JP5665782B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a recording material, and more particularly to an image forming apparatus such as an electrophotographic copying machine or a printer.

  As shown in FIG. 30, output information (RGB image, grayscale image, CMYK image data) from a PC (personal computer) is connected to an image forming apparatus or transmitted to a built-in image processing unit. In the image forming unit, output information from the PC is a gamma correction unit that corrects to a user-preferred gamma condition specified by the printer driver, a conversion unit to L * a * b * (grey is only L *), C It is processed in the conversion unit to 'M'Y'K'.

  For color space conversion from multidimensional to multidimensional such as RGB → L * a * b *, the image processing unit performs conversion using multi-order color conversion table information of the ICC profile.

  FIG. 31 shows a color setting unit of the printer driver, which is a user interface (hereinafter referred to as “UI”) prepared for the user to obtain a desired gradation. From this set value information, the gamma correction unit performs gamma conversion using a one-dimensional LUT.

  In FIG. 30, the image data converted into C′M′Y′K ′ information is further subjected to a one-dimensional LUT process by the engine gradation correction unit. The engine gradation correction unit plays a role of keeping the gradation of the printer engine constant. A one-dimensional LUT is created so as to obtain a specified gradation curve by grasping the state of the engine using a patch image output on paper as a recording material. Hereinafter, the stabilization control using the patch output on the paper is referred to as “automatic gradation correction”.

  The pseudo halftone processing unit is a processing unit that reproduces a halftone using a dither method or the like. Since the engine gradation characteristics vary depending on the type of halftone (number of lines and dot growth method), the gradation correction unit prepares an LUT for each halftone process.

  A technique for ensuring color stability using the engine gradation correction unit has been proposed.

  For example, Patent Document 1 discloses a technique for reading a toner density detection patch pattern formed on a photoreceptor with a density sensor and feeding it back to a toner density control unit in a developing device to control the density to an appropriate level. .

  In general, toner patches can be easily created and erased, but only density information before fixing can be obtained. Therefore, when control based on toner patches is performed, the influence of secondary transfer or fixing process is not affected. There is a problem that it is not reflected.

  Therefore, as typified by Patent Document 2, it has been proposed to read an image with a reader unit (image reading unit) of a copying machine incorporated in the main body of the image forming apparatus and to control image formation based on the read result. ing. In this method, an output product obtained by placing and fixing toner on paper is read by a reader unit.

  As shown in FIG. 32, the reference paper, the non-reference paper A (smooth thin paper), and the non-reference paper B (coarse and thick paper) are printed with the engine image formation conditions (charging / latent image / development conditions) constant. As a result, the density values detected by the leader portion are as shown in FIG. Based on this information, FIG. 33 shows an LUT created for the target density.

  Depending on the surface characteristics, whiteness, thickness, etc. of the paper, the read density value differs even when the same toner amount is placed, and the LUT changes. In the LUT created with the non-reference paper B, since the maximum density does not come out from the target, all the input values after 240 are replaced with 255 signals. The signal values after 240 have no gradation. This is fatal for a user who emphasizes the gradation of the shadow portion.

  Further, when the LUT is created with the non-reference paper A, a signal of 255 is applied around 240 as shown in FIG. That is, even with a solid signal (half-tone dot area ratio 100%), a halftone processing pattern is seen, resulting in degradation of quality and edge jaggy (screen pattern). This leads to deterioration in the quality of characters and lines, which is not preferable.

  In order to solve this problem, Patent Document 3 proposes a technique for setting the OUT side of the LUT to 255 when the input signal is 255 (halftone dot area ratio 100%) in order to secure a certain level of gradation. ing.

  FIG. 34 shows the LUT created using the non-reference paper B and the LUT created using Patent Document 3. It will be understood that the shadow portion is a smooth LUT. FIG. 35 shows density reproducibility using this LUT. In the shadow portion, the tone density is slightly improved although it is far from the target density.

  However, in these techniques, the gradation change in the shadow portion is severe, and an inflection point occurs in the arrow (a) portion (FIG. 35), so that smooth gradation characteristics cannot be obtained. Some professional users pointed out the discontinuity of gradation.

  As another technique related to automatic gradation correction, in Patent Documents 4 and 5, patches are printed on non-reference paper using gradation correction data created by reference paper, and the read result is used as a correction target. Technology is disclosed. An automatic gradation correction method that is not affected by the difference in density or surface property of the paper itself has been proposed.

The density related to the automatic gradation correction described above is not an absolute density but a paper standard density (Null Density: relative density) in many cases. Hereinafter, the paper reference density is referred to as relative density.
Relative density = absolute density-absolute density of paper

  A density management method using relative density is described in ISO 13656 and the like, and is a general index in the printing industry. If the relative density is used, it is not necessary to change the target density even if printing is performed on various papers, so that the versatility is high, and it has been used for management of printing machines of many printing companies.

  As for the automatic gradation correction of the image forming apparatus, automatic gradation correction is performed at the paper reference density in consideration of variations in readers, changes with time, changes in paper density due to different paper lots, and the like.

Japanese Patent Laid-Open No. 1-309082 JP 7-131649 A JP 2006-165752 A JP 2004-289200 A JP 2006-222804 A

  However, in Patent Documents 4 and 5, a reference sheet must be prepared. In addition, it is necessary to grasp the brand of the non-reference paper created from the reference paper and always perform gradation correction on the paper. That is, the non-reference paper is simply replaced with the reference paper. The inventory of non-reference paper registered from the reference paper may disappear. In this case, there are situations in which the paper itself changes, such as when there are surface properties, whiteness, thickness changes, paper eye differences, etc., due to lot differences, and even whiteness changes due to weather resistance (also known as yellowing). Many are conceivable and not a fundamental solution.

  Further, when a plurality of types of non-reference papers are registered in consideration of the non-reference paper being out of stock, the user has to select a paper type to be used for automatic gradation correction, resulting in poor operability. The more sheets that are prepared, the more difficult it becomes to understand and mistakes are likely to occur. Memory capacity must be secured for registration, leading to increased costs.

  Furthermore, the user implements gradation correction data by printing and reading a patch on the reference paper, printing the patch on the non-reference paper using the gradation correction data, and reading and correcting by the image reading unit. Two reading operations are required. It was a gradation correction method lacking in usability.

  Furthermore, electrophotographic colorants have low transmittance and the solid density is hardly affected by the paper density. In the conventional automatic gradation correction in which the printing density measurement method is applied as it is, when the same amount of colorant is placed on two different papers, the relative density changes even if the absolute density is the same. Therefore, when automatic gradation correction is performed on papers having different paper densities, the density results after correction differ, and thus it is necessary to perform automatic gradation correction on the reference paper.

  The present invention has been made in view of the above problems.

That is, an object of the present invention is to provide an image forming apparatus capable of forming an image that emphasizes density and an image that emphasizes gradation.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention , according to the first aspect,
An image forming apparatus that operates in a copy mode for reading an image of a document and copying the image of the read document and a print mode for printing image data transferred from an external device , based on an input signal input An image forming unit for forming an image on a recording material;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
So as to change the area ratio of the halftone dots of an image formed by the image forming unit, correcting the input signal using one of said second data and the first data determined by the determination unit A correction unit to perform,
A setting unit for individually setting, for each of the copy mode and the print mode, whether the correction unit uses the first data or the second data to correct the input signal; , An image forming apparatus is provided.

According to the second aspect,
An image forming apparatus that operates in a copy mode for reading an image of a document and copying the image of the read document and a print mode for printing image data transferred from an external device,
An image forming unit that forms an image on a recording material based on an input signal;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
The reading data indicating the result of reading the recording material on which a plurality of images having different densities are formed by the image forming unit by the reading unit is converted into density data, and the gradation characteristics based on the density data based on the density data Determine the first data so that becomes the target gradation characteristics ,
Based on the read data corresponding to a predetermined high density image of the plurality of images and the read data corresponding to a region where the plurality of images are not formed on the recording material , halftone dot area ratio data is obtained. A determination unit that determines the second data so that the gradation characteristic based on the target gradation characteristic becomes a target gradation characteristic ;
In the copy mode, the input signal is corrected using the first data determined by the determination unit, and in the print mode, the input signal is corrected using the second data determined by the determination unit. An image forming apparatus is provided that includes a correction unit that corrects.

According to the third aspect,
An image forming unit that forms an image on a recording material based on an input signal input;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
A correction unit that corrects the input signal so as to change the area ratio of the halftone dots of the image formed by the image forming unit,
If the density of the recording material on which an image is to be formed by the image forming unit is less than a threshold, the correcting unit corrects the input signal using the first data determined by the determining unit, and the image An image forming apparatus that corrects the input signal using the second data determined by the determination unit when the density of a recording material on which an image is to be formed by the forming unit is equal to or greater than the threshold value. Provided.

According to the fourth aspect,
An image forming unit that forms an image on a recording material based on an input signal input;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
A correction unit that corrects the input signal so as to change the area ratio of the halftone dots of the image formed by the image forming unit,
The correction unit corrects the input signal using the first data determined by the determination unit with respect to a recording material having a basis weight of less than a predetermined value, and the recording material has a basis weight of the predetermined value or more. In contrast, an image forming apparatus is provided that corrects the input signal using the second data determined by the determination unit.
According to the fifth aspect,
An image forming unit that forms an image on a recording material based on an input signal input;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
A correction unit that corrects the input signal so as to change the area ratio of the halftone dots of the image formed by the image forming unit,
If the density of the recording material on which an image is to be formed by the image forming unit is less than a threshold and the basis weight of the recording material is less than a predetermined value, the correcting unit determines the first determined by the determining unit. If the density of the recording material on which an image is to be formed by the image forming unit is at least the threshold value, or the recording material on which the image is to be formed by the image forming unit If the basis weight is equal to or greater than the predetermined value, an image forming apparatus is provided that corrects the input signal using the second data determined by the determination unit.

According to the present invention, for the copy mode and the print mode, it is possible to provide an image that emphasizes density and an image that emphasizes gradation based on the mode. Furthermore, the data can be determined with high accuracy even if it is not a reference sheet by using the halftone dot area ratio when determining data to be used for providing an image that emphasizes gradation. .

1 is a schematic diagram showing the configuration of an embodiment of an image forming system having an image forming apparatus according to the present invention. 1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. FIG. 3 is a diagram illustrating a configuration of an example of a toner amount detection sensor. It is a figure explaining the concept of electric potential control. FIG. 6 is a diagram illustrating a patch used for maximum toner amount control. FIG. 4 is a diagram illustrating a concept of maximum toner amount control. It is a figure explaining the difference in the color of paper. It is a schematic diagram showing the relationship between the difference in thickness of paper and a reflectance. It is the schematic diagram showing the relationship between the difference in the unevenness | corrugation of paper, and a reflectance. FIG. 4 is a flowchart illustrating an example of a control mode of the image forming apparatus according to the present invention. It is a figure which shows one Example of the operation screen of the image forming apparatus of this invention. It is a figure which shows one Example of an automatic gradation correction pattern. It is a brightness | luminance characteristic view when an automatic gradation correction pattern is read by the reader part. It is a figure showing the relationship between the brightness | luminance and density | concentration in a leader part. FIG. 6 is a density characteristic diagram when an automatic gradation correction pattern is read by a reader unit. It is a halftone dot area% characteristic diagram when an automatic gradation correction pattern is read by a reader unit. It is a figure which shows a printer gradation characteristic, LUT, and a target. It is a figure which shows the printer gradation characteristic result by a prior art example and the Example of this invention. 6 is a diagram illustrating a relationship between an input signal and a density in the verification of Example 1. FIG. FIG. 6 is a diagram illustrating a relationship between an input signal and halftone dot area% in the verification of Example 1. FIG. 10 is a diagram illustrating an automatic gradation correction result in the verification of Example 1. It is a figure which shows the relationship between the input signal and density | concentration in Example 2 of this invention. In Example 2 of this invention, it is a figure which shows the input signal and the halftone dot area% which were calculated | required by the halftone dot area% calculation method of Example 1. FIG. FIG. 6 is a diagram showing an automatic gradation correction result corrected by the halftone dot area% calculation method of the first embodiment in the embodiment of the present invention. It is a figure which shows the automatic gradation correction result in Example 2 of this invention. It is a flowchart figure explaining Example 3 of this invention. It is a flowchart figure explaining Example 4 of this invention. It is a figure explaining the gradation correction calculation instruction | indication user interface concerning Example 5 of this invention. It is a figure explaining the gradation correction calculation instruction | indication user interface of the copier and printer concerning Example 5 of this invention. It is a figure which shows the internal structure of the image process part in a prior art example. It is a figure which shows the color setting part of the printer driver in a prior art example. It is a figure showing the paper type and density | concentration characteristic regarding the patent document 2 of a prior art example. It is a figure which shows LUT when automatic gradation correction | amendment is implemented by patent document 2 of a prior art example. It is a figure which shows LUT when automatic gradation correction | amendment is implemented by patent document 3 of a prior art example. It is a figure which shows the correction result when automatic gradation correction | amendment is implemented by patent document 3 of a prior art example.

  In the present invention, by setting the target axis of automatic gradation correction to halftone dot area%, the degree of influence of paper density is changed by gradation (halftone dot%), and the memory cost can be reduced without using reference paper. The feature is that automatic gradation correction with reduced usability and good usability can be executed.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic configuration of an image forming system including an image forming apparatus of the present invention. In FIG. 1, the image forming system includes a host computer 1001 and an image forming apparatus 1030. The host computer 1001 and the image forming apparatus 1030 are connected by a communication line 1002. FIG. 2 shows a schematic configuration of an embodiment of the image forming apparatus 1030 according to the present invention.
[Description of Image Forming Apparatus]
Referring to FIG. 1, in this embodiment, in the image forming apparatus 1030, the printer controller 1031 controls the operation of the entire printer. A host I / F unit 1048 in the printer controller 1031 controls input / output with the host computer 1001.

  The input / output buffer 1032 transmits and receives control codes and data from each communication means via the host I / F unit 1048, and the CPU 1033 controls the operation of the entire printer controller 1031.

  The program ROM 1034 can contain a control program executed by the CPU 1033 and control data. The program ROM 1034 includes an image information generation unit 1041, a patch generation unit 1044, an engine gradation correction table creation unit 1045, and an engine gradation correction execution unit 1042 as program modules. These program modules can be used to control the conversion to luminance information and density information halftone dot area% and the generation of patch images and the like when executing gradation correction described below in cooperation with the CPU 1033. .

  The image information generation unit 1041 can generate various image objects based on data settings received from the host computer 1001. The patch generation unit 1044 can generate a patch image used when measuring halftone dot area% when executing engine gradation correction. The engine gradation correction table creation unit 1045 can create an engine gradation correction table based on the halftone dot area% measurement result. The engine gradation correction execution unit 1042 can perform engine gradation correction based on the result of measuring the dot area percentage of the patch.

  The RAM 1035 can be used as a work memory for control codes, calculation necessary for data interpretation and printing, or processing of print data. In the RAM 1035, an engine gradation correction table storage unit 1050 for storing a correction table can be stored.

  A bitmap image expansion / transfer unit 1040 in the printer controller 1031 can expand an image object into a bitmap image and transfer the expanded bitmap image to the printing apparatus engine unit 1036.

  The printing apparatus engine unit 1036 includes an engine control unit 1049, and can actually print on paper based on the bitmap image developed by the bitmap image development / transfer unit 1040. Here, the engine control unit 1049 can perform control related to each printing process process (for example, a paper feed process) by each mechanism.

  The printing apparatus engine unit 1036 and the printer controller 1031 are connected by an engine I / F unit 1046.

  The operation of the printing apparatus can be performed via the operation panel 1037, and the printer controller 1031 and the operation panel 1037 are connected by a panel I / F unit 1047.

  The external memory unit 1038 can be used for storing print data, information on various printing apparatuses, and the like. The printer controller 1031 and the external memory unit 1038 are connected by a memory I / F unit 1039. Each unit in the printer controller 1031 is connected to the system bus 1043.

  FIG. 2 shows a schematic configuration of an electrophotographic four-color full-color laser beam printer as an embodiment of the image forming apparatus according to the present invention.

The laser beam printer of this embodiment (hereinafter referred to as “image forming apparatus”) is provided with four image forming stations constituting an image forming unit, each of which forms an image of each color of magenta, cyan, yellow, and black. It has been. Each image forming station includes drum-shaped electrophotographic photosensitive members (hereinafter referred to as “photosensitive drums”) 1a, 1b, 1c, and 1d that are image holders that are rotatably supported in the clockwise direction in FIG. I have. The photosensitive drums 1a, 1b, 1c, and 1d are rotated counterclockwise in the figure at a predetermined process speed (circumferential speed). Around the photosensitive drums 1a, 1b, 1c and 1d, primary chargers (charging means) 2a, 2b, 2c and 2d, developing devices (developing means) 4a, 4b, 4c 4d. Further, around the photosensitive drums 1a, 1b, 1c, and 1d, transfer chargers (transfer means) 5a, 5b, 5c, and 5d, and cleaning devices (cleaning means) 6a, 6b, 6c, and 6d are arranged. ing.

  Further, above the photosensitive drums 1a, 1b, 1c, and 1d, exposure devices (exposure means) 3a, 3b, 3c, and 3d for exposing the photosensitive drums 1a, 1b, 1c, and 1d to images are disposed. .

In each image forming station, the photosensitive drums 1a, 1b, 1c, and 1d are uniformly charged by the primary chargers 2a, 2b, 2c, and 2d, and exposed to light by the exposure devices 3a, 3b, 3c, and 3d. Electrostatic latent images are formed on the drums 1a, 1b, 1c, and 1d. This electrostatic latent image is visualized by the developing devices 4a, 4b, 4c, and 4d to be a toner image.

  In the following description, when the above-described members and devices are collectively referred to and when it is not necessary to distinguish colors, the photosensitive drum 1, the primary charger 2, the exposure device 3, the developing device 4, The transfer charger 5 and the cleaning device 6 are described.

  As shown in FIG. 2, the toner amount detection sensor (toner amount detection means) 30 (30a, 30b, 30c, 30d) is arranged. The toner amount detection sensor 30 detects the toner amount of the toner image formed on the photosensitive drum 1, and determines the maximum toner amount condition (grid bias of the primary charger, development bias, laser power). used.

  Below the photosensitive drums 1a, 1b, 1c, and 1d between the developing devices 4a, 4b, 4c, and 4d and the cleaning devices 6a, 6b, 6c, and 6d, there is a transfer that is a recording material conveying unit so as to be in contact with them. A belt 17 is provided. The transfer belt 17 carries a recording material P such as paper or transparent film on its surface, rotates in the direction of arrow R17, and sequentially conveys the recording material P to the photosensitive drums 1a, 1b, 1c, and 1d. The toner images formed on the photosensitive drums 1a, 1b, 1c, and 1d in each image forming station are sequentially transferred onto the recording material P on the transfer belt 17 by the transfer chargers 5a, 5b, 5c, and 5d.

  Since the recording material P is generally “paper” such as transfer paper, the recording material P may be simply referred to as “paper” in the present specification and claims. The recording material P used in the invention is not limited to “paper”.

  Further, the image forming apparatus includes a plurality of paper feeding units, that is, paper feeding cassettes 12, 13, and 14, a manual paper feeding tray 11 that can be pulled out in the direction of arrow R11 in FIG. 2, and a large-capacity paper deck 15. Is provided. The recording material P is supplied from one of these paper supply units to the conveyance belt 17 via a paper supply roller, a conveyance roller, and a registration roller 16.

  As the recording material P is supported on the transfer belt 17 and passes through each image forming station, the toner images of the respective colors formed on the photosensitive drums 1a, 1b, 1c, and 1d are sequentially transferred. When this transfer process is completed, the recording material P is separated from the transfer belt 17 by the separation charger 18 and is transported to the fixing device 20 by the transport belt 19 serving as the recording material guiding means.

  The fixing device 20 includes a fixing roller 21 that is rotatably supported, a pressure roller 22 that rotates while being pressed against the fixing roller 21, a release agent application device 23 that is a release agent supply and application unit, and roller cleaning. Device. Heaters (not shown) such as halogen lamps are respectively disposed inside the fixing roller 21 and the pressure roller 22. A thermistor (not shown) is in contact with each of the fixing roller 21 and the pressure roller 22, and the fixing roller 21 and the pressure roller 22 are controlled by controlling the voltage applied to each heater via the temperature adjustment device 26. The surface temperature is adjusted. The pressure value of the pressure roller 22 and the surface temperature of the fixing roller 21 can be varied by the fixing control mechanism 25.

  A driving motor (not shown) that drives the fixing roller 21 and the pressure roller 22 includes a fixing roller 21 and a pressure roller 22 that pressurize and heat the conveying speed of the recording material P, that is, the front and back surfaces of the recording material P. A speed control device 27 is connected to control the rotation speed. As a result, the unfixed toner image on the surface of the recording material P is melted and fixed, and a full-color image is formed on the recording material P. The recording material P on which the full-color image is fixed is separated from the pressure roller 22 by a separation claw (not shown) and is discharged onto a paper discharge tray 24.

  A document reading unit (image reading unit) 28 and an operation display 29 are disposed on the upper portion of the image forming apparatus shown in FIG. The document reading unit 28 optically scans and reads a document placed on a document table (not shown) to obtain image signals of each color. The operation display 29 is used for command input from an operator (user, serviceman), notification of the device status to the operator, and the like. The automatic gradation correction pattern output from the image forming apparatus is detected using this reading apparatus, and the LUT of the engine gradation correction unit is changed (details will be described later).

[Toner amount detection means]
FIG. 3 shows an example of a toner amount detection sensor which is a toner amount detection means. The toner amount detection sensor 30 includes a light emitting unit 400 having an LED (light emitting diode) and a light receiving unit 401 having a PD (photo detector). The light receiving unit 401 includes two PDs and detects irregularly reflected light.

  The light Io irradiated to the photosensitive drum 1 from the light emitting unit 400 is reflected by the surface of the photosensitive drum 1. The reflected light Ir is received by the light receiving unit 401, and the received light amount information is output to the engine control unit 1049 (FIG. 1). The photosensitive drum 1 used in this embodiment is a smooth drum. On the other hand, when the toner covers the drum, the unevenness becomes intense and the surface becomes rough. That is, the amount of light received increases as the amount of toner increases. Since the toner amount can be grasped by using such a change in the sensor output value, it can be used for maximum toner amount control described later.

  The reflected light measured by the light receiving unit 401 is also monitored by the LED light amount control unit 403. The LED light quantity control unit 403 notifies the main control CPU 311 of the light quantity of the reflected light Io. Before the maximum toner amount control, the main control CPU 311 adjusts the light amount so that Ir becomes a specified value based on the emission intensity of the irradiation light Io and the received light amount (measured value) of the reflected light Ir.

In addition, when the image is not output, the shutter drive control unit 407 is controlled and the shutter unit 40 is controlled.
By operating No. 8, sensor window contamination from toner scattering is avoided.

[Maximum toner amount control]
(Potential control)
Here, the potential control which is the basis of the maximum concentration condition will be described.

  The maximum density condition determines charging, latent image, and development conditions.

  Before a patch is detected by a toner amount detection sensor, which will be described later, target charging potential (VdT), grid bias (Y), and development bias (Vdc) are determined by potential control. By the potential control process, a charging potential or the like according to the environmental conditions (including temperature and humidity conditions) in which the image forming apparatus 1030 is installed can be determined.

  In this embodiment, the engine control unit 1049 performs potential control called two-point electric control. FIG. 4 is a diagram for explaining the concept of potential control by two-point electric control.

In FIG. 4, Vd1 indicates the charging potential under the first charging condition (grid bias 400V), and Vl1 indicates the exposure portion potential formed with the standard (intermediate value of the laser power variable range) laser power. Yes. Vd2 represents a charging potential under the second charging condition (grid bias 800V), and Vl2 represents an exposed portion potential formed with the standard laser power at that time. At this time, the contrast potential (Cont1, Cont2) at the grid bias of 400V and 800V can be calculated from the following equations (1) and (2).
(Cont1) = (Vd1-Vl1) (1)
(Cont2) = (Vd2-Vl2) (2)

Here, the increase amount (ContΔ) of the contrast potential every charging potential 1V can be calculated by the following formula (3) based on the results of the formulas (1) and (2).
(ContΔ) = ((Cont2−Cont1) / (Vd2−Vd1)) (3)

  On the other hand, an environmental sensor (not shown) is provided in the image forming apparatus 1030, and the environmental sensor measures environmental conditions such as temperature and humidity in the image forming apparatus 1030. The engine control unit 1049 obtains an environmental condition (for example, an absolute water content) in the image forming apparatus 1030 based on the measurement result of the environmental sensor. Then, the target contrast potential (ContT) corresponding to the environmental condition is referred to from the environmental table registered in advance.

The relationship between the target contrast potential (ContT) and the increase amount of the contrast potential (ContΔ) can be calculated by the following equation (4).
ContT = Cont1 + X · ContΔ (4)

If the parameter “X” satisfying the relationship of the equation (4) is calculated, the target charging potential (VdT) (hereinafter also referred to as “target potential”) can be calculated by the following equation (5). it can.
VdT = Vd1 + X (5)

The charging potential change amount (VdΔ) per 1 V of the grid bias can be calculated by the following equation (6).
(VdΔ) = (Vd2−Vd1) / (800−400) (6)

The grid bias (Y) that gives the target potential (VdT) can be calculated by the following equation (7).
Target VdT = 400 + Y · VdΔ (7)

  In equation (7), VdΔ can be calculated from equation (6), and VdT can be calculated from equation (5). Therefore, the grid bias (Y) satisfying the relationship of the equation (7) can be finally determined by substituting the potential that is known from the equations (5) and (6).

  Through the above processing, the target potential (VdT) and the grid bias (Y) can be determined according to the environmental conditions. The development bias (Vdc) has a specified potential difference with respect to the target potential (VdT), and can be calculated by subtracting the specified potential from the determined target potential (VdT).

  Subsequent image formation is performed with the determined developing bias (Vdc). Although the potential on each drum is negative, in order to make the calculation process easier to understand, the negative is omitted here.

  Through the above processing, the grit bias and the development bias (Vdc) used at the time of image formation are determined.

(Maximum toner amount control using toner amount detection sensor)
Next, the maximum toner amount control using the toner amount detection sensor (toner amount detection means) will be described.

  The condition obtained by the potential control was determined by determining the target contrast potential corresponding to the environmental condition from the environmental table registered in advance. Since the target contrast is obtained with a certain standard machine, the maximum density often does not reach a predetermined value after machine differences or after durability. Therefore, in this embodiment, the toner amount detection sensor 30 is provided to detect the toner amount on the photoconductor. As a method for adjusting the maximum density condition in this embodiment, the laser power (hereinafter referred to as “LPW”) is changed.

  A pattern in which the maximum loading amount is changed as shown in FIG. 5A is formed on the photosensitive member. For example, a patch is formed with a light amount of 20% Down, 10% Down, a standard value, 10% Up, and 20% Up from a light amount ratio that is normally used. The patch potential at this time is as shown in FIG. 5B, and patches are created from Vl1 suitable for LPW1 (light quantity 20% UP) to Vl2-5.

  The patch size is a 40 mm square patch in consideration of the detection range of the potential sensor. The patches are created by PWM (pulse width modulation: light emission time), and adjustment may be performed by PWM so that the patches have PWM0 and the patch portion has a predetermined light amount. In this embodiment, light is emitted for the longest time per pixel (one pixel of 600 dpi).

The patch potential for each LPW is measured, and the toner amount is detected by the toner amount detection sensor 30. FIG. 6 shows the Vcont (Vdc−Vl) of each patch and the patch detection value of the toner amount detection sensor. In this embodiment, the target is 0.55 mg / cm ² , the relationship between the applied toner amount is derived from the detection result of FIG. 6, and the points are connected by linear (linear) interpolation. Then, Vcont that is 0.55 mg / cm ² may be introduced. In the engine state shown in FIG. 6, 230 V is appropriate for Vcont, and the amount of applied toner can be 0.55 mg / cm ² by increasing LPW by + 9% from the standard state.

The calculation method of the maximum toner amount control is summarized as follows.
Preparation: Vd and Vdc are determined by potential control.
(1): Patch the latent image (charge, laser) with a predetermined LPW (5 points)
(2): Patch potential detected by potential sensor (3): Patch latent image developed (4): (3) detected by toner amount detection sensor (5): LPW, patch potential (Vl), toner amount (To ) (LPW, V1, To) =
(102 levels, 150 V, 0.42 mg / cm ² )
(115 levels, 130 V, 0.45 mg / cm ² )
(128 level, 100 V, 0.49 mg / cm ² )
(141 level, 80V, 0.56 mg / cm ² )
(154 level, 55V, 0.59 mg / cm ² )
(6): Convert Vl to Vcont (Vdc−Vl) (LPW, Vcont, To) =
(102 levels, 165 V, 0.42 mg / cm ² )
(115 levels, 185 V, 0.45 mg / cm ² )
(128 level, 215 V, 0.49 mg / cm ² )
(141 level, 235 V, 0.56 mg / cm ² )
(154 level, 260 V, 0.59 mg / cm ² )
(7): Calculate difference (To−0.55) with respect to target toner applied amount (LPW, Vcont, ΔTo) =
(102level, 165V, -0.13mg / cm 2)
(115 levels, 185 V, -0.10 mg / cm ² )
(128level, 215V, -0.06mg / cm 2)
(141 level, 235 V, 0.01 mg / cm ² )
(154 level, 260 V, 0.04 mg / cm ² )
(8): Extract the minimum difference condition with a positive difference and the minimum difference condition with a negative difference Plus side (LPW (+), Vcont (+), ΔTo (+)) =
(141 level, 235 V, 0.01 mg / cm ² )
Negative side (LPW (−), Vcont (−), ΔTo (−)) =
(128level, 215V, -0.06mg / cm 2)
(9): LPW calculation where To becomes 0.00 (LPW (T))
LPW (+)-((ΔTo (+)-0) / ((ΔTo (+) − ΔTo (−) / (LPW
(+)-LPW (-))))
= 139.1286
Round off
= 139
(10): Registration of potential control target = Vcont (+) − ((Vcont (+) − Vcont (−)) / (LPW (+)
-LPW (-)) * ((LPW (+)-LPW (T))
= 231.9231
Round off
= 232

The registration of the potential control target in (10) above changes the potential control target determined by the environment table. The maximum toner amount control using the toner amount detection sensor needs to print a patch, and the frequency cannot be increased from the viewpoint of toner consumption. Since the potential control can detect the patch potential without developing the toner, fluctuations in a short time can be suppressed by the potential control. In terms of frequency, it is as follows.
High frequency: Potential control Medium frequency: Maximum toner amount control Low frequency (user activation): Automatic gradation correction (described later)

[Auto gradation correction]
The conventional automatic gradation correction is to detect a luminance value of a patch from a gradation patch image printed on paper using a reader unit (image reading unit) 28, and to use a previously obtained luminance density conversion table. This is control for converting to density information and adjusting the LUT so that a predetermined density curve is obtained. As described in the prior art, even if the same toner amount is placed on the paper, the density differs for each paper type. When control is performed so as to match a predetermined density curve, there is an inconvenience in the gradation of the shadow portion (see the conventional example and the problem).

This phenomenon
(A) The paper color (spectral characteristics) is different. (B) The toner melting degree is different depending on the paper thickness difference. (C) The paper surface property (unevenness) is different.

The density is a calculation of how much light (Io) incident from 45 ° is 0 °, and the density is high if the diffuse reflection component is small.
Concentration = −log (Ii / Io)

  In the case (a), as shown in FIG. 7, even when the same toner is loaded in the same pattern and with the same amount of toner, it is affected by the influence of paper white (spectral reflectance of the paper (see FIG. 7C)) 7 that the non-reference paper has a higher density, which also affects the density detected by the reader unit 28.

The above (b) shows a conceptual diagram in FIG. The image forming apparatus allows a predetermined basis weight width, for example, 64 to 128 g / m ² even with the same plain paper setting. Due to this difference in thickness, even if the same toner is placed on the same amount of paper, the amount of heat and pressure applied to the toner in the fixing device will change. Therefore, the thicker the paper, the closer to the spherical shape that is the shape of the toner, and the irregular reflection component increases. In the case of the reference paper in FIG. 8, the regular reflection component increases and the irregular reflection component decreases. In this way, since the amount of irregular reflection changes, the density detected by the reader unit 28 is also affected.

  In the case (c), as shown in FIG. 9, the toner is placed so as to follow the unevenness of the paper. That is, when the paper is smooth, the toner surface is also smooth, and the uneven portion reproduces the unevenness. Even if the same amount of toner is applied, the amount of irregular reflection changes due to the surface unevenness of the paper, so that the density detected by the reader unit 28 is also affected.

  Furthermore, there is a large difference in transmission density between offset printing and electrophotography. The offset printing has a lower transmission density than the electrophotographic method. That is, there is a characteristic that the background of the paper is easy to see through.

The present inventors examined the transmission density of black using a Canon imagePress C1 and an offset printing machine using 81.4 g / m ² of CLC paper. The transmission densitometer used was X-Rite 361t. Printing was performed on the basis of JapanColor under conditions other than the paper of the offset printing press. That is, the paper was adjusted to be within the JapanColor standard with JapanPapar, and a solid patch was printed on the CLC paper under the conditions.

  The following table is obtained by subtracting the transmission density absolute value of the solid patch from the transmission density absolute value of paper, and means the transmission density of ink or toner.

  Thus, the electrophotographic toner has a high transmission density and a low transmittance. This phenomenon is caused by the coloring material, the dispersibility of the coloring material, and the thickness of the material adhering layer. That is, in offset printing, the material layer is 1 μm to 2 μm, while the toner is 5 μm to 10 μm. The difference appears as the transmission density difference.

  Thus, although the electrophotographic method and the offset printing have different influence levels of paper in the vicinity of the solid density, automatic gradation correction has been performed using the relative density. The relative density was subtracted more than necessary near the high density because the paper density was uniformly subtracted in the entire density range.

  In this embodiment, the density information is referred to as a halftone dot area ratio (halftone dot area%) (hereinafter simply referred to as “halftone dot%”) so that the engine gradation correction can be executed even if the density detection result differs depending on the paper type. There is also.)

  By using halftone dots, the influence of the paper density can be increased in the highlight area and decreased in the shadow area.

  One target having a predetermined halftone dot% is prepared, and an LUT is created so that the halftone dot% is obtained. With the above configuration, that is, by controlling the degree of influence of the reflectance of the paper according to the gradation and correcting it to a predetermined gradation characteristic, smooth gradation characteristics without gradation discontinuity in the shadow portion can be achieved with a memory cost. An image forming apparatus with high image quality can be provided without UP.

  The automatic gradation correction of this embodiment will be described with reference to the flowchart shown in FIG.

  Automatic gradation correction is activated by pressing a “gradation correction” button on the operation screen shown in FIG. This control is executed by a user or service person at an arbitrary timing.

  The image forming apparatus whose “tone correction” has been pressed ends the potential control and maximum toner amount control.

  The patch generation unit of the program ROM 1034 prints 64 gradations (gradation test patterns) of CMYK colors on paper as shown in FIG. 12, and reads the luminance signal of the patch using the reader unit 28. The density of the gradation test pattern is darkest at the upper right corner and lightest at the lower left corner, and during that period, the density gradually decreases from right to left, and the density decreases to the second, third, and fourth stages. To go. Four colors for cyan, magenta, yellow, and black are prepared for one color.

  The read signal draws a curve as shown in FIG. The horizontal axis represents the input signal, and the vertical axis represents the reader unit reading luminance value. Note that 255 in the luminance value of the reader unit 28 corresponds to a density of 1.60. (Concentration calculation method is measured with Xrite 500 series, Status T, white backing, Visual filter, absolute value standard). In this description, a black (K) color material is used as a representative value.

  FIG. 14 is a graph in which the luminance value of the reader unit 28 and the density value of the patch formed on the reference paper are normalized and plotted. The density is normalized to 1.60 by 255. Using this luminance density conversion table, the detected luminance value is converted into a density value.

  FIG. 15 shows the tone characteristics (horizontal axis input signal value, vertical axis density value) of the printer using the luminance density conversion table of FIG. 14 for the input signal. Conventionally, a relative density is converted by subtracting the paper density from this density information, and an LUT is created so as to meet a desired relative density target.

  FIG. 16 is a graph in which the density values in FIG. 15 are converted into halftone dot area% using the following Murray-Daviess equation and the relationship with the input signal is plotted. As described above, by converting into halftone dot area% information using the Murray-Daviess formula, even if a change in the maximum read density due to the paper type occurs, the maximum density portion becomes 100% in the halftone dot area%. Furthermore, since the paper density is set to 0%, the density difference due to the paper type difference can be absorbed in the entire gradation without being influenced by the background color.

  In the graph, the dot area of 100% is normalized by 255.

Murray-Daviess type halftone dot area% = ((1-10 ^(−Dt) ) / (1-10 ^(−Ds) ) * 100
Ds = (maximum density−paper density)
Dt = (halftone dot density−paper density)

  The halftone dot density is a measured density of the gradation pattern, and the maximum density is the maximum density of the gradation pattern.

  FIG. 17 shows the printer gradation characteristics, the target curve, and the LUT for the target created with the dot area% in FIG. In this embodiment, when the input signal (input halftone dot area%) is 50%, the target curve has an output signal, that is, the output halftone dot area% is 70%, that is, the dot gain characteristic is 20%. This is a gradation curve.

  The LUT is stored in the engine gradation correction table storage unit 1050 and is executed by the engine gradation correction execution unit 1042 during normal image formation.

  FIG. 18 shows density gradation characteristics when an LUT is created from a density target of a conventional method using the same non-reference paper as the LUT (halftone area% target) created in FIG.

  In the conventional method, gradation discontinuity cannot be avoided at the arrows (a) and (b), since it tries to match the density value.

  On the other hand, by creating an LUT so as to match a predetermined halftone dot area% target with the halftone dot area% as an axis, a difference in paper can be absorbed in the entire gradation. That is, automatic gradation correction control that is not affected by paper is performed by changing the degree of influence of the reflectance of the paper according to the gradation and correcting it to a predetermined gradation characteristic. The predetermined gradation characteristic is a gradation in which the dot gain characteristic is within a predetermined range. The dot gain characteristic is a difference between the input halftone dot area% and the output halftone dot area%.

(Verification of Example 1)
Hereinafter, automatic gradation correction using the Murray-Daviess formula described in the first embodiment will be verified. The focus of verification is to verify whether the problem of the present invention is solved, ie whether the gradation and the influence level of the ground are changed by gradation.
Paper 1: Canon Office Planner 68m ² (plain paper)
Paper 2: Canon PPC color paper 68g / m ² pink (colored paper)
Pattern printing model: imagePressC1
Color: Black Calculation method: Automatic gradation correction shown in Example 1

  FIG. 19 shows the relationship between the input signal (input halftone dot area%) printed under the above conditions and the density. The solid line is paper 1 and the dotted line is paper 2. Since both output under the same conditions and the paper thickness (basis weight) is also the same, the solid density is almost the same. However, the highlight portion is affected by the color of the paper, and the density of the colored paper is about 0.2 and that of the plain paper is about 0.07.

  FIG. 20 is obtained by converting FIG. 19 into halftone dot area% using the Murray-Daviess equation. At this point, the two paper gaps disappeared. Succeeded in absorbing the paper density difference of 0.13. As described in the first embodiment, there is one halftone dot target, and the same LUT is created. FIG. 21 shows the result as a dot gain characteristic (dot gain%) which is the difference between the input halftone dot area% and the output halftone dot area%. Both papers succeeded in creating the same LUT.

  As in the conventional example, when colored paper is used during automatic gradation correction using a relative density target, the solid density is determined to be less than the specified density. That is, the density difference of 0.13 between the white paper and the colored paper is also applied to the solid density. As a result, the color paper has a density lower than the specified level, so that an LUT like the non-reference paper B as shown in FIG. 29 is created. A step at the inflection point is unavoidable due to the termination correction.

  With the automatic gradation correction method of Example 1, it was possible to realize natural gradation with no inflection point even if there was an extreme difference in the type of paper such as colored paper.

  From another viewpoint, the solid density portion is not affected by the paper. On the other hand, in the highlight portion, the paper type difference is absorbed in the calculation process. That is, the influence level of the paper density (that is, the influence degree of the reflectance of the paper) is changed by the gradation (halftone dot%). By making the influence of the paper high in the highlight and low in the shadow part, an automatic gradation correction method that is not affected by the paper could be established.

Example 2
In the second embodiment, a more versatile automatic gradation correction method will be described by remodeling the Murray-Daviess formula. Since the calculation method of the first embodiment is changed, other description is omitted.
Paper 1: Canon Office Planner 68m ² (plain paper)
Paper 2: Color paper for Canon PPC (thick mouth type) 125g / m ² blue (colored paper)
Pattern printing model: imagePressC1
Color: Black Calculation method: Automatic gradation correction shown in Example 1

  The paper 1 is the same paper as the verification in Example 1, and the paper 2 is changed in color and paper thickness (basis weight). Since the phenomenon shown in FIG. 8 described in the first embodiment occurs, the solid density of the paper 2 is lowered (see FIG. 22). Further, the density difference of paper is about 0.1.

  When the automatic gradation correction of Example 1 was performed under these conditions and the density of the output patch was analyzed, the relationship of FIG. 23 was obtained.

  At first glance, it seems to match, but there is a shift of halftone dots in halftones. From this result, an LUT was created so as to match the halftone dot target and the dot gain characteristics were examined. As a result, the relationship shown in FIG. 24 was obtained and the accuracy was lower than the colored paper used in the verification of Example 1. I understood.

  Compared to the conventional example, the gradation is improved, but the engine gradation correction result is different by changing the paper type. Therefore, when automatic gradation correction is performed on different paper (paper 1 and paper 2) and both are printed on some other paper, a density difference occurs in halftone. When both the paper density and the solid density are different from the white paper, the Murray-Daviess formula indicates that there is a limit in accuracy.

  The Murray-Daviess formula is as follows, and Ds and Dt adopt conventional relative concentrations. Therefore, the density difference in the shadow portion cannot be absorbed.

Murray-Daviess type halftone dot area% = ((1-10 ^(−Dt) ) / (1-10 ^(−Ds) ) * 100
Ds = (maximum density−paper density)
Dt = (halftone dot density−paper density)

  In this embodiment, the density difference in the shadow portion is absorbed by performing the two-stage calculation as follows.

First calculation First dot area% = ((1-10 ^(-Dt1) ) / (1-10 ^(-Ds1) ) * 100
Ds1 = (maximum density−paper density)
Dt1 = (halftone dot density−paper density)
Second calculation Halftone dot area% = ((1-10 ^(-Dt2) ) / (1-10 ^(-Ds2) ) * 100
Ds2 = (maximum density−paper density * (100−first dot area%))
Dt2 = (halftone dot density−paper density * (100−first halftone dot area%))

  The first calculation is the same Murray-Daviess formula as in the first embodiment, and is characterized by weighting the paper density of the second calculation using the first halftone dot area% obtained there. .

  The result of finishing the second calculation is shown in FIG. It was confirmed that the same curve was obtained with halftone dot area%. If the halftone dot area% target obtained in these two steps is created, the same gradation correction table can be created even if the paper density and solid density are different, and the resulting dot gain curve has the same characteristics. Draw.

  As described above, by changing the degree of influence of the paper density between the highlight portion and the shadow portion and calculating the halftone dot area%, it is possible to perform automatic gradation correction with high versatility.

Example 3
In the first embodiment, the automatic gradation correction method with high accuracy is described even when the basis weight is the same and the density difference of the paper is generated. In the second embodiment, in addition to the first embodiment, a highly versatile automatic gradation correction method has been described even when the solid density changes due to the difference in basis weight.

  In terms of arithmetic processing and memory capacity, compared to the conventional density calculation, the calculation for converting density to halftone dot% is performed in the first embodiment, and the first halftone dot calculation and the second calculation are performed in the second embodiment. As a result, the processing time and the amount of memory to be temporarily stored are increasing.

  In the third embodiment, a mechanism that does not increase the processing time and the memory amount by changing the calculation contents using the following relationship is provided.

  * 1 is almost the condition of the reference paper, so there is no problem of automatic gradation correction due to the difference in paper, so the calculation is performed with the same density as before. * 2 is not described in Examples 1 and 2, but the amount of density difference due to difference in basis weight is smaller than the difference in media density, so it was determined that only the first calculation of Example 1 is sufficient. * 3 is the content of Example 1. * 4 is the content of Example 2.

  The actual switching method can be dealt with by adding the shaded portion of FIG. 26 to the program of the engine gradation correction table creating portion of FIG.

  The CPU 1033 that has executed the maximum toner amount control grasps the characteristics (basis weight) of paper in order to print 64 patches for automatic gradation correction on the paper, and temporarily stores them in the RAM 1050. Similar to the first embodiment, printing of 64 patches, reading by a reader unit, and luminance → density conversion are executed.

Of the 64 pieces of patch information converted into the density information, the signal value 0, that is, the density of the paper white portion is extracted, and it is determined whether or not it is less than 0.1. Check the next basis weight of less than 0.1, if it is less than 90 g / m ^2, as it creates an LUT in a concentration state. If it is 90 g / m ² or more, it is converted to the first halftone dot%, which is the calculation of Embodiment 1, and an LUT is created.

If the paper density is 0.1 or more, the influence of the paper density is large, so the halftone dot calculation (the first calculation in the first and second embodiments) is executed. If the basis weight is less than 90 g / m ² , the LUT is generated as it is, and if the basis weight is 90 g / m ² or more, the LUT is generated after executing the second operation of the second embodiment.

  With the flow described above, it is possible to automatically change the LUT calculation method according to the necessity (paper basis weight and paper density).

  In this embodiment, the calculation method is switched by automatically detecting the paper density and the basis weight of the paper. However, a configuration designated by the user may be used.

Example 4
The dot percentage calculation, which is a feature of the present invention, is executed in order to suppress the density step due to the end correction and to improve the gradation. This is particularly effective when outputting a printer whose original is a monitor. The monitor is additive color mixing with RGB emission colors, and the printer is subtractive color mixing of object colors that require reference light. Since the coloring mechanism is different, there is almost no demand for general users to precisely match the density of the monitor and the density output on paper.

  However, considering copying, the originals are all object colors such as printing, photographic paper, or the same printer output. Therefore, it is easy to compare the density reproducibility with the original, and it is often required to reproduce the original faithfully.

  For this reason, in this embodiment, the copying LUT generation method performs an operation for adjusting the gradation with respect to the conventional density target, and for generating the LUT for the printer, an operation for adjusting the gradation with respect to the dot area% target.

  In FIG. 27, the flow of the above feature is added based on the fourth embodiment. The patch signal after the density conversion generates a LUT for copying as in the conventional example in the density state. At the same time, a calculation method is selected from the density and basis weight of the paper, a predetermined halftone dot calculation (first only or first and second calculation) is performed, and the result is stored in the table storage unit as a printer LUT.

In actual use, passes the printer or copying of information from the CPU1033 in the engine tone correction execution unit 1042, it processes the LUT in the engine tone correction table storage unit to the image.

  In the printer image according to the present invention, the print information input from the host computer 1001 in FIG. 1 generates an image object by the image information generation unit 1041, and is converted into a bitmap by the bitmap image development / transfer unit 1040. The gradation correction is executed by the engine gradation correction execution unit 1042 in the ROM 1034 and is notified to the engine unit 1036.

  On the other hand, the copy image is read by the document reading unit 28 shown in FIG. 2 and transmitted to the printer controller. After the gradation correction for copying is performed by the engine gradation correction executing unit 1042, the engine unit 1036 again receives the copy image. Notified and output.

  In the present embodiment, the configuration in which two LUTs are created on the premise that the pseudo halftone processing pattern is shared between the printer and the copy is explained. However, the pseudo halftone processing pattern is different between the copy and the printer. If there is, it is not necessary to create two LUTs for one pseudo halftone processing pattern.

Example 5
Furthermore, as a measure for improving usability, the user may be prompted to select as shown in FIGS. In this case, the LUT is generated with the conventional density for emphasizing density, and the first or second embodiment may be used if the gray scale is emphasized.

  As described above, an image forming apparatus that solves the tone discontinuity of the shadow portion that has occurred in the automatic tone correction on non-reference paper and that can perform engine tone correction on non-reference paper is executed. I was able to.

  In each of the above embodiments, the present invention has been described as a direct transfer type color image forming apparatus, but the present invention is not limited to this.

  For example, the present invention may be an intermediate transfer type color image forming apparatus. Such an image forming apparatus temporarily transfers a toner image from an image carrier of each image forming unit to an intermediate transfer body such as an intermediate transfer belt, and then collectively transfers the toner image to a recording medium (paper) to form a color image. Is formed.

  Such an intermediate transfer type color image forming apparatus, of course, is not limited to the color image forming apparatus, and the monochrome image forming apparatus also performs automatic gradation correction control in the same manner as in the first and second embodiments. As a result, a high-quality image can be obtained.

1 (1a, 1b, 1c, 1d) Photosensitive drum (image carrier)
2 (2a, 2b, 2c, 2d) Primary charger (charging means)
3 (3a, 3b, 3c, 3d) Exposure apparatus (exposure means)
4 (4a, 4b, 4c, 4d) Developing device (developing means)
5 (5a, 5b, 5c, 5d) Transfer charger (transfer means)

Claims (10)

An image forming apparatus that operates in a copy mode for reading an image of a document and copying the image of the read document and a print mode for printing image data transferred from an external device, based on an input signal input An image forming unit for forming an image on a recording material;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
The input signal is corrected using either the first data or the second data determined by the determining unit so as to change the area ratio of the halftone dots of the image formed by the image forming unit. A correction unit to perform,
A setting unit for individually setting, for each of the copy mode and the print mode, whether the correction unit uses the first data or the second data to correct the input signal; And an image forming apparatus. The setting unit includes a selection unit that allows a user to individually select whether the correction unit corrects an input signal using the first data or the second data.
The setting unit individually sets each of the copy mode and the print mode so that the correction unit corrects an input signal using data selected by the selection unit. The image forming apparatus according to claim 1. An image forming apparatus that operates in a copy mode for reading an image of a document and copying the image of the read document and a print mode for printing image data transferred from an external device,
An image forming unit that forms an image on a recording material based on an input signal;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
The reading data indicating the result of reading the recording material on which a plurality of images having different densities are formed by the image forming unit by the reading unit is converted into density data, and the gradation characteristics based on the density data based on the density data Determine the first data so that becomes the target gradation characteristics ,
Based on the read data corresponding to a predetermined high density image of the plurality of images and the read data corresponding to a region where the plurality of images are not formed on the recording material , halftone dot area ratio data is obtained. A determination unit that determines the second data so that the gradation characteristic based on the target gradation characteristic becomes a target gradation characteristic ;
In the copy mode, the input signal is corrected using the first data determined by the determination unit, and in the print mode, the input signal is corrected using the second data determined by the determination unit. An image forming apparatus comprising: a correction unit that corrects the image.   4. The image forming apparatus according to claim 3, wherein the read data corresponding to the predetermined high density image is read data of an image corresponding to the maximum density of the plurality of images. The determination unit converts read data corresponding to the plurality of images into density data, and determines halftone dot area ratio data based on the following formula from the density data: {1-10 ^(−Dt) } / { 1-10 ^(-Ds) } × 100
Ds = Dmax−Dp
Dt = D−Dp
Dmax is density data converted based on the read data corresponding to the predetermined high density image,
Dp is density data converted based on read data corresponding to an area where the plurality of images are not formed on the recording material,
5. The image forming apparatus according to claim 3, wherein D is density data converted based on read data corresponding to the plurality of images. The determination unit converts read data corresponding to the plurality of images into density data, and determines dot area ratio data from the density data based on the following expression: {1-10 ^(−Dt2) } / { 1-10 ^(-Ds2) } × 100
Ds2 = Dmax−Dp × (100−N)
Dt2 = D−Dp × (100−N)
N = {1-10 ^(−Dt) } / {1-10 ^(−Ds) } × 100
Ds = Dmax−Dp
Dt = D−Dp
Dmax is density data converted based on the read data corresponding to the predetermined high density image,
Dp is density data converted based on read data corresponding to an area where the plurality of images are not formed on the recording material,
5. The image forming apparatus according to claim 3, wherein D is density data converted based on read data corresponding to the plurality of images. The reading unit is a reader unit that reads an image of a document,
The image forming apparatus according to claim 1, wherein the image forming unit copies an image of the document read by the reader unit in the copy mode. An image forming unit that forms an image on a recording material based on an input signal input;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
A correction unit that corrects the input signal so as to change the area ratio of the halftone dots of the image formed by the image forming unit,
If the density of the recording material on which an image is to be formed by the image forming unit is less than a threshold, the correcting unit corrects the input signal using the first data determined by the determining unit, and the image An image forming apparatus, wherein if the density of a recording material on which an image is to be formed by a forming unit is equal to or higher than the threshold value, the input signal is corrected using the second data determined by the determining unit. An image forming unit that forms an image on a recording material based on an input signal input;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
A correction unit that corrects the input signal so as to change the area ratio of the halftone dots of the image formed by the image forming unit,
The correction unit corrects the input signal using the first data determined by the determination unit with respect to a recording material having a basis weight of less than a predetermined value, and the recording material has a basis weight of the predetermined value or more. In contrast, the image forming apparatus corrects the input signal using the second data determined by the determination unit. An image forming unit that forms an image on a recording material based on an input signal input;
A reading unit that optically reads the recording material on which an image is formed by the image forming unit;
Based on the result of reading the recording material on which a plurality of images having different densities by the image forming unit are read by the reading unit, the density of the image formed by the image forming unit on the recording material and the input signal A determination unit that determines first data for correcting the correspondence and second data for correcting the correspondence between the area ratio of the halftone dots according to the density of the image formed by the image forming unit and the input signal. When,
A correction unit that corrects the input signal so as to change the area ratio of the halftone dots of the image formed by the image forming unit,
If the density of the recording material on which an image is to be formed by the image forming unit is less than a threshold and the basis weight of the recording material is less than a predetermined value, the correcting unit determines the first determined by the determining unit. If the density of the recording material on which an image is to be formed by the image forming unit is at least the threshold value, or the recording material on which the image is to be formed by the image forming unit If the basis weight is equal to or greater than the predetermined value, the input signal is corrected using the second data determined by the determination unit.

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