored. In this embodiment, the AIDC sensor 210 is used as the original gradation curve.
At each level, the gradation curve when the value of the input image signal is linearly converted into the exposure amount and printing is performed is stored. First, (A) the user operates the operation panel 2
The gradation curve is set by 21. The setting may be performed by the tablet editor 232. on the other hand,
(B) Call the original tone curve corresponding to the detection value levels 1-28 of the AIDC sensor 210. Next, (C) the gradation correction data is calculated from the called original gradation curve and the set gradation curve in the same manner as in the case of the standard gradation curve of FIG.

FIG. 20 is a graph showing the procedure of calculating this gradation correction data. In FIG. 20, a certain AIDC
The original gradation curve at the level is indicated by. Is a non-linear gradation curve when the laser exposure amount is linear with respect to the image input level OD (a straight line indicated by a dotted line on the lower side), and R
It is called by OM203. Further, is a gradation curve set by the operator from the operation panel 221. Next, the calculation procedure of the gradation correction data for realizing the set gradation curve using these two gradation curves will be described. The case of the image input level L11 will be described. When the image input level L11 is given, it is necessary to print with the image density indicated by the point C ′ in the set gradation curve. It is understood that the point on the original gradation curve that reproduces the same image density as this point C ′ is point C ″, and this point C ″ is reproduced when the laser exposure amount is P (L11). Therefore, the image input level L
When 11 is given, if printing is performed with a laser exposure amount of P (L11), printing is performed with the gradation characteristics indicated by the set gradation curve. In this way, other image input levels are also converted, and tone correction data showing the relationship between the image input level and the laser exposure amount for realizing the set tone curve is calculated. (D) The correction curve thus obtained is stored in the RAM 20.
4 and is reused when the same gradation setting is performed. In the above description, the case where the gradation curve is set from the operation panel 221 has been described, but in other cases, for example, even in the case of the editors 232, 140, 150, 160, the gradation curve should be calculated from the original gradation curve. Thus, gradation correction data can be obtained.

(H) Printer Control Flow FIG. 21 shows the main flow of the printer control unit 201. First, after performing initial settings (S1), the operation panel 2
21 is performed (S2, see FIG. 22), and the operation waits until the start key 304 of the operation panel 221 is pressed (S3). When the start key is pressed, sensor input processing is performed (S4). Next, the operation panel 221
Input signals from various switches of the printer control unit 201
It is taken into the internal RAM (S5). Next, the gain of the gain switching circuit 255 of FIG. 6 is switched according to the set values obtained in steps S4 and S5, and the semiconductor laser 264
The light intensity level of is set (S6).

Next, the AIDC measurement process is executed, and AI
The toner amount can be obtained by the DC sensor 210 (S
7). In this AIDC process, a reference toner image is formed on a photoconductor, the image reproduction density is detected by the AIDC sensor 210 based on the toner adhesion amount of the image pattern, and is captured in the RAM 204 in the printer control unit 201. Next, based on the density detection level corresponding to the measured toner adhesion amount, the grid potential correction value, the developing bias potential correction value, and the original gradation curve which are set in advance corresponding to this level are selected (S8). ). Next, the gradation correction data is calculated based on the original gradation curve selected in step S8 (S9). Next, the printing operation by the known electrophotographic method is completed based on the grid potential V _G and the developing bias potential V _B selected in step S8 and the gradation correction data obtained by the calculation in step S9. Up to (S10, S11). In the case of a color image, one copy is sequentially processed in the order of cyan, magenta, yellow and black. Therefore, the main flow described above is repeated for each color.

FIG. 22 shows a flow of key input processing (FIG. 21S2). First, the input of the shape of the gradation curve is received (S21), and then the input of the degree of the shape is received (S22). Finally, color balance switch 21
6, the color balance and the density adjustment value are input from the operation panel 221 (S23), and the process returns.

FIG. 23 shows a flow of V _G , V _B and gradation data selection (FIG. 21S8). The grid voltage V _G and the developing bias voltage V _B are selected based on the detection value level of the AIDC sensor 210 (S41). And, (V _G, V _B)
The original gradation curve corresponding to is selected (S42), and the process returns.

(I) Polygonal line approximation of gradation data As described above, in this embodiment, the AIDC sensor 2 is used.
A large amount of original gradation curve is required for 10 levels. In this embodiment, 8-bit (0
Although the data of (1) to (255) is used, the data is treated as 10-bit (0 to 1023) data in order to maintain accuracy. To store the gradation curve as a look-up table for such gradation correction conversion, a large memory capacity is required.

Therefore, in this embodiment, the capacity can be reduced by storing the basic original gradation curve and the selectable gradation curve using the polygonal line approximation. Further, the memory capacity can be further reduced if the gradation correction data calculated from the original gradation curve for the selected gradation curve is also stored by using the polygonal line approximation. The polygonal line approximation does not store all the data corresponding to the image input level (0 to 255), but approximates it by connecting 10 to 20 straight lines in a polygonal line shape. In that case, the coverage coefficient X (N) of each straight line (N =
1 to 10), its inclination coefficient a (N), and intercept coefficient b
A curve is stored in the ROM 203 as (N).
At the time of calculation, for the image input level (0 to 255),
First, the gradation correction data (corresponding to inputs 0 to 255) for realizing the set gradation curve from the original gradation curve and the set gradation curve stored in the polygonal line are sequentially calculated as described above. Then, the data is temporarily stored in the RAM 204 as data corresponding to the inputs 0 to 255. This may be used as the gradation correction data as it is. However, if this is also made into a shape approximated to a polygonal line, the memory capacity can be reduced at the time of saving. Therefore, it is desirable that the calculated data be formed into a polygonal line by using the coordinates determined based on the absolute value of the second-order differentiated value.

In FIG. 24, the light emission data f (x) with respect to the image input level (X) is shown on the upper side, and the primary differential value f ′ and the secondary differential value f ″ thereof are shown at the center and the lower side. The value f ″ may be called, so to speak, the rate of change of the slope of f (x), and it can be said that a portion where the value of f ″ (x) is large has a large change in the slope of f (x). It is possible to improve the accuracy of the actual gradation correction by performing the polygonal line approximation in the form of giving priority to this part.For example, in FIG.
A region where f ″ ≦ q and f ″ ≧ p is determined. Then, for example, when the number of contact points in the polygonal line approximation is set to 10 (not including 0), the priority is set to a predetermined priority such as 4 points in the 0 to R area, 4 points in the S to 255 area, and 2 other points. The number of coordinate points is allocated based on the
First, 0 to R are divided into 5 equal parts, and X = S, S + (255-
S) / 3, S + 2 × (255-S) / 3, 255, and so on.
X = R + (S−R / 3), 1 of R + (2 × S−R / 3)
0 points are decided. A polygonal line approximation formula is created by connecting them with a straight line from the low level side in sequence with the origin 0, and obtaining the corresponding input data level range X (N), slope a (N), and intercept b (N). These are stored in RAM. When the copying operation is started, the exposure output level is obtained from the corresponding a (N) and b (N) according to the input density data from the image reader unit, and the laser is output according to the output. It should be noted that the above-mentioned priority and how to take p and q may be determined according to the number of polygonal line coordinate points,
Further, the highlight part may be given special priority.
These may be set separately for each model.

When determining the second derivative, p and q may be set separately, or only p may be determined as | f ″ |. Corresponding to a predetermined score according to the priority. I explained the coordinate determination that I did, but in addition to this, 0
It is also possible to divide 255 into a region larger than the final contact number and determine from the coordinates with a large second derivative f ″ at the corresponding position. For example, the value of f ″ is calculated for every 4 (F ″ (4), f ″ (8), f ″ (1
2), ... f ″ (252)) In order from the largest of them, the origin 0 and the 9 points (when approximated by 10 broken lines) excluding the Max 255 level are determined, and 0 and 255 are determined.
It is also possible to add a line and create a polygonal line. The polygonal line approximation value created in this way is stored in the RAM.
By storing the same, the same original gradation curve can be repeatedly used when selected. Further, the original gradation curve is approximated by 20 polygonal lines (20 points excluding the number of contact points 0) and stored in the ROM, whereas the calculated gradation correction data is approximated by 10 polygonal lines. In this way, making the number of coordinate points of the original gradation curve larger than the number of coordinate points of the gradation correction data which is the actual calculation result leads to improvement in calculation accuracy.

(J) Use of external storage device The gradation curve can be input from an external storage device such as an IC card. The operation panel 221 shown in FIG. 5 has two ICs.
The card can be inserted into the insertion ports 311 and 312. The memory configuration of the IC card is configured according to the type of main body. 25 and 26 show the external appearance and internal configuration of the IC card.
Here, the conductive portion 131 is printed on the IC card body 130. Power can be supplied from the outside through the conductive portion 131, or data can be transmitted and received by a serial interface with the outside. The control CPU 132 in the IC card is the E ² PROM 133
Management and interface control with the outside. E
^{2 The} data is held in the PROM 133.

FIG. 27 shows the structure of the internal data 134 stored in the IC card. The internal data 134 is divided into blocks 135 of variable length. Then, program data can be written in each block. With this, it is possible to register a plurality of programs in one IC card. 1 block 135
Is composed of various data as described below. That is, in the "header", the program registration /
Unregistered, contains a code indicating the type of program. "Program name" contains the user registration name of the program,
Based on this, the user can easily know the program creator, the purpose of the program, and the like. The "model code" contains the code of the model that created the program.
The "model characteristic information" contains more detailed characteristic information of the model for which the program is created in order to use the IC card between different models. The "various mode memory" stores various copy modes that can be set on the operation panel. By reading this, the mode setting state when this program was created can be faithfully reproduced. As an example, a gradation curve is written in the mode memory, and this gradation curve includes an arbitrary gradation curve 136 and R of the copying machine main body.
One or both of a curve number 137 indicating which gradation curve to select from among several kinds of gradation curves built in the OM 203 are included. Since the model code is also stored in this way, it becomes possible to store the code information of the machine that can be inserted and the gradation curve correction information corresponding to each machine in the IC card. For this reason,
Gradation data can be supplied to multiple machines.

Further, in addition to the gradation curve stored in the data ROM 203 of the main body, an additional selectable gradation curve is stored in the IC card, and by inserting the IC card, I
The additional gradation curve stored in the C card can be displayed on the operation panel. A large storage capacity is required to store a large number of gradation curves, but by using an IC card that is a memory external to the machine,
The number of gradation curves can be increased. At this time, the gradation curve is the same as the curve stored in the data ROM 203 of the main body and the IC.
It is possible to select from both the curves stored in the card. By storing different gradation curves in a plurality of IC cards, the number of gradation curves can be further increased. Also, IC
The card may be provided with a RAM, and this RAM may be provided with a portion for storing the gradation curve data created by the main body. As a result, by storing the gradation curve newly created by the editor 160 or the like described above in the RAM of the IC card, a custom card can be obtained.

FIG. 28 shows the configuration of the control system of the operation panel 221. The panel CPU 190 controls the operation panel 221 while controlling the various input / output devices 191 to 198. The copy mode set on the operation panel 221 is sent as an instruction signal to the printer control unit 201 through the interface. The operation keys 302 to 310, 313, 314 on the operation panel form a key matrix, and the ON / OFF state is read by scanning the key matrix. The LCD interface 191 includes an LCD controller and a video RA.
M, character generator, etc., CP
The display data set from U190 is displayed on the L of the display unit 301.
The data is converted into data to be displayed on the CD module 192 and displayed on the LCD module 192. The IC card interface unit 193 controls the IC card units (IC card readers / writers) 194 and 195 corresponding to the two IC card insertion ports 311, 312, detects the insertion of the IC card, and ejects the IC card. Since data is transmitted and received to and from the IC card through the serial interface, the IC card interface unit 193
The interface control is performed to reduce the load on the CPU 190. Tablet interface unit 196
Performs data transmission / reception control with the above-mentioned tablet editor 232 or other editors 140, 150, 160. Bar code interface section 197
Reads the data read by the barcode reader pen 315, analyzes the data sent, and converts the data into a data format that the CPU 190 can easily process.

Next, the registration of the gradation curve in the IC card will be described. FIG. 29 shows a screen of the display unit 301 for calling the data programmed in the IC card. This screen is displayed when an IC card is inserted and the program call key (not shown) on the operation panel 221.
Displayed when is pressed. And in this screen,
Of all 8 types of programs that can be registered in the IC card,
Currently registered programs are displayed with numbers and titles on the left side of the screen, and conversely, only frames are displayed for unregistered programs. Then, when calling the program, the selection cursor may be moved to the desired place by the cursor key 309, and the enter key 307 of the operation panel 221 may be pressed. Next, in the case of registering the program in the IC card, select "program registration" on the right side of the screen in FIG. 29 and press the enter key 307. Then, the title input screen shown in FIG. 30 is displayed. When a title is input on this screen, "End" is selected at the end and the enter key 307 is pressed, the program registration location selection screen shown in FIG. 31 is displayed. Here, when the selection cursor is moved to the place to be registered and the enter key 307 is pressed, the number and title are added to that place, indicating that the program registration is completed. Here, the contents to be programmed are all the mode setting contents of the copying machine at that time. Then, when the program registered in that program is called next time, the completely same state as when the program was registered can be reproduced. Further, in this embodiment, 2
One IC card can be used at the same time, but which I
The method of calling / registering the program is the same for the C card.

Next, selection of gradation data from the IC card will be described. FIG. 32 shows a gradation curve selection screen when one IC card is set. Eight kinds of gradation curves created by the user can be registered for each program in the IC card. Then, on this screen, the user can select from a total of nine types of gradation curves, four of which and five of the main body standard. FIG. 33 shows a gradation curve selection screen when two IC cards are set. On this screen, four types of gradation curves registered in each IC card are displayed in a menu, and a gradation curve can be selected from them.

FIG. 34 shows an input example using a bar code. The barcode shown in FIG. 34 is attached from the left under samples of five types of image quality, such as flowers, people, fruits, color letters, and dark pictures, and the user can attach the barcode below the sample. By reading it, the gradation curve corresponding to the selected image quality can be set. Further, as shown in FIG. 35, a sample diagram (a landscape image in this example) may be attached to the IC card 130. This facilitates the user's choice of image quality.

[0046]

When there are the target number N of gradation curves and the number M of image density control, the number of gradation curves N × M is required for each color. Even if the storage capacity is reduced by line approximation etc.,
Requires a large storage capacity. However, in the present invention, the gradation correction curve is calculated from the target curve data and the basic gradation data each time to calculate the light emission correction data, so that a large storage capacity is not required. With respect to the deviation of the gradation characteristic of the entire copying apparatus, it is possible to make fine adjustment by switching the basic gradation characteristic data. The storage capacity can be significantly reduced by not calculating all the gradation characteristic data but calculating the values during control. For example, by storing the gradation characteristics in a polygonal line approximation, the storage capacity can be significantly reduced. By storing the additional target gradation curve in the external memory, the selection range is expanded. It is possible to provide a gradation conversion function corresponding to different machines. By storing the newly created gradation curve in an external memory card, a custom card can be created.

[Brief description of drawings]

FIG. 1 is a sectional view showing the overall configuration of a digital color copying machine.

FIG. 2 is a block diagram of an image signal processing unit.

FIG. 3 is a block diagram of a part of a printer control unit.

FIG. 4 is a block diagram of a part of a printer control unit.

FIG. 5 is a perspective view of an operation panel.

FIG. 6 is a block diagram of image data processing in a printer control unit.

FIG. 7 is a diagram schematically showing an arrangement of a charging charger and a developing device around a photosensitive drum.

FIG. 8 is a diagram of sensitometry in reversal development.

FIG. 9 is a diagram showing how to obtain standard gradation correction data.

FIG. 10 is a diagram schematically showing the concept of the shape of a target gradation curve and the stages at which the shape changes.

FIG. 11 is a diagram of a screen for selecting a type of gradation curve.

FIG. 12 is a diagram of a screen for selecting a level of a gradation curve.

FIG. 13 is a diagram of a panel of a tablet editor.

FIG. 14 is an input device of a gradation curve by dial setting at low density and high density.

15 is a diagram showing a gradation curve selected by dial setting in FIG.

FIG. 16 is an input device of a gradation curve by dial setting at low density and high density.

FIG. 17 is a diagram of an input device using keys for setting center, low density, and high density.

FIG. 18 is a diagram showing an input method that can be set at arbitrary breakpoint coordinates.

FIG. 19 is a diagram showing data stored for light emission data calculation.

FIG. 20 is a diagram showing calculation of light emission data.

FIG. 21 is a diagram showing the main flow of the printer control unit.

FIG. 22 is a flowchart of key input processing.

FIG. 23 is a flowchart for selecting V _G , V _B , and gradation.

FIG. 24 is a diagram showing light emission data on the upper side, and a first derivative value and a second derivative value of this light emission data in the center and on the lower side.

FIG. 25 is an external view of an IC card.

FIG. 26 is a diagram showing an internal configuration of an IC card.

FIG. 27 is a diagram showing a structure of internal data stored in an IC card.

FIG. 28 is a diagram of a configuration of a control system of the operation panel.

FIG. 29 is a diagram showing a display screen of a registration program in the IC card.

FIG. 30 is a diagram of a title input screen.

FIG. 31 is a diagram showing a screen for selecting a program registration location.

FIG. 32 is a diagram showing an example of a gradation curve selection screen.

FIG. 33 is a diagram showing an example of a gradation curve selection screen.

FIG. 34 is a diagram showing an input example using a barcode.

FIG. 35 is a view of a card with a sample drawing.

[Explanation of symbols]

201 ... Printer control unit, 203 ... Data ROM,
204 ... RAM, 210 ... AIDC sensor, 232 ...
Tablet editor, 253 ... γ correction unit, 311, 3
12 ... IC card insertion slot, 322, 323 ... Mode setting key.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G03G 15/00 303 15/01 S 15/02 102 15/04 116 (72) Inventor Yoshinobu Hata Osaka 2-13-3 Azuchicho, Chuo-ku, Osaka-shi, Osaka International Building Minolta Camera Co., Ltd. (72) Inventor Hiroyuki Ideyama 2-3-3 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Osaka International Building Minolta Camera Co., Ltd. (72) Inventor Yasunori Ohno 2-3-13 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka Prefecture Osaka International Building Minolta Camera Co., Ltd.

Claims (1)

[Claims] 1. A digital image forming apparatus for forming an image by irradiating a photosensitive member with light whose exposure amount is controlled according to the value of the image signal, and converting the image signal into the exposure amount with predetermined gradation data. In this case, a storage unit that stores a basic gradation characteristic that represents the relationship between the value of the image signal and the density of the image that is formed, a setting unit that sets a target gradation characteristic, and a storage unit that stores the basic gradation characteristic are stored in the storage unit. Based on the basic gradation characteristics, the calculation means for calculating the gradation data showing the relationship between the image signal value and the exposure amount for realizing the set target gradation characteristics, and the calculation means A digital image forming apparatus comprising: means for converting an image signal to be imaged into an exposure amount based on gradation data to form an image.